Why Was Potassium Deficiency a Common Site in Midwest Fields at the End of the 2000 Season?

As the 2000 crops moved to maturity, potassium deficiency was noted in many fields. Severe lodging in many areas made harvest a real challenge. Why are we seeing K deficiency more commonly than we used to? Several factors may be contributing to this:

1. Potassium fertilizer application has decreased over the past 10 years, while yields and thus crop removal have increased. Net removal by crops now exceeds K fertilizer application overall, and the balance is much worse in many individual fields.
2. Mid- to late-season drought in many areas put stress on the plant and reduced the movement of nutrients to the roots within the soil solution.
3. Increase in the intensity of the crop rotation has increased demand for K. Soybeans remove relatively larger amounts of K than corn. The occurence of soybeans more frequently in the rotation in recent years means faster drawdown of K supplies. Often K fertilizer rates have not increased to compensate for the increased removal.
4. Reduced tillage means more of the nutrients are near the soil surface. When the soil dries out late in the season, as it did in 2000, roots near the surface can no longer supply water and nutrients, so roots deeper in the profile must take over. With reduced tillage there is a tendency for subsoil nutrient levels to not be as readily replenished, so lower profile soil tests have declined, and cannot meet the demands.
5. Wet soils in the spring resulted in more compaction than usual. Combined with the other factors above, this led to more restriction on roots being able to reach adequate water and nutrient supplies.
6. A combination of several factors led to increased stalk diseases in 2000, resulting in reduced plant health, decreased root function, and premature death. Often it was difficult to assess the real cause/effect relationship. Several possible scenarios were playing out by the end of the growing season and severe lodging resulted in many areas.

1. Be sure a recent accurate soil test is available and use it to guide application of adequate K as fertilizer or manure to maintain or build soil K levels as required. The cost of the fertilizer is much less than the cost of deficiency.
2. Don't wait until visible symptoms occur. Yield and profit loss have become a factor long before symptoms are noted.
3. Take some plant samples during the next season to be sure hidden deficiencies are not present.
4. Review yield maps and note locations of low yield areas as potential nutrient deficient areas. Use these maps as a guide for scouting and sampling.
5. Be sure nutrient applications are at least adequate to maintain soil test K levels. Use accurate yield data to determine crop removal. Monitor soil test trends to be sure you are getting the desired response to applications. Adjust future applications as necessary.