Nutrient management over extended cropping periods in the shifting cultivation system of south-west Cote d'Ivoire

<br/>Intensification of food crop production in shifting cultivation systems can contribute to protection of tropical forest. For such an intensification knowledge of soil fertility and its dynamics is essential. It was tested whether intensification could be achieved by extending the cropping period in on-farm field trials with controlled management. These trials were conducted on locations along catenas ranging from the crest to the fringe of the valley bottom. On the (moderately) well drained soils P proved to be the yield-limiting nutrient. In extended cropping systems with alternately rice and maize, applications of N, P and K were not sufficient to maintain the yield level obtained in the first season after clearing. Yield decline was much less pronounced for maize than for rice. In the eighth season after clearing yields of over 4 ton of maize per ha were still obtained. Data on the efficiency of utilization of absorbed P indicate that factors other than P deficiency caused the yield decline. A probable cause is deterioration of soil physical properties. Fertilizer recommendations (N,P,K) are formulated for the well drained soils of the upper/middle slopes and for the moderately well drained soils of the lower slope.