Gypsum material effects on peanut and soil calcium

Abstract

Adequate availability of calcium (Ca) in the upper 7–10 cm of soil is extremely important for pod development and therefore for production of quality peanut (Arachis hypogaea L.). Supplemental Ca is usually applied as gypsum, however, availability of Ca may depend on the type of gypsum. The objective of a laboratory study was to evaluate recovery of Ca in Mehlich I, 0.01 M NaNO₃ and deionized water extractants from seven gypsum materials which varied physically from fine and coarse powders to crystals, granules and pellets. Overall, recovery of Ca was much greater in Mehlich I (89.5–99.6% of total Ca) than in either 0.01 M NaNO₃ (81.0–98.4%) or deionized water (78.7–97.5%). However, for 3 sources, recovery of Ca was very similar in NaNO₃ solution and deionized water. Field experiments were conducted on Lakeland sand (Mehlich I Ca = 127 kg/ha, 0–15 cm) and Tifton loamy sand (Mehlich I Ca = 665 kg/ha) soils to study the effects of the gypsum materials on Florunner peanut grade and yield. Effects of gypsum treatments on Mehlich I‐ and 0.01 M NaNO₃‐extractable soil Ca were also evaluated during peanut pod development. On the Lakeland soil, Mehlich I Ca increased from 127 to a range of 420–737 kg/ha following application of gypsum depending on the type of gypsum material. Percent sound mature kernels were significantly greater where gypsum was applied than in the control treatment, regardless of source. Total sound mature kernel yield and gross return were greatest for the more soluble sources. The yield vs. soil test Ca relationship 90 d after planting revealed that yield response was very minimal if soil Ca was greater than 290 and 85 kg/ha of Mehlich I and 0,01 M NaNO₃‐extractable Ca, respectively. Application of gypsum to the Tifton soil, regardless of type of material, had no significant effect on yield, grade or gross return because Mehlich I extractable Ca in the control treatment was well over 560 kg/ha; the critical soil test Ca for runner peanut according to the current Georgia soil test recommendation.