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Ionic Balance in Coastal Bermudagrass Influenced by Nitrogen Fertilization and Soil Salinity¹

A stimulus in yields of coastal bermudagrass [Cynodon dactylon (L.)] with N on moderately saline soils previously reported may be due to cation-anion balance. Other investigators have shown that a normal organic anion (C-A) concentration was one of the conditions necessary for maximum growth, and they have postulated that yield response to N fertilization of saline soils was due to the substitution of NO₃, for Cl and an increase in (C-A) concentration of the grass. The objective of this study was to compare the relation between yield and (C-A) concentration of coastal bermudagrass under several N fertilizer-soil salinity regimes.

The grass was grown in pots in a greenhouse on Brennan fine sandy loam (Aridic Haplustalfs). The soil was salinized by treatment with saline water to develop four salinity treatments (S₀, S₁, S₂, and S₃) with electrical conductivities (EC) of 1.2, 4.8, 9.6, and 14.4 mmho/cm, respectively. Fertilizer treatments were applied in a factorial arrangement with N rates of 0, 67, 133, and 200 mg/kg of soil and P rates of 0, 20, 40, and 60 mg/kg. The concentration of organic anions in the grass was determined as the difference between the concentration of cations (Na, K, Ca, Mg) and of inorganic anions (Cl, NO₃, H₂PO₄, SO₄).

Nitrogen fertilization increased the (C-A) concentration of the grass at all salinity levels. The increase in Cl concentration with increasing salinity decreased (C-A) concentrations. An increase in growth was associated with an increase in the (C-A) concentration. However, SO₄ deficiency apparently controlled growth on the adequately N fertilized nonsaline soil, and cation accumulation in the salinized soils depressed growth.

Key Words: Organic anions • Chloride • Inorganic SO₄ • deficiency • Foliage mineral composition • Cynodon dactylon L.

² Soil scientists, Soil and Water Conservation Research, USDA, SEA, AR, Weslaco, TX 78596, and Southern Piedmont Conservation Res. Lab., USDA, SEA, Watkinsville, GA 30677.

Received for publication June 25, 1979.