Coal fly ash and phospho-gypsum mixture as an amendment to improve rice paddy soil fertility

Abstract

Rice is a plant that requires high levels of silica (Si). As a silicate NOD source to rice, coal fly ash (hereafter, fly ash), which has an alkaline pH and high available silicate and boron (B) contents, was mixed with phosphor-gypsum (hereafter, gypsum, 50%, wt wt(-1)), a by-product from the production of phosphate fertilizer, to improve the fly ash limitation. Field experiments were carried out to evaluate the effect of the mixture on soil properties and rice (Oryza sativa) productivity in silt loam (SiL) and loamy sand (LS) soils to which 0 (FG 0), 20 (FG 20), 40 (FG 40), and 60 (FG 60) Mg ha(-1) were added. The mixture increased the amount of available silicate and exchangeable calcium (Ca) contents in the soils and the uptake of silicate by rice plant. The mixture did not result in accumulation of heavy metals in soil and an excessive uptake of heavy metals by the rice grain. The available boron content in soil increased with the mixture application levels up to 1.42 mg kg(-1) following the application of 60 Mg ha(-1) but did not show toxicity. The mixture increased significantly rice yield and showed the highest yields following the addition of 30-40 Mg ha(-1) in two soils. It is concluded that the fly ash and gypsum mixture could be a good source of inorganic soil amendments to restore the soil nutrient balance in rice paddy soil.