Increase of available phosphorus by fly-ash application in paddy soils

Abstract

Fly ash from the coal- burning industry may be a potential inorganic soil amendment to increase rice productivity and to restore the soil nutrient balance in paddy soil. In this study, fly ash was applied at rates of 0, 40, 80, and 120 Mg ha(-1) in two paddy soils ( silt loam in Yehari and loamy sand in Daegok). During rice cultivation, available phosphorus ( P) increased significantly with fly ash application, as there was high content of P ( 786 mg kg(-1)) in the applied fly ash. In addition, high content of silicon ( Si) and high pH of fly ash contributed to increased available-P content by ion competition between phosphate and silicate and by neutralization of soil acidity, respectively. With fly- ash application, water- soluble P ( W- P) content increased significantly together with increasing aluminum- bound P ( Al- P) and calcium- bound P ( Ca- P) fractions. By contrast, iron- bound P ( Fe- P) decreased significantly because of reduction of iron under the flooded paddy soil during rice cultivation. The present experiment indicated that addition of fly ash had a positive benefit on increasing the P availability.