Effects of incubation period and Christmas Island rock phosphate with different rate of rice straw compost on phosphorus availability in acid soil

Abstract

Phosphorus (P) availability is limited in tropical acid soil due to fixation of soluble inorganic P by aluminium (Al) and iron (Fe). Liming is one of the common ways to overcome this problem. However, this practice is not economical. The aim of this study was to evaluate the effects of laboratory incubation period and different rates of rice straw compost on the soil P availability. During the incubation study, Christmas Island rock phosphate (CIRP) fertilizer was amended with different rates of rice straw compost (5, 10, 15, and 20 t ha−1). Treatments were incubated in the laboratory for 30, 60, and 90 days. Application of rice straw compost with CIRP significantly increased soil available P at 30, 60, and 90 days of incubation, respectively. This implies rice straw compost plays an important role on soil P availability by decreasing the P adsorption due to the competing adsorption sites by organic anion and dissolving the mineral associated P by low-molecular-weight organic acids. Besides, rice straw compost also increased the soil pH, and, at the same time, reduced exchangeable acidity, exchangeable Al and Fe. As the soil pH increased, the compost effectively fixed the Al and Fe in the soil instead of P, thus increasing the P availability in the soil. However, there was no significant increase/loss of available P when the incubation time increases under treatments with rice straw compost. This implies the effectiveness of rice straw compost in minimizing the loss of P due to P fixation in soil and slow microbially mediated mineralization of soil organic P to inorganic P as incubation time increases. The findings suggest that the application of rice straw compost altered soil chemical properties in a way that enhanced the availability of P in the Rengam acidic soil.