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Total Sulfur and Sulfate Sulfur Content in Subterranean Clover as Related to Sulfur Responses¹

ABSTRACT

Subclover was grown on sulfur deficient soil in the greenhouse and in the field with various rates of S applied. Plants were harvested in the greenhouse when the first, third, and fifth flower per stem appeared, and the plant material was separated into leaflets, petioles and stems. The total S and SO₄-S concentrations in the plant did not change significantly over the three stages of growth.

The first 20 pounds per acre increased yield and the organic-S concentration, but did not change the SO₄-S concentration in the plant. Rates of S > 20 pounds per acre did not increase the yield, but increased the SO-₄S more than the organic S fraction in the plant. More SO₄-S accumulated in the stems than in the petioles or leaflets at high rates of applied S, but at low levels of S there was little difference between the SO₄-S concentration of the three plant parts. There was more organic-S in the leaflets than the other plant parts at all levels of applied S.

The SO₄-S concentration was determined in whole subclover tops grown in the greenhouse on 13 soils fertilized with sulfur and phosphorus. Eight of the soils produced clover with SO₄-S concentrations of 170 ppm. or less when unfertilized and each of these soils produced more clover when sulfur was applied if adequate phosphorus was available. The SO₄-S concentration in whole subclover plants showed the same relation to yield in the field as in the greenhouse. The SO₄-S concentration in subclover identified plants deficient in S, but did not indicate the degree of S deficiency.

¹ Contribution of the Agronomy Department, University of California, Davis.

² Assistant Agronomist, University of California, Hopland Field Station, Hopland, Calif.

Received for publication November 24, 1961. Accepted for publication January 3, 1962.