Modeling magnesium uptake from an acid soil: IV. Depletion of magnesium, calcium, and potassium from soluble and exchangeable phase

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Abstract
Two ryegrass (Lolium multiflorum Lam.) cultivars were grown in a greenhouse on an acid Stough soil (thermic Fragiaquic Paleudult) amended with three rates each of CaO and MgCl2. Initial amounts of K, Ca, and Mg in the soil solution were replenished up to 12.3, 1.2, and 2.5 times, respectively, in order to sustain plant growth. Larger exchangeable pools effectively buffered solution concentrations of Ca and Mg but not that of K in the later stages of plant growth. It appeared that nonexchangeable K was utilized by ryegrass as well. Liming allowed greater accumulation of K, Ca, and Mg by shoots of two ryegrass cultivars in the grazing stage (35‐day‐old plants). The extent of the Ca‐Mg complementary‐ion effect occurring at the soil‐root interface may be cultivar‐dependent. When grown on unlimed soil, the relatively Al‐tolerant cultivar Gulf had significantly lower shoot K/(Ca+Mg) equivalent ratio compared to the relatively Al‐sensitive cultivar Wilo. Liming considerably reduced K/(Ca+Mg) ratio in shoots of both cultivars.