Phosphorus dynamics in forest and savannah agro-ecological Alfisols incubated with different phosphorus fertilizers
2008
Oluleye, Anthony K. | Akinrinde, Ezekiel A. | Obigbesan, Gabriel O.
Incubation study on phosphorus (P) release in two Nigerian Alfisols, A and B (from Ikere-Ekiti Forest and Omuo-Ekiti savannah agro-ecologies, respectively) was conducted to evaluate the effectiveness of alternative P sources (ground phosphate rock, PR - 9% P; fortified PR organo-mineral fertilizer, OMF - 11% P and single superphosphate, SSP - 7.7% for reference). Soil samples (200 g; 0-20 cm depth), each filled into 20 plastic beakers were treated in triplicates and in Completely Randomized Design to 0 and 12.9 mg P kg -1 soil, using each P source. All samples were adjusted to soil water tension measured at M Ψm = 0.03 MPa. Changes in applied P were evaluated at 2, 6, 12 and 24 weeks after which data were analysed using ANOVA and correlations. Twenty four weeks after OMF application, P release varied with soil type. However, highest P fraction (72.9-97.2 mg kg-1) was Ca-bound in the two soil types. With SSP or PR application, highest P fraction (74.6-94.1 and 76.2-86.3 mg kg-1, respectively) was also Ca-bound that constituted more than 50% of inorganic P. The lowest P fractions released were Al-bound (0.7-1.1 mg kg-1). SSP transformed mostly to Fe-bound P in both soils while PR transformed largely into insoluble and chemically more stable residual P. These fractions correlated positively (r = 0.69, P<0.05) with soil properties and constituted major sources and sinks of plant-available P. Application of OMF or PR to the soils is highly beneficial for P nutrition as P emanating from them constituted more than 50% of inorganic P fractions. Organic P constitutes the largest percentage of total P in these soils; hence application of OMF enhances P nutrition in these soils.
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