Enhancement of phosphate desorption by silicate in soils with salt accumulation

Abstract

To increase phosphate availability in plastic film house soils with salt accumulation, silicate was applied to silt loam (SiL, T-P 3,980 mg kg^-1) and loam (L, T-P 5,560 mg kg^-1) soils, and the effects of silicate on phosphate desorption were investigated under the different conditions; temperature: 10, 20, and 35°C, Si concentration: 0-2 mmol L^-1, and pH 2-12. Silicate efficiency in phosphate desorption increased with the Si concentration increment and temperature rise, irrespective of the soil texture. There was a linear relation between the amount of phosphate displaced and silicate adsorbed, even though direct mol for mol exchange did not occur. Desorption of phosphate by silicate was nearly equilibrated within 3 h, and there were no apparent differences in the time required for reaching the phosphate desorption equilibrium among the temperatures. The highest silicate efficiency in phosphate desorption was achieved in the range of pH 7 to 9 in the two soils at 20°C, and the effect of silicate on the increase of phosphate desorption was only observed between pH 6 and pH 10. Consequently, silicate was able to improve the phosphate status of the soils with phosphate accumulation in plastic film houses, and to reduce the level of phosphate fertilization by the increase of phosphorus availability.

Key words:

• silicate
• phosphate desorption
• competitive adsorption
• phosphate accumulation