Dynamics of phosphorus fractions in a savanna Alfisol under continuous cultivation |
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Authors: | J. O. Agbenin J. T. Goladi |
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Affiliation: | Department of Soil Science, Institute for Agricultural Research, Ahmadu Bello University, Zaria, Nigeria. School of Science, College of Education, Akwanga, Nasarawa State, Nigeria. |
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Abstract: | Abstract. We examined the dynamics of inorganic P (Pi) and organic P (Po) pools of a savanna Alfisol under continuous cultivation complemented with nitrogen (N) and phosphorus (P) fertilizers with or without cow manure (D), using a modified Hedly fractionation. Continuous cultivation without P fertilizer decreased the concentration of Pi and Po, pools including the residual P fraction compared with an unfertilized treatment with natural vegetation. Adding P fertilizers alone or in combination with D (P, NPK, D+P, D+NP and D+NPK) increased the concentration of labile Pi pools, but decreased the concentration of Po, pools and the residual P fraction. The tendency of the residual P fraction to decrease along with Po pools suggested that the residual P fraction was largely Po. This is consistent with the correlation between the residual P fraction and total Po (r=0.74**) and the residual P fraction and organic carbon content (r=0.47**). Analysis of the relationships between plant available P, estimated by resin-extractable P, and the more stable Pi and Po, pools indicated that 85% of the variation in resin-P was atiributable to the hydroxide extractable Pi, (OH-Pi) and HCI-Pi which acted as sinks for fertilizer-P. The contribution of the residual P fraction to resin-P was indirect via bicarbonate-extractable Po (HCO3-Po) and OH-Po. These results also clarify why attempts to find P extraction methods which correlate well with response to P and to P uptake in the savanna have given inconsistent results. |
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Keywords: | Continuous cropping phosphorus fertilizers cattle manure phosphorus savanna soils |
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