Potash-related problems are certainly not new to crops in Mississippi, but this year we have had a reminder of how important this element is. There is no mystery to the story of potash nutrition, but many of us are questioning the reason for increased incidence of this problem in 2014.
During one of my visits to a farm in the southwest part of Mississippi I ran across an example of severe potash deficiency in soybeans. A field which had low soil test potash had received a fairly moderate rate of potash fertilizer at planting and the crop had responded well to it. Plants did not show deficiency symptoms for this element, except that in one field the grower had run out of potash and had not been able to complete the application on a portion of one field.
This area exhibited the worst potassium deficiency I had ever witnessed in soybeans with some plants almost dead as a result. Less than 5 feet away from severely affected plants were normal plants with good yield potential. This confirmed to me that in cases of potash deficiency, the element should be applied in spring rather than fall, especially on sandy or silt loam soils.
Another example of the importance of good potash fertilization has been the incidence of verticillium and fusarium wilts in cotton, along with high incidence of the common leaf blight diseases. These problems have been extremely common in cotton fields all over the region this year and in many cases can be linked to soil test potash levels that are less than ideal.
We have also witnessed the presence of another wilt-like disease in cotton that resembles verticillium but does not discolor the xylem tissue of the stems as in verticillium. With this disease the plants wilt and defoliate much like plants infected with verticillium, but when we do the customary stem splitting test for verticillium diagnosis, the stem is found to be free of any discoloration. In some fields where this condition has been found, other plants may show the symptoms of verticillium, suggesting that both this newcomer and verticillium may be present.
I understand that efforts are being made to determine the severity of this new disease that has contributed to early senescence and defoliation of several fields of cotton in this region, however, it would be premature to suggest that we know everything we need to know about it.
Personally, I feel that the extended period of frequent rainfall during the early portion of the growing season produced shallow rooting, thereby limiting the amount of soil accessed for potassium and other elements. Other issues that may limit the availability of micronutrients needed to combat disease may also be involved. Hopefully we will soon have a better handle on the reason for this problem so that we can plan to avoid it in the future.
For now, we need to concentrate on what we know. Fields that were affected should be sampled and tested, along with other fields that have not been tested recently. As I always say, if you guess about soil fertility you will sooner or later guess wrong.
Can you afford to be wrong?