THE EFFECT OF CROP RESIDUE AND FERTILIZER USE ON PEARL-MILLET YIELDS IN NIGER

A field study was conducted over a 4-year period in Niger, West Africa , to determine the effects of crop residue (CR), fertilizer, or a comb ination of crop residue and fertilizer (CRF) on yields of pearl millet (Pennisetum glaucum [L.1 R. Br.). Despite a decline in yields of cont rol plots (initial yields were 280 kg grain ha-1 declining to 75 kg gr ain ha-1 over 4 years), yields of fertilizer plots were maintained at 800-1,000 kg grain ha-1. Continued application of CR slowly augmented yields to levels similar to those of the fertilized plots. The effects of CR and fertilizer were approximately additive in the CRF plots. Ad dition of CR and fertilizer increased soil water use over the control by 57 mm to 268 mm in an average season and helped trap wind-blown soi l. These plots tended to exhibit slightly higher soil pH and lower Al saturation than did the fertilized treatments. Return of CR to the soi l resulted in significantly reduced export of most plant nutrients, es pecially Ca, Mg, and K.