AUTHOR : UZOHO, BETHEL UGOCHUKWU (PhD)
DEPARTMENT : SOIL SCIENCE AND TECHNOLOGY
AFFILIATION : FEDERAL UNIVERSITY OF TECHNOLOGY
Soil nitrogen and phosphorus dynamics of municipal solid waste compost (MSWC)-amended Ultisol in Owerri, Southeastern Nigeria were evaluated. Three rates, each equivalent to 0, 4 and 6 Mg MSWC ha-1, 0, 20 and 40 kg P2O5 ha-1 and 0, 100 and 150 kg N ha-1 were incubated with 200 g soil in a split–split plot setup, arranged in completely randomized design with 3 replications and N and P mineralization and immobilization patterns determined. Also crops (maize and cowpea) were grown (twice) in pots using 3 rates each of MSWC (0, 4 and 6 Mg ha-1), P2O5 (0, 20 and 40 kg ha-1) and N (0, 100 and 150 kg ha-1) plus a uniform dose of 30 kg K2O ha-1 for maize and 3 rates of MSWC (0, 4 and 6 Mg ha-1), P2O5 (0, 40 and 60 kg ha-1), N (0, 20 and 30 kg ha-1) plus a blanket dose of 20 kg K2O ha-1 for cowpea. The experimental design was the same as for incubation study above and plant height, leaf area, girth size and number of leaves at weekly intervals and dry matter yields at 8 weeks after planting (WAP) were determined. Similarly, crops were grown ( twice yearly in 2006 and 2007) in the field using similar treatments as maize and cowpea in the pot study above but in a split-split plot setup, arranged in randomized complete block design with 3 replications. Soil NH4-N, NO3-N, Bray II P and water soluble P at two depths (0 – 15 and 15 – 30 cm) and crop (maize and cowpea) NH4+, NO3– and P uptake at monthly intervals after treatment (MAT) were determined for three months. Maize and cowpea grain yields were equally determined at maturity. In addition mean maize and cowpea heights, leaf area, girth size, number of leaves and dry matter yields were correlated with mineralized inorganic N + Bray II P and NO3 + NH4 + H2O soluble P. Equally, maize and cowpea grain yields were correlated with surface NO3 + NH4 + H2O soluble P and inorganic N + Bray II P. Finally Pedotransfer functions of subsoil NO3-N and maize and cowpea N and P uptake from surface N + Bray II P were estimated. Nitrogen and phosphorus mineralization and immobilization patterns varied with MSWC x P x N rates, time, and N and P forms. Also, maize and cowpea height, leaf area, girth size and number of leaves increased with time of MSWC x P x N application, with the extent depending on treatment rates. Equally, dry matter yields varied with MSWC x P x N rates. Mineralized inorganic N + Bray II P correlated significantly with maize heights, girth size, number of leaves and only first maize leaf area and dry matter yields while NO3 + NH4+ H2O soluble P correlated significantly with only first maize leaf area, girth size, number of leaves and second maize dry matter yield. Similarly, mineralized inorganic N + Bray II P related seriously with cowpea leaf area and girth size and only first cowpea height while NO3 + NH4+ H2O soluble P correlated significantly with cowpea girth size and number of leaves but with only first cowpea leaf area and second crop height. Optimum rates for crop grain yields include M0P40N100 for first and M6P40N150 for second maize and M4P60N0 or M6P60N0.for cowpea. Cowpea and not maize grain yields correlated significantly with surface inorganic N + Bray II P and NO3 + NH4+ H2O soluble P. Integrations of MSWC x P x N increased surface and subsurface NH4–N but depressed N03–N, Bray II P and water soluble P with time but with the extent depending on treatment rates and crop types. Similarly, integrations of MSWC x P x N increased maize NH4+ and NO3– uptake with time but depressed cowpea uptake beyond the second month of application while P uptake increased with time for both crops, exception being first cowpea in 2006. Finally, more than 50% of the relationship between surface inorganic N + Bray II P and subsoil NO3-N and crop P uptake could be estimated by the Pedotransfer function. Generally, knowledge of soil N and P dynamics could be effective for efficient nutrient management and environmental sustainability.
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