Gypsum and Excessive Rain Peanut Notes No. 121 2019

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While many areas of the state have continued to be dry other areas of the state have received excessive rainfall, often in a single event. This brings up questions about status of calcium in the pegging zone and whether or not additional gypsum should be applied. See page 29 in 2019 Peanut Information for a more detailed discussion of this topic. Generally, if you receive 5 inches of rain over a short period of time this time of year after gypsum is applied, a second application of ½ the suggested use rate is one way to minimize the risk of not having adequate calcium to ensure adequate pod and kernel development. Dr. Anco sent the following information out to growers in South Carolina:

The guideline I use for excessive rainfall affecting land plaster in a field is more than 5 inches of rain in a short period of time (a few hours). This is based off David Jordan’s recommendation in North Carolina. I have found David’s recommendations to be sound advice and applicable for peanuts in South Carolina as well. If more than 5” does come down in a short timeframe soon after applying gypsum, a half rate application can help buffer us against a possible shortage for healthy pod fill that can otherwise contribute to pops. Outside of the excellent gypsum standard, there are many calcium products on the market, and some growers have reported good results with some of these. No matter how a product is marketed, for pod fill calcium needs to be available in the soil to be absorbed through the developing pod. There is no pod benefit to foliar absorbed calcium.