Response to Comment Posted in 2014 Peanut Notes No. 242 2020
Comment on post from September 5, 2014, about potash and gypsum:
I received feedback a few days ago from a post made in 2014. Not sure if that was someone looking at older posts and commenting recently or a comment made in 2014 that for some reason just showed up in the anonymous comments section. None-the-less my answer was not adequate.
We encourage people to apply potash based on soil test values for peanuts a few weeks ahead of time if possible and incorporate into the root zone prior to planting. This gets the K down in the root zone where it is needed and prevents having a high concentration in the pegging zone. High levels of K and Mg can interfere with Ca presence in the pegging zone and possible uptake into developing pods. However, if the soil test calls for K then it needs to be applied. It is not overly risky to apply it to the soil surface, but in this case it is important to make sure the recommended gypsum rate is applied. Some folks are cutting back on gypsum rates and that would be risky if K levels are naturally high or if a fertilizer application is made to the soil surface and not incorporated. I have not been able to demonstrate the adverse effects of K on the soil surface in research with realtively low, remedial rates. My impression is that 250 pounds/acre potash applied to the soil surface poses minimal risk as long as the 1X rate of gypsum is applied based on recommendations. We have not been able to document that increasing the rate to 1.5 times the suggested rate of gypsum is better than applying a 1.0X rate. In fact, if your soil pH is lower than recommended (5.5 or lower) the higher rate of gypsum causes a negative response.
Part of the issue with my answer in 2014 was that I did not address the K-I (which was based on cotton in the question) at all or at least not very well. I will include K indices (and other nutrients in 2021 Peanut Information for quick reference.) My answer is going to always be for K in peanuts that if the soil test calls for K for peanuts then it needs to be applied. However, it is important that K is incorporated as much as possible before planting. But if that is not possible, make sure the 1X gypsum rate is applied. Where this approach is used (K applied to soil after planting or to the soil surface, for example, in reduced tillage) it is not a good practice to decrease the gypsum rate.
The other issue I did not address well was late-season applications of K. We do see nutrient deficiencies in peanuts using tissue analysis late in the season. Part of this is a high pod load. In the few times I have applied K at this timing (potash in late August or September, many years ago), I did not get a response to potash. We have not looked at liquid materials to correct a deficiency. I think the deficiencies we see late in the year are not yield limiting, however. If someone is seeing this it is likely a better approach (for the future) to apply adequate K before planting and in some cases apply a remedial rate of K (about 250 lbs/acre) even when soil tests indicate that K levels are adequate. If this is done, it is best to incorporate and it is important to apply a 1X rate of gypsum.
I will include K index values (and other nutrients) in 2021 Peanut Information.