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Calcium-supplying Characteristics of Two Gypsum Materials on Southeastern Coastal Plain Soils¹

ABSTRACT

Field studies were conducted on two soils to study the manner in which finely and coarsely divided gypsum materials supplied Ca to the soil depth where peanut (Arachis hypogaea L.) fruit absorb Ca. The finely divided material was characterized chemically as CaSO₄ · 2H₂O, approximately 72% CaSO₄ or 20.2% Ca and physically as having 88% of the particles < 0.25 mm in diameter. The coarsely divided material was characterized chemically as CaSO₄, approximately 92% CaSO₄ or 26.5% Ca and physically as having 82% with particle diameters < 4.2 mm, but > 0.5mm. Each material was applied at three rates in randomized complete block experiments. At approximately 3-week intervals, composite soil samples were collected at the 0- to 5-, 5- to 10-, and 10- to 15-cm depths and extracted with acid (0.05N HCl + 0.025N H₂SO₄) extractant which was analyzed for Ca.

The amount of Ca transported to a given soil depth was found to be related to the magnitude, order, and frequency of rainfall events. Generally, several small rainfall events resulted in accumulation of Ca near the soil surface, whereas, larger rainfall events resulted in a reduced Ca concentration near the soil surface for both materials. The fine gypsum material was found to be more effective in supplying Ca to the soil depth where peanut fruit are absorbing it early in the growing season than the coarser material.

Dissolution of gypsum sources consisting of different particle sizes and subsequent transport of Ca into the fruiting zone of peanuts was not always closely related to the total amount of rainfall. Either the finely or coarsely divided gypsum could supply more Ca to the fruiting zone depending on the rainfall pattern.

¹ Contribution of the Univ. of Georgia, Tifton, Ga.

² Assistant Professors, Dep. of Agron., Coastal Plain Exp. Stn., Tifton, GA. 31794. The first author is now at Texas A & M Univ. Agric. Res. & Ext. Cent., Overton, TX 75684.

Received for publication March 4, 1977. Accepted for publication February 6, 1978.