AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Summer 2001, No. 4
In more arid regions of the U.S., potassium soil supplies have been naturally high. For decades, farmers in these areas have assumed that potassium levels were adequate. Their focus in nutrient management has been on nitrogen and phosphorus. But years of neglect has mined soils down to yield-limiting levels of potassium in many areas. Farmers in these regions now have an additional nutrient to worry about – a nutrient they have traditionally not had to manage.
What are the consequences of not worrying about potassium? Letting soil supplies of potassium dwindle to inadequate levels has several very negative consequences. Crop yield, the sole source of revenue on many farms, takes a hit. The lower potassium levels drop, the more likely larger yield reductions become. Efficiency of water use, so important in the more arid areas, is also reduced. Crop quality may also be compromised, possibly cutting into revenue based on value-added traits. Inadequate supplies of potassium are also detrimental on compacted soils, where a shallower rooting volume limits access to water and nutrients lower in the soil profile.
Potassium deficiency may not be readily visible. When potassium deficiency symptoms are seen in the season, there is a good chance that yield reductions have already occurred. But there is also “hidden hunger.” Plants may not show many symptoms, but potassium levels in the plant may be too low to allow the crop to express its full yield potential. To get at this “hidden hunger”, take some plant tissue samples and send them to a reputable laboratory. If rectifying deficiencies is not possible this season, use the information to plan for next year.
Money spent on nitrogen may not go as far when potassium is limiting. Potassium can help crops make better use of nitrogen. For instance, data from Ohio have shown that adequate soil supplies of potassium help corn reach higher yields with less nitrogen. That means for every dollar spent on nitrogen, soils adequate in potassium provide greater returns than soils that are deficient. Higher nitrogen prices and continued low crop prices make potassium more important than ever.
University nitrogen recommendations usually assume other nutrients are at adequate levels. When research is conducted to determine the optimum nitrogen rates to apply, other nutrients are normally held at levels considered sufficient. If you are following university guidelines for nitrogen rates, then potassium levels need to be adequate. Deficiencies in potassium lead not only to poorer potassium efficiencies but also to increased risk that more nitrogen will be lost to surface and ground water. Balanced fertility is a key to profit and environmentally responsible nitrogen applications.
Keep an eye on potassium. Don’t let concern over nitrogen upset a balanced approach to fertility. Being diligent in all aspects of nutrient management is the only way to realize the agronomic, economic, and environmental benefits possible.