On‐Farm Spatial and Temporal Variability of Soil and Water in Pearl Millet Cultivation

Abstract

Crust‐prone sandy soils of low fertility, combined with unreliable and erratic rainfall, affect spatial variability of crop growth in the Sahel. We hypothesized that spatial variability in soil properties and soil water content on a hillslope scale affected pearl millet [Pennisetum glaucum (L.) Br.] yields. We focused on the effects of crust development, micro topography, rill distribution, and soil nutrients on crop yield variability within and between years (1994–1996) in a farmer's field in semi‐arid Niger. Yields in plots of 15 by 6 m varied within a year by a factor of 46 for nonfertilized millet (27–1249 kg ha−1), and by a factor of 16 (76–1213 kg ha−1) for fertilized millet. Despite this variation, a linear yield gradient was observed along the 300‐m‐long field with a gentle 1 to 3% slope. Grain yields decreased 0.5 kg ha−1 for nonfertilized millet and 1 kg ha−1 for fertilized millet per meter along the slope when moving from the bottom to the top of the field. Soil water availability varied greatly, with individual neutron probe access tubes (36 tubes on an 8‐ha field) presenting a percent infiltration ranging from 15 to 182% of rainfall for individual rainstorms. Upslope had significantly lower percent infiltration (75%) than both midslope (90%) and downslope (84%). Between years, soil water and nutrients alternated in limiting crop growth, depending on rainfall distribution (annual rainfall ranging from 488–596 mm). However, in all three years toposequence related factors dominated yield variability and caused similar yield gradients along the slope.