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Effect of Irrigation Water Quality on the Leaching and Desorption of Phosphorous from Soil

Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of Ca2+ concentration of irrigation water on phosphorus (P) leaching and kinetic release in columns of sandy soil. Phosphorous sorption in the presence of CaCl2 solutions with Ca2+ concentrations of 3, 5, 10, and 15 mM CaCl2 was determined to understand the transport and leaching of P in the sandy soil. The geochemical Visual MINTEQ was used to calculate saturation indices. A considerable number of leachate samples contained P at concentrations that could cause eutrophication. Total P leached from soil due to application of different CaCl2 solutions ranged from 1.7 to 1.8 kg ha−1 after 20 pore volumes had passed through the soil. Comparison of the leaching experiments results with the kinetic desorption data indicated that leaching removed on average 50 times less P than cumulative P desorbed by successive extractions with different CaCl2 solutions. Leaching in presence of different CaCl2 solutions was controlled by rate-limited dissolution of calcium hydroxyappatite and ß-tricalcium phosphate.