Potassium management

Due to the run up in the cost of potash, many farmers cut back on the amount of potash they applied for crop production, especially in 2008 and 2009. Due to adequate levels of potassium (K) in the soil or the ability of soils to supply K, crop biomass and grain yields may not have been seriously affected. However, applying less than crop removal over several years will gradually reduce the reserve amounts of K in the soil. Some summaries of soil test values over the past few years indicate available K levels have been drawn down. Fields where the whole crop biomass has been removed (corn silage, forages, straw removal) are the ones where the most change may have occurred and need attention first. It is important to be applying at least what will be removed from the field in the harvested portion of the crop (see table). With the price of potash coming down to a more reasonable level, now is the time to look at improving the K level of field soils used for crop production. The first step is sampling the soil in your fields and having it tested to determine the available K status and need for additional K.

For improving the potassium (K) status of the soil broadcast and incorporation of potash is the best approach. On no-till soils, broadcasting the potash as far ahead of planting is desirable. This will provide more time for the potash to dissolve and move downward into the soil root zone. Banding some potassium (20 to 40 lbs K2O/a) at planting is a way to improve potassium use efficiency, improve early plant growth and improve crop yield under certain situations or soil conditions. Banding potassium at planting is most likely to be beneficial under no-till and heavy residue situations, and in soils having low to moderate levels of available K. Sandy soils are more likely to have inadequate potassium. In recent years, there have been a number of cases where soybeans growing on sandy soils have developed potassium deficiency, which undoubtedly ultimately reduced crop yield. On these sandy soils banding or broadcasting potash may be essential for soybeans as well as corn.

Amounts of K2O removed from the field in the harvested portion of the crop.

Alfalfa                    50 lbs/ton
Clover-grass hay     39 lbs/ton
Corn                      0.27 lbs/bu
Corn silage             8.0 lbs/ton
Soybeans               1.4 lbs/bu
Wheat, grain           0.37 lbs/bu
Wheat, straw          23 lbs/ton

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