Question: I have been reading several Agweb blogs on fertilizer recommendations for corn versus soybeans. I was wondering if the potash we put out in 2010 on soybeans was really doing any good, or if it was just as well to put out a little more to the corn land the previous year since we have a corn-soybean-corn rotation? If the beans don’t really benefit from applied potassium (K), then what are my benefits to applying K before I plant soybeans if the soil levels are adequate? Would K be available if I applied it to the bean land in the fall of the previous year after we cut the corn?
Answer: Soybeans are big users of potash. A 60 bu/A soybean crop removes 87 lbs K20 which is equal to 145 lbs potash (0-0-60) per acre. A 200 bu/A corn crop removes 58 lbs K20 which is equal to 97 lbs of potash. So yes, soybeans need potash as well as does corn. Depending on soil type and soil test levels, some growers choose to apply potash one time for both crops. In this yield example, you would need to apply 242 lbs of potash just for crop removal on soybeans and corn. A soil test will tell you what levels you have in the soil. If your soil-test levels are medium or below, you may want to consider fertilizing for each crop each year (removal rates + soil test build levels). If you have high soil test levels you may be able to fertilizer two crops in one year. Sandy and sandy loam soils may not be able to hold large amounts of potash, so consider every year spreads on these soil types as well. Also, consider the economic aspects as well. Potash price and grain prices have fluctuated greatly over the last several years. Fall applications of potash can work well. More information on this topic is provided at the following link.
Value of Potash
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