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In Rwanda, mulch is applied in coffee fields to control soil erosion. The objective of this paper is to quantify the effects of different types of mulch on soil properties and soil erodibility in coffee farming systems in three different agro-ecological zones of the highlands of Rwanda. The treatments consisted of five mulching systems (T1: Cympobogon spp.; T2: Panicum spp.; T3: Cympobogon spp. and Panicum spp.; T4: Eucalyptus spp. and Cympobogon spp.; T5: mixed residues) and control (un-mulched coffee - T6). The mulching systems were selected in coffee plantations to which the same mulch material had been applied annually at an average rate of 15–21 t mulch ha− 1 for at least three consecutive years before we started field experiments in 2007. We tested the effects from 2007 to 2008 on two soil types. A factorial two-way ANOVA was used to assess the effects of the application of different mulch types on the soil organic carbon, bulk density, wet aggregate stability, and soil erodibility at each site. The application of mulch significantly reduced the bulk density and soil erodibility (P < 0.001) and significantly increased the soil organic carbon and wet aggregate stability (P < 0.001), mainly at Kibirizi and Karongi. In addition, the effects of the interactions between the type of mulch and type of soil were site specific (P < 0.001). Low bulk densities and soil erodibility as well as high soil organic carbon and wet aggregate stability values were observed mainly in response to the application of a mixture of mulches, particularly T4 and T5 at rates of above 17 t ha− 1. The maximum erodibility values coincided with the lowest values of soil organic carbon and wet aggregate stability and the highest bulk density. In addition, soil erodibility was also affected by soil texture; high sand and very fine sand fractions increased the vulnerability of soils to erosion. Mulching demonstrated positive effects on soil properties and soil erodibility, but the effects were site specific, depending on the agro-ecological conditions of the study sites and the types of mulch used.

Food security in Sub-Saharan Africa, particularly in semi-arid tropics (41% of the region; 6 months of dry season) is threatened by droughts, dry spells and infertile soils. In Zimbabwe, 74% of smallholder farming areas are located in semi-arid areas mostly in areas with soils of low fertility and water holding capacity. The dominant crop in these areas, maize (Zea mays L.), is susceptible to drought. Under smallholder farming in Zimbabwe, conventional tillage entails cutting and turning the soil with a mouldboard plough thereby burying weeds and crop residues. Seed is planted by hand into a furrow made by the plough, ensuring that crops germinate in relatively weed free seedbeds. Inter-row weed control is performed using the plough or ox-drawn cultivators and hand hoes. Conventional tillage has been criticised for failure to alleviate negative effects of long dry spells on crops and to combat soil loss caused by water erosion estimated at 50 to 80 t ha-1 yr-1. Therefore, conservation tillage has been explored for improving soil and water conservation and crop yields. Our objective was to determine the maize yield advantage of the introduced technology (conservation tillage) over conventional tillage (farmers’ practice) based on a review of experiments in semi-arid Zimbabwe. We use a broad definition of conservation tillage instead of the common definition of =30% cover after planting. Eight tillage experiments conducted between 1984 and 2008 were evaluated. Conventional tillage included ploughing using the mouldboard plough and digging using a hand hoe. Conservation tillage included tied ridging (furrow diking), mulch ripping, clean ripping and planting pits. Field-edge methods included bench terraces (fanya juus) and infiltration pits. Results showed small yield advantages of conservation tillage methods below 500 mm rainfall. For grain yields =2.5 t ha-1 and rainfall =500 mm, 1.0 m tied ridging produced 144 kg ha-1 and mulch ripping 344 kg ha-1 more than conventional tillage. Above 2.5 t ha-1 and for rainfall >500 mm, conventional tillage had =640 kg ha-1 yield advantage. Planting pits had similar performance to ripping and conventional tillage but faced digging labour constraints. Experiments and modelling are required to test conservation tillage seasonal rainfall thresholds. Constraints to adoption of conservation tillage by smallholder farmers necessitate best agronomic practices under conventional tillage while work on adoption of alternative tillage methods continues.

This study assesses potential impacts of climate change on maize and wheat yields in the Central Rift Valley (CRV) of Ethiopia. We considered effects of elevated atmospheric carbon dioxide (CO2) and changes in rainfall during the main (Kiremt) and the short (Belg) rainfall cropping seasons during the two future periods (2020–2049 and 2066–2095). The MarkSimGCM daily weather generator was used to generate projected rainfall and temperature data using the outputs from ECHAM5 general circulation model and ensemble mean of six models under A2 (high) and B1 (low) emission scenarios. Crop yield simulations were made with the FAO’s AquaCrop model. The projected rainfall during Kiremt increases by 12–69 % while rainfall during Belg decreases by 20–68 %. The combined effect of elevated CO2 and projected climate factors increases maize yield by up to 59 % in sub-humid/humid areas of the CRV, but could result in a decrease of up to 46 % in the semiarid areas under ECHAM5 model. However, the maize yield increases in all parts of the CRV under the ensemble mean of models. Wheat yield shows no significant response to the projected rainfall changes, but increases by up to 40 % due to elevated CO2. Our results generally suggest that climate change will increase crop yields in the sub-humid/humid regions of the CRV. However, in the semi-arid parts the overall projected climate change will affect crop yields negatively.

Preventing the off-site effects of soil erosion is an essential part of good catchment management. Most efforts are in the form of on-site soil and water conservation measures. However, sediment trapping can be an alternative (additional) measure to prevent the negative off-site effects of soil erosion. Therefore, not all efforts should focus solely on on-site soil conservation but also on the safe routing of sediment-laden flows and on creating sites and conditions where sediment can be trapped. Sediment trapping can be applied on-site and off-site and involves both vegetative and structural measures. This paper provides an extensive review of scientific journal articles, case studies and other reports that have assessed soil conservation efforts and the sediment trapping efficacy (STE) of vegetative and structural measures. The review is further illustrated through participatory field observation and stakeholders’ interview. Vegetation type and integration of two or more measures are important factors influencing STE. In this review, the STE of most measures was evaluated either individually or in such combinations. In real landscape situations, it is not only important to select the most efficient erosion control measures but also to determine their optimum location in the catchment. Hence, there is a need for research that shows a more integrated determination of STE at catchment scale. If integrated measures are implemented at the most appropriate spatial locations within a catchment where they can disconnect landscape units from each other, they will decrease runoff velocity and sediment transport and, subsequently, reduce downstream flooding and sedimentation problems.

Despite decades of international attention to find solutions for the annual food shortages in Ethiopia, the problem still persists. This study, carried out in the Central Rift Valley (CRV) of Ethiopia, focuses on farmers׳ strategies to counter yield failures and food shortages. It reveals that farmers indeed perceive a decrease in crop productivity and food production over the last decades, and that they blame a decline in rainfall for this. As a consequence, farmers apply different strategies to cope with, and adapt to perceived rainfall shortages and related expected yield losses: i.e. they sell more livestock, they migrate elsewhere, they change their crops and agricultural practices, and they rely more heavily on food relief programs. However, an analysis of rainfall data in the CRV shows that rainfall characteristics (mainly annual rainfall total) have not changed over the last three decades. Moreover, according to analysis of official data, crop productivity per hectare in the CRV even shows a slight increase over the last decade. The interpretation of this result is not straightforward. The farmers׳ perception of a decline in crop productivity and rainfall may be related to (i) the increased demand to grow more crops to feed the rapidly growing population (hence, food availability per capita has declined), and (ii) the lower moisture availability for plant growth resulted from soil fertility decline and soil erosion. Nevertheless, additional empirical research is needed to figure out the root causes of food shortage and yield failure in the CRV of Ethiopia.

The use of co-investment activities to motivate farmers to carry out sustainable land management is increasingly recognized. Several co-investment efforts have been implemented to combat land degradation and increase agricultural production in the Ethiopian highlands. Nevertheless, these co-investment activities have not been documented. Moreover, the impacts of these activities have not been evaluated. This study presents a co-investment initiative for sustainable land management in the Galessa watershed in Ethiopia. It documents successful co-investment activities that trigger farmers to carry out land management practices, and assesses the impact of these activities on farmers’ land management investments. The most important co-investment activities that trigger farmers to invest in land management are co-investments in awareness creation, water provision, technology, and governance. Of these activities, co-investing in water provision is most successful, because it directly solves one of the basic needs of farmers in the watershed. Results reveal that the experimental group of farmers (participants in the co-investment initiative) – compared to the control group (nonparticipants) – invested significantly more in land management practices such as soil bunds, composting, and tree planting. This article concludes that use of multiple co-investment activities are crucial to trigger farmers to invest in land management in Ethiopia.

Since the 2007 food crisis, the Government of Benin has created enabling conditions that urge small scale farmers to intensify rice production in inland valleys. Unsuitable irrigation infrastructures and lack of willingness to act collectively has led farmers to complain about water shortage. Adoption of mitigating technologies offered by government (extension) and scientists (e.g. Benin Agricultural Research Institute, AfricaRice) has been low due to the institutional context within which farmers are working. A socio-technical approach which combines technical and institutional dimensions was used to identify and test mulching as a potential method for improving irrigation water efficiency in growing rice in upland parts of Benin's inland valleys. Rice farmers (from three production areas), an extension agent and a researcher formed a multi-stakeholder platform and collaborated to test the application of mulch (three doses) and the use of a lowland rice variety in replacement of an upland rice variety during two growing seasons. Multiple methods derived from researchers and farmers’ perspectives were used to evaluate trial results: quantitative scientific evidence was combined with qualitative evaluation using indicators agreed upon by the collaborative group. Results show that the lowland rice variety IR-841 with 10 Mg ha−1 ‘rice-straw’ mulch allows farmers to better use available water in the upland areas and increase yields. Although the preference for IR-841 over the special bred upland variety Nerica-4 is risky because of its high water demand and the uncertainty in rainfall, farmers use IR-841 for profit maximisation. Beyond its technical output, the joint experimentation facilitated the interaction of knowledge, experiences and practices among the involved actors.

Le developpement agricole de la zone soudano-sahelienne africaine souffre de deux carences principales: la secheresse climatique et la pauvrete des sols. Pour faire face a la pression demographique, les paysans ont developpe deux series d'amenagements: des micro-barrages semi-permeables pour ralentir les eaux de surface (alignements et cordons de pierres ou de vegetaux) et des techniques de stockage localise du ruissellement, des nutriments et sediments qu'elles vehiculent (paillis, zai, cuvettes, demi-lunes, mares, seuils et diguettes dans les bas-fonds, etc.). Chaque amenagement et techniques culturales sont decrits, analyses et des ameliorations proposees (en particulier l'adaptation des fumures organiques et minerales). Aucune ne suffit a resoudre tous les problemes, mais leur combinaison permet d'ameliorer le milieu et la vie des paysans, tout en retablissant une plus grande biodiversite dans des systemes agro-sylvo-pastoraux. (Resume d'auteur)

Extreme rainfall events have serious implications for economic sectors with a close link to climate such as agriculture and food security. This holds true in the Central Rift Valley (CRV) of Ethiopia where communities rely on highly climate-sensitive rainfed subsistence farming for livelihoods. This study investigates changes in ten extreme rainfall indices over a period of 40 years (1970–2009) using 14 meteorological stations located in the CRV. The CRV consists of three landscape units: the valley floor, the escarpments, and the highlands all of which are considered in our data analysis. The Belg (March–May) and Kiremt (June–September) seasons are also considered in the analysis. The Mann-Kendall test was used to detect trends of the rainfall indices. The results indicated that at the annual time scale, more than half (57 %) of the stations showed significant trends in total wet-day precipitation (PRCPTOT) and heavy precipitation days (R10mm). Only 7–35 % of stations showed significant trends, for the other rainfall indices. Spatially, the valley floor received increasing annual rainfall while the escarpments and the highlands received decreasing annual rainfall over the last 40 years. During Belg, 50 % of the stations showed significant increases in the maximum number of consecutive dry days (CDD) in all parts of the CRV. However, most other rainfall indices during Belg showed no significant changes. During Kiremt, considering both significant and non-significant trends, almost all rainfall indices showed an increasing trend in the valley floor and a decreasing trend in the escarpment and highlands. During Belg and Kiremt, the CDD generally showed increasing tendency in the CRV.

Man-made and natural sediment sinks provide a practical means for reducing downstream reservoir sedimentation by decreasing soil erosion and enhancing the rate of sedimentation within a catchment. The Minizr catchment (20 km2) in the northwest Ethiopian highlands contains numerous man-made soil and water conservation (SWC) structures such as soil bunds (Erken), fanya juu ridge (Cab) and micro-trenches and natural sediment sinks such as wetlands, floodplains and grassed waterways. These sediment sinks reduce downstream sedimentation into the Koga reservoir, located at the catchment outlet, however, a large quantity of sediment is still reaching the reservoir. This study evaluates the function and effectiveness of both man-made SWC structures and natural sediment sinks in reducing sediment export from the Minizr catchment. SWC structures and natural sediment sinks were digitized using Google Earth Imagery. Sediment pins and vertical sampling through the deposit were used to quantify the amount of deposited sediment. In addition, inflow and outflow of suspended sediment data were used to calculate the sediment-trapping efficacies (STE) of man-made SWC structures (soil bunds and fanya juu ridges) and natural sediment sinks. Results reveal that 144 km soil bunds and fanya juu ridges trapped 7,920 Mg y−1 (55 kg m−1 y−1) and micro-trenches trapped 13·26 Mg y−1, each micro-trench on average trapped 23 kg y−1. The 17 ha floodplain located in the centre of the catchment trapped 9,970 Mg y−1 (59 kg m−2 y−1), while a wetland with a surface area of 24 ha, located near the outlet of the catchment, trapped 8,715 Mg y−1 (36 kg m−2 y−1). The STEs of soil bunds and fanya juu ridges, wetlands and floodplains were 54%, 85% and 77%, respectively. Substantial differences were observed between the STE of grassed and un-grassed waterways at 75% and 21%, respectively. Existing man-made and natural sediment sinks played an important role in trapping sediment, with 38% (26,600 Mg y−1) of transported sediment being trapped, while 62% (43,000 Mg y−1) is exported from the catchment and thus enters the Koga reservoir. Therefore, additional catchment treatment measures are required as an integrated catchment scale sediment trapping approach to help reduce sediment loads entering Koga reservoir. Moreover, to maximize the effectiveness of sediment trapping measures, avoid structural failure and ensure their sustainability, regular maintenance is needed.

BackgroundSome evidence suggests that forests attract rain and that deforestation contributes to changes in rainfall and temperature. The evidence, however, is scant, particularly on smaller spatial scales. The specific objectives of the study were: (i) to evaluate long-term trends in rainfall (1970–2009) and temperature (1981–2009) and their relationships with change in forest cover, and (ii) to assess the influence of remnant forests and topographical factors on the spatial variability of annual rainfall.MethodsThis study investigated the forest-rainfall relationships in the Central Rift Valley of Ethiopia. The study used 16 long-term (1970–2009) and 15 short-term (2012–2013) rainfall and six long term (1981–2009) temperature datasets. Forest and woodland cover decline over the past 40 years (1970–2009) and the measured distances between the remnant forests and rainfall stations were also used. The long-term trends in rainfall (1970–2009) and temperature (1981–2009) were determined using Mann-Kendall (MK) and Regional Kendall (RK) tests and their relationships with long-term deforestation were evaluated using simple linear regression. Influence of remnant forests and topographical variables on the spatial variability of rainfall were determined by stepwise multiple regression method. A continuous forest and woodland cover decline was estimated using exponential interpolation.ResultsThe forest and woodland cover declined from 44% in 1973 to less than 15% in 2009 in the Central Rift Valley. Annual rainfall on the valley floor showed an increase by 37.9 mm/decade while annual rainfall on the escarpments/highlands decreased by 29.8 mm/decade. The remnant forests had a significant effect (P-value 2 = 0.40) on the spatial variability of the number of rainy days observed over two years (2012–2013), but had little effect on the variability of rainfall distribution. For the total annual rainfall, slope was the best predictor which explained 29% of the rainfall variability in the Central Rift Valley. For the annual number of rainy days, both slope and elevation explained most of the variability (60%) of annual number of rainy days.ConclusionThis study did not find a significant correlation between long-term rainfall trend and forest and woodland cover decline. The rift valley floor warmed significantly due to long-term deforestation in the Central Rift Valley. Topographic factors play a significant role than forest cover in explaining the spatial variability of annual rainfall in the long-term and short term time scale in the Central Rift Valley. But, the short-term rainfall data indicated that the remnant forest had a significant effect on the spatial variability of the number of rainy days.

Agricultural development is complex, highly dynamic and differs among varying contexts. Decision-making for sustainable agricultural development cannot be based on generalized science-based knowledge, but should include context-specific knowledge and values of local stakeholders. Computer models seem a useful tool to integrate scientific knowledge include local-specific data, and explore local-specific solutions. In this paper we study whether and how a multiple goal linear program (MGLP) model could enhance learning for sustainable development. According to the learning theory, multi-actor learning is only productive when it consists of first-order (experiential) learning and second-order (social) learning. We applied an action-research approach and explored the value of an MGLP model SHARES (SHAred RESources) for learning by agricultural extension staff and farmers in an integrated rural development project in Burkina Faso. Fieldwork showed the main value of SHARES in the capacity to generate farm scenarios and trigger second-order learning about tacit frames-of-reference. People rarely engage in secondorder learning, but pursue different objectives and often remain trapped in confusing discussions and action. SHARES was a critical boundary-spanning object that facilitated communication between farmers and agricultural staff, enhanced mutual understanding, and the determination of area- and category-specific farm development goals.

Maize ( Zea mays L.), the dominant and staple food crop in Southern and Eastern Africa, is preferred to the drought-tolerant sorghum and pearl millet even in semi-arid areas. In semi-arid areas production of maize is constrained by droughts and poor rainfall distribution. The best way to grow crops in these areas is through irrigation, but limited areal extent, increasing water scarcity, and prohibitive development costs limit the feasibility of irrigation. Therefore, there is need for a policy shift towards other viable options. This paper presents daily rainfall analysis from Rushinga district, a semi-arid location in Northern Zimbabwe. The purpose of the rainfall analysis was to assess opportunities and limitations for rainfed maize production using 25 years of data. Data was analysed using a variety of statistical methods that include trend analysis, t -test for independent samples, rank-based frequency analysis, Spearman's correlation coefficient and Mann–Whitney's U test. The results showed no evidence of change in rainfall pattern. The mean seasonal rainfall was 631 mm with a standard deviation (SD) of 175 mm. December, January and February consistently remained the major rainfall months. The results depicted high inter-annual variability for both annual and seasonal rainfall totals, a high incidence of droughts ≥3 out of every 10 years and ≥1 wet year in 10 years. Using the planting criteria recommended in Zimbabwe, most of the plantings would occur from the third decade of November with the mode being the first decade of December. This predisposes the rainfall to high evaporation and runoff losses especially in December when the crop is still in its initial stage of growth. On average 5 to more than 20 days dry spells occupy 56% of the rainy season. Seasonal rainfall exhibited negative correlation ( P R = −0.746) with cumulative dry spell length, and wet years were free from dry spells exceeding 20 days. The most common dry spells (6–10 days), are in the range in which irrigated crops survive on available soil water. Therefore, they can be mitigated by in situ rainwater harvesting (RWH) and water conservation. The potential evapotranspiration of a 140-day maize crop was estimated to be 540 mm. Consequently, short season maize cultivars that mature in less than 140 days could be grown successfully in this area in all but drought years. However, sustainable maize production can only be achieved with careful management of the soil as a medium for storing water, which is essential for buffering against dry spells. To this end soil restorative farming systems are recommended such as conservation farming, in situ RWH techniques for dry spell mitigation and a cropping system that includes drought-tolerant cereal crops as for example sorghum and pearl millet, and perennial carbohydrate sources as for example cassava to provide stable crop yields.

This study tests a rapid, user-friendly method for assessing changes in erosion risk, which yields information to aid policy development and decision-making for sustainable natural resources management. There is currently a lack of timely, up-to-date and current information to support policy development on sustainable natural resources management in Uganda. The study was carried out in the Ngenge watershed, a typical catchment in the Ugandan Highlands, characterised by deforestation in favour of subsistence agriculture without adequate soil and water conservation measures. The watershed is experiencing soil erosion, sedimentation and flooding problems which are threatening agricultural productivity and food security. Sustainable management of environmental resources is needed to ensure a livelihood for the rural population which is dependent on the land. Historical erosion risk was evaluated in three steps using multi-temporal satellite data. First, current erosion risk was assessed by combining slope and vegetation cover during periods of high intensity rainfall. The data used for the assessment was obtained from public (free) satellite images. Erosion risk was then linked to land use and finally to the change in vegetation cover over the years 1980–2000. The analysis of erosion risk using rainfall, slope and NDVI (Normalised Difference Vegetative Index) as a proxy for vegetation cover gives an indication of the current erosion risk in the area. The results of historical vegetation cover change analysis indicate an overall increase in areas under erosion risk in the study area from 1980 to 2000. This method of erosion risk mapping provides a quick and straightforward means for identifying priority areas for interventions for soil and water resource management. Considering that resources are limited, the interventions to be appropriate have to be focused mainly on areas affected by degradation.

In semi-arid Sahel, soil erosion by water is one major factor accounting for negative nutrient balances in agricultural systems. A field experiment was conducted on a Ferric Lixisol in Burkina Faso to assess the effects of soil and water conservation barriers (stone rows or grass strips of Andropogon gayanus), the sole use of organic (compost) or mineral (urea) source of nitrogen (N), and the combined use of barriers and compost or urea nitrogen on soil nutrient and sediment erosion. The run-off barriers were put along contours. Organic carbon (OC) and nutrients losses through run-off and sediments were monitored during 2001 and 2002. Carbon and nutrient concentrations of generated sediments were very high, of 14-29 g kg-1 OC, 1.0-3.7 g kg-1 N and 0.32-0.71 g kg-1 total P. concentration in run-off water reached 0.023 g L-1 in stone rows treatments compared to only 0.002 g L-1 with treatments without barriers. Annual losses of organic C, N, P, and K were high and greatly dependant on soil loss magnitude. Compared to the control plots, soil losses were reduced on average by 84% during the 2 years with stone rows treatments, while by 71% with grass strips treatments. Compost application reduced soil loss by 75% in plots without barriers and by 89% in plots with stone rows as compared to control plots. With urea application, soil loss was on average 13% lower than in plots with compost. Integrated water and nutrient management can effectively alleviate soil, carbon, and nutrients losses by water erosion, therefore may contribute to intensifying crop production in Sahelian smallholder farming.

The synergistic effect of soil and water conservation (SWC) measures (stone rows or grass strips) and nutrient inputs (organic or mineral nutrient sources) was studied at Saria station, Burkina Faso. The reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriers + mineral N and 84% in plots with barriers + organic N, as compared with the control plots. Plots with no SWC measure lost huge amounts of soil (3 t ha-1) and nutrients. Annual losses from eroded sediments and runoff reached 84 kg OC ha-1, 16.5 kg N ha-1, 2 kg P ha-1, and 1.5 kg K ha-1 in the control plots. The application of compost led to the reduction of total soil loss by 52% in plots without barriers and 79% in plots with stone rows as compared to the losses in control plots. SWC measures without N input did not significantly increase sorghum yield. Application of compost or manure in combination with SWC measures increased sorghum grain yield by about 142% compared to a 65% increase due to mineral fertilizers. Yields increase did not cover annual costs of single SWC measures while application of single compost or urea was cost effective. The combination of SWC measures with application of compost resulted in financial gains of 145,000 to 180,000 FCFA ha-1 year-1 under adequate rainfall condition. Without nutrient inputs, SWC measures hardly affected sorghum yields, and without SWC, fertilizer inputs also had little effect. However, combining SWC and nutrient management caused an increase in sorghum yield.

In the 20th century, much research was done on desertification. Desertification developed into a complex and vague construct that means land degradation under specific conditions. Projects focusing on land degradation in semiarid East Africa have met with limited success because farmers prioritize drought as the major productivity-reducing problem. Yet studies on long-term rainfall trends have not confirmed that droughts are more frequent. In this article, we combine drought and land degradation effects into an Agricultural Drought Framework, which departs from the farmers' prioritization of drought and accommodates scientists' concern for land degradation. It includes meteorological drought, soil water drought, and soil nutrient drought. The framework increases insight into how different land degradation processes influence the vulnerability of land and farmers to drought. A focus on increased rainwater use efficiency will address both problems of land degradation and drought, thereby improving productivity and food security in semiarid East Africa.

Soil loss from an 8% sloping Teff field in north-western Ethiopia is significant (~ 70 t ha− 1 yr− 1), and thus found to be an important source of sediment. Grass barriers showing sediment trapping efficacy (STE) are important measures in trapping sediment inside Teff fields and protecting downstream reservoirs and lakes from sedimentation. There are many indigenous grass species available that have the potential to act as sediment trapping measure when used in strips downstream of sloping crop fields. However, their STE and their key functional traits that determine their STE are not yet known. This negatively influence agricultural extension agents in disseminating conservation technology to farmers at larger scales. The indigenous grass species Desho (Pennisetum pedicellatum), Senbelet (Hyparrhenia rufa), Sebez (Pennisetum schimpri) and Akirma (Eleusine floccifolia) and one exotic species, Vetiver (Vetiveria zizanioides) were tested for two years (2013 and 2014) in 1.5 m wide strips below Teff fields at 8% slope in the Debre Mewi watershed, northwest Ethiopia. The average runoff during the study was 79, 64, 69, 71, 74 and 75 l m− 2, with 7.0, 1.7, 2.9, 3.6, 4.5 and 5.6 kg m− 2 yr− 1 of sediment from the Control, Desho, Vetiver, Senbelet, Akirma and Sebez treatments, respectively. Differences in key functional traits affected the STE of the different grass barriers. Desho with the highest tiller number and density, and the second highest root length (depth) showed better STE (76%) than the other grass species, Vetiver (59%), Senbelet (49%), Akirma (36%) and Sebez (20%). This indicates that grass barriers can be used as a soil conservation measure replacing the costly and more maintenance demanding physical structures like trenches and ridges. As a co-benefit, grass barriers provided important fresh biomass for livestock, thereby helping to reduce the feed shortage. Thus we conclude that indigenous grass species provided a practical means to reduce soil loss from Teff fields (up to 8% slope) in the northwest Ethiopia and can be easily adopted by farmers due to their combined soil conservation and feed value.

Whether it is traditional, modern or ‘‘sustainable’’ agriculture, soil organic matter plays a key role in sustaining crop production and in preventing land degradation. A field experiment was conducted on a Ferric Lixisol at Gampela (Burkina Faso) in 2000 and 2001 to carried out the effects of tillage, fertilisation and their interaction on soil organic carbon (SOC) (0–10 cm), crop performance and microbial activities. Maize straw or sheep dung were applied separately or combined with urea in a till or no-till systems and compared with urea only and a control treatment. Sampling was done each year at 2 months after sowing and at harvest. SOC was increased in the tillage treatments in 2000 by 35% but only with 18% in 2001 suggesting reduced carbon accumulation in the absence of organic and mineral restitution. Ploughing in maize straw under conditions of N deficiency led to a drastic decrease in SOC due microbial priming effect that, was not observed when ploughing in sheep dung. In no-till system, losses, organic amendment N concentration and the soil N status determined the impact on SOC and crop productivity. The negative effect on SOC in the tillage treatment with maize straw (4.1 g kg � 1 ) was less when maize straw was combined with urea (6.2 g kg � 1 ). It is concluded that in semi-arid West Africa, without both organic resource and N inputs, soil organic matter ‘‘pays’’ for crop N nutrition. Increasing SOC accumulation while improving crop yield may be conflicting under low-input agricultural systems in semi-arid West Africa. Therefore, optimum soil organic carbon and crop performance results from a judicious combination of organic resources and inorganic N mediated by microbial activity. # 2006 Elsevier B.V. All rights reserved.

Information related to rainfall erosivity in the Andes is scarce. This study was carried out to determine the characteristics of rainfall events at the La Encanada watershed, northern Peru, using daily rainfall data from the 1995 to 2000 period that included all the El Nino and Southern Oscillation (ENSO) phases. Three weather stations were installed within the study area, at the top, middle and bottom of the watershed. We analysed the total amount, duration, intensity, kinetic energy and probability of return of rainfall events. In general, 80% of the rainfall events at watershed level had an average rainfall intensity lower than 2.5 mm h−1 and only 4% had an average intensity larger than 7.5 mm h−1. Rainfall erosivity registered at the bottom of the watershed was slightly higher than in the rest of the area. The highest intensities were observed during an El Nino year whereas a La Nina year was characterized by the highest amount of total rainfall compared to the other ENSO phases and by the low intensity rain events. Simulations using the WEPP model estimated higher sediment yield and runoff for the bottom of the watershed during a La Nina year versus El Nino or Neutral years. Even when the analysed rainfall data was too limited to conclude erosion and runoff during any ENSO phase, the simulated results showed us the trend of the behaviour of rainfall erosivity under the ENSO phases at different locations.

Despite several approaches that aimed at mobilising East African farmers to embrace soil and water conservation (SWC) activities, farmers hardly responded since they were seldom involved in the planning of SWC activities. Two tools that employ farmers' participation were developed and applied at Gikuuri catchment in Kenya. The first tool involved farmers to map soil erosion using their own indicators and determine the soil erosion status at catchment scale. This formed the basis upon which they undertook to plan for SWC measures at catchment scale. Farmers also predicted crop yield losses based on the soil erosion status. Farmers widely approved the soil erosion status map since their own indicators and perceptions were used. The second tool provided cash flow trends for a variety of SWC activities and farmer situations. Farmers can use land with a high, moderate or low erosion status and often have rather different socio-economic settings. The net benefits over 5 yr for bench terraces, fanya juu terraces and grass strips were illustrated to assist farmers in making informed decisions on SWC adoption. The two tools increased awareness on the need for collective actions among farmers and showed fields that cause run-on on downslope fields. The improved awareness of erosion problems and the related financial consequences increased farmers' willingness to share the investment costs for cut-off drains.

Soils in many agro-ecological zones in Eritrea, a country in sub-Saharan Africa, are low in productivity due to erosion, low organic matter and poor soil management. Recently, mechanised farming has been intensively practiced to increase agricultural food production. However, the use of heavy machinery and vehicles can cause soil compaction that reduces soil productivity and crop yield. A study was conducted to determine the in-situ soil compaction and the probability of exceeding a root restricting threshold penetration resistance (PR) value of 2 MPa in three agro-ecological zones that varied in soil type, topography and climate. Soil cone penetration resistance measurements were taken up to a depth of 600 mm in 30 m by 30 m field plots with three replicates located in the three agro-ecological zones. Simultaneously, core samples were collected to determine soil moisture and bulk density from surface and subsurface soil layers. In all the soils, moisture contents during soil penetration resistance measurements were nearly the same as the field capacity soil moisture content (¿10 kPa soil moisture suction). Penetration resistance values measured from 0 to 600 mm were averaged in depth increments of 100 mm. For clay loam (Adiguadad) and loam (Sheeb) soils, the penetration resistance values up to a soil depth class of 0¿300 mm were statistically insignificant and categorised as minimum mechanical impedance to root growth (

Integrated watershed management (IWM) is emerging as an alternative to the centrally planned and sectoral approaches that currently characterize the planning process for dam construction in Ethiopia. This report clarifies the concept of IWM, and reviews the major social, environmental and economic problems caused by dams in Ethiopia and elsewhere. Dams are planned from a top-down perspective in Ethiopia, some people are relocated against their will, haphazard land-use changes can occur, and soil erosion and reservoir sedimentation can increase. Many communities affected by dam constructions have not been sufficiently recognized or compensated, and environmental protection measures such as land-use planning and soil and water conservation have not been adopted in watersheds in which construction of dams is occurring. Furthermore, revenues generated from hydropower and water supplies often benefit urban dwellers, or the national economy, at the expense of rural inhabitants in watersheds. Creation of a multistakeholder platform, integration of soft system methodology with hard system tools, and completion of environmental protection measures should be among the major components of an improved planning methodology for construction of new dams in Ethiopia. This translates into an environment wherein science and knowledge can help watershed inhabitants create a diversity of locally appropriate resource management solutions. Effective implementation of environmental policies and strategies could improve the quality of watershed-based developments. The conclusion is that the IWM approach is a good alternative to effectively address the social, environmental and economic problems associated with planning and constructing new dams in Ethiopia.

Targeting agri-environmental measures (AEM) improves their effectiveness in the delivery of public goods, provided the necessary coordination with other incentives. In less favoured areas (LFA) measures focusing on the conservation of extensive farming contribute to sustainable land management in these areas. In this paper we investigate the implementation of a possible AEM supporting the improvement of permanent pastures coordinated with the extensive livestock and single farm payments actually in place. Through applying a spatially-explicit mixed integer optimisation model we simulate future land use scenarios for two less favoured areas in Portugal (Centro and Alentejo) considering two policy scenarios: a 'targeted AEM', and a 'non-targeted AEM'. We then compare the results with a 'basic policy' option (reflecting a situation without AEM). This is done with regard to landscape-scale effects on the reduction of fire hazard and erosion risk, as well as effects on farm income. The results show that an AEM for permanent pastures would be more cost-effective for erosion and fire hazard mitigation if implemented within a spatially targeted framework. However when cost-effectiveness is assessed with other indicators (e.g. net farm income and share of grazing livestock) 'non-targeted AEM' implementation delivers the best outcome in Alentejo. In Centro the implementation of an AEM involves important losses of income compared to the 'basic policy'. 'Targeted AEM' tends to favour farms in very marginal conditions, i.e. targeting is demonstrated to perform best in landscapes where spatial heterogeneity is higher. The results also show the risk of farm abandonment in the two studied less favoured areas: in all three scenarios more than 30% of arable land is deemed to be abandoned.

A methodology is presented for assessing the seriousness and impact of land degradation, from a historical and a farmer perspective, in regions where data are not available. Farmers have been directly involved in the assessment of soil, productivity and vegetation cover loss over the past decades, both on cropland and on rangeland. The results for the Bolivian mountain valleys in north Chuquisaca show that the intensive use of small cropland fields has increased soil degradation and consequently led to less water and nutrient availability. Due to the subsequent productivity loss many cropland fields have been abandoned. Rangeland is also severely degraded as a result of the excessive removal of vegetation and subsequent soil loss. Farmers are very concerned, but consider the impact of changed rainfall and less available cropland beyond their control. Consequently, no serious initiatives are taken to solve the land degradation problem. This research adduces evidence of increased land degradation in the Bolivian mountain valleys over recent decades, and stresses the need for urgent (integrated) action with regard to soil and water conservation

Tillage, organic resources and fertiliser effects on soil carbon (C) dynamics were investigated in 2000 and 2001 in Burkina Faso (West Africa). A split plot design with four replications was laid-out on a loamy-sand Ferric Lixisol with till and no-till as main treatments and fertiliser types as sub-treatments. Soil was fractionated physically into coarse (0.250–2 mm), medium (0.053– 0.250 mm) and fine fractions (< 0.053 mm). Particulate organic carbon (POC) accounted for 47–53% of total soil organic carbon (SOC) concentration and particulate organic nitrogen (PON) for 30–37% of total soil nitrogen concentration. The POC decreased from 53% of total SOC in 2000 to 47% of total SOC in 2001. Tillage increased the contribution of POC to SOC. No-till led to the lowest loss in SOC in the fine fraction compared to tilled plots. Well-decomposed compost and single urea application in tilled as well as in no-till plots induced loss in POC. Crop N uptake was enhanced in tilled plots and may be up to 226 kg N ha � 1 against a maximum of 146 kg N ha � 1 in no-till plots. Combining crop residues and urea enhanced incorporation of new organic matter in the coarse fraction and the reduction of soil carbon mineralisation from the fine fraction. The PON and crop N uptake are strongly correlated in both till and no-till plots. Mineral-associated N is more correlated to N uptake by crop in tilled than in no-till plots. Combining recalcitrant organic resources and nitrogen fertiliser is the best option for sustaining crop production and reducing soil carbon decline in the more stabilised soil fraction in the semi-arid West Africa. # 2005 Published by Elsevier B.V.

The objective of this study was to test the practicability of defining hydrologic response units as combinations of soil, land use and topography for modelling infiltration at the hillslope and catchment scales. In an experimental catchment in the East African Highlands (Kwalei, Tanzania), three methods of measuring infiltration were compared for their ability to capture the spatial variability of effective hydraulic conductivity: the constant head (CH) method; the tension infiltration (TI) method; and the mini-rainfall simulation (RS) method. The three methods yielded different probability distributions of effective hydraulic conductivity and suggested different types of hydrologic response units. Independently from these measurements, the occurrence of infiltration-excess overland flow was monitored over an area of 6 ha by means of overland flow detectors. The observed pattern of overland flow occurrence did not match any of the patterns suggested by the infiltration measurements. Instead, clusters of spots with overland flow were practically independent from field borders. Geostatistical analysis of the overland flow confirmed the absence of spatial correlation for distances over 40 m. The RS method yielded the pattern closest to the observations, probably because the method simulated better the processes that trigger infiltration-excess overland flow, i.e. soil sealing and infiltration through macroporosity. The RS hydrologic response unit correlated significantly with observed overland flow frequency. However, the location of clusters and 'hot spots' of overland flow remained largely unexplained by land use, soil and topographic variables. It is concluded that using such landscape variables to define hydrologic units may create artificial boundaries that do no correspond to physical realities, especially if the stochastic component within hydrologic units is neglected.

The contribution of local knowledge to ecological sciences has not been fully exploited: there is still a gap between the recognition of farmers' knowledge as valid and an effective use of such knowledge in activities aimed at sustainable development. This study explores the use of farmers' indicators of erosion for developing a rapid tool for water erosion assessment at field level in the West Usambara Mountains (Tanzania). Two extensive field surveys were conducted in the research area concurrently. One survey consisted of applying an established erosion assessment method, the Assessment of Current Erosion Damage (ACED). According to the erosion features observed, fields were classified into five erosion classes, from very slightly eroded to very severely eroded. The second survey consisted of recording the type and number of indicators of erosion listed by farmers and present in the fields. The number of farmers' indicators per field increased with erosion intensity, from less than four in slightly eroded fields to more than eight in severely eroded fields. All farmers' indicators were positively correlated to the ACED erosion assessment classes. However, two groups of farmers' indicators could be distinguished in terms of erosion assessment: strong indicators, which were observed in more than 70% of cases in severely eroded fields, and weak indicators, which were observed more frequently in slightly and moderately eroded fields. Weak indicators appeared to be indicative of other land degradation phenomena, such as chemical fertility decline. Strong indicators and number of indicators were used to create a field erosion assessment tool in the form of a classification tree. The tree was built using one half of the field survey data and validated using the other half. The tree consisted of a hierarchical sequence of questions. Presence of rills and number of farmers' indicators were the most important factors of the tree. The validation yielded a highly significant Spearman's rho correlation coefficient (0.81). The contingency table showed that more than 80% of very severely eroded fields were correctly classified, whereas most misclassification occurred among slightly and moderately eroded fields. Farmers include land degradation phenomena and soil fertility decline in their definition of soil erosion. Soil and water conservation planning should address this broader farmers' perception by including, e.g., soil fertility improvements beside soil conservation. The distinction between strong and weak indicators of erosion is important in recommending the right intervention in the right spot, e.g., by counteracting soil erosion where strong indicators are present and by improving chemical fertility where weak indicators are present. The classification tree is of empirical nature and may need adaptation before being applied to other areas. The proposed methodology can be easily replicated and showed a high potential to provide extensionists with a field tool for erosion assessment. The classification tree was a successful example of integrating different types of knowledge for enhancing the co-operation between stakeholders involved in the erosion-control activities

Water harvesting techniques (WHT) play an important role in water resources conservation in (semi-) arid environments. However, the impacts of WHT are not clearly understood. This paper presents a method to measure increased water availability to olive (Olea europeae) trees grown on the terraced area of a traditional WHT site in southern Tunisia (jessr) and to translate these measurements into effects on yield. Although the WHT were shown to greatly enhance possibilities for olive growing, yields remain dependent on water supply (rainfall+run-on) in spring. Critical factors in the method described are the maximum available soil water capacity (ASWmax), crop and yield response factors (kc, kyveg and kyfruit) and the yield consistency index (YCI). Detailed accounts are presented for the costs and benefits of jessr construction and olive production, and the WHT are evaluated using cost-benefit analysis. Difficulties and assumptions are discussed and it is concluded that on-site effects alone might not justify investing in the construction of WHT.

A field experiment was laid out in Burkina Faso (West Africa) on an Eutric Cambisol to investigate the interaction of organic resource quality and phosphate rock on crop yield and to assess the contribution of earthworms (Millsonia inermis Michaelsen) to P availability after phosphate rock application. Organic resources of different quality were applied at a dose equivalent to 40 kg N ha−1 with or without phosphate rock from Kodjari (Burkina Faso) at a dose equivalent to 25 kg P ha−1, and were compared with control and single phosphate rock treatments in a factorial complete block design with four replicates. Sorghum (Sorghum bicolor L. Moench) variety SARIASSO 14 was grown. Sheep dung had the highest impact on earthworm casting intensity followed by maize straw. Combining organic resources with phosphate rock reduced earthworm casting activities compared to a single application of organic resources or phosphate rock. Addition of phosphate rock to maize straw reduced P availability in earthworm casts whereas combining sheep dung or compost with phosphate rock increased P availability. The contribution of earthworms to Kodjari phosphate rock solubilisation mainly occurred through their casts, as the available P content of casts was 4 times higher than that of the surrounding soil.

In West Africa, many people suffer from micronutrient deficiencies. Current interventions have low chances of succeeding. Therefore, a food chain approach including local practices is proposed. This article takes local ecological, cultural, and socio-economic aspects into account through a household survey in northern Burkina in 2002. Farmers¿ knowledge was compared with available scientific information. Organic matter production is a function of the number of animals owned and the availability of labor and equipment. Organic resources are allocated to various fields according to soil texture and the crop to be grown. Farmers were unable to link micronutrient deficiency in the soil directly to food quality and human health. However, they indicated that some disorders (e.g., fatigue in adults, stunted growth of children, anemia) are associated with a low level of micronutrients in the diet. For the application of organic amendments to be modified to improve grain yield and food quality in the Sahel, the relation between organic amendment and food quality must be better understood by both scientists and farmers

Soil organic matter (SOM) controls the physical, chemical and biological properties of soil and is a key factor in soil productivity. Data on SOM quantity and quality are therefore important for agricultural sustainability. In 1990, an experiment was set up at Saria, Burkina Faso on a sandy loam Lixisol to evaluate long-term effects of tillage (hand hoeing or oxen ploughing) with or without 10 t ha-1 yr-1 of manure and fallowing on SOM and N concentrations and their distribution in particle size fractions. The field was sown annually to sorghum (Sorghum bicolor [L.] Moench). Ten years later, total organic C and total N, SOM fractions and their N concentrations, and sorghum yield were determined. Continuous sorghum cultivation without organic inputs caused significant losses of C and N in the hoed and ploughed plots. However, addition of manure to hoed plots was effective in maintaining similar levels of C and N to fallow plots. Without manure, SOM was mainly stored in the size-fraction

This paper describes the results of a survey on farmers' perceptions of the effect of woody natural vegetation on wind erosion. Sixty farmers were interviewed in three villages in northern Burkina Faso. The farmers mentioned that the presence of woody vegetation between the crops could benefit yield, but feared competition between the natural vegetation and the crop. Vegetation in a field was considered to increase deposition and decrease erosion on that field. The most important vegetative characteristics that affect wind erosion were, according to the farmers, vegetation's shape, porosity, flexibility and arrangement of the vegetation in the field. At present, most farmers do not apply this knowledge to the management of the natural woody vegetation on their fields

In the semiarid regions of sub-Saharan Africa, fertilizer recovery and nutrient release from organic sources are often moisture limited. Moreover, in these regions runoff brings about large nutrient losses from fertilizer or organic inputs. This study was conducted in the north sudanian climate zone of Burkina Faso (annual rainfall 800 mm, PET 2000 mm yr-1). We assessed the combined and interactive effects of two types of permeable barriers (stone rows and grass strips of Andropogon gayanus Kunth cv. Bisquamulatus (Hochst.) Hack.) and organic or mineral sources of nitrogen on erosion control and sorghum yield. The field experiment (Ferric Lixisol, 1.5% slope) was carried out during three rainy seasons and consisted of 2 replications of 9 treatments, in which the barriers were put along contours and combined with compost, manure and fertilizer nitrogen (N). Compared with the control plots, the average reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriers + mineral N and 84% in plots with barriers + organic N. On average, stone rows reduced soil erosion more than grass strips (66% versus 51%). Stone rows or grass strips without N input did not induce a significant increase of sorghum production. Supplying compost or manure in combination with stone rows or grass strips increased sorghum grain yield by about 142%, compared with a 65% increase due to mineral fertilizers. The sorghum grain yields at 1m upslope from the grass strips were less than those 17m from the grass strips. As stones do not compete with plants, the opposite trend was observed with stone rows. We conclude that for these nutrient depleted soils, permeable barriers improve nutrient use efficiency and therefore crop production. However, grass strips must be managed to alleviate shade and other negative effects of the bunds on adjacent crops.

In Sehoul, Morocco, the use of marginal land for agriculture became a necessity for the local population due to increased poverty and the occupation of the best land by new owners. Desertification poses an additional threat to agricultural production on marginal slopes, which are often stony and degraded. In a participatory process embedded in the EU DESIRE research project, potential sustainable land management measures were selected to address land degradation and desertification. Promising experiences with no-tillage practices elsewhere in Morocco had motivated the Moroccan government to promote conservation agriculture throughout the country. This combination of crop rotation, minimal soil disturbance and soil cover maintenance, however, had not yet been tested on sloping degraded land. Field trials of grazing enclosure combined with no or minimum tillage were conducted on the plots of two farmers, and trial results were analyzed based on stakeholders’ criteria. Results suggest that increased soil cover with barley residues improved rainwater use efficiency and yields only slightly, although soil water was generally enhanced. Soil moisture measurements revealed that no-tillage was favorable mainly at soil depths of 5 cm and in connection with low-rainfall events (

We studied fine-scale spatial plant distribution in relation to the spatial distribution of erodible soil particles, organic matter, nutrients and soil water on a sandy to sandy loam soil in the Sahel. We hypothesized that the distribution of annual plants would be highly spatially autocorrelated and that this would be positively linked with the spatial distribution of erodible soil particles, soil organic matter and nutrients. Further, we hypothesized that larger vegetated patches (a relatively high vegetation cover at coarser spatial scale) will be stronger linked with erodible soil particles, organic matter and nutrients than smaller vegetated patches (a relatively low vegetation cover at coarser spatial scale). Generally, for `low cover' and `high cover' plots, spatially confined micro-elevations with a relatively high volume percentage of erodible very fine – medium sand (50–400 μm), were linked with a higher cover of annual plants. The robustness of vegetation patchiness (expressed as the proportion of the total variance accounted for by spatial dependent variance) was significantly higher for the `high cover' plots. For the `low cover' plots, higher vegetation cover was associated with higher elevations, soil moisture, and volume percentage of very fine to medium sand, but lower organic matter, total N and P. For the `high cover' plots, micro-elevations also consisted of a relatively high volume percentage of very fine to medium sand, and this was associated with dryer conditions and higher total N. Additionally, dryer conditions were weakly correlated with higher organic matter. So, micro-elevations were indirectly associated with dryer and more fertile conditions, which was opposite to what we found for the `low cover' plots.

In the Sahel, poor soil quality and rainfall levels have a great influence on pasture production and hence on secondary output. In areas where rainfall is the limiting factor for primary production, recovery of primary and secondary production after the dry season depends on soil type. On sandy soils a large fraction of rainfall infiltrates and becomes available for plant growth, stimulating fast herbage growth, while on clayey and loamy soils low infiltration rates generate runoff, leading to slower herbage growth rates. The very different moisture retention characteristic of sands and clays is another possible cause for the observed differences in growth rates. lit this paper we investigate the herbage growth rate from the onset of the rainy season. We hypothesise that, in areas where rainfall is the limiting factor for primary production. the vegetation growth rate on clayey soils is lower than that on sandy soils. We will test this hypothesis using long-term rainfall, soil types and satellite derived normalised difference vegetation index data. This research shows that the growth rates on sandy soil are significantly greater than that on clayey soils during the early part of the rainy season. We also show that these differences can be detected at large scales using satellite imagery. We also conclude that, at this scale, movement strategies of pastoralists would be intrinsically linked to not only rainfall patterns and distribution. but also to the underlying soil types in the region as this affects the quality and quantity of fodder available. (C) 2002 Elsevier Science B.V. All rights reserved.

Recent theoretical studies have shown that spatial redistribution of surface water may explain the occurrence of patterns of alternating vegetated and degraded patches in semiarid grasslands. These results implied, however, that spatial redistribution processes cannot explain the collapse of production on coarser scales observed in these systems. We present a spatially explicit vegetation model to investigate possible mechanisms explaining irreversible vegetation collapse on coarse spatial scales. The model results indicate that the dynamics of vegetation on coarse scales are determined by the interaction of two spatial feedback processes. Loss of plant cover in a certain area results in increased availability of water in remaining vegetated patches through run-on of surface water, promoting within-patch plant production. Hence, spatial redistribution of surface water creates negative feedback between reduced plant cover and increased plant growth in remaining vegetation. Reduced plant cover, however, results in focusing of herbivore grazing in the remaining vegetation. Hence, redistribution of herbivores creates positive feedback between reduced plant cover and increased losses due to grazing in remaining vegetated patches, leading to collapse of the entire vegetation. This may explain irreversible vegetation shifts in semiarid grasslands on coarse spatial scales.

Eritrea’s coastal zone has been identified as an area of substantial development potential. About 14,000 ha of this 5 million ha area (i.e.

Heterogeneity in space and time makes it difficult to evaluate the hydrologic effects of hedgerows in between crops. In this study a robust modelling system for designing hedgerow barrier systems is introduced. The system is demonstrated with experimental data over three years from a site in central Burkina Faso. Soils at the site are prone to crusting and consist of a sandy loam in the top layer and clay in deeper layers. Measurements comprise runoff from differently sized plots (1, 5 and 10 square meters), water storage into the soil, and rainfall. It appears that the relevant hydrologic processes can be represented with the available measurements by two compact dynamic models, each comprising two states (runoff and soil water; water use and soil water), one input (rain; potential evapotranspiration) and two spatial units (hedgerow and cropped area). The analysis of the phase planes of the models reveals which combinations of alley length and hedgerow type lead to desirable combinations of both runoff and evapotranspiration. This information can be interpreted directly in a qualitative sense or alternatively used for a Monte-Carlo analysis of the system.

The rehabilitation of vegetation on structurally crusted soils by triggering termite activity through mulch was studied on three soil types in northern Burkina Faso, West Africa. A split-plot design was used in a fenced environment for the experiment. Insecticide (Dieldrin) was used at a rate of 500 g a.i. (active ingredient)/ha to create nontermite and termite plots. Three mulch types consisting of straw (Pennisetum pedicellatum), woody material (Pterocarpus lucens), and a composite mulch (straw and woody material) applied at a rate of 3, 6, and 4 tons/ha, respectively, were used to trigger termite activity. The grasses and woody species on the plots were surveyed. Nontermite plots responded weakly to mulch treatments, but even in the first year vegetation established on termite + mulch plots. Termite activity resulted in the increase of plant cover, plant species number, phytomass production, and rainfall use efficiency. Infiltrated water use efficiency and plant diversity were not statistically different among treatments during the first 2 years but were in the third. Woody species established only on termite plots. The three types of mulch plots showed greater vegetation development than bare plots, which remained bare throughout the experiment. Analysis of the termite and mulch interaction indicated that mulch plots without termites did not perform better than bare plots, especially in the case of woody plant regeneration. Vegetation rehabilitation was best with composite and straw mulches with termites, followed by woody mulch with termites; it was worst on bare plots.

Investments by farmers in soil and water conservation (SWC) practices are influenced by the physical effectiveness, financial efficiency, and social acceptability of these practices. The objective of this study is to evaluate different SWC practices in the north-western highlands of Ethiopia using various qualitative criteria and weightings based on ecological, economic and social impacts using Multi-Criteria Analysis (MCA). The study reveals that MCA is a useful evaluation tool that takes into account non-monetary and less quantifiable effects of SWC practices. Farmers employ a range of criteria to evaluate the performance of SWC practices. The relative importance of each criterion in their selection of SWC alternatives depends mostly on slope categories. In steeply sloping areas, farmers assigned the highest score for criteria related to ecological impacts; whilst preferring practices with stronger positive economic impacts in moderate and gentle sloping areas. Policy makers and development practitioners are encouraged to pay greater attention to both farmer preferences and slope specific circumstances when designing SWC strategies and programmes.

Under low and poorly distributed rainfall higher food production can be achieved by increasing crop water use efficiency (WUE) through optimum soil fertility management and selection of deep-rooting cultivars, appropriate plant density and planting dates. We explored AquaCrop's applicability in selecting adaptive practices for improving maize yield and WUE under rainfed smallholder farming in semi-arid Zimbabwe. AquaCrop was first tested using field measurements without calibration. The model was subsequently applied to estimate the effect of effective rooting depth (ERD), plant density and planting date on maize yield. Simulations were done with daily rainfall data for 25 seasons. During model testing AquaCrop simulated canopy cover development well and simulated biomass accumulation showed good agreement with measured values. The model overestimated soil water, and observed final biomass and grain yield were 96 and 92% of simulated values, respectively. Model application showed that increasing ERD from 0.40 m at 32,500 plants ha−1 to 0.60 m at 44,400 plants ha−1 increased grain yield from 6.0 to 7.8 t ha−1, biomass water use efficiency by 20.5%, grain water use efficiency by 23.6% and transpiration water use efficiency by 26.8%. At 0.60 and 0.80 m ERD and 44,400 plants ha−1, biomass and grain yield, and WUE, were similar. Drainage below the rootzone was ≥40% of non-productive water losses in normal and wet seasons whilst soil evaporation contributed 47% in dry seasons at 0.80 m ERD. To improve yield and WUE, we recommend: incorporation of deep-rooting legumes, deeper-rooting cultivars (≥0.60 m effective rooting depth) and practices that improve ERD, a plant density of 44,400 plants ha−1; and practices that reduce soil evaporation e.g. mulching and addition of organic fertilisers to improve soils’ available water capacity and enhance response to mineral fertilisers. Further research should include field testing of results from this study with farmers.

Rice production in inland valleys in Southern Benin was initiated by the public sector. The subsequent devolution of responsibility for maintaining the collective irrigation infrastructure to farmers created an opportunity to study the factors that affect cooperation in canal maintenance. We used a social dilemma perspective to compare three rice production areas that differed in the extent of cooperation, based on focus group interviews, surveys, and archival research. The findings draw attention to the nature of the resource, the characteristics of the user group, and farmer-based institutional arrangements as explanatory variables. Specifically these include (1) the balance between water demand and availability, (2) the existence of inequities and privileged positions within the group, and (3) the strength of group organization and the ability to sanction uncooperative behaviour. The existence of alternative sources of livelihood also influenced cooperation. Contrary to our expectations, the largest and most diverse group of producers appeared best organized and equipped to engage in cooperation. Size and diversity might actually allow (1) the emergence of institutional arrangements that can overcome social dilemma situations and demotivation emanating from customary privileges and exemptions and (2) better use of Africa's irrigation potential.

Realising that rainwater harvesting (RWH) improves crop productivity, smallholder farmers in semi-arid Zimbabwe modified contour ridges traditionally used for rainwater management by digging infiltration pits inside contour ridge channels in order to retain more water in crop fields. However, scientific studies on crop yield benefits of infiltration pits have not been conclusive. Combining field-edge RWH methods such as contour ridges with infiltration pits with in-field practices may enhance crop yield benefits. Thus, the objective of the study was to assess soil moisture and maize yield improvement of combining infiltration and planting pits. Field experiments were conducted in Rushinga, Zimbabwe for three seasons at three sites using a split-plot design: main-plot factor, field-edge rainwater management method (RWMM); and split-plot factor, tillage method. Soil moisture content was measured weekly using gravimetric and Time Domain Reflectometry (TDR) methods. A household and field survey to establish farmers’ perceptions, typology and availability of field-edge RWMM was conducted. In order to share experiences and enhance stakeholders’ learning, field days were held. Lateral movement of soil water was measured up to 2 m downslope from infiltration pits, hence infiltration pits did not improve maize yield and soil moisture content in the cropping area. Maize yield (kg ha−1) was 45% higher under conventional tillage (2697) than planting pits (1852) but the yield gap decreased from 90 to 30% in the first and third year respectively. The value of infiltration pits is in reducing soil erosion by water and growing high value horticultural crops inside and close to pits, a view shared by host farmers and other stakeholders. Planting pits are an option for farmers without access to draught power and a fall-back method. Research is required to determine soil moisture, maize yield benefits and waterlogging risk in fields with underlying impermeable layers that enhance lateral flow of water.

Developing models to predict on-site soil erosion and off-site sediment transport at the agricultural watershed scale represent an on-going challenge in research today. This study attempts to simulate the daily discharge and sediment loss using a distributed model that combines surface and sub-surface runoffs in a small hilly watershed ( 0.9. With the simple input data needs, PLER model is a useful tool for daily runoff and soil erosion modeling in small hilly watersheds in humid tropical areas. Copyright (c) 2013 John Wiley & Sons, Ltd.