Effect of saline-sodic solutions on column leaching of potassium from sandy soil

Abstract

Sodium (Na+), calcium (Ca2+), and magnesium (Mg2+) in poor quality irrigation water participate in ion-exchange processes in soil, resulting in displacement and leaching of K+ from micaceous minerals into solution and in the potential for elevated concentrations in groundwater. Knowledge of the rate of decrease of K+ from soils resulting from poor quality water application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. The effect of base cations on K+ leaching from a sandy soil was studied using leaching columns. Nine treatment solutions consisting of all possible combinations of three levels of sodium adsorption ratio (SAR) (5, 15, 45) and three ratios of Ca2+:Mg2+ ratios (1:3, 1:1, or 3:1), each having at a total electrolyte concentration of 100 mmolc l−1 were composed in the laboratory using solutions of NaCl, CaCl2, and MgCl2. With the application of solutions, exchange occurred between incoming and exchangeable cations resulting in the displacement and leaching of cations. Sodium adsorption ratio treatment level affected the quantity of K+ leached. Increasing the level of SAR from 5–15 and 45 resulted in increased leaching of K+ from soil. Increasing proportions of Ca2+ relative to Mg2+ in solution favored the leaching of K+ in SAR treatments 15 and 45. The maximum (279.3 kg ha−1) and minimum (168.8 kg ha−1) K+ was leached by SAR 45 and SAR 5 solutions, respectively. The constant b in the power equation defined as the leaching rate, with different SAR solutions having a Ca2+:Mg2+ ratio of 3:1, were in the order SAR 45 (0.8399) > SAR 15 (0.8389) > SAR 5 (0.7312). This indicates that as b increases towards 1 the relationship between the cumulative K+ leached and pore volumes become more linear. Results of present study suggest that long-term use of saline-sodic irrigation water can lead to increase leaching of K+ from soil and may impose the risk of pollution of groundwater.