LEGUME ROTATION IN THE MOIST TROPICAL SAVANNA - MANAGING SOIL-NITROGEN DYNAMICS AND CEREAL YIELDS IN FARMERS FIELDS

The contribution of root and leaflitter to soil nitrogen dynamics, nit rogen uptake and balance was evaluated under cereal-legume rotations i n a tropical moist savanna soil. Two legumes, soyabean (Glycine max) a nd style (Stylosanthes hamata), and maize (Zea mays) as a control were grown in four farmers' fields of different native fertility in 1993. At the end of the season, soyabean grain and stover were harvested and style biomass was removed for fodder. At the beginning of the 1994 se ason levels of total mineral nitrogen at a soil depth of 0-30 cm were 75, 52 and 44 kg ha(-1) following soyabean, style and maize respective ly. Total nitrogen uptake by maize was over 25% higher following legum es than following maize. Maize yield was 20 and 24% higher when grown after style and soyabean than after maize in spite of the removal of t he standing legume biomass from the plots. Sorghum grain yield and nit rogen uptake were not significantly affected by the previous crops. Ni trogen balance estimates indicated that loss of nitrogen, probably due to leaching, was lowest in the plots previously planted with style. R esults indicated opportunities to integrate appropriate legume-based t echnologies into the farming systems based on an identification of inh erent nitrogen-release patterns.