Search

This study evaluated changes in land cover in the Chemoga watershed, headwater to the Blue Nile. Two sets of aerial photographs (1957 and 1982) and a multispectral Spot image (1998) were used as inputs to produce 3 GIS-based land cover maps of the area. The results show that during the last 41 years, forest cover increased at a rate of about 11 ha per annum in the 36,400-ha watershed. Woodlands and shrublands decreased between 1957 and 1982 but increased between 1982 and 1998, approximately to their previous levels. Farmland and settled areas gained from the other cover types (13% increase) in the first period but lost around 586 ha (2% decrease) in the second. Grassland and degraded land decreased, accounting for 4.8% of the total area of the watershed in 1982 and 3.5% in 1998, as against 9.6% in 1957. Riverine trees suffered the greatest destruction, shrinking by 79% over the 4 decades; much of this decline was due to cultivation. Marshlands increased in the first period and decreased in the se...

Population and environment debates regarding Africa, whether Malthusian or Boserupian in nature, focus on population levels as the driving force behind the relationship between environment and society. This article argues, instead, that how people adjust to their rise in numbers is more important than are population levels. It focuses on the role of local informal institutions, such as land tenure systems, but also on customs, norms, and networks, and their change over time in mediating the relationship between people and the environment. The article is based on fieldwork conducted between 1995 and 1998 in the Sahelian and Sudano-Sahelian zones of Africa, as well as on a review of colonial documents pertaining to the area written in the first half of the twentieth century. The article concludes that adaptations made to local, informal institutions within the past century have enabled an environmentally sustainable land use within the context of a rising population and growing scarcity of natural resources.

Population and environment debates regarding Africa, whether Malthusian or Boserupian in nature, focus on population levels as the driving force behind the relationship between environment and society. This article argues, instead, that how people adjust to their rise in numbers is more important than are population levels. It focuses on the role of local informal institutions, such as land tenure systems, but also on customs, norms, and networks, and their change over time in mediating the relationship between people and the environment. The article is based on fieldwork conducted between 1995 and 1998 in the Sahelian and Sudano-Sahelian zones of Africa, as well as on a review of colonial documents pertaining to the area written in the first half of the twentieth century. The article concludes that adaptations made to local, informal institutions within the past century have enabled an environmentally sustainable land use within the context of a rising population and growing scarcity of natural resources.

Hypotheses about the origin of vegetation pattern formation in semi-arid areas around the world almost all include a common feature of semi-arid areas: the presence of a positive feedback between plant density and water infiltration. We investigate whether this positive feedback and the spatial redistribution of runoff water are sufficient to explain vegetation pattern formation. For this purpose, we analyze a spatially explicit model consisting of partial differential equations using a method for demonstrating pattern formation (Turing analysis). Our analysis reveals that pattern formation can occur in semi-arid areas given only the positive feedback between plant density and local water infiltration coupled with the spatial redistribution of runoff water. Thus, slope and underlying heterogeneity are not essential conditions. Other factors in the model, such as herbivory, plant dispersal, rainfall, and drought tolerance of plants, appear to determine under what conditions pattern formation is likely but are not the primary factors that generate the patterns. The model is in agreement with field observations and indicates the conditions for which vegetation pattern formation can be expected in arid and semi-arid grazing systems.

Hypotheses about the origin of vegetation pattern formation in semi-arid areas around the world almost all include a common feature of semi-arid areas: the presence of a positive feedback between plant density and water infiltration. We investigate whether this positive feedback and the spatial redistribution of runoff water are sufficient to explain vegetation pattern formation. For this purpose, we analyze a spatially explicit model con- sisting of partial differential equations using a method for demonstrating pattern formation (Turing analysis). Our analysis reveals that pattern formation can occur in semi-arid areas given only the positive feedback between plant density and local water infiltration coupled with the spatial redistribution of runoff water. Thus, slope and underlying heterogeneity are not essential conditions. Other factors in the model, such as herbivory, plant dispersal, rainfall, and drought tolerance of plants, appear to determine under what conditions pattern formation is likely but are not the primary factors that generate the patterns. The model is in agreement with field observations and indicates the conditions for which vegetation pattern formation can be expected in arid and semi-arid grazing systems.

Metadata only record Soil and water conservation interventions in Africa have had a checkered history, calling into question the way in which soil and water conservation technologies have been studied in the past. This article draws on a case study from eastern Burkina Faso to explore an area usually ignored by soil and water conservation studies-the role of social institutions in guiding decisions regarding the use of technologies. It looks at soil and water conservation through the historical development of what the authors call the 'cultural economy', that is, a system of exchange in which the market economy has mixed with pre-existing forms of exchange. The approach adopted by the authors identifies concepts on which the cultural economy is based and uses these ideas to analyse institutions that affect the choice of soil and water conservation technologies. The article shows how this approach leads to a reconceptualization of the ways in which soil and water conservation technologies are to be considered.

Peter Oksen's comments on our paper about farmer-herdsman relations in Burkina Faso raise some interesting issues, notably regarding problems of interpretation of oral and archival sources and regarding the broader relevance of insights gained from an in-depth case study. Before answering straightforwardly to his objections, it is useful to clarify the misunderstanding which appears to exist about the meaning we attribute to 'symbiosis' and 'symbiotic relations'. In our article we restricted the use of these terms to the way in which past relations between farmers and herdsmen, depicted as undifferentiated groups, are often represented. In discussions about the change of these relations, the emphasis is on progressive deterioration, again without attention paid to the possible existence of intra-group differentiation or of heterogeneity of relations across group boundaries. In this regard, it is remarkable that from colonial documents the interests of farmers and herdsmen emerge as equally irreconcilable as they are often considered today, and that, just as at present, competition over scarce natural resources constituted a major factor in inter-group relations. If we therefore reject 'symbiosis' as a correct description of formerly existing inter-group relations, we do not intend to imply that complementary links - such as those we describe for present-day relations between Mossi and Fulbe - did not exist in the past. A major aspect of our argument is that inter-group relations, whether past or present, cannot be subsumed under simplifying labels such as 'symbiosis'. Neither can changes in these relations be understood in terms of uni-directionally processes of deterioration. Hence, present-day 'complementary' links across the ethnic boundary - established by certain, but not all, Mossi and Fulbe actors - are but a manifestation of the continued presence of diversity of relations, not of 'symbiosis'. They point to mutual interests between certain actors belonging to different ethnic groups, not between the groups as such.

Spate irrigation has been practised over 100 years in the Red Sea coastal zone of Eritrea such as the Sheeb area. Main problem of the spate irrigation system is water shortage caused by irregular rainfall in the highlands of Eritrea and breaching of the irrigation structures by destructive big floods. Annually, a tremendous amount of soil with nutrients is eroded from the adjacent highlands, transported by seasonal streams (wadis) and deposited on the lowlands in the irrigated fields. The dominant types of soils of Sheeb area are the Fluvisols, which have good physical and chemical properties. The annual sedimentation on the spate fields enables the farmers to harvest a crop without application of fertilisers. A nutrient balance study revealed no soil mining in the spate fields. Farmers in Sheeb could obtain a more uniform water distribution over their fields with better levelling. Of the total area of Sheeb (8,000 ha), about 3,160 ha of land was classified as highly and moderately suitable for spate irrigation. When the flood diversion structures (at wadis Laba and Maiule) are made more permanent, an additional 2, 000 ha of land can be irrigated. In general, spate irrigation production system is a 'cost effective' system if the irrigation structures are properly maintained at low cost and if the fields receive enough water and nutrients.

Metadata only record This book describes the dynamics of actors in Sahelian villages, natural resource dynamics, and interventions by land users.

Spate irrigation has been practised over 100 years in the Red Sea coastal zone of Eritrea such as the Sheeb area. Main problem of the spate irrigation system is water shortage caused by irregular rainfall in the highlands of Eritrea and breaching of the irrigation structures by destructive big floods. Annually, a tremendous amount of soil with nutrients is eroded from the adjacent highlands, transported by seasonal streams (wadis) and deposited on the lowlands in the irrigated fields. The dominant types of soils of Sheeb area are the Fluvisols, which have good physical and chemical properties. The annual sedimentation on the spate fields enables the farmers to harvest a crop without application of fertilisers. A nutrient balance study revealed no soil mining in the spate fields. Farmers in Sheeb could obtain a more uniform water distribution over their fields with better levelling. Of the total area of Sheeb (8,000 ha), about 3,160 ha of land was classified as highly and moderately suitable for spate irrigation. When the flood diversion structures (at wadis Laba and Maiule) are made more permanent, an additional 2, 000 ha of land can be irrigated. In general, spate irrigation production system is a 'cost effective' system if the irrigation structures are properly maintained at low cost and if the fields receive enough water and nutrients.

The efficiency of five aeolian sand samplers was tested via wind tunnel experiments and field measurements. The samplers were: the Big Spring Number Eight (BSNE) sampler, the Modified Wilson and Cooke (MWAC) sampler, the Suspended Sediment Trap (SUSTRA), the Pollet catcher (POLCA), and the saltiphone. In the wind tunnel, the samplers were calibrated against an isokinetic sampler (a modified Sartorius SM 16711 sampler with adjustable flow rate), and this for three sand types (median diameter: 132, 194 and 287 μm) and five wind speeds (ranging from 6.6 to 14.4 m s−1). In the field, seven calibration tests of two weeks each were conducted. The absolute efficiencies of the BSNE, MWAC and POLCA are more or less comparable and vary between 70% and 120%, depending on sediment size and wind speed. For the SUSTRA, the efficiency is somewhat lower for fine sands and for wind speeds above 11 m s−1. Finally, the saltiphone can accurately detect the periods of saltation transport, but in its current version, the instrument is not accurate when measuring the absolute saltation flux. The most recommendable sampler in the test is the MWAC, not only because of its high efficiency, but also because its efficiency is independent of wind speed.

Soil and water conservation is at the top of development agendas in Africa. Virtually every project related to agriculture or the environment has a soil and water conservation component to it and environmental protection plans are being drawn up by African governments in which soil and water conservation figures dominantly. This focus on soil and water conservation is due to its being perceived as a way to address both productivity and environmental sustainability questions. Land degradation and population growth are thought to be rampant in Africa and soil and water conservation helps to increase productivity to feed a growing population and does so in an environmentally sustainable way.Three broad approaches characterize how soil and water should be conserved. The first is a focus on capital-led intensification in the form of machinery and purchased inputs (such as mineral fertilizer and pesticides). This school of thought claims that this is the only way to obtain a fast enough increase in productivity to feed the growing population. The second approach instead focuses on "indigenous technologies", or what farmers develop, adapt, and innovate on their own account. This school claims that technologies will only be used if they are developed by and with farmers so as to take into consideration their social and environmental contexts. There is also what is called the neo-liberal approach in which it is argued that it is not enough to look at technologies, but also policies, infrastructure and markets need to be in place to stimulate the appropriate kinds of land husbandry practices.Despite these variegated approaches, soil and water conservation projects have, at best, had a checkered history. There is a need thus to look at the problem in a different manner than is done by studies that have lead to the above approaches. This study picks up this challenge and tries to theorize and operationalize a different approach to the study of soil and water conservation. It uses elements from previous studies but integrates them in a new way. In part 1 of the book approach, analytical framework and methods are discussed, while part 2 consists of a case study in Burkina Faso (former Upper Volta) in which the proposed approach is put into practice.Chapter 1 describes this approach which is based on three elements: (1) working in an interdisciplinary fashion to allow the integration of different aspects of soil and water conservation, (2) using a grounded theory methodology in which the principal element relates to starting out broad and allowing the concepts and principles to be studied to emerge from fieldwork, and (3) giving particular attention to developing a mutual relationship of trust with villagers in order to allow their opinions and views to influence the focus of the study.Chapter 2 presents the analytical framework that emerged out of the grounded theory methodology. It is an end-product of the research but, nonetheless, figures at the beginning of the book, as a guide to the analysis in part 2. It is presented by discussing the most influential theories that have affected the study of soil and water conservation, followed by an explanation of which elements of these theories have been used in the analytical framework. Malthus and Boserup have had a strong impact on how the land degradation problem is perceived. Both of their theories place the emphasis on population pressure as either a cause or a remedy to land degradation. Because Africa has been experiencing such strong population growth rates since the 1960s, these theories have been particularly influential in placing the emphasis on soil and water conservation technologies as a remedy to an otherwise serious land degradation problem. Neo-Malthusians argue that without outside intervention in soil and water conservation, there will be widespread death and degradation. Neo-Boserupians, instead, explain that once population pressure increases to above certain thresholds, it will act as a stimulus for populations to intensify agriculture and therefore develop better land husbandry practices. Here too, outside intervention can help stimulate this process of intensification.The framework resulting from this study instead, influenced by political ecology, indigenous knowledge, and social anthropological approaches, argues that the dynamics behind African agricultural systems are much more variegated than a single trend towards land degradation allows. The framework questions land degradation narratives and, rather than focus on population density as the harbinger or cure to land degradation, it focuses on the interactions of social and environmental histories of an area in order understand the dynamic landscapes that emerge as a consequence thereof. Part 2 of the book operationalizes this approach by paying attention to social historical processes that took place in the research area within the past century (chapter 4), focusing on long-term environmental change (chapter 5), looking at farmers' soil and water conservation technologies (chapter 6), understanding local economic concepts that influence allocative decisions in agriculture (chapter 7), and how social institutions, and their change over time, affect agriculture in the study region (chapter 8). The last chapter of part 2 pulls the different parts of the analysis together to explain how, in a region that is experiencing all of the trends thought to be harbingers of land degradation, no evidence of land degradation is found (chapter 9). The contents of each of these chapters will be discussed in detail below.The approach used in this study requires a wide variety of methods because different aspects of soil and water conservation need to be studied and because the emphasis on allowing the relevant research concepts to emerge from fieldwork requires starting out in a broad fashion. Chapter 3 presents the methods used in this study and explains the reasoning why these methods were used.Part 2 of the book presents the chapters that aim at answering the three main research questions: (1) what evidence is there of land degradation? (2) how do people go about conserving soil and water? (3) why do people conserve soil and water in the way that they do? Chapter 4 introduces the research area and villages and focuses on the social history of the area since the late nineteenth century. The study takes place in two villages in the eastern region of Burkina Faso and focuses on the Gourmantché system of agriculture. The emphasis on historical changes experienced in this system allows the analyses of the following chapters to be placed within a broader historical picture. Some of the major changes experienced within the last century that have significantly altered the livelihood system are an increased individualization of production and consumption in conjunction with a decline of traditional authorities, increasing cultivation in bush camps, more extensive livestock ownership among the Gourmantché, and an increased monetization and market orientation. These changes have been spurred, among others, by oppressive colonial practices and increased market integration. At the same time, population and livestock densities have risen steeply, raising the question how this has influenced the state of natural resources.Chapter 5 picks up on this question and conducts a multi-scale analysis of the indicators and proxies that are normally used to argue the presence of land degradation trends. Crop yields, agricultural productivity, biodiversity, and soil fertility are analyzed both spatially and temporally at the national, regional, and village levels. No evidence is found to support the land degradation narrative. Furthermore, the chapter highlights some of the weaknesses inherent in the methods used to analyze land degradation. Given the lack of evidence of land degradation, the strong population growth experienced over the last 40 years, and the relatively high rural population densities found in large parts of the country, the chapter excludes Neo-Malthusian predictions of widespread degradation and starvation. In agreement with Boserupian thinking, the evidence put forward in this chapter suggests that some form of agricultural intensification is instead taking place that allows food production to grow along with population. However, contrary to Boserup's theory, there seems to be little evidence that this form of intensification is based on high use of external inputs and increased mechanization. Neither are there any indications that certain population thresholds need to be surpassed before farmers undertake intensification or improve the environmental sustainability of their land use practices. How this intensification takes place and in what form is the topic of the chapters that follow.Chapter 6, takes an indigenous knowledge approach to the study of farmers' soil and water conservation technologies, but focuses not only on descriptions of the technologies as is common in indigenous knowledge studies, but also looks at farmers' theories of soil formation and degradation processes and their own roles within these processes as users of the land. It is found that Gourmantché farmers make use of an extensive repertoire of soil and water conservation practices, most of which are agronomic/biological practices that make use of management skills and biological material. Mechanical practices that make use of physical structures are used, but to a limited extent, and they seem to have declined compared to some 30 to 40 years ago. It is argued, based on stories of informants and an analysis of aerial photographs, that this is not an indication of a decline of "traditional" practices, but an adaptation of their use to changing environmental conditions.One of the most important points raised in this chapter is that Gourmantché farmers adapt their management practices sequentially in the course of a single growing season, as well as during the cultivation cycle of a field. This process of adaptive management has allowed farmers to maintain soil fertility or even improve it on cultivated fields relative to uncultivated land. Adaptive management involves strategic thinking and experimentation, as well as responses to changing soil fertility and unpredictable environmental and socio-economic production constraints. Thus adaptive management is a dynamic process of experimentation, fine-tuning and exploration of new opportunities.As was argued in the analytical framework, an absence of land degradation is not only a sign that appropriate technologies and inputs are being used in a cultivation system, but also that there is a social organization around the land that allows resources necessary for an environmentally sustainable form of agriculture to be accessed. Chapter 7 analyzes the concepts that guide economic action in order to then, in chapter 8, be able to analyze how these concepts influence access to resources for agriculture. Chapter 7 analyzes the local economy by making no a priori assumptions about the type of economy, traditional or market, that guides allocative decisions. Instead, the chapter explores the concepts guiding local economic reasoning. It was found that these concepts cannot be categorized as either purely capitalistic nor traditional. Rather, a mixture is found of market principles and social considerations. Market transactions are pervasive and livelihoods are earned not only through subsistence farming but also through incomes earned with off-farm activities and livestock husbandry. People also engage in profit making activities such as buying grain when it is cheap and reselling it when prices are high, or livestock fattening. At the same time social transactions such as gifts or interest-free loans form an important part of daily life. Even market transactions are characterized by the giving of gifts or discounts. Together, these transactions aim at a delicate balance between earning profits and establishing and maintaining social networks. An analysis of the historical development of market and social institutions does not indicate that the latter are being replaced by the former. The resulting mixture of principles that guide economic action is what we term the cultural economy.Chapter 8 looks at how the mixture of social and market principles affect the way in which agriculture is practiced, and in specific, how they influence the way land is conserved. The chapter highlights how social networks have changed to increasingly be used to access resources for agriculture. With the increased use of land for cultivation, borrowing of land is an option used for not over-cultivating one's own lineage land; as production units have been getting smaller, networks are increasingly used to access labor; with women's greater involvement in agriculture, their natal family ties are used to access necessary resources for conducting agriculture; as more technologies are available for cultivating, networks are used to access them; as Fulbe settle on village territories, new forms of network building are created to allow the rearing of livestock; and finally, as cash needs become greater, ways of networking to access cash are being developed. By looking at networks as a source of access to resources, the issue of accessibility is treated in a broader way than most studies on agricultural productivity and environmental sustainability that instead focus on access of resources through monetary means.The various analyses of the chapters 4 through 8 are drawn together in chapter 9 to explain the lack of land degradation found in the study region while the final chapter of the book draws the conclusions from this case study to a theoretical level. The most important conclusions relating to the study of soil and water conservation are (1) land degradation narratives need to be questioned by analyzing the data on which they are based; (2) while population densities can act as a stimulus to technological intensification, farmers respond to more than just population densities in order to change their agricultural practices. It is therefore necessary to study how populations adapt to changes in the social, economic and physical contexts; (3) technological intensification obtained by some African agricultural systems is based on the knowledge of crops, soils and the environment and the management skills with which this knowledge is applied. This form of intensification has obtained higher levels of productivity and environmental sustainability than approaches advocating capital-led intensification recognize; (4) there is a need for improved scientific methods for understanding the effects of farmers' practices on the environment and agricultural productivity; (5) institutional development that takes on other than capitalistic forms, can, contrary to the assumptions made by studies of capital-led intensification, lead to productive and environmentally sustainable agricultural practices; (6) social networks are not the unchanging characteristics of a traditional system but rather change as a result of people dealing with changing social, economic, and environmental contexts. As such they can be fundamental to making an agricultural system productive and environmentally sustainable; (7) people dispose of both technical as well as social means to affect agricultural performance; (8) forms of intensification in African production systems can only be understood in terms of the dynamic interplay between social and environmental histories. Consequently, there is a need for analytical frameworks that focus on this interplay between social and environmental contexts, rather than assume a simple trend towards increasing land degradation. This kind of approach reveals the dynamic and contrasting trends that can be present in different localities at different points in time. This study offers an example of such an analytical framework and how it can be operationalized, leading to innovative perspectives on African land use systems.The authors can be contacted at: VMazzucato@rcl.wau.nl & DNiemeijer@rcl.wau.nl

Vertical splash drift profiles and horizontal splash drift amounts were measured during a very wet week on a 7.5 ha agricultural field in Gronheim, Germany. Splash was measured on 45 plots distributed all over the field, at seven (Or eight) heights above the surface. The data show that the vertical splash drift profile is best described by a power function of the form G = a.z(b) (or, alternatively, G = c.z(b) - 1), where G is the total mass of sediment splashed up to a height z and a, b and c are empirical parameters. The decrease of G with height z is highly variable within the field, even for one and the same rain shower. Also, the total horizontal splash drift amounts show significant differences within the field. There is no clear relationship between these splash characteristics on the one hand and the topographic position or the properties of the topsoil on the other. It is suggested that spatial variations in rainfall during the rain events are the major cause of the differences in splash drift over the field. Total horizontal splash flux is fairly well predicted by a theoretical splash transport model developed earlier by the second author. Due to the effect of the wind (causing oblique rainfall and an extra-displacement of the soil particles in the downwind direction) the observed fluxes are somewhat higher than the predicted ones, but both are of the same order. The difference indicates the significance of the inclination of the rain with respect to the process of hydraulic splash. ispartof: Agronomie vol:20 issue:3 pages:271-282 status: published

Metadata only record Burkina Faso is a landlocked country in the West-African Sahel. The agricultural sector is the mainstay of the economy but it has to operate in the face of many constraints. Over the last few decades, rainfall has become increasingly unreliable and the country suffered major droughts in the 1970s and 1980s. Pressure on natural resources is increasing. Farmers have to maintain their livelihoods in these unfavorable and changing conditions, and find solutions that will allow them to continue cultivating in a sustainable way. This chapter analyses the dynamics of soil management in two villages and focuses on several promising technologies which include composting with rock phosphate, planting pits (zaïs) and methods to control soil erosion.

Wind Erosion Processes and Control Techniques in the Sahelian Zone of Niger G. Sterk, L. Stroosnijder, and P.A.C. Raats Abstract The objective of this paper is to present the main results and conclusions from three years of field research on wind erosion processes and control techniques in the Sahelian zone of Niger. Sediment transport was quantified with sediment catchers, and storm based maps of mass transport were made by applying geostatistics. The maps were used to calculate soil losses from the plot. In total, 45.9 Mg ha-1 were lost during four storms. Samples of trapped material were collected and analyzed on total element (TE) contents of K, C, N, and P. The losses of these elements during two storms were equal to approximately 3% of the TE masses that were present in the top 0.10 m of the soil. Wind erosion can be reduced by applying erosion control techniques. A survey in seven villages revealed that mulching with crop residues is the main control technique applied by farmers. Field tests with flat pearl millet stalks showed that small quantities of 1000 and 1500 kg ha-1 can significantly reduce sediment transport during most storms. But, the availability of crop residues for mulching is limited due to other uses. Therefore, future research should concentrate on enhancement of biomass production for wind erosion control purposes.

Wind Erosion Processes and Control Techniques in the Sahelian Zone of Niger G. Sterk, L. Stroosnijder, and P.A.C. Raats Abstract The objective of this paper is to present the main results and conclusions from three years of field research on wind erosion processes and control techniques in the Sahelian zone of Niger. Sediment transport was quantified with sediment catchers, and storm based maps of mass transport were made by applying geostatistics. The maps were used to calculate soil losses from the plot. In total, 45.9 Mg ha-1 were lost during four storms. Samples of trapped material were collected and analyzed on total element (TE) contents of K, C, N, and P. The losses of these elements during two storms were equal to approximately 3% of the TE masses that were present in the top 0.10 m of the soil. Wind erosion can be reduced by applying erosion control techniques. A survey in seven villages revealed that mulching with crop residues is the main control technique applied by farmers. Field tests with flat pearl millet stalks showed that small quantities of 1000 and 1500 kg ha-1 can significantly reduce sediment transport during most storms. But, the availability of crop residues for mulching is limited due to other uses. Therefore, future research should concentrate on enhancement of biomass production for wind erosion control purposes.

The effect of termites on the breakdown of Pennisetum pedicellatum straw under Sahelian conditions was studied in northern Burkina Faso during the dry and wet seasons of 1995. Litterbags were laid on plots treated with drieldrin at a rate of 500 g a.i. (active ingredient) ha–1 to exclude termite activity and on untreated plots. Termites were the only macroscopically visible consumers which were observed in the litterbags during the dry and wet season. In litterbags with no termites present the rate of breakdown of straw was lower during both the dry or wet seasons than in litterbags with termites. In the litterbags with termites, much of the mulch was taken off and replaced by termite-made sheeting. From April to September over 60% of the added material disappeared from termite litterbags, while only 18% of the added straw disappeared from litterbags without termites. From October to December, 28% of the straw disappeared from termite-infested litterbags versus 8% from litterbags without termites. The contribution of termites to the breakdown of straw was estimated to be over 70% for each of the two experiments. Under Sahelian conditions, the breakdown of organic residues is strongly influenced by termites.

This paper analyzes the use of stratification in the modeling of dependence for regionalized variables in space and time. Stratification enables optimal use of available information, and it is used when deterministic, small-scale information is combined with large-scale random variation: on the one hand, the problem of having too few data to reliably estimate statistical parameters may be solved by stratification; on the other hand some variation may be so obvious that it serves as a prerequisite for obtaining any form of stationarity. The paper is illustrated with four case-studies. The first study analyzes optimization of an extant groundwater monitoring network within a catchment of the river Rhine. Stratification in space enabled 5 cm precision of predicted levels at critical locations, something that could not be reached without stratification. The second study analyzed variability in space and time of wind erosion in a field. Erosion by four storms was measured with 21 devices. Use of temporal stratification to overcome lack of spatial data resulted, in one instance, in a decrease of 17 percent in mean absolute error. The third study addressed changes in the soil solution influenced by environmental deposition over a period of six years. Stratification was made in space to enable analysis in the time domain and to obtain spatio-temporal maps. The fourth study used a general space-time model to evaluate the development of root-rot in soybean, caused by naturally occurring pathogens. Predictions were made at unvisited times to estimate the probability of occurrence of root rot. We conclude that use of stratification enhances the utility of space-time statistics for the solution of various environmental and agricultural problems.

Peter Oksen's comments on our paper about farmer-herdsman relations in Burkina Faso raise some interesting issues, notably regarding problems of interpretation of oral and archival sources and regarding the broader relevance of insights gained from an in-depth case study. Before answering straightforwardly to his objections, it is useful to clarify the misunderstanding which appears to exist about the meaning we attribute to 'symbiosis' and 'symbiotic relations'. In our article we restricted the use of these terms to the way in which past relations between farmers and herdsmen, depicted as undifferentiated groups, are often represented. In discussions about the change of these relations, the emphasis is on progressive deterioration, again without attention paid to the possible existence of intra-group differentiation or of heterogeneity of relations across group boundaries. In this regard, it is remarkable that from colonial documents the interests of farmers and herdsmen emerge as equally irreconcilable as they are often considered today, and that, just as at present, competition over scarce natural resources constituted a major factor in inter-group relations. If we therefore reject 'symbiosis' as a correct description of formerly existing inter-group relations, we do not intend to imply that complementary links - such as those we describe for present-day relations between Mossi and Fulbe - did not exist in the past. A major aspect of our argument is that inter-group relations, whether past or present, cannot be subsumed under simplifying labels such as 'symbiosis'. Neither can changes in these relations be understood in terms of uni-directionally processes of deterioration. Hence, present-day 'complementary' links across the ethnic boundary - established by certain, but not all, Mossi and Fulbe actors - are but a manifestation of the continued presence of diversity of relations, not of 'symbiosis'. They point to mutual interests between certain actors belonging to different ethnic groups, not between the groups as such.

Soil tillage is the manipulation of soil which is generally considered as necessary to obtain optimum growth conditions for a crop. In the same time the resulting modification of soil structure has serious implications for the behaviour of the soil to erosive forces by water and wind. In Chapter 1 an introduction is given to the most important aspects: the objectives of tillage, the conflicting requirements set to tillage, the characteristics of soil and water conservation in the semi-arid tropics, and the nature of tillage research including modelling.Chapter 2 treats in detail the characteristics of the soils often found in the semi-arid tropics: the SCH soils (sealing, crusting and hardsetting). Sealing and crusting causes problems with emergence of seedlings and with infiltration. The hardsetting soils are difficult to manage, particularly when tillage has to be performed with limited energy inputs. Physical characteristics and low organic matter contents are primarily responsible for SCH behaviour.In case 1, research undertaken in Mali is reported. Sandy soils of the Sahel area, mainly cropped to millet (Pennisetum glaucum (L.) R.Br.) are very sensitive to crust formation. These crusts were found to strongly reduce infiltration capacity. On the typically gently (1-3%) fields runoff is a widespread phenomenon; on the average 25% of the rain (mainly in the form of a few large storms during the rainy season) is lost by runoff. Crust formation and its effect on the infiltration rate was studied in experiments using a rainfall simulator are discussed. On untilled soils the presence of a crust is a permanent feature, and the effect of superficial tillage on crust disturbance disappeared quickly under subsequent rainfall. It was established that rainfall characteristics (aggressiveness, intensity) play a key role in crust formation.Research reported in case 2 was carried out in Niger. Here, important processes of soil structural changes under rainfall were assessed, to obtain a basis for a proper development of improved soil management methods. Soil and rainfall characteristics of a millet growing area close to Niamey, were determined. Laboratory tests showed a confirmation of what was observed in the field, namely that the coarse sandy soil of the area shows a mechanical behaviour which is extremely dependent on the moisture content at the time of soil handling. Therefore, the workability range is very narrow. Special tillage under wet conditions, resulting in smearing of the surface layer caused a condition which was more resistant to wind erosion. In an extension of the analyses reported in case 1, it was found the rainfall in this region is aggressive; even small storms may fall with high intensities.The major rainfall characteristics of the Sahel differ significantly from those of other semi-arid areas (such as India). The erratic rainfall pattern in combination with the sandy nature of the soil in the region studied, leads to an extremely small number of days available for planting millet, on average around 11 for the season. Therefore, time-efficiency of soil preparation and planting methods is even more important than a positive effect on SWC and crop emergence aspects.Chapter 3 gives a review of the various tillage systems as they may be applied for soil and water conservation, based the soil characteristics and on different mechanization levels.A study carried out in Brazil is presented in case 3. In a highly mechanized farming situation, erosion problems on sloping, red soils in the state of Paraná are high. Conventional tillage is based on the use of heavy disk ploughs and repeated passes with disk harrows in order to prepare a seedbed. This system causes severe erosion damage because of reduced infiltration rates and unstable topsoil. The zero-tillage system is a promising and realistic alternative, but is not suited for all farms in the state (small fields, high capital investment for equipment required, lacking knowledge and experience of farmers). The possibilities for the use of chisel ploughs (as an alternative between these two systems) on wheat stubble in a wheat-soybean rotation were investigated.Experiments showed that, compared to conventional tillage systems with disc implements, chisel ploughing left more plant residue at the surface. Except for the duckfoot type, the chisels were able to penetrate down to the bottom of a compacted layer at 12-20 cm depth. In addition, fuel consumption was significantly lower than disc ploughing and slightly higher than heavy disc harrowing. The capacities of the chisel ploughs were comparable to the heavy disc harrow. On the other hand, weeds and large amounts of straw may cause considerable practical difficulties and require adequately dimensioned chisel ploughs. Thus when applying the alternative tillage, adapted sowing equipment, able to cope with surface residue is required.In case 4, studies on the agronomic effect of tillage systems fit for animal traction in West Africa are reported. Crop establishment is an important yield factor for pearl millet in the Sahel. Therefore, a series of experiments was conducted to determine the effects of seed size, depth and method of planting, millet variety, tillage, and soil fertilization upon seedling emergence, crop establishment, and yield. All experiments were conducted on a sandy Psammentic Paleustalf in Niger. Three millet varieties were studied, and for all of these, out of a range of sowing depths from 1 to 7 cm, a sowing depth of 3-5 cm resulted in the highest percentage emergence, the highest above-ground biomass, and most secondary roots. High soil temperatures are common during establishment, typical maximum temperatures at a depth of 1 cm exceed 46 °C. It was found that the adverse effects of wind erosion and these high temperatures were least when sowing in hills (the traditional hand-method); establishment, crop stand survival, and yield were better under hill planting than drilling seed.Tillage of the field before sowing increased initial stands and their survival, the latter also depending on fertility. Thus, improved crop yields result from better stand survival and higher yields per hill. Fertilizer application (17 kg ha -1P and 40 kg ha -1of N) caused a threefold increase in grain yields. Ridging without prior tillage and ploughing increased grain and stover yields two- to three-fold. In combination with fertilizer application, sixfold yield increases were obtained. In view of the time limitations, ridging without prior tillage was preferable to ploughing, as it is a much faster operation giving equally good results in terms of crop establishment and yield.Chapter 4 deals with simulation models for soil and water conservation and the difficulties of modelling tillage effects. A review of the most important models currently used in SWC is presented with a brief indication if and how tillage is incorporated in these models. Various options of approaching tillage effects by modelling are given.In case 5, the development and application of a model simulating the role of tillage in SWC is presented. The data used are mainly from the situation prevailing in the West African Sahel and Sudan zone, characterized by a low input (particular N and P) rainfed farming system, growing cereal crops such as millet. Two types of soil tillage are distinguished: tillage aimed at water conservation (by increasing infiltration and/or surface roughness) and tillage aimed at weed control. Various scenarios are evaluated by combining simulation models for plant production (WOFOST) and soil water movement (SWATRE), developed and adapted for application in these regions. Based on simulations of 35 years of weather data, it was found that water conserving tillage as such has a very small yield-conserving effect because of the limitations set by the nutrient status. Elimination by tillage of the competition by weeds had a larger effect on the grain yield of a millet crop.In case 6, the water balance for millet fields and for permanently crusted natural pastures is described, with special emphasis on the role of the crust in governing infiltration and runoff. This study was based on the same field experiments in Mali as described in case 1. It was tried to quantify the effect of tillage as it destroys the crust and increases the surface storage for rainwater. The crust-breaking effect was found to last for only a few rainshowers, but the increase of surface storage is more permanent. The effect of a tillage system on the water balance of a millet crop was calculated. From this calculation it was concluded that tied ridges, giving a surface storage of 20-30 mm, could completely prevent runoff, compared to about 50% loss under the conventional system. Such a savings would allow earlier sowing and thus prolong the vegetative growth by as much as 20 days, which might increase the average millet yield (500 kg ha -1) by 40%.In Chapter 5, the prospects for development of tillage systems for the difficult SCH soils are discussed. Analysis of the various options shows that no-tillage is not a solution for the semi-arid tropics with hardsetting soils. It also can be argued that the introduction of animal traction in situations with purely handlabour, in many cases is not feasible, and notwithstanding all other problems, tillage by tractors should be investigated as a serious option.

Soil tillage is the manipulation of soil which is generally considered as necessary to obtain optimum growth conditions for a crop. In the same time the resulting modification of soil structure has serious implications for the behaviour of the soil to erosive forces by water and wind. In Chapter 1 an introduction is given to the most important aspects: the objectives of tillage, the conflicting requirements set to tillage, the characteristics of soil and water conservation in the semi-arid tropics, and the nature of tillage research including modelling.Chapter 2 treats in detail the characteristics of the soils often found in the semi-arid tropics: the SCH soils (sealing, crusting and hardsetting). Sealing and crusting causes problems with emergence of seedlings and with infiltration. The hardsetting soils are difficult to manage, particularly when tillage has to be performed with limited energy inputs. Physical characteristics and low organic matter contents are primarily responsible for SCH behaviour.In case 1, research undertaken in Mali is reported. Sandy soils of the Sahel area, mainly cropped to millet (Pennisetum glaucum (L.) R.Br.) are very sensitive to crust formation. These crusts were found to strongly reduce infiltration capacity. On the typically gently (1-3%) fields runoff is a widespread phenomenon; on the average 25% of the rain (mainly in the form of a few large storms during the rainy season) is lost by runoff. Crust formation and its effect on the infiltration rate was studied in experiments using a rainfall simulator are discussed. On untilled soils the presence of a crust is a permanent feature, and the effect of superficial tillage on crust disturbance disappeared quickly under subsequent rainfall. It was established that rainfall characteristics (aggressiveness, intensity) play a key role in crust formation.Research reported in case 2 was carried out in Niger. Here, important processes of soil structural changes under rainfall were assessed, to obtain a basis for a proper development of improved soil management methods. Soil and rainfall characteristics of a millet growing area close to Niamey, were determined. Laboratory tests showed a confirmation of what was observed in the field, namely that the coarse sandy soil of the area shows a mechanical behaviour which is extremely dependent on the moisture content at the time of soil handling. Therefore, the workability range is very narrow. Special tillage under wet conditions, resulting in smearing of the surface layer caused a condition which was more resistant to wind erosion. In an extension of the analyses reported in case 1, it was found the rainfall in this region is aggressive; even small storms may fall with high intensities.The major rainfall characteristics of the Sahel differ significantly from those of other semi-arid areas (such as India). The erratic rainfall pattern in combination with the sandy nature of the soil in the region studied, leads to an extremely small number of days available for planting millet, on average around 11 for the season. Therefore, time-efficiency of soil preparation and planting methods is even more important than a positive effect on SWC and crop emergence aspects.Chapter 3 gives a review of the various tillage systems as they may be applied for soil and water conservation, based the soil characteristics and on different mechanization levels.A study carried out in Brazil is presented in case 3. In a highly mechanized farming situation, erosion problems on sloping, red soils in the state of Paraná are high. Conventional tillage is based on the use of heavy disk ploughs and repeated passes with disk harrows in order to prepare a seedbed. This system causes severe erosion damage because of reduced infiltration rates and unstable topsoil. The zero-tillage system is a promising and realistic alternative, but is not suited for all farms in the state (small fields, high capital investment for equipment required, lacking knowledge and experience of farmers). The possibilities for the use of chisel ploughs (as an alternative between these two systems) on wheat stubble in a wheat-soybean rotation were investigated.Experiments showed that, compared to conventional tillage systems with disc implements, chisel ploughing left more plant residue at the surface. Except for the duckfoot type, the chisels were able to penetrate down to the bottom of a compacted layer at 12-20 cm depth. In addition, fuel consumption was significantly lower than disc ploughing and slightly higher than heavy disc harrowing. The capacities of the chisel ploughs were comparable to the heavy disc harrow. On the other hand, weeds and large amounts of straw may cause considerable practical difficulties and require adequately dimensioned chisel ploughs. Thus when applying the alternative tillage, adapted sowing equipment, able to cope with surface residue is required.In case 4, studies on the agronomic effect of tillage systems fit for animal traction in West Africa are reported. Crop establishment is an important yield factor for pearl millet in the Sahel. Therefore, a series of experiments was conducted to determine the effects of seed size, depth and method of planting, millet variety, tillage, and soil fertilization upon seedling emergence, crop establishment, and yield. All experiments were conducted on a sandy Psammentic Paleustalf in Niger. Three millet varieties were studied, and for all of these, out of a range of sowing depths from 1 to 7 cm, a sowing depth of 3-5 cm resulted in the highest percentage emergence, the highest above-ground biomass, and most secondary roots. High soil temperatures are common during establishment, typical maximum temperatures at a depth of 1 cm exceed 46 °C. It was found that the adverse effects of wind erosion and these high temperatures were least when sowing in hills (the traditional hand-method); establishment, crop stand survival, and yield were better under hill planting than drilling seed.Tillage of the field before sowing increased initial stands and their survival, the latter also depending on fertility. Thus, improved crop yields result from better stand survival and higher yields per hill. Fertilizer application (17 kg ha -1P and 40 kg ha -1of N) caused a threefold increase in grain yields. Ridging without prior tillage and ploughing increased grain and stover yields two- to three-fold. In combination with fertilizer application, sixfold yield increases were obtained. In view of the time limitations, ridging without prior tillage was preferable to ploughing, as it is a much faster operation giving equally good results in terms of crop establishment and yield.Chapter 4 deals with simulation models for soil and water conservation and the difficulties of modelling tillage effects. A review of the most important models currently used in SWC is presented with a brief indication if and how tillage is incorporated in these models. Various options of approaching tillage effects by modelling are given.In case 5, the development and application of a model simulating the role of tillage in SWC is presented. The data used are mainly from the situation prevailing in the West African Sahel and Sudan zone, characterized by a low input (particular N and P) rainfed farming system, growing cereal crops such as millet. Two types of soil tillage are distinguished: tillage aimed at water conservation (by increasing infiltration and/or surface roughness) and tillage aimed at weed control. Various scenarios are evaluated by combining simulation models for plant production (WOFOST) and soil water movement (SWATRE), developed and adapted for application in these regions. Based on simulations of 35 years of weather data, it was found that water conserving tillage as such has a very small yield-conserving effect because of the limitations set by the nutrient status. Elimination by tillage of the competition by weeds had a larger effect on the grain yield of a millet crop.In case 6, the water balance for millet fields and for permanently crusted natural pastures is described, with special emphasis on the role of the crust in governing infiltration and runoff. This study was based on the same field experiments in Mali as described in case 1. It was tried to quantify the effect of tillage as it destroys the crust and increases the surface storage for rainwater. The crust-breaking effect was found to last for only a few rainshowers, but the increase of surface storage is more permanent. The effect of a tillage system on the water balance of a millet crop was calculated. From this calculation it was concluded that tied ridges, giving a surface storage of 20-30 mm, could completely prevent runoff, compared to about 50% loss under the conventional system. Such a savings would allow earlier sowing and thus prolong the vegetative growth by as much as 20 days, which might increase the average millet yield (500 kg ha -1) by 40%.In Chapter 5, the prospects for development of tillage systems for the difficult SCH soils are discussed. Analysis of the various options shows that no-tillage is not a solution for the semi-arid tropics with hardsetting soils. It also can be argued that the introduction of animal traction in situations with purely handlabour, in many cases is not feasible, and notwithstanding all other problems, tillage by tractors should be investigated as a serious option.

This book is written for students and researchers with a keen interest in the quantification of the field soil water balance in tropical environments and the effect of conservation farming on crop production. Part 1 deals with the potential production, i.e. crop growth under ample supply of water nutrients in a pest-, disease- and weed-free environment. Part 2 deals with crop production under rainfed or water-limited conditions by including the crop water balance as well as the soil water balance. Both models use maize as an example. The way the MAIZE models are presented differs from the modular structure of present day models, where separate data blocks for soil, crop and climate are added at the end of a main programme. Here, the explanatory text follows, as closely as possible, the computer listing of the model. Each chapter starts with a number of lines which were copied from the listing. Subsequently, the terminology is justified and the input data and the dimensions of variables are explained. Another special feature is the fact that parameter and function values are defined directly after the line in which they are used for the first time. This method highlights the places where the model needs input from the user. In this way it is stressed that the accuracy of the model depends on the availability and quality of the input data, together with the correct understanding and description of the processes involved. The third part of this book contains a number of applications

When vegetation is drastically reduced as a result of drought or an increase in herbivore numbers, it does not simply recover if periods with normal rainfall follow or if herbivores are removed. These are commonly recognized catastrophic phenomena of semi-arid grazing systems in general and of the African Sahel in particular. The main aims of this thesis are to provide an effective explanation of the catastrophic properties of vegetation dynamics in these systems and to predict under which conditions they might be expected.We start with a description of Sahelian rangeland vegetation dynamics, to reveal its catastrophic properties. This exercise appeared a very useful first step in the growth of our ideas about catastrophic vegetation dynamics because: 1) it translated rather vague concepts into a verifiable format by deducing hypotheses about the conditions under which catastrophic vegetation dynamics might be expected, and 2) it generated the notion that soil degradation could somehow be an important factor attributing to catastrophic vegetation dynamics in semi-arid grazing systems. This is in contrast with models that emphasize herbivore feeding characteristics or plant competition as possible mechanisms underlying catastrophic vegetation dynamics. We tested the hypothesis that soil degradation, i.e. soil erosion by run-off and wind and the consequent loss of water and nutrients, is sufficient to explain catastrophic vegetation dynamics by mathematical modelling.Our model studies indeed show that soil degradation can effectively explain the catastrophic properties of semi-arid grazing systems. Soil degradation can cause a positive feedback between reduced resource (soil water and nutrients) availability and reduced vegetation biomass which may lead to collapse of the system. This positive feedback loop can be triggered by grazing. We argue on the basis of a large body of literature that this is an important mechanism causing catastrophic vegetation dynamics in semi-arid grazing systems. Furthermore, our model studies predict for which site-specific properties catastrophic vegetation dynamics may be expected, that is on loamy or clayey soils in case of water-limited vegetation biomass production, and on sandy soils in case of nutrient-limited biomass production. This is because sandy soils have higher water infiltration rates but are more vulnerable to nutrient loss through erosion than loamy or clayey soils.Based on our models, we hypothesized that the removal of aboveground herbaceous biomass would lead to a reduced soil water content and biomass production because of reduced water infiltration and increased run-off. We tested this hypothesis in a semi-arid savanna in Tanzania (East Africa). Indeed, as a consequence of biomass removal, a reduction in soil water content and biomass production occurred. But it appeared that increased loss of soil water through increased soil evaporation as a consequence of litter removal ultimately outbalanced all other effects on soil water content. Several factors might have contributed to the importance of increased soil evaporation, overriding that of reduced water infiltration and increased run-off. The soil in the research area was a sandy loam, with higher water infiltration rates than soils with a lower percentage sand and higher perentage clay, while rainfall primarily occurred in light showers. Thus, under these conditions, when the positive feedback between reduced water infiltration and reduced biomass does not operate, another positive feedback that is between increased soil evaporation and reduced biomass may become prominent.We further hypothesized that at a certain range of herbivore impact small initial differences in plant cover and amount of soil resources can magnify to alternative states which persist in time due to positive plant-soil feedbacks. We tested this hypothesis in a semi-arid grazing system in Burkina Faso (West Africa), where we studied vegetation patchiness along a gradient of herbivore impact. Indeed, the occurrence and likely persistence of a spatial pattern of vegetated patches alternating with bare soil at a certain range of herbivore impact could be explained by the positive plant-soil feedback between vegetation biomass and water infiltration.We stress the general applicability of our models by comparing catastrophic vegetation dynamics of the semi-arid grasslands of the African Sahel with the arctic salt marshes along the Hudson Bay in Canada. We argue that in both systems, an increase of herbivory triggered a catastrophic vegetation shift, which was ultimately caused by a positive plant-soil feedback, leading to desertification.One of our model assumptions was that herbivore density is not regulated by vegetation biomass. In the general discussion, I investigated the influence of a positive feedback between vegetation biomass and water infiltration on the dynamics of a plant-herbivore system, where herbivore density depends on vegetation biomass. As a consequence of the positive feedback and if herbivore reproduction is efficient, I predict that the plant-herbivore system could destabilize and collapse. In this chapter I also stress the practical relevance of our studies as our approach may finally lead to objective ecological criteria on which pastoral managers can base their decision how to evade the hazard of degradation of their rangelands.I highlight three topics which deserve more priority on the reseach agenda concerning semi-arid grazing systems in the near future. Hereby, I want to stress that it is important to put experimental and empirical studies into a clear theoretical framework, whereby mathematical modelling should play an important role. The three topics are:spatial heterogeneity and vegetation pattern formation,facilitation and competition between functional plant groups within the herbaceous layer andthe effects of positive plant-soil feedbacks on herbivore dynamics.

Termites are an important component of agroecosystems, particularly in developing countries where they are an alternative to high priced inputs. Given the major problems in the Sahel of soil crusting and nutrient depletion, this paper shows that termites associated with proper management techniques can play a vital role. Termites contribute to the rehabilitation of crusted soils, i.e. by opening up voids on the sealed surface leading to improved infiltration capacity, and consequently improved water availability. It is recommended, however, that participatory on-farm research should be carried out on how to increase the contribution of termites towards soil management and to reduce the harmful effects.

This book is written for students and researchers with a keen interest in the quantification of the field soil water balance in tropical environments and the effect of conservation farming on crop production. Part 1 deals with the potential production, i.e. crop growth under ample supply of water nutrients in a pest-, disease- and weed-free environment. Part 2 deals with crop production under rainfed or water-limited conditions by including the crop water balance as well as the soil water balance. Both models use maize as an example. The way the MAIZE models are presented differs from the modular structure of present day models, where separate data blocks for soil, crop and climate are added at the end of a main programme. Here, the explanatory text follows, as closely as possible, the computer listing of the model. Each chapter starts with a number of lines which were copied from the listing. Subsequently, the terminology is justified and the input data and the dimensions of variables are explained. Another special feature is the fact that parameter and function values are defined directly after the line in which they are used for the first time. This method highlights the places where the model needs input from the user. In this way it is stressed that the accuracy of the model depends on the availability and quality of the input data, together with the correct understanding and description of the processes involved. The third part of this book contains a number of applications

Research themeThe central theme of this thesis is the relation between irrigation development and gendered poverty alleviation in rural areas in developing countries. The focus is on the role of the irrigation sector. The sector comprises national and international governmental and non-commercial non-governmental agencies which develop irrigation infrastructure. They provide organizational, technical, and financial support to that end and participate in arranging the vesting of rights to the improved resources of irrigated land and water. The research questions concern, firstly, the effects of access by poor men and women to irrigated land and water on both poverty alleviation and productivity; secondly, inclusion and exclusion processes in irrigation; and, thirdly the role of the irrigation sector in these processes. This provides insight into the agencies' targeting of their support, and into the factors that critically contribute to vesting rights to irrigated land and water in poor men and women, and, hence, to poverty alleviation and productivity.The analysis explicitly includes rural women. They constitute the majority of the poor. Improvement of their incomes strongly contributes to family welfare and to the reduction of fertility rates. A gender-differentiated analysis requires the distinction of intra-household production units and women's and men's own resource rights.MethodThe three research questions are addressed in a review of global literature (Chapter Two, Three and Four), and in two field studies on external irrigation support for rice cultivation. The case in Burkina Faso concerns public irrigation by a state agency. The intervention is accompanied by land expropriation and reallocation. Ten subsequently constructed schemes are studied. Rice cultivation is a female cropping system in the region (Chapter Five). The subject in Bangladesh is NGO-supported private pump ownership by groups of marginal farmers and landless women and men, who use the water for irrigating their own household land and for sale. A country-wide study is made of 52 irrigation groups in which the irrigation loans are taken in women's names. They are supported by six NGOs. Irrigated rice cultivation is a male cropping system there (Chapter Six).Irrigation, poverty alleviation and productivityAccess to irrigated land and water by poor men and women generally improves their well-being (Chapter Two). Water is often a leading input for agricultural intensification, and for stabilization and growth of production during a longer period of the year. It fits the needs of farmers in increasingly smaller holdings. Water sale by smallholders and landless people provides an income, in principle. Remarking these positive effects is not to deny that lack of access to irrigated land and water is only one aspect of the state of multidimensional deprivation which poverty is. Improved access is not necessarily the most urgent need, the sufficient solution, nor the most feasible solution. It is a potential solution for only part of the world's poor. It is a sustainable solution only if the ecological resource base is conserved.The field study in Burkina Faso highlights the importance of women's own resource rights for their own well-being and for family welfare, and also for improved productivity. In Bangladesh, however, there appear to be hardly or no economic benefits from water sale for most irrigation groups. On the other hand, the non-economic status of women members of irrigation groups tends to improve, in the sense of women's self-concept and public behavior and their status within the family and the community.In many circumstances, access to irrigated land and water by the poor not only alleviates poverty but also leads to higher productivity (Chapter Two). Evidence shows that agricultural output per unit of land in smaller irrigated holdings is higher than in larger holdings. This relative higher productivity may disappear, however, if large farmers adopt large-scale mechanization; secondly, if the poor have limited access to other agricultural inputs; and, thirdly, if income diversification strategies lead the poor to take up employment far from home. There is also considerable evidence in the literature that gender by itself does not effect a farmer's production efficiency. The case studies also indicate the relatively good performance of poor producers and water sellers. In female cropping systems, like rice cultivation by most ethnic groups studied in the Burkina Faso case, women are the main producers.Evidence in the literature shows that if larger farmers obtain access to irrigated land and water, this may provide paid employment and a commercial offer of water to smallholders, and thus alleviate poverty indirectly. An increased food supply lowers the food prices. However, the effects are limited since the larger farmers largely set the terms of inclusion. The purchasing power of poor net buyers of food may still be too limited to buy the increased food supply. Poor net producers of food, on the other hand, benefit from high food prices. Moreover, access to irrigated land and water by larger farmers can also be at the direct expense of the poor. Such competition is likely to become more severe with growing water scarcity. Therefore, the irrigation sector contributes optimally to both poverty alleviation and productivity by targeting the poor and avoiding leakage of external support to the non-poor.TargetingThe contribution that the irrigation sector can make to poverty alleviation and increased productivity, given its mandate and core competence, is in vesting rights to irrigated land and water primarily in poor men and women, and redressing existing imbalances in resource rights in favor of the poor. The role of the irrigation sector in providing some users' groups with access to newly developed irrigated land and water, and excluding others, is identified in Chapters Three and Four, and empirically researched in the field studies. The type of irrigation support, the phase of a scheme, and the communication networks at the interface of agency and local people, are important variables in these inclusion and exclusion processes.The influence of the agency is especially strong in public irrigation, which is defined as irrigation in which the external agencies bear most of the costs of the infrastructure. Agencies usually have a powerful say in the physical design, and as investors their definition of their own claims and the users' claims to the water tends to be seen as legitimate. In private irrigation the water users are the main investors in the infrastructure. These private investors largely decide on the physical characteristics of the scheme and dispose of the water conveyed. The steering role of agencies is indirect and usually more limited.The definition of rights, and the role of agencies, differ according to the phase of a scheme. Usually the most important negotiations on the rights to irrigated land and water take place when infrastructure is newly constructed. Participation in these investments, either in cash or kind, are a firm basis to claim rights to the fruits in later phases, and over the generations. New construction is rare nowadays. Instead, the major redefinition of water rights occurs in irrigation management transfer and rehabilitation programs.It is an empirical question in which social fields the expropriation and reallocation of resource rights of users are negotiated under intervention, but, generally, these fields are embedded in the communication networks between local people and external agencies. Processes of inclusion and exclusion of the poor take place in these fields. If the poor are included in these networks, this network is called an 'inclusive forum'. Any new initiative of the agency, such as rehabilitation or irrigation management transfer, entails more or less substantially restructuring the local networks and redefining their competences.From the analysis of inclusion and exclusion processes in externally supported irrigation development, according to the literature and as studied in the field, it is concluded that there is considerable scope to improve the performance of the irrigation sector in vesting rights to irrigated land and water primarily in poor men and women, and in avoiding leakage. A combination of the following factors in agencies' targeting approaches appears to be pivotal.Organizational supportTargeting support is only possible if agencies work through inclusive forums at local level, composed of the priority target groups. The earlier these forums are established in an intervention process, the fewer rights become vested in the non-poor, which would hamper the later inclusion of new groups, in particular the poor. Organizational support in creating this forum is required, since poor women and men are usually not organized to that end.By now, several governmental and non-governmental irrigation agencies worldwide have succeeded in establishing such forums. These agencies have explicit and clear target group criteria, and adhere to those criteria during implementation. Culturally appropriate forms for effective participation of women in mixed-sex forums are created as well. Women are even the majority of the members of such forums in, for example, NGO-supported groups in Bangladesh.Poor people's existing organizations, and their motivation to be included in irrigation development, provide a substantive basis for these inclusive forums. In the later schemes studied in Burkina Faso, inclusive forums with women emerged even in spite of the male-biased targeting approach of the project management, which they had already implemented in earlier schemes. Such inclusion better fitted the prevailing social relations of production, for which the field staff was more receptive than the management.A rather poorly documented but important factor in excluding the poor from irrigation development appears to be the tendency of agencies themselves to confine their interactions to the decentralized branches of administrative and technical ministries, and to the local people who have most contacts with these institutions. These communication channels are dominated by the male local elite. By defining irrigation development as a matter of neutral tasks, and by failing to specify who at local level is supposed to participate and to be vested with the rights to these resources, the male elite act as a quick and effective partner in implementing these tasks. Tight implementation schedules and task-oriented reward structures for agencies' staff foster this. Within these task-oriented local networks, the elite easily claim the rights to the newly developed resources. In the early schemes studied in Burkina Faso, women lost their former land rights in this way, whereas men were endowed with rights they traditionally never had. The project's unrealistic concept of the unitary household farm represented by the male head was instrumental in this.The social fields in which rights are defined evolve over time as the social fields in which rights are implemented. In the use phase this social field is currently called a water users' organization. Membership of these organizations is closely related to having legitimate rights to irrigated land and water. Exclusion of women implicitly takes place if rights are vested in households, thought to be represented by the male head. Womens' inclusion requires the separate vesting of rights in both men and women. Poor land users with weak land rights are included as potential right holders if water rights are disconnected from land ownership. The recognition of pre-project rights, including those according to local legal systems, as a basis to vest new rights is likely to favor the poor, who, in the past, often lost their former rights without compensation.Only through inclusive forums can technical and financial support reach the poor. The types of technical and financial support, in their turn, further shape the organizational support required.Technical supportIn public irrigation, the technical support in the construction, operation and maintenance of infrastructure entails major inclusion or exclusion processes in two respects. Firstly, the site-selection, layout and division structures heavily influence whose land can be irrigated, and how well. If land tenure in the command area does not change, the physical design directly determines whether the poor or the non-poor obtain access to irrigated land. In the past, the non-poor have often been favored in this way. If land reform in the command area is possible or needed, this usually offers good opportunities to provide primarily the poor with access to irrigated land. However, these opportunities are rarely used. Land expropriation even ousted poor men and especially poor women not only in Burkina Faso but also elsewhere.Secondly, agencies in public irrigation can vest users' rights to the newly developed water, and sometimes to irrigated land as well, by arranging co-investments in construction and maintenance work in the form of labor and/or other contributions. An effective means to include the poor is explicitly opening up these opportunities to poor men and women. Timely and transparent procedures better guarantee that investments by the poor are effectively linked to rights. Poor women have often been entirely excluded from these opportunities, or their investments did not lead to rights as they did for men.In private irrigation, the poor obtain access to irrigated land and water as owners of equipment if appropriate equipment and energy sources are available. Commercial technology often does not fit these needs, or collective ownership is needed. The latter has been studied in Bangladesh. A free technology choice for optimal adaptation to local conditions, is primordial. Some NGOs develop appropriate equipment for small-scale or individual use.Financial supportInvestments in infrastructure are often the most costly part of irrigation. The poor typically lack the access to capital and to longer-term credit facilities that prosperous farmers tend to have. Hence, subsidized investments in public irrigation infrastructure should support the poor especially in obtaining access to irrigated land and water. In reality, however, these funds for irrigated land and water development have often leaked to the well-off. In private irrigation longer-term credit facilities for the poor are primordial. The study in Bangladesh shows that the poor take even substantial risks as soon as these credits are available. Therefore, sound feasibility studies and safety nets are warranted.The poorest of the poor tend to be excluded as owners of modern infrastructure, because they lack a minimal regular source of income for long-term repayment of credits. They remain largely dependent on the targeting efforts of irrigation agencies in public and private irrigation, and on the terms of inclusion set by private or semi-private owners of infrastructure, who sell the water.Order informationOrdering copies 'More jobs per drop: targeting irrigation to poor women and men' by Barbara van KoppenISBN 90 683201242Price f 49,-Via:KIT PublishersPostbus 950011090 HA AmsterdamTel. 31 20 5688406Fax31 20 5688286Email kitpress@kit.nlOr via:IT Publications103-105 Southampton RowLondon WC1B 4HHUnited KingdomTel 44 171 436 9761Fax 44 171 436 2013Or via:Eiron Inc.P.O. Box 40072Washington D.C. 20016USATel 1 202 966 3240Fax 1 202 244 0913Email Eironinc@aol.com

The tree-shrub savanna ‘Forêt Classée de Nazinon’ (Burkina Faso) is submitted to a management of grazing and rotational cutting of Detarium microcarpum. This species resprouts after cutting. In order to investigate whether this silvopastoral land use system is sustainable, aboveground herbaceous biomass was measured on subplots under uncut trees (‘uncut’), next to the stubs of cut trees (‘cut’) and on subplots not influenced by the (former) crowns of trees (‘open grassland’) in four lots. These lots were cut one, three, six and seven years before the study. Vegetation composition of the lots and the composition of the diet of cattle were also determined. Comparisons were made between treatments and lots. Herbaceous biomass was lower in the open grassland subplots than in uncut or cut subplots. We speculate that soil enrichment and more efficient precipitation input in (former) tree crown zones could have resulted in this pattern. Cutting and subsequent resprouting of trees did not lead to significant differences in herbaceous biomass between cut and uncut subplots. The most simple explanation for this is that the trees could extend their roots beyond the location of their neighbouring trees. Biomass and coverage of perennial grasses, mainly Andropogon ascinodis and Andropogon gayanus, did not change in lots cut one, three or six years before the study, but decreased dramatically in lots that were cut seven years before the study. When foraging, cattle spent more than 90% of their time feeding on these species. This indicates that, as a consequence of tree cutting, forage availability may be reduced to the point where local herdsmen are forced to take their cattle to another region.

When vegetation is drastically reduced as a result of drought or an increase in herbivore numbers, it does not simply recover if periods with normal rainfall follow or if herbivores are removed. These are commonly recognized catastrophic phenomena of semi-arid grazing systems in general and of the African Sahel in particular. The main aims of this thesis are to provide an effective explanation of the catastrophic properties of vegetation dynamics in these systems and to predict under which conditions they might be expected.We start with a description of Sahelian rangeland vegetation dynamics, to reveal its catastrophic properties. This exercise appeared a very useful first step in the growth of our ideas about catastrophic vegetation dynamics because: 1) it translated rather vague concepts into a verifiable format by deducing hypotheses about the conditions under which catastrophic vegetation dynamics might be expected, and 2) it generated the notion that soil degradation could somehow be an important factor attributing to catastrophic vegetation dynamics in semi-arid grazing systems. This is in contrast with models that emphasize herbivore feeding characteristics or plant competition as possible mechanisms underlying catastrophic vegetation dynamics. We tested the hypothesis that soil degradation, i.e. soil erosion by run-off and wind and the consequent loss of water and nutrients, is sufficient to explain catastrophic vegetation dynamics by mathematical modelling.Our model studies indeed show that soil degradation can effectively explain the catastrophic properties of semi-arid grazing systems. Soil degradation can cause a positive feedback between reduced resource (soil water and nutrients) availability and reduced vegetation biomass which may lead to collapse of the system. This positive feedback loop can be triggered by grazing. We argue on the basis of a large body of literature that this is an important mechanism causing catastrophic vegetation dynamics in semi-arid grazing systems. Furthermore, our model studies predict for which site-specific properties catastrophic vegetation dynamics may be expected, that is on loamy or clayey soils in case of water-limited vegetation biomass production, and on sandy soils in case of nutrient-limited biomass production. This is because sandy soils have higher water infiltration rates but are more vulnerable to nutrient loss through erosion than loamy or clayey soils.Based on our models, we hypothesized that the removal of aboveground herbaceous biomass would lead to a reduced soil water content and biomass production because of reduced water infiltration and increased run-off. We tested this hypothesis in a semi-arid savanna in Tanzania (East Africa). Indeed, as a consequence of biomass removal, a reduction in soil water content and biomass production occurred. But it appeared that increased loss of soil water through increased soil evaporation as a consequence of litter removal ultimately outbalanced all other effects on soil water content. Several factors might have contributed to the importance of increased soil evaporation, overriding that of reduced water infiltration and increased run-off. The soil in the research area was a sandy loam, with higher water infiltration rates than soils with a lower percentage sand and higher perentage clay, while rainfall primarily occurred in light showers. Thus, under these conditions, when the positive feedback between reduced water infiltration and reduced biomass does not operate, another positive feedback that is between increased soil evaporation and reduced biomass may become prominent.We further hypothesized that at a certain range of herbivore impact small initial differences in plant cover and amount of soil resources can magnify to alternative states which persist in time due to positive plant-soil feedbacks. We tested this hypothesis in a semi-arid grazing system in Burkina Faso (West Africa), where we studied vegetation patchiness along a gradient of herbivore impact. Indeed, the occurrence and likely persistence of a spatial pattern of vegetated patches alternating with bare soil at a certain range of herbivore impact could be explained by the positive plant-soil feedback between vegetation biomass and water infiltration.We stress the general applicability of our models by comparing catastrophic vegetation dynamics of the semi-arid grasslands of the African Sahel with the arctic salt marshes along the Hudson Bay in Canada. We argue that in both systems, an increase of herbivory triggered a catastrophic vegetation shift, which was ultimately caused by a positive plant-soil feedback, leading to desertification.One of our model assumptions was that herbivore density is not regulated by vegetation biomass. In the general discussion, I investigated the influence of a positive feedback between vegetation biomass and water infiltration on the dynamics of a plant-herbivore system, where herbivore density depends on vegetation biomass. As a consequence of the positive feedback and if herbivore reproduction is efficient, I predict that the plant-herbivore system could destabilize and collapse. In this chapter I also stress the practical relevance of our studies as our approach may finally lead to objective ecological criteria on which pastoral managers can base their decision how to evade the hazard of degradation of their rangelands.I highlight three topics which deserve more priority on the reseach agenda concerning semi-arid grazing systems in the near future. Hereby, I want to stress that it is important to put experimental and empirical studies into a clear theoretical framework, whereby mathematical modelling should play an important role. The three topics are:spatial heterogeneity and vegetation pattern formation,facilitation and competition between functional plant groups within the herbaceous layer andthe effects of positive plant-soil feedbacks on herbivore dynamics.

Historical data on land use can be used as input into watershed models to simulate past hydrological conditions and erosion. A better understanding of past conditions is useful to position the present situation on a dynamic scale and to assess future trends and options therefrom. Conversely, knowledge acquired from bio-physical studies of the present can be used to get a better grasp of certain phenomena in the past. This has been done with a watershed model which was developed for the upper Konto watershed area in Java. After a general introduction on conditions in the upper Konto watershed area and the purpose and design of the watershed model, this article describes the origin, nature and quality of the historical land use data, and how they were interpreted, complemented, balanced and eventually incorporated into the model. The results of the simulation of historical watershed conditions are presented and their plausibility is discussed in the light of historical evidence. A comparison of the modeling results for past conditions and for present conditions shows that the hydrological effects one may wish to achieve with land use changes in the future specified in different development scenarios are unlikely to be of the same order of magnitude as the changes that have occurred over the last 150 years.

Research themeThe central theme of this thesis is the relation between irrigation development and gendered poverty alleviation in rural areas in developing countries. The focus is on the role of the irrigation sector. The sector comprises national and international governmental and non-commercial non-governmental agencies which develop irrigation infrastructure. They provide organizational, technical, and financial support to that end and participate in arranging the vesting of rights to the improved resources of irrigated land and water. The research questions concern, firstly, the effects of access by poor men and women to irrigated land and water on both poverty alleviation and productivity; secondly, inclusion and exclusion processes in irrigation; and, thirdly the role of the irrigation sector in these processes. This provides insight into the agencies' targeting of their support, and into the factors that critically contribute to vesting rights to irrigated land and water in poor men and women, and, hence, to poverty alleviation and productivity.The analysis explicitly includes rural women. They constitute the majority of the poor. Improvement of their incomes strongly contributes to family welfare and to the reduction of fertility rates. A gender-differentiated analysis requires the distinction of intra-household production units and women's and men's own resource rights.MethodThe three research questions are addressed in a review of global literature (Chapter Two, Three and Four), and in two field studies on external irrigation support for rice cultivation. The case in Burkina Faso concerns public irrigation by a state agency. The intervention is accompanied by land expropriation and reallocation. Ten subsequently constructed schemes are studied. Rice cultivation is a female cropping system in the region (Chapter Five). The subject in Bangladesh is NGO-supported private pump ownership by groups of marginal farmers and landless women and men, who use the water for irrigating their own household land and for sale. A country-wide study is made of 52 irrigation groups in which the irrigation loans are taken in women's names. They are supported by six NGOs. Irrigated rice cultivation is a male cropping system there (Chapter Six).Irrigation, poverty alleviation and productivityAccess to irrigated land and water by poor men and women generally improves their well-being (Chapter Two). Water is often a leading input for agricultural intensification, and for stabilization and growth of production during a longer period of the year. It fits the needs of farmers in increasingly smaller holdings. Water sale by smallholders and landless people provides an income, in principle. Remarking these positive effects is not to deny that lack of access to irrigated land and water is only one aspect of the state of multidimensional deprivation which poverty is. Improved access is not necessarily the most urgent need, the sufficient solution, nor the most feasible solution. It is a potential solution for only part of the world's poor. It is a sustainable solution only if the ecological resource base is conserved.The field study in Burkina Faso highlights the importance of women's own resource rights for their own well-being and for family welfare, and also for improved productivity. In Bangladesh, however, there appear to be hardly or no economic benefits from water sale for most irrigation groups. On the other hand, the non-economic status of women members of irrigation groups tends to improve, in the sense of women's self-concept and public behavior and their status within the family and the community.In many circumstances, access to irrigated land and water by the poor not only alleviates poverty but also leads to higher productivity (Chapter Two). Evidence shows that agricultural output per unit of land in smaller irrigated holdings is higher than in larger holdings. This relative higher productivity may disappear, however, if large farmers adopt large-scale mechanization; secondly, if the poor have limited access to other agricultural inputs; and, thirdly, if income diversification strategies lead the poor to take up employment far from home. There is also considerable evidence in the literature that gender by itself does not effect a farmer's production efficiency. The case studies also indicate the relatively good performance of poor producers and water sellers. In female cropping systems, like rice cultivation by most ethnic groups studied in the Burkina Faso case, women are the main producers.Evidence in the literature shows that if larger farmers obtain access to irrigated land and water, this may provide paid employment and a commercial offer of water to smallholders, and thus alleviate poverty indirectly. An increased food supply lowers the food prices. However, the effects are limited since the larger farmers largely set the terms of inclusion. The purchasing power of poor net buyers of food may still be too limited to buy the increased food supply. Poor net producers of food, on the other hand, benefit from high food prices. Moreover, access to irrigated land and water by larger farmers can also be at the direct expense of the poor. Such competition is likely to become more severe with growing water scarcity. Therefore, the irrigation sector contributes optimally to both poverty alleviation and productivity by targeting the poor and avoiding leakage of external support to the non-poor.TargetingThe contribution that the irrigation sector can make to poverty alleviation and increased productivity, given its mandate and core competence, is in vesting rights to irrigated land and water primarily in poor men and women, and redressing existing imbalances in resource rights in favor of the poor. The role of the irrigation sector in providing some users' groups with access to newly developed irrigated land and water, and excluding others, is identified in Chapters Three and Four, and empirically researched in the field studies. The type of irrigation support, the phase of a scheme, and the communication networks at the interface of agency and local people, are important variables in these inclusion and exclusion processes.The influence of the agency is especially strong in public irrigation, which is defined as irrigation in which the external agencies bear most of the costs of the infrastructure. Agencies usually have a powerful say in the physical design, and as investors their definition of their own claims and the users' claims to the water tends to be seen as legitimate. In private irrigation the water users are the main investors in the infrastructure. These private investors largely decide on the physical characteristics of the scheme and dispose of the water conveyed. The steering role of agencies is indirect and usually more limited.The definition of rights, and the role of agencies, differ according to the phase of a scheme. Usually the most important negotiations on the rights to irrigated land and water take place when infrastructure is newly constructed. Participation in these investments, either in cash or kind, are a firm basis to claim rights to the fruits in later phases, and over the generations. New construction is rare nowadays. Instead, the major redefinition of water rights occurs in irrigation management transfer and rehabilitation programs.It is an empirical question in which social fields the expropriation and reallocation of resource rights of users are negotiated under intervention, but, generally, these fields are embedded in the communication networks between local people and external agencies. Processes of inclusion and exclusion of the poor take place in these fields. If the poor are included in these networks, this network is called an 'inclusive forum'. Any new initiative of the agency, such as rehabilitation or irrigation management transfer, entails more or less substantially restructuring the local networks and redefining their competences.From the analysis of inclusion and exclusion processes in externally supported irrigation development, according to the literature and as studied in the field, it is concluded that there is considerable scope to improve the performance of the irrigation sector in vesting rights to irrigated land and water primarily in poor men and women, and in avoiding leakage. A combination of the following factors in agencies' targeting approaches appears to be pivotal.Organizational supportTargeting support is only possible if agencies work through inclusive forums at local level, composed of the priority target groups. The earlier these forums are established in an intervention process, the fewer rights become vested in the non-poor, which would hamper the later inclusion of new groups, in particular the poor. Organizational support in creating this forum is required, since poor women and men are usually not organized to that end.By now, several governmental and non-governmental irrigation agencies worldwide have succeeded in establishing such forums. These agencies have explicit and clear target group criteria, and adhere to those criteria during implementation. Culturally appropriate forms for effective participation of women in mixed-sex forums are created as well. Women are even the majority of the members of such forums in, for example, NGO-supported groups in Bangladesh.Poor people's existing organizations, and their motivation to be included in irrigation development, provide a substantive basis for these inclusive forums. In the later schemes studied in Burkina Faso, inclusive forums with women emerged even in spite of the male-biased targeting approach of the project management, which they had already implemented in earlier schemes. Such inclusion better fitted the prevailing social relations of production, for which the field staff was more receptive than the management.A rather poorly documented but important factor in excluding the poor from irrigation development appears to be the tendency of agencies themselves to confine their interactions to the decentralized branches of administrative and technical ministries, and to the local people who have most contacts with these institutions. These communication channels are dominated by the male local elite. By defining irrigation development as a matter of neutral tasks, and by failing to specify who at local level is supposed to participate and to be vested with the rights to these resources, the male elite act as a quick and effective partner in implementing these tasks. Tight implementation schedules and task-oriented reward structures for agencies' staff foster this. Within these task-oriented local networks, the elite easily claim the rights to the newly developed resources. In the early schemes studied in Burkina Faso, women lost their former land rights in this way, whereas men were endowed with rights they traditionally never had. The project's unrealistic concept of the unitary household farm represented by the male head was instrumental in this.The social fields in which rights are defined evolve over time as the social fields in which rights are implemented. In the use phase this social field is currently called a water users' organization. Membership of these organizations is closely related to having legitimate rights to irrigated land and water. Exclusion of women implicitly takes place if rights are vested in households, thought to be represented by the male head. Womens' inclusion requires the separate vesting of rights in both men and women. Poor land users with weak land rights are included as potential right holders if water rights are disconnected from land ownership. The recognition of pre-project rights, including those according to local legal systems, as a basis to vest new rights is likely to favor the poor, who, in the past, often lost their former rights without compensation.Only through inclusive forums can technical and financial support reach the poor. The types of technical and financial support, in their turn, further shape the organizational support required.Technical supportIn public irrigation, the technical support in the construction, operation and maintenance of infrastructure entails major inclusion or exclusion processes in two respects. Firstly, the site-selection, layout and division structures heavily influence whose land can be irrigated, and how well. If land tenure in the command area does not change, the physical design directly determines whether the poor or the non-poor obtain access to irrigated land. In the past, the non-poor have often been favored in this way. If land reform in the command area is possible or needed, this usually offers good opportunities to provide primarily the poor with access to irrigated land. However, these opportunities are rarely used. Land expropriation even ousted poor men and especially poor women not only in Burkina Faso but also elsewhere.Secondly, agencies in public irrigation can vest users' rights to the newly developed water, and sometimes to irrigated land as well, by arranging co-investments in construction and maintenance work in the form of labor and/or other contributions. An effective means to include the poor is explicitly opening up these opportunities to poor men and women. Timely and transparent procedures better guarantee that investments by the poor are effectively linked to rights. Poor women have often been entirely excluded from these opportunities, or their investments did not lead to rights as they did for men.In private irrigation, the poor obtain access to irrigated land and water as owners of equipment if appropriate equipment and energy sources are available. Commercial technology often does not fit these needs, or collective ownership is needed. The latter has been studied in Bangladesh. A free technology choice for optimal adaptation to local conditions, is primordial. Some NGOs develop appropriate equipment for small-scale or individual use.Financial supportInvestments in infrastructure are often the most costly part of irrigation. The poor typically lack the access to capital and to longer-term credit facilities that prosperous farmers tend to have. Hence, subsidized investments in public irrigation infrastructure should support the poor especially in obtaining access to irrigated land and water. In reality, however, these funds for irrigated land and water development have often leaked to the well-off. In private irrigation longer-term credit facilities for the poor are primordial. The study in Bangladesh shows that the poor take even substantial risks as soon as these credits are available. Therefore, sound feasibility studies and safety nets are warranted.The poorest of the poor tend to be excluded as owners of modern infrastructure, because they lack a minimal regular source of income for long-term repayment of credits. They remain largely dependent on the targeting efforts of irrigation agencies in public and private irrigation, and on the terms of inclusion set by private or semi-private owners of infrastructure, who sell the water.Order informationOrdering copies 'More jobs per drop: targeting irrigation to poor women and men' by Barbara van KoppenISBN 90 683201242Price f 49,-Via:KIT PublishersPostbus 950011090 HA AmsterdamTel. 31 20 5688406Fax31 20 5688286Email kitpress@kit.nlOr via:IT Publications103-105 Southampton RowLondon WC1B 4HHUnited KingdomTel 44 171 436 9761Fax 44 171 436 2013Or via:Eiron Inc.P.O. Box 40072Washington D.C. 20016USATel 1 202 966 3240Fax 1 202 244 0913Email Eironinc@aol.com

Models that explain the discontinuous behaviour of semi-arid grazing systems usually emphasize herbivore feeding characteristics or plant competition as possible mechanisms. Field studies indicate, however, that plant-soil relations could be more important. We show by means of a graphical model that the interactions between water infiltration or nutrient retention and plant density potentially give rise to the existence of alternate stable vegetation states and threshold effects in semi-arid grazing systems, even without the effect of a non-linear herbivore functional response or plant competition. These interactions may trigger a positive feedback between reduced plant density and reduced resource availability, and lead to a collapse of the system. The model results are in line with well-documented observations of spatial and temporal patterns such as two-phase mosaics and stably degraded grasslands.

In the Sahelian zone of Niger, severe wind erosion occurs mainly in the first half of the rainy season (May - July), when violent winds preceding thunderstorms result in intense sediment transport. Quantification of this wind erosion is difficult due to a high degree of temporal and spatial variability in wind-blown particle mass fluxes. Using improved techniques to collect field data in Niger and developed models revealed that a single wind erosion event may result in severe losses of soil particles and nutrients from unprotected fields. The many technical measures available to reduce wind erosion do not always fit into the Sahelian farming systems. A survey revealed that mulching with crop residues is the main control technique applied by Nigerien farmers, but the quantity of crop residues available for soil conservation is limited, as stover has also other important uses. Field tests with flat pearl millet stalks showed that small quantities can significantly reduce sediment transport during moderate storms. However, sediment transport may actually be intensified by small quantities of mulch during severe storms, because of increased turbulence around the stalks.

During recent decades Sahelian soils have gone through various forms of degradation, the most spectacular one being the extension of bare and crusted soils. Mulch, when placed on a crusted and bare soil, triggers termite activity within a few months. Many burrows are opened through the sealed surface of the soil due to the borrowing activity of the termites. Throughout the soil profile, macropores with irregular shapes and with different diameter sizes are created. As a result of changes in soil structure, other soil physical properties are also improved. Soil resistance to cone penetration is reduced from a critical to a suitable level for vegetation growth. Bulk density is decreased and soil hydraulic conductivity is greatly increased. Water infiltration and drainage are also greatly improved. The combination of the increase of porosity and infiltration and the cover effect of mulch results in an increase of soil water availability in the soil profile during the growing season. Termite activity enhances decomposition of the mulch and hence nutrient release in the soil. The change of soil characteristics due to termite activity was enough to create conditions necessary for natural vegetation development and crop production on previously degraded bare soils in the Sahelo-Soudanian zone of northern Burkina Faso.