Residual effect of organic fertilization on maize yield in an agroforestry system

The objective of the present study was to evaluate, during a period of two years, the residual effects of organic fertilization with animal manure or gliridicia prunings on the fertility of soil and on productivity and nutrient accumulation by maize cultivated either isolated (SA) or intercropped within alleys of gliricidia (CA). The study was conducted during 2006 and 2007 in the Centro Agroecologico Sao Miguel, headquarters of the NGO AS-PTA, in Esperanca, PB, Brazil. The experiment was established in a split-plot design, arranged in randomized blocks, with the type of cropping system (SA or CA) as the main treatments and the organic fertilization (animal manure, gliricidia prunings or control plots) as the secondary treatments, with four replications. The organic fertilization with animal manure led to a residual effect increasing maize productivity during the two years, but the fertilization with gliricidia prunings had no residual effect. The residual effect on maize productivity was more pronounced in the SA plots, compared to the plots with gliricidia alleys (CA). Probably, the lower residual effect within the CA system was due to the competition between maize and gliricidia for resources (nutrients, water and light), which indicates the need for higher rates or more frequent fertilizer applications in these systems. The contents of P, K, Ca and Mg in the soil was higher in the plots that received animal manure within both types of cropping systems.