Long-term effects of tillage, phosphorus fertilization and crop rotation on pearl millet-cowpea productivity in the West-African Sahel

The millet (Pennisetum glaucum)-based cropping systems that dominate the Su dano-Sahelian Zone of West Africa cannot, as they are currently practised, meet the growing food needs of the region. They must therefore be intensifi ed in a sustainable manner. The present study was initiated in 1986 and con tinued until 1996 to evaluate the effects of phosphorus (P) fertilization, tillage and rotation with sole cowpea (Vigna unguiculata) on an operational scale with two cropping systems, namely, sole miller and millet-cowpea int ercropping. A randomized complete block design with four replications was u sed. The effects of P fertilization, ridging with animal traction and plant ing on ridges (AT), and rotation with sole cowpea increased the productivit y of miller substantially in 10 of the 11 years. Based on the 11-year avera ge, P fertilization alone improved grain yield by 52%, and AT with P fertil ization improved grain yield by nearly 135%. Combining AT, P fertilization and the sole cowpea rotation resulted in a 200% increase in grain yield com pared with the traditional system of production. Miller productivity did no t show a significant decline when intercropped with cowpea. Stability and r elative stability analysis showed that the traditional system was more stab le than the various agronomic packages, but had the least yield. Conversely the agronomic package with the highest yield advantage over the traditiona l system was the least stable. A major portion of the annual variation in t he environmental index for grain yield and total dry matter was attributed to the seasonal variation in rainfall and organic matter depletion. Organic matter levels declined linearly with years of cultivation. Significant dif ferences were found in the rare of depletion between the various agronomic treatments tested. After 11 years, nearly 60% of the organic matter was dep leted irrespective of the agronomic treatments.