The effects of sources of phosphorus on yield and nutrient uptake under mucuna - maize rotations

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The effects of Rock Phosphate (PR) and Triple Super Phosphate (TSP), applied to Mucuna fallow, on the yield and nutrient uptake under Mucuna -maize rotations were evaluated in an On-station and On-farm trials to study treatment responses. The study was carried out in the Sunyani district, which lies in the transitional zone, in the Brong Ahafo Region. The study period was from 2000 major season to 2001 minor season. At the On-station, five rates of PR (0, 20, 40, 60 and 80 kg P ha-1) were applied to Mucuna fallow whiles the On-farm had 50 kg P h-1of TSP and 50 kg P h-1 of PR. At both sites, natural fallow served as a control. The experimental design was a Randomized Complete Block Design (RCBD) with 4 and 10 replicates for the On-station and On-farm, respectively. Response variables measured were maize density at establishment and harvest, Mucuna biomass, maize dry matter yield, number of cobs per plant, thousand grain weight, maize yield (t ha-1 ) and, N and P uptake in maize grain and straw. At both sites, maize stover and grain yields responded to phosphorus (P) application. Improvements in soil available P (ppm) had a significant effect (P< 0.05) on maize stover and grain yields. However, the yield efficiency revealed that 1 kg of phosphorus (P) application increased output only at 80 kgPh-1 of PR application. Uptake of N and P in maize stover and grain responded (P<0.05) to the P application but the effect on the uptake of calcium, magnesium and potassium was not significant (P>0.05). The study showed an enhancement in Mucuna biomass build up with the application of P, but this was less persistent and broke down rapidly with the on-set of harmattan. Nitrogen and phosphorus uptake in the Mucuna biomass improved significantly (P<0.05) at both sites with application of the treatments, which reflected in improvements in maize stover and grain yields. Lower weed biomass recorded on Mucuna plots showed and confirmed the positive effect of Mucuna biomass on weed control in the succeeding maize. This reduced the number of weeding on the Mucuna plots. While natural fallow plots were still dominated by Chromolaena odorata, Euphorbia sp. dominated the Mucuna plots Improvements in soil available phosphorus influenced nitrogen fixation, and this was found to be positively correlated (r2 = 0.98) with Mucuna dry matter production at both sites. However, changes in soil organic matter was not significant (P>0.05). The study revealed that, phosphorus is essential for Mucuna -maize production system. This is because the maize crop benefited from improvements in soil nitrogen and organic matter through Mucuna and phosphorus application. Soil fertility management with the use of cover crops should consider an integrated system where deficiencies under legume fallow could be addressed through mineral fertilizer amendments.
A thesis submitted to the Department of Crop Science, College of Agriculture and Natural Resources in partial fulfilment of the requirements for the degree of Master of Philosophy in Agronomy, 2002