Calcium Availability to Runner-type Peanut (Arachis hypogaea L.) in the Southeastern United States

Abstract

Sandy soils in major peanut producing areas in the southeastern United States may be low in plant available Ca. Insufficient Ca supply to developing peanut may result in undeveloped pods and finally low yield, substandard grade, and poor seed quality. Over time peanut varieties change, which may affect Ca absorption physiology, and Ca supplementation products change, which may affect their ability to provide Ca. As a result of these factors, several studies were conducted to reevaluate Ca fertility questions associated with peanut. The objectives of this study were to i) evaluate Ca uptake within peanut maturity classes using the hull-scrape method to determine the potential for early season seed quality assessment; ii) evaluate effect of Ca source and timing on peanut yield, grade, seed Ca, and germination; and iii) evaluate relationships and predictability major soil Ca tests in Coastal Plain soils. Experiments were conducted on a Lucy loamy sand (loamy, kaolinitic, thermic Arenic Kandiudults), a Dothan sandy loam (fine-loamy, kaolinitic, thermic Plinthic Kandiudults), and a Malbis fine sandy loam (fine-loamy, siliceous, subactive, thermic Plinthic Paleudults) in South Alabama. Application of 1120 kg ha-1 gypsum or lime significantly improved seed Ca concentration and total seed Ca. As peanut size increased, more Ca was absorbed, thus increasing total Ca, but maintaining a relatively consistent seed Ca concentration. Since seed Ca concentration was relatively consistent during 4 wk prior to harvest, seed Ca concentration could be used as an indicator for early season seed quality evaluation. Three commercial types of gypsum had similar effectiveness on supplying Ca to peanut; however, USG 500®, a commercially mined gypsum, tended to perform better than AgriCal®, a flue-gas desulfurization (FGD) gypsum, and PCS Wetbulk®, a phosphogypsum. When applied at the same rate, lime was as effective as gypsum. Application of Hi-Cal®, a liquid Ca fertilizer, could provide adequate Ca to peanut as dry forms of gypsum and lime. There were no significant differences between application of gypsum at planting and early bloom. Split applications of gypsum at early/mid bloom tended to have greater efficacy on improving seed Ca and germination than a single application with an equivalent rate at early bloom. Combined application of lime and gypsum did not show benefits over treatment receiving only lime. Addition of Hi-Cal® at mid bloom as a supplement to gypsum applied at early bloom did not significantly improve peanut yield, grade, seed Ca, or germination relative to treatments receiving only gypsum at early bloom. Soil extractable Ca with Mehlich 1 (M1) and Mehlich 3 (M3) was similar and significantly greater than 1N ammonium acetate (AA) and 0.01 M sodium, nitrate (SN). Application of gypsum shortly before soil sampling had minimum effect on correlations among soil Ca by the four tests. However, application of lime led to weaker correlations. Mehlich 1 may overestimate available Ca to peanut in soils recently amended with lime. The AA-extractable Ca showed the best predictability for Ca supplementation for peanut. Mehlich 1-extractable Ca is the second best.