All summer you were convinced your corn was displaying symptoms of a lack of P and K, but were always told it was a result of the drought, and the lack of moisture uptake prevented adequate absorption of P and K for the benefit of the corn stalk. After crops come out of the field, you will be able to take the soil tests you thought were needed, but unfortunately, fertility researchers at Iowa State University will tell you that the soil tests will also show results that stem from the drought. The Iowa State researchers advise that, “No matter the option used to estimate grain or biomass P and K concentrations, there is a great deal of uncertainty and variability concerning drought effects. Depending on moisture availability during different portions of the growing season, there could be relatively more or less grain dry matter production than nutrient uptake and translocation from vegetative plant parts to the grain, which would result in lower or higher concentrations, respectively.” 

The problem with P & K measurement is the fact that dry soils do not give adequate measurement because the lack of rainfall has prevented certain salts in the topsoil to leach out, and it is difficult to interpret the readings provided by a soil testing company. They advise to wait until the soil has better moisture resources before taking a soil sample. An alternative is to compute the amount of P and K removed from the field by the grain and/or biomass that you may have harvested. “For example, values from PM 1688 for corn grain are 0.375 lb P2O5/bu and 0.30 lb P2O/bu; and for soybean grain values are 0.80 lb P2O5/bu and 1.5 lb K2O/bu.” 

There is also a problem with good soil testing after a drought, according to the Iowa State fertility specialists, which is difficulty in controlling the sampling depth in dry soil, and particularly dealing with the powdery soil at the upper layer of the profile.


The drought will result in many issues that farmers typically can avoid during a more regular year. However, there will be both challenges and opportunities that result from the change, whether it be in tillage or nutrient management. There obviously are many more such issues, and they will be explored as they are identified. 


Read the article at Farmgate blog.