Effects of applications of lime, wood ash, manure and mineral P fertilizer on the inorganic P fractions and other selected soil chemical properties on acid soil of Farta District, Northwestern highland of Ethiopia

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 cmolc 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 (Pox) 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.