Nigerien subsistence farmers increasingly rely on marginal lands for food production as a result of ongoing soil degradation, limited fertile land availability and growing population pressure. These degraded lands, however, generally provide poor yields, which is largely assigned to an increased vulnerability to drought, as a major part of the rainfall is lost through inefficient rain water distribution. More efficient use of rainwater can be achieved with the aid of water and soil conservation (WSC) techniques, which positively alter the soil water balance in favour of productive water. In Niger, zaï and demi-lunes WSC techniques improve yields, but their adoption has not been widespread, and the dissemination generally encounters difficulties. To identify and quantify the importance and presence of several adoption constraints in the Tillabéri region, we conducted 100 households surveys exploring farmers' erosion perception, WSC technique knowledge and resource availability. Although important adoption triggers such as food insecurity and limited fertile land availability are present, the region's WSC adoption rate is low. The application is limited by manure shortage and a lack of specific erosion knowledge, indicating the need of an efficient and specialized policy focusing on more than yield increase alone. Most farmers have little awareness of erosion causes and effects and therefore do not relate WSC techniques to the indirect benefits, which are to be taken into account to secure sustainable solutions to drought and food insecurity.

The hazard for recurring food insecurity in the Sahel is largely affected by insufficient biomass productivity of degraded, marginal lands. In general, water and soil conservation (WSC) techniques are believed to tackle the deterioration of soil quality by enhancing soil hydraulic properties, soil life, and soil organic carbon (SOC) content, but this beneficial effect on soil quality is hardly ever quantified in WSC research. This study therefore evaluates the effect of WSC on soil chemical, physical, and biological quality indicators by means of an in situ experiment, which was installed in 2011 nearby Sadoré, Niger. The treatments include the following: zaï + manure (Z), demi‐lunes + manure, scarification + manure, control + manure, and control. WSC increases grain yields up to 0·7 ± 0·2 Mg ha−1 on degraded, marginal lands, which is similar to yields produced on fertile lands in the area. Nevertheless, a trade‐off between biomass production and SOC accumulation was observed. After three growing seasons, SOC was found to rise significantly for the treatments provided with manure, from ±2·5 to ±5 g kg−1, but the increase was lowest for Z, which produced the highest yields. WSC also showed significantly elevated nematode counts but did not considerably affect other soil chemical and soil physical properties. Hence, on the short term, WSC does not improve soil quality, as was widely proclaimed. Therefore, future research should include the assessment of long‐term WSC effects and the evaluation of integrated management combining WSC with alternative, yield‐enhancing strategies. Copyright © 2015 John Wiley & Sons, Ltd.

No abstract

Whether aggravated agricultural drought in the Sahel is related to a changing climate (meteorological drought, i.e., deficit of rainfall or unfavourable rainfall distribution) or to land use and land degradation (soil-water drought, i.e., decreased water infilitration and water holding capacity) is a much-debated issue. Global climate models and trend analysis show little agreement on how rainfall and meteorological drought are changing in the region, and research has increasingly attributed agricultural drought to an imbalanced rainwater distribution over the root zone caused by human-induced land degradation. This paper investigates the extent of both meteorological and soil-water drought on "laterite" soils in the Tillaberí region of Niger and their effect on millet (Pennisetum glaucum (L.) R. Br.) growth by combining monthly and daily rainfall analysis with analysis of the root zone water distribution under different management practices. The treatments include: zaï + manure (Z), demi-lunes + manure (DL), scarification + manure (SCAR), control + manure (CF) and control (C). Our findings suggest that increasing agricultural drought does not originate from a decreasing annual amount of rainfall. However, other daily rainfall parameters more important for crop biomass productivity than total rainfall amount, such as the number of dry spells, do appear to have recently worsened. Dry-spell analysis showed increased drought risks during the vegetative growth phase (0-40 DAS) and the vulnerable grain formation phase (90-110 DAS, Days After Sowing). The extremely low grain yields and values of soil-water storage below the critical value for water stress of the control treatments, moreover, confirm poor root zone water distribution. DL and Z however, show potential, to mitigate both dry spells and soil-water drought, as they induce an important increase of soil-water storage, resulting in higher grain yields. In order to optimize these water and soil conservation (WSC) techniques and to increase their potential for drought mitigation, the underlying features enabling increased soil-water storage, including water balance analysis, soil physical properties, nutrient management and system design, should be tackled in future studies.

Poor soil fertility remains a threat to crop production and livelihoods in the Sahel. Understanding the impacts of proposed soil fertility management technologies on soil fertility status and millet yield is essential. We conducted a 2-year experiment to assess changes in selected physical properties of an Arenosol and their impacts on millet yields at Karabedji, Niger. Treatments consisted of four fertilizer rates applied on top and bottom farm types selected from a long-term experiment. Mixed-model analyses indicated considerable effects (P=0.055) of fertilizer rates and farm types on soil structural stability being higher in the top farm than in the bottom farm type. Dexter's soil physical quality index (S) varied significantly with soil depth. A significant correlation (R-2=0.24) was found between the aggregate stability index and S. Plant available water recorded in fertilizer-treated soil was higher than the control and higher on the top farm than in the bottom farm. Fertilizer rates and farm types influenced millet yields. Moreover, we obtained positive relationships between millet yield and soil aggregate stability, and plant available water, thereby elucidating the significant role played by soil physical properties in influencing crop yields. S can be a simple way for assessing the physical quality of Sahelian sandy soil