Millet response to microdose fertilization in south–western Niger: Effect of antecedent fertility management and environmental factors

Soil fertility is a major constraint to agricultural development in most of the Sahel, with P being the mostlimiting nutrient for millet production on acid sandy soils. To address this issue, microdose applicationsof P fertilizer have been widely advocated in recent years. However, little is known regarding the effectof farmer management practices and environmental factors on millet’s yield response to this technique.For this purpose, 276 farmer demonstrations were setup across a 3-year period in the Fakara region,western Niger. Five strata were considered based on antecedent organic manure management (corrallingor transported manure). At each demo site, conventional management was compared to basal microdosefertilizer application of DAP (2 g hill−1), NPK (6 g hill−1), or DAP (2 g hill−1) with urea (1 g hill−1) appliedat tillering. Millet grain yields on control plots were low (84% < 400 kg ha−1), reflecting the unfavorableenvironmental conditions of the area. On average, the application of DAP, NPK and DAP + urea increasedgrain yields by 43, 46 and 69 kg ha−1(2001–2002). A positive response to microdose fertilization wasobserved for 92% of the sites where yields on control plots were <100 kg ha−1but only for 32% of thesites where yields on control plots were >500 kg ha−1. In particular, the positive response to microdosingincreased with later sowing given that late sowing tended to reduce yields on control plots. Higherrainfall during the early growing season favored a positive response to microdosing. On average overDAP and DAP + urea, 36% of the demonstrations had value-cost ratios (VCR) < 1. However, for low yieldingcontrol plots (<200 kg grain ha−1), 26% of the demonstrations had VCR < 1, whereas for high yielding plots(>400 kg grain ha−1), 55% had a VCR < 1. Not accounting for labor, DAP and DAP + urea had similar economicreturns. The use of NPK could not be recommended as the cost per unit P is 3 times higher than DAP. Itappears that, for the Fakara study area, microdosing may best be targeted to areas with low expectedyields. In particular, it may serve as a famine mitigation strategy in case of late sowing. Nevertheless, forpoorly endowed areas such as the Fakara, the economic risk associated with microdosing (2 g DAP hill−1)appears higher than has hitherto been reported and widespread adoption may not be warranted withoutinstitutional support.© 2014 Elsevier B.V. All rights reserved