Abstract

An incubation study was conducted for two months to evaluate the effects of different treatments on the inorganic P fractions and other chemical properties on an acidic soil. Four rates of lime and wood ash (3.5, 7.0, 9.2, 11.2 tons CaCO₃ equivalent ha^-1) were separately applied to obtain target soil pH values of 5.5, 6.0, 6.5 and a lower pH obtained with half of the lime requirement needed to bring the pH to 5.5. Three rates of mineral P fertilizer and manure P (32.5, 65, 130 kg P ha^-1) were separately applied into the whole soil volume. Additionaly, wood ash (7 tons CaCO₃ ha^-1) and lime (7 tons CaCO₃ ha^-1) were combined separately with each of the manure and mineral P rates. The experiment was laid down in a completely randomized design with two replications. Lime and wood ash treatments showed a significant effect on the pH and exchangeable acidity compared to manure. The highest lime and wood ash rates (11.2 tons CaCO₃ ha^-1) increased the pH from 4.89 to 6.03 and 5.93; decreased the exchangeable acidity from 2.22 to 0.14 and 0.16 cmol_c kg^-1, respectively. The maximum increment in Olsen P by 132%, aluminum bound P (Al-P) by 160%, iron bound P (Fe-P) by 22% and oxalate extractable P (P_ox) by 33% were observed by the application of mineral P at 130 kg P ha^-1 plus wood ash (7.0 tons CaCO₃ ha^-1). Therefore, lime and wood ash applications in acidic soils can effectively ameliorate H⁺ and Al³⁺ toxicity and P deficiency.

Key words: Acidity, incubation, lime requirement, P form.