Agricultural drought trends and mitigation in Tillaberí, Niger

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 (1905–1996) and daily (1989–2010) 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.