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Effects of Saline-Sodic Soil Chemistry on Soybean Mineral Composition and Stomatal Resistance¹

ABSTRACT

Soybean [Glycine max (L.) Merr.] productivity is severely limited by saline-sodic soil conditions that occur in isolated spots in the river bottoms of western Kentucky. Productivity of soybeans grown on a gradient of soils of increasing saline-sodic character were studied in greenhouse experiments. Soils with electrical conductivity (EC) exceeding 3.20 dS m^–1 would not support soybean growth. Soybean plants accumulated significant quantities of Na when soil solution sodium adsorption ratio (SAR) exceeded 6.4 and relative tissue Na accumulation was highly correlated with SAR. Estimates of potential productivity were made by stomatal diffusive resistance measurements at three vegetative growth stages. Potential productivity was severely limited under conditions of high soil salinity. In soils of lower EC (< 2 dS m^–1), soybean performance was affected to a greater extent by changes in SAR than by changes in EC. Dry matter production decreased with increasing SAR under low EC soil conditions.

In a second experiment, saline-sodic soil was amended with four rates of gypsum (CaSO₄·2H₂O), (0, 2.6, 6.0, and 12.9 g kg^–1). Gypsum-amended pots were leached until EC was < 3.0 dS m^–1. Plant dry matter production was minimized with the 2.6 g kg^–1 amendment, which also produced plants with significantly reduced and negligible Na contents. At early growth stages (V4 and V7), stomatal diffusive resistance of plants grown on the gypsum-amended soils was not affected by increasing SAR. Diffusive resistance measurements of large vegetative plants (V10) increased significantly at low soil solution SAR. The addition of gypsum apparently reduced the detrimental effects of physical impedence to root development and function in the poorly structured soil as well as soil solution SAR. The improved physical structure of the gypsum-amended soil could improve root development, function, and crop productivity.

Key Words: Glycine max (L.) Merr. • sodium • gypsum-amended soils • stomatal diffusive resistance • alkali soils • saline soils • porometer

¹ Contribution from the Dep. of Agron., Univ. of Kentucky, Agric. Exp. Stn., Lexington, KY 40546-0091. The investigation reported in this paper (83-3-246) is in connection with a project of the Kentucky Agric. Exp. Stn. and is published with the approval of the director.

² Graduate research assistant and assistant professors, respectively, Dep. of Agron., Univ. of Kentucky, Lexington.

Received for publication December 12, 1983.

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