Oct. 8, 2012 -- Soils in the southeastern U.S. are suited to peanut production but often lack sufficient calcium to maximize yield, grade or seed germination. Additionally, calcium recommendations to peanut producers are based on cultivars that are no longer in production. Compared to those cultivars, current runner peanuts are larger in seed size and have enhanced disease resistance, which may affect peanut calcium requirements. Advances in peanut cultivars prompted re-evaluation of calcium requirements by researchers at Auburn University and University of Georgia.
Julie Howe, Auburn University, and Glen Harris, University of Georgia, evaluated the effect of calcium fertilization and irrigation on the yield, grade, and germination of current runner peanut cultivars.
Calcium recommendations to growers currently differ by state. In Alabama, additional calcium is recommended if levels in a pegging zone soil test (top 3-7 inches of soil) are less than 300 lb per acre. Georgia, meanwhile, recommends additional calcium when levels are less than 500 lb per acre, unless the calcium to potassium ratio is less than 3:1.
Additional calcium is often added in the form of gypsum, which provides calcium without changing soil pH. Several trials evaluating the response of two cultivars of runner peanut (Georgia Green and Georgia-06G) to gypsum applications (0, 500, 1000, and 1500 lb per acre) and irrigation were conducted between 2008 and 2010 in southern Alabama and Georgia. Trials were conducted in Coastal Plain soils with pegging zone calcium between 356 and 996 lb per acre. Using the Alabama criterion, none of the soils would have had a calcium fertilization recommendation, but using the Georgia criterion, five of the 14 soils would.
Results from the experiments showed an increase in yield, grade, and germination in response to gypsum application when peanuts were grown under dryland conditions. In contrast, peanut yield in irrigated sites did not respond to gypsum applications, but there was a slight increase in grade and germination. Thus, the recommendation of adding calcium only when the pegging zone soil had levels less than 300 lb per acre was adequate for irrigated peanut production but inadequate for dryland production. Re-evaluation of dryland trials with pegging zone soil calcium levels greater than 500 lb per acre demonstrated that there was no additional increase in yield due to applied gypsum, thus suggesting that this critical value is more appropriate for dryland peanut production.
Seed calcium was highly influenced by gypsum treatment, irrigation, and peanut cultivar and was a good indicator of soil calcium availability. Adsorption of calcium was detected throughout the development phase of the peanut indicating that calcium should be present throughout the entire growing season for maximum uptake. The data also suggest that loss of calcium from the pegging zone through high rainfall events could affect late season calcium acquisition.
Overall, production of peanuts without irrigation, especially in drier years, can benefit most from gypsum applications. Yield was increased by 30% with gypsum applications without irrigation. This translates to 500 to 1000 lb per acre of additional peanut yield and a 3.5 to 5% increase in peanut grade. Improvement of yield and grade directly translates into higher peanut prices. Using 2011 peanut prices with the yield and grade of dryland Georgia-06G peanuts from these studies, the price increased by $103, $127, and $199 per acre with the addition of 500, 1000, and 1500 lb gypsum per acre, respectively, compared to the no gypsum treatment. These returns are more than four times larger than for the irrigated Georgia-06G trials and sufficiently high to recoup the $12-32 per acre cost of gypsum (assuming $50 per ton).
This study filled a need to evaluate calcium requirements of peanut cultivars currently in use in the Southeast. Both irrigation and gypsum addition affected peanut yield and grade leading to separate calcium recommendations for dryland versus irrigated soils. The key role of soil moisture is not surprising given that calcium availability depends upon soluble forms of calcium and diffusion into the peanut pod. The important role of soil moisture in calcium acquisition suggests that it should be considered when calcium recommendations are made.
J. A. Howe, R. J. Florence, G. Harris, E. van Santen, J. P. Beasley, J. P. Bostick and K. B. Balkcom. 2012. Effect of Cultivar, Irrigation, and Soil Calcium on Runner Peanut Response to Gypsum. Agron. J. 104(5): 1312-1320 View abstract