This time of year, growers are applying gypsum to ensure an adequate amount of calcium is in the pegging zone. The plant cannot supply enough calcium to developing pegs and pods through the root system to reproductive structures. An elevated concentration in the pegging zone (upper 2-3 inches of soil) is needed. All Virginia market types need supplemental calcium, while runner market types have a lower requirement but often need soil calcium to be supplemented with gypsum. This is another case of looking locally to folks with experience and data can help you make the decision on use.

There are multiple factors that can affect whether you will get a yield increase or improvement in market grades when gypsum is applied. Soil calcium levels, soil pH, soil texture, rainfall, product and rate, and variety (primarily market type) impact response. From a research standpoint, there is a significant body of evidence for Virginia market types showing a positive response to gypsum in terms of both yield and grades. But we may not see a response in a single trial. On average, yield increases and percentages of sound mature kernels and the extra large kernel fraction go up.

In North Carolina, I’ve been giving growers a few scenarios where rates below what we normally recommend can be applied. However, those rates are never below half of the recommended rate, and we need to consider the uniformity of the application when we shave rates. You can find that information if you search the Peanut Notes series at our Extension portal (https://peanut.ces.ncsu.edu/).

We have data showing that it is unlikely to get a positive response to gypsum when soil pH is low, in the 5.5 range. In fact, when the soil pH is low and we apply too much gypsum, yields go down.

In this issue, weather and climate are a part of the discussion. As I write this, we have received very little rain in April and May and so far in June across many pockets in North Carolina. It seems that when we do get rain, it is likely that some folks will get a lot of it in a short period of time. One of my concerns is how do we handle gypsum recommendations if we get extensive thunder showers that wash soil and gypsum off beds. When we apply gypsum very early (early to mid-June) if peanuts are small, some of that gypsum will wash down to the middles along with soil. If you are planting flat, that is less of an issue. In North Carolina, we don’t need calcium in the pegging zone until early to mid-July depending on planting date and flowering. Late June is when I would target application of gypsum. This does two things. It gives us greater plant growth that will minimize washing of soil into middles if we get a big rain. Given we need calcium in the pegging zone in July and August, applications in late June and into July gives a greater chance of adequate levels of calcium being present throughout the entire season.

So here are thoughts about gypsum in the real world. Logistics around gypsum have become much more challenging. There are currently no proven substitutes for gypsum. Sometimes getting gypsum out earlier helps farmers avoid some of the bottlenecks. This is reality. As we address the logistics, however, we need to consider the risk with timing of gypsum applications as outlined above.