By Harold Watters, Ohio State University Extension agronomist
Where to start? Rain delays, dry weather following — that is the most common reason for our not so great crop appearance. These issues led to:
- Compaction — you worked the ground too wet: or for no-tillers, you planted too wet. And then we had little chance for recovery.
- Potassium deficiency — this problem continues, again it is probably compaction causing the temporary deficiency.
- Nitrogen and placement — this will take a little longer to discuss.
Potassium — possible reasons for deficiencies
- Low soil potassium test. The coming update to the Tri-State Fertilizer Recommendations suggest that we ought to target 120 ppm K or above for our potassium test. If below that you are more likely to see a benefit to adding potassium fertilizer.
- Fertilizer applications are made today with high-speed broadcast spreaders, that may not deliver a full rate to the outside of the field. I have seen this numerous times now when the grower shows me the soil test with adequate P for the whole field, but then when we test the edges of the field we find low or deficient areas.
- Compaction reduces root growth. It is made worse in a year like this with wet conditions early and then dry after we see reduced or restricted root growth. Anything that compromises root growth can lead to K deficiencies, usually temporary though.
- Soybean cyst nematode can also reduce root growth and lead to less K uptake.
- Little winter freezing and thawing occurred this winter. Some have thought this reduced freeze-thaw may lead to less K availability, and certainly could lead to reduced compaction alleviation.
- The ratio of K to Magnesium may be off and lead to reduced potassium uptake. This is another idea we are kicking around. Typically we don’t think this should be an issue but my industry buddy thinks folks have overdone the high-Mag lime applications and led to some potassium issues. This is something to think about as you choose your next lime source.
- And Steve Culman, our OSU soil fertility specialist, remarked that over-fertilizing with potassium fertilizer may not help. We are better off just applying crop removal.
Lastly, can we spray on something in season to fix it? The short answer is no. The long answer is, don’t let yourself get into this situation in the first place as it is not easily remedied.