Nitrogen fixation and balance in burned versus mulched Mucuna pruriens var. utilis and Pueraria phaseoloides relay maize cropping systems

Abstract

The contribution of the cover crops Mucuna pruriens var. utilis and Pueraria phaseoloides to the N balance of a sole maize relay cropping system was estimated. Over 4 consecutive years, amounts of N in 8-9 months old aboveground M. pruriens, P. phaseoloides and natural fallow biomass and litter were determined. Fallow biomass was either burned or retained as mulch. Maize aboveground N uptake and N export with grain was determined. The amount of N2-fixed was estimated with the N difference method. In 1998, 1999, and 2000, N content in M. pruriens and P. phaseoloides biomass was higher than in natural fallow. In 2000 and 2001 biomass in previously burned plots contained less N than when biomass had been retained. Fallow-type and biomass management did not interact. Maize N uptake was higher after biomass burning in 1998, yet thereafter higher when biomass was retained. Fallow type had only in 1999 an effect, with highest maize N uptake in the P. phaseoloides system, followed by the M. pruriens system and the natural regrowth. The estimated amounts of N2-fixed were higher in the P. phaseoloidessystem; biomass management had no effect. Nitrogen export with maize grain was highest in the P. phaseoloides system, followed by the M. pruriens system; biomass management had no effect. Maize N uptake into the aboveground biomass and N export with grains was balanced by the amount of N in fallow biomass in all systems when biomass was retained. The amount of N2-fixed did not balance the amount taken up by the maize. In the M. pruriens system the N exported with grains was not balanced by N2 fixation, the P. phaseoloides system had a positive balance of N export in grain versus the amount of N2 fixed.