Abstract

The distribution of phosphorus (P) fractions down the soil depth varies depending on the soil type as being affected by the surrounding soil management practices. A 10 km by 10 km site was chosen in the savanna zone of Nigeria for the study. Modal soil profile pits were dug to identify the different soil types while soil sampling was done at 0-20 cm, 20-40 cm, 40-80 cm and 80-120 cm depth. Resin P was the largest extractable P fraction while residual P was the least in the soil series characterized, down the soil depth. Fractionation results showed that there was variation down the soil depth. The conc. HCl-Pi was not observed at the 0-20 cm depth, NaHCO₃-Pi and Po was small while NaOH-Pi and Po was observed at this depth. Initial decrease at the 20-40 cm depth was observed for most of the P fractions while more of the P fractions were observed at the 40-80 cm depth. The values observed at the 80-120 cm depth was however small compared to other soil depth. Resin P was the sink of P and would serve as a reserve of P in the soil series. However, organic and inorganic P extractable with NaOH i.e. NaOH Pi and Po which were high at the 0-20 cm depth would be mainly responsible for the availability of P in the soil solution for plant uptake.

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