The Potential of Green Manures to Increase Soil Fertility and Maize Yields in Malawi

Abstract

ABSTRACT The effect of sole maize and green manures (Mucuna pruriens, Crotalaria juncea and Lablab purpureus) on maize for two successive cropping seasons was determined in on-farm experiments at five locations in Malawi from 1996 to 1999. Legume residues were incorporated at two different times; ‘early’ at peak biomass and ‘late’ when the plants started to senesce. After growing and incorporating the green manures at the end of the 1996/97 growing season, maize was planted in 1997/98 and 1998/99 to test the effect of the legumes on maize yields compared with continuous maize. Biomass production from early incorporated legume residues was 6.7 t ha−1 for Mucuna, 4.9 t ha−1 for Crotalaria and 4.9 t ha−1 for L. purpureus; and for late incorporated legume residues it was 5.9, 5.2 and 4.1 t ha−1 for the same legumes, respectively. Of the three legumes, L. purpureus produced less biomass (average 4.2 t ha−1) than the other two green manures and Mucuna produced the highest seed yield. Over the two seasons and åcross the five sites the application of inorganic fertilizer (35 or 69 kg N ha−1) to maize significantly increased maize yields at all the sites. Maize yields following green manures without inorganic fertilizer additions were much higher than yields from continuous maize with no fertilizer addition. Addition of inorganic fertilizer to legume crop residues resulted in increased maize yields at all the sites, but the highest fertilizer use efficiency was obtained from the addition of 35 kg N ha−1. There were no significant maize yield differences when maize followed early or late incorporated green manures across season and sites for all three legumes. Results indicate that all the three green manures have potential to increase maize yields when used as sole green manures or in combination with inorganic fertilizers compared with sole maize alone.