GYPSUM AMENDMENT AND EXCHANGEABLE CALCIUM AND MAGNESIUM EFFECTS ON PLANT NUTRITION UNDER CONDITIONS OF INTENSIVE NUTRIENT EXTRACTION

Abstract

In general, increasing the concentration of one cation species in soil solution can decrease levels of other cations in plants. It is not clear whether adjusting soil cation ratios or adding gypsum will improve plant growth. We studied the effect of adding gypsum to unleached soil, and the effect of changing soil-exchangeable Ca/Mg ratios on corn root and shoot growth and nutrient concentrations. Soil-exchangeable Ca/Mg ratios (8.0, 4.9, 1.8, 0.7, and 0.5) were obtained by leaching soil with Ca and Mg chloride, followed by leaching with Ca and Mg sulfate to remove chloride. An unleached soil treated with gypsum and an untreated control soil were also included. Corn plants were grown for 23 days in a replicated greenhouse experiment. Exchangeable Ca/Mg ratios did not substantially affect root and shoot growth in the leached soils, nor did gypsum addition to the unleached soil. However, growth in the leached soils was less than that in the unleached soils, probably because of removal of K in the leaching process. Shoots from plants from treatments with lower leached Ca/Mg ratios had less Ca and more Mg but showed no consistent changes in K. Addition of gypsum to unleached soil decreased P, increased K and Ca, and did not affect N and Mg concentrations in shoots.