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Climate change is projected to have a serious impact on all sectors of the world. The agriculture sector is one of the most vulnerable sectors with implications for smallholder farmers in semi-arid regions of Africa in terms of poverty and food security. Several researches have been carried out on perception and adaptation with a little investigation to unpack the gender differences and how this influence adaptation strategies. This research investigates gender difference and gender-specific adaptation strategies to climate change and variability. A household survey was conducted from August to December 2014 using a pre-tested questionnaire where 150 males and 150 female farmers were randomly sampled from 14 communities within the Bolgatanga Municipality and Bongo district. Results show the existence of gender differences in the adaptation strategies. Both gender groups perceived climatic change and variability but only 49% male and 40% female headed household (HH) have adopted strategies to cope with increasing temperatures while 56% male and 49% female have adapted to decreasing precipitation. On the other hand, 62% male and 60% female HH have adapted to increasing drought spells. The main differences between male and female adaptation strategies are that males prefer to migrate and seek employment in other parts of the country whereas females prefer to engage in off-farm jobs such as trading, basketry and shea-butter processing. The age of farmers, access to extension services, credit, perceived loss of soil fertility, among other factors influenced farmers adaptation strategies. Policy decisions to promote adaptation to climate change and variability should take these factors into consideration.

Regional climate change assessments show a likely temperature increase that is higher than the global average for all seasons in Africa, which would have extreme negative implications for ecosystem health and productivity. Most extreme climate change effects in West Africa are predicted to occur in desert and grassland areas. It is important for smallholder farmers in this region to understand the implications of these projections to their livelihood and to identify appropriate adaptation strategies. A grazing game was used to explore gender-specific adaptive responses to climate variability in the semiarid region of Ghana. The game was designed to understand the decision-making processes that result in the overgrazing of animals, leading to desertification based on the players’ interactions with the environment. A total of 44 grazing games comprising 22 games for male-headed households (HH) and 22 games for female-HH were played from August to December 2014 from 14 communities within the Bolgatanga Municipality and the Bongo district. The study revealed that males migrate to the southern part of the country to work on other people’s farms during the dry season as an adaptation strategy, while females engage in off-farm activities such as shea-butter production and basketry. Results of the game showed that males produced the highest number of cattle but created the largest desert patches. Females, on the other hand, were more conscious about the environment (long-term condition of the rangeland) than the short-term income benefits from the sale of cattle, hence, they created fewer desert patches. Strategies such as reducing the number of cattle to allow for the re-growth of vegetation in periods of feed scarcity, ploughing for one another using bulls, and family support using income from the sale of livestock were employed by both gender groups. The involvement of female farmers in decision-making is crucial to improve natural resource management.

Climate change and variability challenge crop productivity and resource use efficiency in West Africa. Despite abundant research on climate change impact on crop yields and food security, little is known about climate change effects on the resource use efficiencies of the main staple crops in the dry savanna agro-ecological zone of northern Benin, West Africa. This study assessed the impact of climate change on water- and N-use efficiencies, and yields of maize and sorghum in the dry savanna of northern Benin considering three soil fertility management options (return of crop residues, mineral NPK fertilizer application, and combinations of both) and three bias-corrected ensemble mean predictions (BNU-ESM, CanESM2, and MPI-ESM-MR models) of future climate (2080–2099) under Representative Concentration Pathways (RCPs) of 2.6, 4.5, and 8.5. Seasonal rainfall is projected to decrease by 2% under RCP 2.6 and by 4% under RCP 4.5, and to increase by 1% under RCP 8.5 relative to the baseline mean (1986–2005). Increasing trends in minimum temperature of +1.0 °C (RCP 2.6), +2.0 °C (RCP 4.5), +4.7 °C (RCP 8.5) and maximum temperature of +1.1 °C (RCP 2.6), +2.0 °C (RCP 4.5), +4.6 °C (RCP 8.5) are also predicted. Solar radiation was projected to decrease by about 0.4 MJ m−2 d-1. Under these projected climate scenarios, both CERES-Maize and CERES-Sorghum simulated positive responses in aboveground biomass accumulation during the vegetative growth stages. The predicted increase in aboveground biomass growth will be largest under RCP8.5 and smallest under RCP 2.6. This impact can be enhanced by improved soil fertility management, albeit with a crop-specific magnitude. Across the soil fertility management options, CERES-Maize predicted decreases in water-use efficiency by 17–53%, partial factor productivity of nitrogen (N) by 10–47%, and internal N-use efficiency by 5–33% for maize. Similarly, CERES-Sorghum simulated decreases in water-use efficiency (23–51%), partial factor productivity of N (22–49%), and internal N-use efficiency (13–47%) for sorghum. The largest overall loss in resource efficiency and yield were predicted for the RCP 8.5 scenario. The projected climate change for the dry savanna in northern Benin will likely reduce water- and N-use efficiencies as well as grain yields of maize and sorghum considerably but these results should be treated with caution due to shortcomings in the models structure for dealing with effects of enhanced CO2. For reliable assessments of climate change impact on WUE, it is critically important to update parameterization and code of the CERES crop models in DSSAT to have a sufficiently strong effect of CO2 on stomatal conductance and on transpiration.

Cotton is an important cash crop in many West African countries. Hence, its sustainable production will support the national economies as well as the livelihoods of the farming population alike and in turn help easing wide-spread poverty. However, future climate change may affect the productivity of cotton in West Africa. Therefore, the objectives of this study were to (i) parameterize the Cropping System Model- CROPGRO-Cotton to simulate growth, seed cotton yield, and in-season soil water dynamics and nitrogen (N) uptake, and (ii) apply the model to estimate potential climate change impacts on cotton growth, yields, and water- and N- productivity under different soil-fertility management practices. The CROPGRO-Cotton model was first parameterized and evaluated using datasets collected in three field experiments conducted in 2014 and 2015 in the Dry Savanna of northern Benin, West Africa. The model was next applied to determine long-term responses of cotton to historical (1986–2015) and projected climate (2080–2099) for three Representative Concentration Pathways (RCPs 2.6, 4.5, and 8.5). CROPGRO-Cotton accurately simulated in-season soil water dynamics (nRMSE of 12–27%, d-values of 0.79–0.88), N uptake (nRMSE of 31–44%, d-values of 0.89–0.96), and biomass accrual (nRMSE of 31–46% and d-values of 0.91–0.97), as well as seed cotton yield at harvest (nRMSE of 24–39% and d-value of about 0.81). The model predicted higher seed cotton yield with planting dates in June compared to July. Under the climate change scenario of RCP2.6, CROPGRO-Cotton predicted a decrease in water use efficiency (WUE) by 20% without any soil amendment, and by 4% with an integrated soil-crop management compared to the historical run, but an increase of 2% with a high use of mineral fertilizer. With the RCP4.5 and 8.5 scenarios, the predicted changes in WUE varied between −1% and 17% across the soil fertility management options. CROPGRO-Cotton predicted increases in N-partial factor productivity by 7 to 31%. The N uptake varied between −7% and 46% whilst seed cotton yield varied between −7 and 41%. The findings underlined that the predicted future increases in water and N productivity in cotton will be driven by CO2 fertilization, increases in temperatures as well as rainfall variability, but at the expense of soil fertility leading to soil mining. Yet, even if cotton, unlike some other crops in the region, will likely respond positively to climate change, adequate soil fertility management practices are essential to ensure efficient and sustainable water- and N- use in the expected future.

Syahrinudin, Denich M, Becker M, Hartati W, Vleg PLG. 2020. Biomass and carbon distribution on Imperata cylindrica grasslands. Biodiversitas 21: 74-79. Invasive plants can alter the diversity and composition of ecological communities leading to ecosystem change both function and biodiversity issues. Imperata cylindrica is an invasive grass thrives on wide range of soil fertility and climatic condition forming a vast grassland area of this species. Conversion of such lands into agriculture and plantation is costly and high capital demanding. This work was devoted to investigate CO2 mitigation potential of the conversion I. cylindrica grassland to plantations in Sumatra and East Kalimantan, Indonesia. Stratified sampling technique was applied for the determination of biomass and carbon stock of the system studied. Results show that I. cylindrica grassland stored only a relatively small amount of biomass C (5.9-7.6 mg ha-1) implying that conversion into a more C-rich tree-based system would be promising tool to enhance C sequestration. Soil C content at both study sites decreased significantly with depth from the top 15 cm to the 3-m depth and was considerably higher in East Kalimantan than in Sumatra. Provided similar land-use history, the differences in soil C are likely to be related to the level prior to the invasion. Roots of I. cylindrica extended to a maximum depth of only 180 cm, but most of these roots being confined to the topsoil, little organic material is deposited in deeper layers. Despite the dense mat of rhizomes, the extent of C stored in the topsoils was modest. As sequestration is of global concern, the conversion of this grassland into systems with higher biomass accumulation and deeper root penetration is required.

Jatropha curcas has been introduced as a low-cost energy crop in Burkina Faso for the production of straight vegetable oil (SVO) and biodiesel. It is cultivated in different plantation systems including smallholder inter-plantings with annual crops, large-scale monoculture, afforestation on marginal land, in traditional hedge systems along contour stone walls, and in living fences. We performed Life Cycle Assessment of these Jatropha systems using empirical data on yields and carbon stocks, and accounting for changes in agro-ecosystem provisioning and regulating services that occurred after the land conversion to Jatropha. The study found that all J. curcas production pathways substantially reduced greenhouse gas emission (68–89%) and saved energy (65–90%) compared to diesel fuel. Highest values are achievable under the assumption that by-products (husks, seed cake, glycerin) are used for energy generation. The decentralized production of SVO supplied by feedstocks from intercropping and hedgerow systems seems to be most promising option. However, very low land-use efficiency (6.5–9.5 GJ ha− 1 production) characterized Jatropha intercropping and monoculture plantations, rendering the plant a competitor to food crops and increasing the risk of conversion of savanna land to Jatropha cultivation. Jatropha plantings on marginal lands largely failed. High labor requirements constrain integration of Jatropha plantation systems within small farmholdings. Currently, the traditional hedge systems show the lowest land-use replacement potential and labor needs while providing multiple ecosystem services, but alone cannot satisfy rural energy needs. In order to reach energy supply targets without claiming more land and compromising other ecosystem services, the J. curcas plantation systems in Burkina Faso need to be made more efficient through plant breeding and improved agronomic management.

Land and water degradation due to on-site soil/nutrient loss and off-site pollution/sedimentation are serious environmental problems. Landscape planning and management tools are essential to implement best management practices targeted at locations where they are needed most. Although many soil/water-landscape studies have been published in the last 2 decades, progress in developing operational tools for supporting landscape planning to minimize land and water degradation in developing regions is still modest. Some of the existing tools are data demanding and/or complicated to be useful to data scarce regions. Some require detailed understanding of the hydrological and modelling processes and thus less applicable to local stakeholders involved in land use planning and management. A user-friendly LAndscape Planning and MAnagement Tool (LAPMAT) developed to facilitate land management decision-making. LAPMAT is a menu-oriented interactive graphical user interface that can aid decision makers identify hotspot areas of soil erosion and evaluate the effects of alternative land use management practices at a catchment scale. The modelling framework and its interfaces are designed to guide the user through a series of menus that: 1) allow input model parameters, adjusting coefficients, visualizing input parameters and executing the model; 2) enable changing land use and management practices and re-evaluating potential consequences; 3) allow viewing results in tabular, graphical or map form side-by-side; and 4) (re)-evaluating the respective impacts of management/conservation options. The framework has been applied to assess the severity of soil erosion and simulate the impact of different land management practices using the Revised Universal Soil Loss Equation (RUSLE) adjusted for sediment delivery ratio in an example catchment of northern Ethiopia. The results showed average sediment yield rate of 55 t ha−1 y−1. Conservation measures targeted at high soil loss areas and gullies gave the maximum reduction in sediment yield by about 80 %. Since LAPMAT allows users handle the selection of management/planning options and provide fast and responsive outputs, it can assist in effective multi-stakeholder negotiations over land-use planning where the minimization of land/water degradation is the ultimate goal., Water Resources Management, 28 (2), ISSN:0920-4741, ISSN:1573-1650

International audience; There is a significant gap between the rhetoric of claims about adoption of farm-level natural resource management practices and the reality. New empirical evidence of low adoption from several developing countries suggests that on-farm natural resource management practices face significant constraints to adoption, and that they deliver heterogeneous private and public benefits. Five recommendations are given to the research community related to: targeting; scaling-up; the proper role of research; trajectories of diffusion; and measurement of environmental impacts.

Surface observations provide ground evidence of climate change to support the scientific guidance paving the way to better adaptation and mitigation actions. The West African Science Service Centre on Climate Change and Adapted Land Use (WASCAL) has designed a multi-stakeholder initiative to rescue the deteriorated near-surface weather, climate and hydrological equipment of West African countries. The main goal for this multi-stakeholder framework was to monitor the climate and collect long term and high-quality records of essential climate variables in support of research, education, capacity building, and climate services provision. Proactive and inclusive partnership initiatives were developed to jointly (re)design and (re)implement near surface observatiories with the national meteorological and hydrological services or agencies (NMHS/As) in West Africa. The co-production scheme used by this framework succeeded in evaluating the existing observations networks, to modernizing sensors and field equipment, and densifying the sites in order to improve the quality of data collection, transmission, archiving, processing and sharing policies. After more than four years of community-of-practice, the existing regional basic hydroclimatic was increased/upgraded by 45% with automatic weather observing systems while fifty automatic water level, ten water quality sensors, three mesoscale research catchments, and several pilot sites to benefit countries’ services provision, research infrastructure, education, and capacity building. Country-specific data sharing policies were harmonized and signed to support data services delivery. This practice paper exposes the concepts, outcomes, challenges, lessons learned and the ways forward in setting-up the framework and keeping it on working to leverage the co-production of data & information services for better-informed decision-making in the field of sustainable development in West Africa.

Soil degradation is a serious environmental problem in Ethiopia. However, little information is documented on indicators such as variations in soil properties across different landforms in a catchment. This study was aimed to assess soil properties and their changes across sites with different erosion statuses, and identify landscape positions that require prior management attention in the Mai-Negus catchment, northern Ethiopia. Three types of erosion-status sites (stable, eroding and aggrading) were identified using reconnaissance surveys, and then the corresponding soil samples were collected and analyzed. The major soil properties were significantly varied (P ≤ 0.05) among the three erosion-status sites. The highest soil pH, organic carbon, total nitrogen, cation exchange capacity, iron and zinc were recorded from the aggrading sites in the reservoir and valley landforms of the study catchment. A higher bulk density was generally recorded in the eroding sites, whereas a lower value was observed in the aggrading sites. The highest sand content was observed in the eroding sites of the mountain followed by the central ridge landform. The paired mean difference and the correlation matrix of most soil properties between the different erosion statuses also showed significant differences. About 95% of the erosion-status sites were correctly classified by the discriminant function, indicating that the field survey-based classification was acceptable for decision making. On the basis of this study, suitable interventions should thus be introduced to the prioritized landforms, which are the mountain and central ridge, and eroding sites with severely degraded soil properties across the catchment.

Resource scarcity (labor, water, and energy) and high production costs are challenging the sustainability of conventional methods for rice and wheat establishment in Central Asia. Water saving irrigation and conservation agriculture (CA) practices (e.g., dry seeded rice, zero tillage wheat, residue retention) are potential alternative, resource-saving establishment methods. The Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model (CSM) can both be a valuable ex-ante and ex-post tool to evaluate the effects of water saving irrigation and resource saving CA-practices. The CSM-CERES-Rice and CSM-CERES-Wheat models of DSSAT were evaluated using experimental data from the 2008 to 2010 rice and wheat seasons as monitored in Urgench, the Khorezm region of Uzbekistan for growth, development of these crops, as well as soil mineral nitrogen (N) and volumetric soil moisture content in these cropping systems. Thereafter, the models were used to explore the long-term impact of water saving irrigation and CA-practices on grain yield, soil organic carbon (SOC) dynamics, N dynamics, and water balance in a rice–wheat rotation for 39 years starting from 1971. The simulation results showed that the simulated yield of water-seeded rice without residue retention and flood irrigation (WSRF-R0-FI) is likely to remain the highest and constant over 39 years. The simulated yield of dry seeded rice (DSR) with alternate wet and dry (AWD) irrigation and varying levels of residue retention was penalized for the initial years. However, the simulated rice yield increased after 13 years of CA-practices and continued to increase for the remaining years. Wheat did not experience a yield penalty for any of the treatments and simulated yield increased over time across all CA-practices based treatments. In the long-term, the effect of tillage methods and different residue levels for both rice and wheat were apparent in terms of grain yield and SOC build up. The results of the sensitivity analysis showed that WSR using AWD irrigation with puddling (WSRF-R0-AWD-Puddled) could give equivalent yield with that of WSRF-R0-FI and that irrigation water for rice could be reduced from 5435 mm to 2161 mm (or by 60%). Deep placement of urea in DSR (CT-DSR-AWD-DPUS) has the potential to increase yields of DSR by about 0.5 t ha −1 . Despite the huge water saving potential through the adoption of water saving AWD irrigation in DSR, a major challenge will be to prevent N losses. Substantial amounts of N losses through leaching, immobilization by residue mulch, combined with gaseous losses through volatilization and denitrification are the major causes for the lower simulated yield of rice for the AWD treatments. During the rice season, the implementation of water saving irrigation can improve water use efficiency by reducing percolation and seepage losses, which is an option in particular for WSRF-R0-FI. For both crops, the water use efficiency can be improved by lowering evaporation losses e.g. through residue retention on the soil surface. The creation of a sub-surface hard pan (puddling) and deep placement of urea super granules/pellet (DPUS) fertilizer could be the key for water saving and better yields of rice. Because CA-practices require almost three times less irrigation water than conventional method, and provide a long-term positive impact on grain yields of both crops, the CA-practices should be considered for double, no-till, rice–wheat cropping systems in the irrigated semi-arid drylands of Central Asia.

a b s t r a c t Mismanagement of irrigation water and the ensuing secondary salinization are threatening the sus- tainability of irrigated agriculture especially in many dryland regions. The permanent raised-bed/furrow system, a water-wise conservation agriculture-based practice, is gaining importance for row- and high value-crops in irrigated agriculture. However, because of additional surface exposure and elevation, raised beds may be more prone to salt accumulation especially under shallow water table conditions. A field study was carried out in 2008 and 2009 in the Khorezm region, Central Asia, to investigate the effect of three furrow irrigation methods on salt dynamics of the soil and the performance of the cot- ton crop on the raised bed-furrow system. The irrigation methods compared included (i) Conventional furrow irrigation wherein every furrow was irrigated (EFI) at each irrigation event; (ii) Alternate skip furrow irrigation (ASFI where one of two neighbouring furrows were alternately irrigated during con- secutive irrigations events; and (iii) Permanent skip furrow irrigation (PSFI) during which irrigation was permanently skipped in one of the two neighbouring furrows during all irrigation events. For salinity management with PSFI a 'managed salt accumulation and effective leaching' approach was pursued. The EFI method increased salt accumulation on the top of the raised beds. In contrast, the PSFI method allowed an effective salt leaching from the top of the raised beds. After leaching, salinity on top of the beds under PSFI was reduced to

Apart from the earmarked Ramsar sites along the coastal zones of Ghana, no inventory has been conducted to determine the location, distribution, and status of wetlands within any of its river basins. In this study, a logistic regression model was used within the GIS platform to predict, at pixel level, the presence of a wetland in the basin of the White Volta River. The output consisted of a map and also indicated that a total of 259.5 km2 of the land mass is estimated as probable floodplain wetland sites. The model used resulted in a high level of accuracy in predicting wetland presence.

In Central Asia, the increasing water shortage and labor scarcity, high cost of production, increasing secondary soil salinization, and land abandonment are compelling farmers to change to water saving irrigation and conservation agriculture (CA) technologies. Such CA practices aim at maximizing profits while making a better use of soil and water resources lowering labor demands, farm power and production costs. The CA experiments with rice–wheat systems combined two establishment methods (beds and flats) with three residue levels (all zero tillage) and with alternate wet and dry (AWD) irrigation followed by surface seeded wheat (SSW); and conventional tillage (dry tillage) and continuously flooded rice (water seeded rice, WSR) followed by SSW. These were evaluated for 2 years (2008–2010) by using several financial indicators such as gross margins (GMs) estimates and benefit/cost ratio (BCR) while accounting for the soil water balance and soil salinity dynamics. The GM and BCR were higher under WSR–SSW than under treatments of dry seeded rice (DSR)–SSW. Both were higher under residue removal compared to residue retainments in DSR-SSW. Surface seeded wheat, which involved minor production costs, yielded >6 t ha−1 in both years in all treatments. Furthermore, >80% of the total irrigation water was applied to rice. Yet, >90% from WSR–SSW and ∼67% from DSR–SSW were lost through seepage and percolation. Dry seeded rice in bed (DSRB)–SSW saved 15% more irrigation water compared to dry seeded rice in flat (DSRF)–SSW and 67% compared to WSR–SSW. Soil salinity decreased with rice cultivation. After 2 years, WSR–SSW had the lowest while residue-removed DSRB–SSW had the highest salinity level at all soil depths. Groundwater salinity under deep groundwater tables was higher under treatments of DSR–SSW than under WSR–SSW. However, under shallow groundwater tables, groundwater salinity was higher under WSR–SSW than under DSR–SSW. Under the conditions that irrigation water is subsidized or even free of charge, conventional WSR–SSW into the standing rice field (20 days before rice harvest) is the most profitable option. However, under water scarce conditions, the CA based rice–wheat system could be a suitable alternative to cope with water scarcity and secondary soil salinization. Before this crop production system can be advocated and promoted, it needs to be flanked by adequate water pricing policies.

This study assesses the economic value of supplemental irrigation as a rainfall variability adaptation strategy in a small catchment in south-western Burkina Faso. The bio-economic model built for the catchment maximises net cash income by optimally allocating land, labour, water and capital. Yields vary according to soil type, agricultural practice and the type of rainy season. We introduced farm ponds as an adaptation strategy – called supplemental irrigation – for grain crops during long dry spells in the rainy season. Simulation results show that supplemental irrigation can be cost effective and increase incomes, particularly during years with poor rainfall. However, in this catchment, gains from supplemental irrigation are limited because labour and capital are constraints on pond implementation.

Identification and social–ecological characterization of areas that experience high levels of persistent productivity decline are essential for planning appropriate management measures. Although land degradation is mainly induced by human actions, the phenomenon is concurrently influenced by global climate changes that need to be taken into account in land degradation assessments. This study aims to delineate the geographic hotspots of human-induced land degradation in the country and classify the social–ecological characterizations of each specific degradation hotspot type. The research entailed a long-term time-series (1982–2006) of Normalized Difference Vegetation Index to specify the extents of areas with significant biomass decline or increase in Vietnam. Annual rainfall and temperature time-series were then used to separate areas of human-induced biomass productivity decline from those driven by climate dynamics. Next, spatial cluster analyses identified social–ecological types of degradation for guiding further investigations at regional and local scales. The results show that about 19% of the national land mass experienced persistent declines in biomass productivity over the last 25 years. Most of the degraded areas are found in the Southeast and Mekong River Delta (17,984 km 2 ), Northwest Mountains (14,336 km 2 ), and Central Highlands (13,504 km 2 ). We identified six and five social–ecological types of degradation hotspots in agricultural and forested zones, respectively. Constraints in soil nutrient availability and nutrient retention capability are widely spreading in all degradation hotspot types. These hotspot types are different from each other in social and ecological conditions, suggesting that region-specific strategies are needed for the formulation of land degradation combating policy.

The cultivation of the biofuel crop Jatropha curcas L. in Burkina Faso may contribute to ameliorating the soil fertility of severely declining cropland through increased organic matter input and erosion control. This study addresses the potential for the soil organic carbon (SOC) sequestration in traditional and newly introduced J. curcas production systems. Five prevailing systems included interplanting with annual crops, intensely managed monoculture plantations, afforestation of abandoned cropland, plantings along contour stone walls, and traditional living fences. The SOC was analyzed in 20 paired sites of 1- to 4-year-old J. curcas plantings and adjacent cropland. Paired sites with living fences involved a longer chronosequence with 15- and 20-year-old plantings. Additionally, the contribution of J. curcas to SOC sequestration was investigated by comparing the 13C signature of the C inputs in four J. curcas sites with that of sorghum cropping. Linear regression analysis did not reveal a clear trend of SOC dynamics over time for the short-term chronosequences, nor could the isotopic tracer technique prove a contribution of 4-year-old J. curcas trees to the SOC stock. The 20-year chronosequence of J. curcas living fences exhibited a significant SOC increase of 62 ± 23 g m−2 y−1. Considering soil coverage of 1,200 m2 ha−1 by living fences (400-m hedge with a width of 3 m), 1.5 Mg SOC was sequestered. Also, changes in δ13C values indicated a contribution of C3-derived C to the SOC stock. These findings on traditional J. curcas systems indicate the potential of this biofuel crop for improving cropland soil fertility in the long run. Copyright © 2014 John Wiley & Sons, Ltd.

In the subsistence-based, nutrient-poor soils, and fertilizer-limited agriculture of northern Ghana, 45–65 % of land cover is annually burned for purposes of hunting and agricultural land preparation. The effects of burn-season, fractional nutrient losses, combusted plant parts and vegetation type on the fire-mediated nutrient cycling are unclear. We estimate and compare the plant nutrient losses associated with different savanna covers in the early and late burn-seasons and fractionate the losses into actual losses, which should be the cause for concern and the losses due to particulate redistribution. The tissue-moisture and fuel-load elemental concentrations are predominant factors that determine the quantity of fire-induced nutrient losses. About 50 % of total combusted phosphorus, potassium, calcium and magnesium load; and ~99 % of the carbon and nitrogen loads are directly lost from burned sites during burns. Generally, calcium and magnesium are redistributed in particulate forms (~100 and ~90 % respectively) and not lost from the region, phosphorus and potassium are lost in both particulate (~50 and ~75 % respectfully) and non-particulate forms (~50 and ~25 % respectively), whereas the carbon and nitrogen are mostly lost in gaseous forms (~95 %). In the early-burn season high tissue-nitrogen concentration and low phosphorus-concentration renders burn vulnerable to high nitrogen-losses/emissions and low phosphorus-losses per unit burnt biomass. A comparatively high tissue moisture, however, impedes the early burns, resulting in patches of burned and unburned vegetation that reduce the occurrence of late burns and the total losses of plant-nutrients. Early burns reduce the quantity of nutrient losses towards a more secured food production.

Tesfahunegn G.B., Vlek P.G.L. (2014): Assessing sediment enrichment ratio in Mai-Negus catchment, northern Ethiopia. Soil & Water Res., 9: 38–45. Soil degradation is a threat to sustainable development in Ethiopia. However, degradation indicators, such as sediment enrichment ratio (SER), are not adequately documented in literature. This study aims to investigate the SER of different erosion-status sites (aggrading, stable, eroded) in various landforms in Mai-Negus catch ment, northern Ethiopia. The erosion-status sites in the landforms were identified using field indicators, and soil samples were collected for analysis of selected soil parameters. In this study, due to the ratio of aggrading to eroded or stable sites at catchment and landform levels, the SER of soil nutrients and fine soil particles was > 1. But due to the ratio of aggrading to eroded sites in the landforms the average SER of the soils were higher (1.42–7.22) as compared to the ratios of aggrading to stable sites (1.10–3.66). The SER significantly ( P ≤ 0.05) differed among the landforms, which indicated differences in the effect of erosion. The relationships between the SER of fine soil particles and soil nutrients were strong. Thus, priority for introducing appropriate anti-erosion measures should be given to sources of high SER sites such as the mountainous and central ridge landforms in the catchment using the limited resources available.

Recognizing the socio-economic and biophysical causes of land degradation at the national level is important for cause-targeted strategies when designing policies for combating land degradation. This study aims to identify the biophysical and socio-economic factors that significantly affect land degradation across Vietnam and to interpret the causalities underlying the effects. The dependent variables considered in the study are spatial, the extent and intensity of degradation in three land-use zones (agriculture, forest and severely degraded abandonment). The hypothesized explanatory variables are common economic and demographic drivers and bio-physical factors such as soil, terrain constraints, and neighborhood land-use structures that are often neglected in many large-scale land degradation assessments. Instead of using a single inferential statistic technique, we used multi-linear regression and binary logistic regression in a complementary manner to increase the detectability and credibility of the degradation cause analyses. The results showed agricultural production growth had strong and consistent effects on land degradation extent and intensity. Population growth, especially in rural areas, had a strong effect on the extent of overall land degradation. The importance of a neighboring forest was revealed for its ability to reduce land degradation intensity in abandoned, unproductive lands. The concrete faceting of the causal analysis for each land-use zone as social–ecological stratum allowed us to combine the defined social–ecological contexts, contemporary theories, and hypotheses in the field to clarify the causal factors of a complex phenomenon like land degradation. The study demonstrates these contemporary inferential statistics can be complementarily used to sufficiently detect and understand land degradation causes at the national level. The results suggest implications for national land management policy: internalizing land degradation costs in the farming system evaluation for payment for ecosystem services policy, restricting forest conversion, and improving extension services and education in agrarian communities.

Management practices may influence yield and nitrogen (N) use efficiency of irrigated cotton (Gossypium hirsutum L.) in irrigated arid lands such as those of the Aral Sea basin. A field experiment was conducted to compare the effects of conservation tillage (permanent raised beds; PB) with conventional plow tillage (CT) under three different N application rates (0, 125 and 250 kg ha−1) on cotton growth, yield, N use efficiency and N balance in irrigated arid lands of Uzbekistan for two years. Raw cotton yield and yield components were not affected by tillage methods in both years. However, yield and yield components significantly increased when N fertilizer rate was increased from zero to 125 kg ha−1 N application. When the N rate was doubled from 125 to 250 kg ha−1, a relatively much lower increment was observed in both tillage methods. The groundwater nitrate concentration was reduced considerably, while efficiency of applied N was increased in 2009, i.e., after introduction of the cover crop in the cotton mono cropping system, compared to 2008. The efficiency of the applied N decreased with increased N application rate. Tillage method did not affect agronomic N use efficiency in both years. However, in the 2nd year, apparent N recovery efficiency was higher in PB than in CT, while physiological N use efficiency with N-250 was 54% lower in PB than in CT. The apparent system N balance was negative with N-0 and N-125, but positive (N loss) with high N application (250 kg ha−1) with both tillage methods. A significant interaction effect between tillage and N level was observed; with N-0, CT had a 32% higher negative N balance than PB. With N-250, CT had a significantly higher positive N balance (N loss), more than twice as high (66 kg ha−1) as for PB. Thus, cotton cultivation in PB with proper N application and the introduction of a winter cover crop can be considered a viable alternative to the present unsustainable CT cotton mono-cropping system in irrigated arid lands, assuming the patterns are confirmed in the long-run.

The linearity and slope of biomass-density trajectories of forests became a classical topic of discussion in the ecological literature since the 1930s. In 2003, a theoretical framework partially based on empirical evidence from mangrove forests articulated disparate available knowledge. The present article is the first empirical test of the framework for which data from Cuban mangroves were used. Nine plots were surveyed in 2005 in a predominantly Avicennia germinans monospecific forest on the south coast of La Habana province. For one of the plots data from 1980s were available and quoted. Instead of calculating mean biomass per individual, the present article addressed basal area per individual in order to allow a more direct use of the surveyed data (DBH) and avoid introducing further uncertainties in the discussion. The two empirical linear trends detected in the trajectory of individual mean basal area vs density of individuals (self-thinning) were explained by the theoretical framework. The qualitative validity of the framework stands. The observation of two linear self-thinning trends can be empirical evidence that the slope is specific to site conditions and can also change if site conditions change. Potential for further theoretical and modeling work can exist in revisiting available data in historical records of Cuban research organizations. Key words: Self-thinning, stem diameter, skewness, model, mangroves RESUMEN La linealidad y pendiente de trayectorias biomasa-densidad de bosques devino un tema clásico de discusión en la literatura ecológica desde los años 1930. En 2003, un marco teórico parcialmente basado en evidencias empíricas de bosques de manglar armonizó antecedentes contradictorios. El presente artículo es la primera evaluación empírica de dicho marco teórico, para lo que se emplearon datos de manglares cubanos. Se muestrearon nueve parcelas en el 2005 en un bosque predominantemente monoespecífico de Avicennia germinans en la costa sur de provincia La Habana. Para una de las parcelas, estaban disponibles datos de 1980 y fueron citados. En lugar de calcular biomasa media por individuo el presente artículo se enfoca en área basal por individuo para usar más directamente los datos colectados (DBH) y evitar la introducción de mayores incertidumbres en la discusión. Las dos tendencias lineales empíricas detectadas en la trayectoria de área basal individual media vs densidad de individuos (auto-raleo) fueron explicados por el marco teórico. La validez cualitativa del marco teórico se mantiene. La observación de dos tendencias lineales de auto-raleo puede ser evidencia empírica de que la pendiente es específica de cada sitio y puede cambiar si las condiciones en el sitio cambian. Los datos disponibles en registros históricos de organizaciones de investigación en Cuba pueden tener potencial para más trabajo teórico y de modelación. Palabras clave: Auto-raleo, diámetro del tronco, asimetría, modelo, manglares

Rice is the second major food crop in central Asia. Climate change may greatly affect the rice production in the region. This study quantifies the effects of projected increases in temperature and atmospheric CO2 concentration on the phenological development and grain yield of rice using the “ORYZA2000” simulation model. The model was parameterized and validated on the basis of datasets from three field experiments with three widely cultivated rice varieties under various seeding dates in the 2008–09 growing seasons in the Khorezm region of Uzbekistan. The selected rice varieties represent short-duration (SD), medium-duration (MD), and long-duration (LD) maturity types. The model was linked with historical climate data (1970–99) and temperatures and CO2 concentrations projected by the Intergovernmental Panel on Climate Change for the B1 and A1F1 scenarios for the period 2040–69 to explore rice growth and yield formation at eight emergence dates from early May to mid-July. Simulation results with historical daily weather data reveal a close relationship between seeding date and rice grain yield. Optimal emergence dates were 25 June for SD, 5 June for MD, and 26 May for LD varieties. Under both climate change scenarios, the seeding dates could be delayed by 10 days. Increased temperature and CO2 concentration resulted in higher rice grain yields. However, seeding rice before and after the optimal seeding dates reduced crop yield and yield stability significantly because of spikelet sterility induced by both high and low temperatures. As the grain yield of SD varieties could be adversely affected by climate change, rice breeding programs for central Asia should focus on developing appropriate heat-tolerant MD and LD varieties.

Intensive soil tillage and mismanagement of irrigation water and fertilizers are increasing production costs, reducing soil fertility and crop water productivity and threatening the sustainability of crop production systems in the irrigated arid lands of Uzbekistan, Central Asia. Conservation agriculture (CA) practices combined with optimum nitrogen (N) management can counterbalance some of these adverse effects. Most work has been done in rainfed areas so there is less information available for irrigated production systems. This study compared the effects of tillage, crop residue management and N rates on yield and water productivity for irrigated cotton, winter wheat and maize grown in a two-year rotational sequence in Uzbekistan under CA practices vs. current conventional farmer practices. Permanently raised beds (PB) and conventional tillage (CT) were compared under two crop residue levels (retained residue – RR and removed residue – RH), and three N levels (zero, medium and high, with actual rates depending on the crops) on a sandy loam to loam soil. Raw cotton yield, yield components and water productivity were not affected by tillage methods. However, the following crops, wheat and maize, produced 12 and 42% higher grain yields, respectively, under PB than under CT. Under PB, water productivity increased in wheat by 27% and in maize by 84%, while 11% less water was applied during wheat and 23% during maize production, compared to CT. All three crops showed a considerable increment in yield and water productivity when N fertilizer levels were increased from zero to medium N application, and a relatively much lower increment when the N rate was doubled from medium to high N, for both tillage methods. In maize, the response to applied N was more pronounced with PB than with CT. Irrespective of tillage method, RR increased the grain yield of wheat by 5% compared to RH. In maize, RR in PB increased grain yields by 15% compared to RH. RR had no effect for CT. The positive effect of PB and RR on yield and water productivity of wheat and maize and the lack of negative effects on cotton yield reflect that PB with RR and proper N application may be viable alternatives to the present, unsustainable conventional agriculture practices in these irrigated arid lands, assuming the patterns are confirmed in the long-run.

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to adopt resource conservation technologies, such as dry seeded, non-flooded rice. Alternate wet and dry (AWD) water management combined with alternative establishment methods, e.g., zero tillage planting in bed and flat layouts, and residue retention, may substantially reduce rice irrigation water requirement. Field experiments were conducted in a rice–wheat cropping system to evaluate these technologies and to identify the underlying processes responsible for possible reductions in rice yield. Zero till dry seeded rice (DSR) on the flat (DSRF) and on raised beds (DSRB), combined with three levels of wheat and rice straw residue retention – none (R0), 50% (R50) and 100% (R100) were therefore evaluated during the 2008 and 2009 growing seasons, using AWD water management. These treatments were compared with water seeded rice (WSR) grown with conventional tillage (dry tillage) on the flat under continuous flood irrigation (WSRF-R0-FI) or alternate wet and dry irrigation (WSRF-R0-AWD). The use of AWD reduced irrigation amount to only 30% of the amount of water applied to continuously flooded rice. However, yield of residue removed AWD treatments was lower than yield of the continuously flooded treatment by 27% in 2008 and by 40% in 2009. The significant reduction in rice yield in all treatments with AWD was caused by reduced growth rate, resulting in lower biomass, leaf area, panicle density, number of florets panicle−1 and floret fertility, with significant differences in the second year. In 2008, this appeared to be due to water deficit stress in the AWD treatments. In 2009, the reduction in growth and yield with AWD was greater, and more so as the level of residue retention increased. Residue retention reduced rice yield by 59% in 2009 with R100 compared to the R0. By far the biggest cause was a reduction in floret fertility. The reduction in fertility with AWD in 2009 appeared to be due to cold damage, whereas the continuously flooded rice appeared to have been protected from cold damage by the floodwater. The weather during the period from panicle initiation (PI) to flowering in 2009 was very cold, with 20 days with minimum temperature less than 15 °C. About 1 in 10 years experience such low temperatures in this region. Therefore, the development of varieties with greater cold and water deficit stress tolerance is needed if non-flooded rice culture and surface residue retention are to be adopted in this region.

Soil quality (SQ) assessment from farmers' point of view can be used as a primary indicator for planning sustainable agriculture. Despite this fact, limited information is documented with regard to SQ indicators, for example weed species, crop types and management practices from farmers' knowledge perspectives. The aims of this study are to analyse factors that determine farmers' knowledge of SQ, identify SQ indicators of weed species and crop types across different SQ status and assess soil-and-crop management practices that maintain SQ in the Mai-Negus catchment, northern Ethiopia. Fifty-two farmer household heads were chosen randomly for questionnaire interview. The results showed significant (p ≤ 0·05) differences in the proportion of respondents who used different crop-and-soil management practices. The success of overall prediction by the logistic regression model (model χ2 = 0·84, p

Even though soil degradation challenges sustainable development, the use of degradation indicators such as nutrient export (NE) and nutrient replacement cost is not well documented at landform level. This study is aimed to investigate the extent of soil degradation, NE rates, and their replacement cost across landforms in the Mai-Negus catchment, northern Ethiopia. Different erosion-status sites (aggrading, stable, and eroded) in the landforms were identified, and soil samples were randomly collected and analysed. Nutrient export, replacement cost, and soil degradation were calculated following standard procedures. This study showed that soil degradation in the eroded sites ranged from 30 to 80% compared to the corresponding stable site soils, but the highest was recorded in the mountainous and central ridge landforms. Average NE of 95, 68, 9.1, 3.2, 2.5, and 0.07 kg ha−1 y−1 for soil calcium, carbon, nitrogen, potassium, magnesium, and phosphorus, respectively, was found from the landforms. Significantly strong relationships between NE and sediment yield in the landforms were observed. Annual nutrient replacement costs varied among the landforms though the highest was in the reservoir (€9204 in May 2010). This study thus suggests that while introducing antierosion measures, priority should be given to erosion sources to the reservoir such as mountainous and central ridge landforms.

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to develop and adopt resource conservation technologies. Nitrogen (N) is the key nutrient for crop production in rice–wheat cropping systems in this region. Nitrogen dynamics of dry seeded rice-(aerobic, anaerobic) planted in rotation with wheat (well drained, aerobic) can differ greatly from those of conventional rice cultivation. Soil mineral N dynamics in flood irrigated rice has extensively been studied and understood, however, the impact of establishment method and residue levels on this dynamics remains unknown. Experiments on resource conservation technologies were conducted between 2008 and 2009 to assess the impact of two establishment methods (beds and flats) in combination with three (R0, R50 and R100) residue levels and two irrigation modes (alternate wet and dry (AWD) irrigation (all zero till), and a continuously flooded conventional tillage (dry tillage)) with water seeded rice (WSR) on the mineral N dynamics under dry seeded rice (DSR)-surface seeded wheat systems. N balance from the top 80 cm soil layers indicated that 32–70% (122–236 kg ha −1 ) mineral N was unaccounted (lost) during rice cropping. The amount of unaccounted mineral N was affected by the irrigation method. Residue retention increased ( p 4 N consistently remained at very high levels, while, NO 3 N remained at very low levels in all treatments. In rice, the irrigation method affected NH 4 N content. Effect of residue retention and establishment methods were not significant on NH 4 N and NO 3 N dynamics in both crops and years. Further evidence of the continuously fluctuating water filled pore spaces (WFPS) of 64% and the microbial aerobic activity of 93% at the top 10 cm soil surface during rice growing season indicates soil in the DSR treatments was under frequent aerobic–anaerobic transformation, a conditions very conducive for higher amounts of N loss. In DSR treatments, the losses appeared to be caused by a combination of denitrification, leaching and N immobilization. When intending to use a DSR management strategies need to be developed for appropriate N management, irrigation scheduling, and residue use to increase mineral N availability and uptake before this practices can be recommended.

Understanding the patterns of land degradation indicators can help to identify areas under threat as basis for designing and implementing site-specific management options. This study sort to identify and assess the patterns of land degradation indicators in selected districts of western Kenya. The study employed the use of Land Degradation Sampling Framework (LDSF) to characterize the sites. LDSF a spatially stratified, random sampling design framework consisting of 10 km × 10 km blocks and clusters of plots. The study broadly identified and classified the indicators and attributes of land degradation into soil and site stability, hydrologic function and biotic integrity. Assessment of general vegetation structure showed that over 70% of the land was under cropland with forests accounting for 8% of the area. Sheet erosion was the major form of soil loss. High variability was observed for the soil properties and this can be due to both inherent soil characteristics as well as land management practices. There was distinct variation in the soil properties between the topsoil (0–20 cm) and the subsoil (20–30 cm) with the topsoil having higher values for most of the parameters compared to the subsoil. Using coefficient of variation (CV) as criteria for expressing variability, Ca, TON, Mg, SOC and silt were most variable soil properties for the 0–20 cm depth. Moderate variability (CV 0.15–0.35) was observed for CEC, P, K and clay while Na, Sand and pH had the least variability (CV

Like many irrigation schemes in Central Asia, the one in Khorezm faces a two-fold challenge: on the one side, the severe problems inherited from the past need to be remedied and on the other side, the rising supply–demand gap driven by sharpening competition for water and climate change must be dealt with. Located in the lower part of the Amu Darya basin, Khorezm irrigation and drainage scheme is particularly vulnerable to supply–demand gaps. Promising solutions towards adaptation comprise modified strategies of land and water use towards higher efficiency and flexibility in combination with measures to lessen the constraints of the system itself, which was initially designed for the management of a few, large and uniform production units and not for many diverse and small units. Solutions consist of flexible, modeling-based approaches, re-arranging institutional settings and establishing economic incentive systems. Flexible modeling allows an integrated use of surface and groundwater resources avoiding or minimizing the impact of water stress on yield. Institutional settings strengthen the position of water users via improved participation and transparency of processes in Water Consumers Associations (WCAs). Economic measures support sustainable resource use strategies and improve the functioning of WCAs. The findings could be extrapolated to other regions of Central Asia with similar conditions and challenges.

Inappropriate agricultural practices and conversion of marginal land to cultivation and grazing have led to severe land degradation in the Ethiopian highlands. Consequently, the government has invested substantial resources in soil and water conservation (SWC). One of such interventions was exclosure, which was aimed restoring biodiversity, biomass and soil fertility. The aim of this study was to analyze the impact of exclosures on soil fertility restoration and examine its variability across age, agro-ecology and landscape position. The study was conducted in the Gubalafto district of North Wello Zone, northern Ethiopian highlands. Vegetation cover was estimated and soil samples were collected from three age categories (open sites, 10- and 27-year-old exclosures), two agro-ecological zones (mild and cool) and in three landscape positions (lower, mid and upper). The samples were analyzed for selected soil physico-chemical properties using standard laboratory procedures. The results were statistically tested using analysis of variance (ANOVA). Vegetation ground and canopy cover increased with exclosure age. The soils of the exclosures showed significantly higher organic carbon (9 g/kg) and total nitrogen content (1.2 g/kg p ≤ 0.06 at α = 0.05) than the open sites. However, no statistical significant difference was observed between the 10- and 27-year-old exclosures, indicating that the restoration rate decreased with increasing exclosure age. This could be related to the low quantity and quality of the biomass, which influenced organic matter input and mineralization. Exclosures in the mild zone showed significantly higher soil fertility restoration than those in the cool zone. The differences between the two zones could be attributed to the effect of micro-climate on biomass production, vegetation types and organic matter mineralization. The soil physico-chemical properties neither had significant differences nor followed a regular trend across the landscape positions. The non-significant soil fertility restoration variation across the landscape positions could be attributed to complementary effect of structural SWC measures. Therefore, exclosure implementation and utilization planning should consider soil fertility restoration variation with age, agro-ecology and management conditions of the respective exclosure.

In this study we use agent-based simulations to explore the impact of social-mix policies on the segregation dynamics of São José dos Campos, a medium-sized Brazilian city. We use the model MASUS, Multi-Agent Simulator for Urban Segregation, to test two policy strategies: one based on the spatial dispersal of poverty, and the other on the spatial dispersal of wealth. The experiments indicated that these strategies reveal varying shortcomings and complementary benefits in cities such as São José dos Campos. While poverty dispersal provides immediate results on segregation levels and direct benefits for the assisted families, wealth dispersal can produce long-term outcomes and promote a positive change in the overall levels and patterns of segregation in the city. Keywords: urban segregation, social mix, urban policies, social simulation, agent-based model, Brazil

Under low input subsistence farming systems, increased pressure on land use and decreased fallow periods have led to a decline in soil productivity. The soils in sub-humid region of Ghana are generally poor and require mineral fertilizer to increase crop productivity. This paper presents the use of Agricultural Production Systems sIMulator (APSIM) to simulate the long term influence of nitrogen (N) and phosphorus (P) on maize (Zea mays L.) yield in Sub-humid Ghana. The APSIM model was evaluated at two sites in Ejura, on a rainfed experiment carried out on maize in 2008 major and minor seasons, under various nitrogen and phosphorus rates. The model was able to reproduce the response of maize to water, N and P, and hence simulated maize grain yields with a coefficient of correlation (R2) of 0.90 and 0.88 for Obatanpa and Dorke cultivars, respectively. A 21-year long term simulation, with different rates of N and P mineral fertilizer application, revealed that moderate application of N (60 kg N ha−1) and 30 kg P ha−1 improves both the long term average and the minimum yearly guaranteed yield. Variability in grain yield increased with increasing application of N fertilizer in both seasons. Treatments with P fertilizer application shows a similar trend for the major season and reverse trend for the minor season, thereby suggesting an interactive effect with rainfall amounts and distribution. Application of 30 kg P ha−1 significantly increased the response to N. The response to mineral fertilizer (N and P) applications varied between seasons, suggesting the need to have a range of fertilizer recommendations to be applied based on seasonal weather forecast.

Afforestation of degraded croplands by planting N2-fixing trees in arid regions is highly recognized. However, fixation of atmospheric nitrogen gas (N2) by woody perennials is often limited on phosphorus (P) poor soils, while any factor limiting N nutrition inhibits tree growth. In a two-factorial field experiment, the effect of three P amendments was examined during 2006–2008 on N2 fixation, biomass production, and foliage feed quality of actinorhizal Elaeagnus angustifolia L. and leguminous Robinia pseudoacacia L. With the 15N natural abundance method, N2 fixation was quantified based on foliar and whole-tree sampling against three non-N2-fixing reference species: Gleditsia triacanthos L., Populus euphratica Oliv., and Ulmus pumila L. The P applications, in March 2006 and April 2007 only, included (i) high-P (90 kg P ha−1), (ii) low-P (45 kg P ha−1), and (iii) 0-P. After 3 years, the average proportion of N derived from atmosphere (Ndfa, %) increased from 78 % with 0-P to 87 % with high P when confounded over both N2-fixing species. With the used density of 5,714 trees ha−1, the total amount of N2 fixed (Ndfa, kg N ha−1) with high-P increased from 64 kg N ha−1 (year 1) to 807 kg N ha−1 (year 3) in E. angustifolia and from 9 kg N ha−1 (year 1) to 155 kg N ha−1 (year 3) in R. pseudoacacia. Total above-ground biomass increases were too variable to be significant. Leaf N content and therewith also leaf crude protein content, which is an indicator for feed quality, increased significantly (24 %) with high-P when compared to 0-P for E. angustifolia. Overall findings indicated the suitability of the two N2-fixing species for afforestating salt-affected croplands, low in soil P. With P-applications as low as 90 kg P ha−1, the production potential of E. angustifolia and R. pseudoacacia, including the supply of protein-rich feed, could be increased on salt-affected croplands.

Leaf chlorophyll meters can be used to support easy and efficient crop nitrogen (N) management. They can be used on tree species native to Central Asia that have been suggested for afforesting salt-affected croplands, but its use demands a priori calibration as the relationship between chlorophyll meter measurements and leaf N contents is crop/species specific. Data collected with a SPAD-502 leaf chlorophyll meter during 2006–2008 was used to generate a calibration dataset for the leaf N status of three tree species. The second-degree polynomial relationships between the SPAD-502 readings and total leaf chlorophyll and N content had higher predictive power than linear relationships for all species, although with differences among them. The validation was completed with the same species grown at a different location (difference in space) and with older trees (difference in age). The comparison between predicted and spectrophotometrically determined leaf N content showed a root mean square error (RMSE) of 25 mg g−1 DM, which corresponds to a relative RMSE of 10% for Elaeagnus angustifolia. For Gleditsia triacanthos and Robinia pseudoacacia they were 11 mg g−1 DM and 16%, 14 mg g−1 DM and 10%, respectively. The findings demonstrate that the SPAD-502 can with confidence be used for non-destructive assessment of tree foliar N status of these three species, although only within the range of the SPAD-502 values used for the calibration. Options for the use of the SPAD-502 for forest management in agroforestry-based land use systems in Central Asia are addressed.

Stable soil aggregates and high microbial diversity are essential for efficient nutrient recycling in soil. This study evaluated effects of different arable land-use systems on soil aggregation and associated composition and total diversity of bacteria and fungi. For this purpose, 5- and 3-year-old field trials were selected, two in sub-humid (orthic Acrisols and oxidic Ferralsols) and one in semi-arid (chromic Cambisol) region in Kenya. The treatments included combinations of tillage (conventional tillage [CT] and reduced tillage [RT]), crop residue management (0 and 2 t ha?1 maize stover) and cropping systems (continuous maize, maize-soybean intercropping and rotation) in the sub-humid sites, and of different tillage (CT, no-till and tied-ridging) and organic fertilization management (manure and crop residue) in semi-arid Kenya. The innovativeness of this study is the research in tropical soils where the concept of aggregate hierarchy is not generally accepted yet. The results showed that aggregate mean weight diameter (MWD) at 0-15 cm depths had increased from 19 to 34% under RT relative to CT management (P < 0.05). Crop residue additions also significantly increased MWD by 22% at the top 5 cm (P < 0.01) compared to treatments without residue in oxidic Ferralsols. At all the three sites, tillage resulted in greatest shifts of bacterial and fungal community composition, while cropping system had largest positive effect on the total microbial diversity indices. Total microbial diversity indices as well as MWD were higher in soybean-maize intercropping systems than under rotation or continuous maize cropping. Changes in total bacterial diversity related inversely to changes in the amount of free silt + clay, while fungal diversity related inversely to the contents of soil macro-aggregates >2 mm (P < 0.05). We conclude that RT plus supply of organic resources and intercropping are best strategies to increase total diversity of soil bacteria and fungi and improve soil structure in these tropical soils.

This study has assessed the seasonal occurrence of annual vegetation fires and defined inter-seasonally burned area for the different vegetation cover types across Ghana and the northern region of Ghana using 10-year (2001–2010) remote sensing data. These values were used with fire induced elemental losses to estimate greenhouse gas emissions and net plant nutrient loss due to gross bush fire nutrient transfers and annual atmospheric nutrient depositions. About 21, 68, 10 and 1 % of annual burns across the northern region of Ghana take place in the months of November, December, January and February respectively. As much as 68 ± 4 thousand km2 (25–32 %) and 37 ± 2.6 thousand km2 (46–60 %) of dry land are annually burned across Ghana and the northern region of Ghana respectively, with 53–56 % of the total annual burns across the country taking place in the northern region. About 10,100–28,400 Gg of C, comprising 215–4,700 thousand Gg of CO2 equivalent (CO2, CH4) potential global warming green house gases and 48–324 thousand Gg of local pollutants (CO, NOx) are estimated to be released annually through bush fire occurrence across Ghana. Net negative balance for P between fire-induced nutrient transfers and, annual wet and dry nutrient deposits is of concern given the high P-sorbing mineral content of the soils. The temporal loss of P suggest an input source than wet and dry atmospheric P depositions for the sustenance of the ecosystem or predict a long term threat to regional food production.

Separating human-induced land degradation from that caused by natural processes in the world of global climate and atmospheric change is a challenging task, but important for developing mitigation strategies. Current remote-sensing data and spatio-temporal analyses allow the distinction of climate and human-induced land degradation on a sub-continental scale, but the underlying processes cannot be discerned at this scale. This study is conducted at a river-basin scale to (1) identify land degradation hotspots in a basin or sub-basin, and (2) assess the correspondence and divergence of land degradation assessed by NDVI shifts with and without accounting for atmospheric fertilization with that based on soil erosion assessment at a sub-basin scale. Long-term remote sensing (NDVI) and rainfall data were used to identify human-induced land degradation hotspot areas in the Volta basin. The results were compared with the critical zone of soil loss in the White Volta sub-basin derived from a spatially distributed soil erosion model, validated by field-measured data. A spatial comparison of the above studies revealed that the biomass productivity (NDVI)-based land degradation assessment grossly underestimated the extent to which soil is being lost, unless a correction was included to account for atmospheric fertilization. Based on inter-annual NDVI signals land degradation was evident in about 8% of the Volta basin's landmass, but when accounting for atmospheric fertilization, as much as 65% of the land is losing some of its vital attributes such as soil quality or vegetation productivity. The study demonstrates the need for using a multi-pronged assessment strategy in land degradation assessment that offers an insight of the processes involved in land degradation.

Soil degradation by erosion is the most serious threat to food security in Ethiopia. Thus, effective management strategies (scenarios) that reduce soil degradation are crucial. However, the application of models such as Soil and Water Assessment Tool (SWAT) that simulate the impact of different scenarios on soil degradation by erosion in Ethiopia condition is limited. This study is aimed to evaluate the effectiveness of different scenarios in reducing runoff, sediment and soil nutrients losses using the SWAT model for the Mai-Negus catchment, northern Ethiopia. The highest erosion in terms of runoff, sediment yield, total nitrogen (TN) and phosphorus (TP) losses was simulated by the baseline scenario at the catchment outlet as 168 mm, 42,000 t year−1, 22,400 and 1,360 kg year−1, respectively. In contrast, the lowest runoff, sediment yield, TN and TP losses were simulated by the scenario that integrated land-use redesign and conservation measures (scenario 6c) at catchmen level as 50 mm, 9,215 t year−1, 6,284 and 341 kg year−1, respectively. These indicate that reduction of sediment, TP, TN and runoff losses by 78, 75, 72 and 70%, respectively, can be achieved by scenario 6c compared to the baseline scenario. Thus, scenario 6c appears relatively more effective as potential management strategy in reducing soil degradation than the other scenarios. This study demonstrates that SWAT model is powerful to select the most technically effective management strategies in reducing soil degradation in a catchment. However, further research is required related to the cost-benefits of such management strategies.

Climate change is projected to have serious environmental, economic, and social impacts on Ghana, particularly on rural farmers whose livelihoods depend largely on rainfall. The extent of these impacts depends largely on awareness and the level of adaptation in response to climate change. This study examines the perception of farmers in Sekyedumase district of Ashanti region of Ghana on climate change and analyzes farmers’ adaptation responses to climate change. A hundred and eighty farming households were interviewed in February and October 2009. Results showed that about 92% of the respondents perceived increases in temperature, while 87% perceived decrease in precipitation over the years. The major adaptation strategies identified included crop diversification, planting of short season varieties, change in crops species, and a shift in planting date, among others. Results of logit regression analysis indicated that the access to extension services, credit, soil fertility, and land tenure are the four most important factors that influence farmers’ perception and adaptation. The main barriers included lack of information on adaptation strategies, poverty, and lack of information about weather. Even though the communities are highly aware of climate issues, only 44.4% of farmers have adjusted their farming practices to reduce the impacts of increasing temperature and 40.6% to decreasing precipitation, giving lack of funds as the main barrier to implementing adaptation measure. Implications for policymaking will be to make credit facilities more flexible, to invest in training more extension officers and more education on climate change and adaptation strategies.