Above-ground biomass, nutrients, and persistence of an early and a late maturing Mucuna variety in the Forest–Savannah Transitional Zone of Ghana

Many farmers in West Africa have adopted the herbaceous legume, Mucuna pruriens, as a fallow species to control weeds and to increase soil fertility on crop lands. This paper presents the biomass, nutrient content, and persistence results of farmer managed trials with late maturing M. pruriens var. utilis (L.) D.C. and an early maturing unclassified Mucuna cultivar relative to a short season natural fallow (control). From August until December 1998 and from June 1999 until March 2000, research was conducted at different farm locations in the Forest–Savannah Transitional Zone and in the Guinea Savannah Zone of Ghana. The following parameters were evaluated: (1) accumulation of above-ground Mucuna biomass during the short rainy season; (2) atmospheric N2 fixation during the same period; (3) Mucuna seed yield components; (4) persistence of above-ground Mucuna and natural fallow biomass throughout the dry season; (5) nutrient concentration and nutrient accumulation of Mucuna and natural fallow at the beginning and the end of the dry season; and (6) percentage ground cover by various biomass components throughout the dry season. During the first 2 months of establishment, M. pruriens grew slowly, producing 163 kg ha−1 above-ground biomass after 30 days and 1472 kg ha−1 after 60 days, but produced 4003 kg dry matter ha−1 after 90 days. Atmospheric nitrogen (N2) fixed by late maturing M. pruriens was estimated at 107.7 kg ha−1 but only 46.1 kg ha−1 for the early maturing Mucuna cultivar. The estimated amount of N2 fixed was significantly correlated with the amount of Mucuna biomass produced with R2 = 0.75 for the early maturing cultivar and R2 = 0.69 for M. pruriens. The nutrient uptake of macronutrients other than N in the Mucuna fallow did not differ significantly from that of the natural fallow treatment for either cultivar. Following a linear regression model, total above-ground biomass on M. pruriens plots declined by 503 kg ha−1 every 4 weeks from November until March, while the biomass on plots planted with the early maturing Mucuna cultivar declined by 911 kg ha−1. While ground coverage (including weeds and crop residues) on fields planted with M. pruriens was still 89.7% at the end of the dry season, coverage on fields planted with the early maturing Mucuna variety averaged only 72%.