Question:

With the correlation between excessive potassium levels and increased incidence of pod rot, is that mechanism more so related to weaker pods (due to reduced Calcium uptake from the excessive K+ ions)?  Or is it related to an interaction with the fungal pathogens utilizing that potassium in some measure to be more virulent?  Just a curiosity after examining several years of soil reports alongside scouting records.

Jordan:

The two are tied together. Higher levels of K often means there is less calcium in the pegging zone. K can be held on sites and if they occupy most of the CEC the calcium will likely move through the pegging zone. It does not have to go far to be unavailable for movement directly into pegs and pods. Lack of calcium can make cell walls less than ideal for protection from infection and spread of pathogens. That is my impression on pod rot and K. It really is about calcium nutrition. If you have high K and it occupies sites, under dry conditions where water is limited, I suspect the issue would be even more pronounced. Very little is going on and uptake of calcium is limited because of soil water limitations. That would be the case even without high K. With more soil water there is a greater chance of K and calcium exchange, but the calcium will move through the soil profile more quickly. But too, more rain will move the K through the profile more quickly, so that would be a plus. We tend to see pod rot more often under dry conditions. That could relate to calcium nutrition, but possibly the causal agent for pod rot is more effective at drier conditions because of the limited calcium nutrition. Not sure on that. Our stem rot fungicides do fairly well on pod rot. I've seen pod rot mostly late in the season.

Question 2:

I appreciate the insight, it was brought up during a series of conversations with a grower who historically has been planting 50% of their acres behind (heavily fertilized) tobacco, with the rest behind cotton and last year we noticed very extreme differences in soil-borne disease of all stripes with those rotations.  I think the rotation itself may be the main culprit, but some delayed stem rot sprays, excessive K carryover on finer-textured land (indexes in 85-100 range), may have helped contribute to what we saw late in the summer.

Jordan:

Agree, tobacco is not the best rotation and we do worry about high K behind tobacco and cotton. Tillage can help.

Jordan:

I did not respond to the K affects virulence of the pathogen in my answer. Forgot to do so. I'm not sure on that question. I think with peanuts, I would lean more toward calcium nutrition and cation balance.