We conducted laboratory research to determine the effects of exchangeable Mg-to-Ca ratios on the accumulation of exchangeable Na and K. Soil samples were washed with solutions containing Na at 60 or 120 mmol L−1 or K at 10 or 20 mmol L−1 and Mg-to-Ca ratios ranging from 0 to 1 with a constant concentration of Ca + M g of 8 mmol L−1. The results showed that as the ratio of Mg to Ca increased, the exchangeable Na or K increased. In these soils the exchange between Mg and Ca indicated a preference for Ca, which explains why Na and K are more competitive against Mg than against Ca. The exchangeable Na ratio (ESR) was negatively correlated with organic C contents of soils for both Ca-Na and Mg-Na systems, but the relative preference for Na in Mg-Na systems compared with Ca-Na systems was not consistently related to organic C.
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