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A bstract A field study was conducted over a 4-year period in Niger, West Africa, to determ ine th e effects of crop residue (CR), fertilizer, or a combination of crop residue and fertilizer (C R F) on yields of pearl millet (Pennisetum glaucum [L.] R. Br.). Despite a decline in yields of control plots (initial yields w ere 280 kg grain ha~J declining to 7 5 k g grain h a-1 over 4 years), yields of fertilizer plots were m aintained at 800-1,000 kg grain h a-1. Continued application of. CR slowly augm ented yields to levels similar to those of the fertilized plots. The effects of CR and fertilizer were approxim ately additive in the C RF plots. Addition of C R and fertilizer increased soil water use over the control by 57 mm to 268 mm in an average season and helped trap wind-blown soil. These plots tended to exhibit slightly higher soil pH and lower A1 saturation than did the fertilized treatm ents. R eturn of C R to the soil resulted in significantly reduced export of most plant nutrients, especially Ca, Mg, and K.

Mineral fertilizer use is increasing in West Africa though little information is available on yield response in farmers' fields. Farmers in this region plant at low density (average 5,000 pockets h a-1, 3 plants pocket-1), which can affect fertilizer use efficiency. A study was conducted with 20 farmers in Niger to assess the response of pearl millet [Pennisetum glaucum (L.) R. Br.] to phosphorus and nitrogen fertilizers under farm conditions. In each field, treatments included control, single superphosphate (SSP) only, SSP plus N (point placed near plant), and either SSP or partially acidulated phosphate rock (PAPR) plus N broadcast. N and P were applied at 30 kg N ha-1 and 30 kg P2O s h a-1. Farmers were allowed to plant, weed, etc., as they wished and they planted at densities ranging from 2,000 to 12,000 pockets h a-1. In the absence of fertilizer, increasing density from 2,000 to 7,000 pockets h a-1 increased yield by 400%. A strong interaction was found between fertilizer use and density. Farmers planting at densities less than 3,500 pockets h a-1 had average yields of 317 kg grain hawhile those planting at densities higher than 6,500 pockets h a-1 showed average yields of 977 grain h a-1. Though phosphate alone increased yields significantly at all densities, little response to fertilizer N was found at densities below 6,000 pockets h a-1. Significant residual responses in 1987 and 1988 were found to P applied in high-density plots in 1986. Depending on fertilizer and grain prices, analysis showed that fertilizer use must be be combined with high plant density (10,000 pockets h a-1) or no economic benefit from fertilizer use will be realized.