Comparative value of Buffalo beans(mucuna sp.)as a green manure crop on maize growth and yield
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Maize is a major staple food crop widely grown in Zambia. Low soil fertility and high cost of chemical fertilizers are some of the major factors limiting maize productivity. The use and integration of legume green manure species in the cropping system is an important alternative to inorganic fertilizer use. A study was conducted at the field station of the School of Agricultural Sciences, University of Zambia to evaluate the comparative value of buffalo beans as a green manure crop on maize growth and yield. The objectives of the study were: (a) To compare the effect of the selected green manure species, kraal manure and inorganic fertilizer on maize growth and yield; (b) To compare the biomass production of the selected green manure species; (c) To determine the mineralization rate of biomass from the selected green manure species; (d) To determine nitrogen fixation in legume species; and (e) To determine the cost effectiveness of organic and inorganic fertilizers. The first stage involved the growing of three green manure crops, application of kraal manure and then the ploughing under of the biomass at flowering stage. The experiment was arranged in a Randomised Completely Block Design (RCBD).Kraal and green manures were labelled with 10 atom% 15N urea and incorporated in the soil. The second experiment was composed of two factors: maize variety at 3 levels and fertilizer source at 5 levels replicated four times in a Randomised Completely Block Design (RCBD). Maize was grown after the green manure had been ploughed under. Green manure biomass was harvested and later incubated in the laboratory in the ratio of 100 g biomass to 2 kg of soil. The maize grain was milled and analysed for 15N. The results showed that local velvet beans had higher dry matter biomass (12.0 ton/ha) than the improved velvet beans (10.9 ton/ha) and buffalo beans (7.7 ton/ha) by 55.8% than buffalo beans. The three green manure crops increased the concentration in the soil of exchangeable aluminium and acidity, hydrogen, calcium, phosphorus, nitrogen, organic matter, manganese and copper but reduced the magnesium and iron compared to the control. Buffalo beans and improved velvet beans fixed nitrogen by 40% more than the local velvet beans. The mutant derived velvet bean line fixed more nitrogen than its parent the local velvet by 11.3%. The mineralization rate for ammonium for the improved velvet beans and buffalo beans was higher than for local velvet beans but for nitrate and total N was similar for the three green manure crops. The earliest variety in maturity was ZMS 402 (70.5 days) but local maize and MRI 455 were later by almost 5 days. The grain yield response to the fertilizer sources was higher with ZMS 402 (2.6 ton/ha) than MRI 455 (2.3 ton/ha). The lowest was with local maize (1.8 ton/ha). ZMS 402 was more efficient in the utilization of kraal manure and buffalo beans than MRI 455 and local maize, and so it can be a preferred maize variety to be used in the organic manure cropping system. The fertilizer N in the maize grain varied with the nitrogen source and maize varieties indicating that the quality of the green manure was different with buffalo beans and local velvet beans. Fertilizer nitrogen in the maize grain was similar in ZMS 402 and MRI 455 with inorganic fertilizer and the improved velvet beans. ZMS 402 was however observed to be superior by 64.8% to MRI 455 with buffalo beans. Generally, ZMS 402 applied with local velvet beans gave the highest return and local maize applied with kraal manure was the least among the treatments.
- Agricultural Sciences