The combination of inorganic fertilizers, and organic manures from cattle or legumes crops is recognised as one way to reduce the costs of inorganic fertilizers and to reduce the decline of soil fertility under smallholder cropping systems in Malawi. An experiment was conducted from the 1994/95 to the 1996/97 cropping seasons to determine the effects of organic legume residues and inorganic fertilizer nitrogen (N) on soil N and maize (Zea mays) yield. The experimental design was a split-plot in which seven cropping systems (legume residues from maize/legume intercrops, and from sole legume crops or sole maize were main plots and three N levels (0, 46, and 96 kg N ha-1) were sub-plots. Results showed that the initial release of N was high from plots that received inorganic fertilizer without the addition of legume residues. The release of N from legume residues was retarded initially due to high [lignin + polyphenol]/N ratios. The combination of inorganic N and organic residues improved the release of N from plots with organic residues, suggesting that a starter N is required to reduce the immobilization capacity of legume residues. Nitrogen application resulted in significant yield increases over the no fertilizer application. The application of 48 kg N ha-1 gave the largest yield increments of 982 kg ha-1 in the 1995/96 cropping season and 1196 kg ha-1 in the 1995/96 and the 1996/97 cropping season. The highest grain yields of maize were obtained when maize was grown in rotation with legume crops [pigeon pea (Cajanus cajan) + maize, sunnhemp (Crotalaria junacea) + maize or mucuna (Mucuna aterrima)+ maize]. In the 1995/96 cropping season, grain yields of maize from these legume+maize rotation systems were 25 to 29% higher than maize yields from the continuous maize system (maize-maize) which yielded 4669 kg ha-1. In the 1996/97 cropping season, the pigeon pea -maize-maize rotation gave the highest yield of 6616 kg ha-1 which was 1257 kg ha-1 higher than the yield from the three-year continuous maize system. Only the maize/sunnhemp intercropping system gave significantly higher maize yield than the continuous maize system. The combination of inorganic fertilizers and organic legume residues improved yields of maize, but the largest increments were obtained when maize was grown in the maize/legume intercropping systems.|The agronomic results showed that sole legume crops when grown in rotation with maize can result in increased maize yields than when grown in intercropping systems, largely due to higher biomass production. An economic analysis, however, showed that sole continuous maize gave the highest net benefit. The best intercrop with fertilizer was pigeon pea at 96 kg N ha-1 or sunnhemp at 48 kg N ha-1. The maize+legume rotations (mucuna, sunnhemp or pigeon pea) had the lowest net benefits.|

English

9906|AGRIS 9902|R98-99ANALY

Jose Juan Caballero

CIMMYT Publications Collection