Effect of Exchangeable Sodium on Soil Properties and on Growth and Cation Content of Alfalfa and Cotton
1955
Chang, C. W. | Dregne, H. E.
Identical portions of productive Gila clay loam, an important irrigated soil in the southwest, were treated with Na₂CO₃ to obtain increasing levels of exchangeable sodium. After being incubated to equilibrium at field (moisture) capacity the soils were dried, ground and sieved for laboratory tests and greenhouse experiments. The treated soils showed increases in exchangeable sodium percentage, soluble Na, soluble carbonate and pH, and a decrease in soluble Ca. Approximately 75% of the added Na₂CO₃ was adsorbed as exchangeable sodium. The dispersion ratio and moisture retention of the soil increased with the increase in exchangeable sodium percentage. Alfalfa and cotton were grown under greenhouse conditions, and the plant tissues were analyzed. Reduction in yield of alfalfa and cotton was first noticeable at about the 35% level of sodium saturation. Treating the soil with a synthetic soil conditioner increased growth of the alfalfa at sodium levels that were detrimental on the unconditioned soils. The synthetic soil conditioner had no appreciable effect on cotton growth. This finding indicates that exchangeable sodium probably has a direct as well as an indirect, adverse influence on crop growth. Associated with decreased yields of the plants tested was an increase in the sodium content and a corresponding decrease in the calcium content of the plant tissues. This reciprocal relation between Ca and Na in soil and in the plant tissue suggests the feasibility of determining the sodium status of a soil by plant analysis. The term “sodium-induced Ca deficiency” in plant nutrition is proposed. A reddish coloration on the lower leaves of alfalfa, followed by collapse of the petioles, appears to be indicative of this “sodium-induced Ca deficiency.”
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