Legume Rotation in the Moist Tropical Savanna: Managing Soil Nitrogen Dynamics and Cereal Yields in Farmers' Fields

Abstract

The contribution of root and leaf litter to soil nitrogen dynamics, nitrogen uptake and balance was evaluated under cereal–legume rotations in a tropical moist savanna soil. Two legumes, soyabean (Glycine max) and stylo (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 stylo biomass was removed for fodder. At the beginning of the 1994 season levels of total mineral nitrogen at a soil depth of 0–30 cm were 75, 52 and 44 kg ha−1 following soyabean, stylo and maize respectively. Total nitrogen uptake by maize was over 25% higher following legumes than following maize. Maize yield was 20 and 24% higher when grown after stylo and soyabean than after maize in spite of the removal of the standing legume biomass from the plots. Sorghum grain yield and nitrogen uptake were not significantly affected by the previous crops. Nitrogen balance estimates indicated that loss of nitrogen, probably due to leaching, was lowest in the plots previously planted with stylo. Results indicated opportunities to integrate appropriate legume-based technologies into the farming systems based on an identification of inherent nitrogen-release patterns.

Integrated soil fertility management involving promiscuous dual-purpose soybean and upland NERICA enhanced rice productivity in the savannas

“…However, legume residues containing 81-160 kg N ha -1 were returned to the soil prior to the rice crop in their study. Our values are, however, lower than the 75 kg N ha -1 earlier reported for a similar system in which the promiscuous soybean was harvested and exported from the field but the leaf litter and roots contributed N to the soil in soybean-maize rotation systems in the NGS of Nigeria (Oikeh et al 1998).…”

“…IRAT 136, without N fertilizer application. The positive effect of previous soybean to the NERICA rice could be attributed to N contribution by the soybean cultivars used in the present study as reported earlier (Carsky et al 1997;Oikeh et al 1998;Vanlauwe et al 2001b) and partially due to the nitrate-sparing effect (Peoples et al 1995) resulting from the previous soybean absorbing less soil N than the previous rice crop. In addition, soybean has a large belowground biomass including nodules which release N to subsequent crop through biomass decomposition Abaidoo et al 1999Abaidoo et al , 2007.…”

“…Farmers have often been reluctant to devote their land solely to legume cover crops that would not provide food value for human consumption in spite of the positive benefits in weed suppression Johnson 1998, 1999) and impact in restoring soil fertility (Oikeh et al 1998;Vanlauwe et al 2001a). Therefore, the use of dual-purpose grain soybean varieties with potential for good surface cover to suppress weeds and for soil conservation particularly in the NGS and with grains for immediate economic benefits may be attractive to smallholder farmers in the Republic of Benin.…”

“…Furthermore, the combined use of legume cover crops and sparingly soluble indigenous phosphate rock has also been recommended as a relatively inexpensive means to increase the supply of both N and P and enhance upland rice productivity in acid soils (Somado et al 2003;Oikeh et al 2008a). However, farmers in West Africa are often reluctant to adopt legume cover crops that are not for human consumption or without a direct economic benefit, in spite of the positive impact on restoring soil fertility (Oikeh et al 1998;Vanlauwe et al 2001a).…”

Effect of tillage, rhizobium inoculation in maize-soybean based cropping systems and nitrogen fertilizer application on chemical fertility status of savanna Alfisol, Nigeria

“…The value of bulk density was slightly above 1.39 Mg m -3 reported for surface soil of the same Northern Guinea savanna (Oikeh et al, 1998). The slightly acidic nature of the soil, low TN and OC reflected the true characteristic of a savanna Alfisol, which was due to uptake of basic cation by plant through cultivation and, partly, to the overall removal of crop residues by farmer after harvest.…”