October 2, 2013
Iowa State has now released official recommendations for field moist potassium measurements. The changes were initially announced online: www.extension.iastate.edu/CropNews/2013/0920mallarinosawyer.htm
As we all know, land grant university recommendations do not change very often so we are very happy that they have provided actionable recommendations on how their research can be used in the field.
Some highlights follow below:
Research has indicated that the moist K test is more reliable than the test based on dried samples and is a better predictor of crop K fertilization need.”
The amounts of K extracted can differ greatly between moist and dried samples, and the differences change greatly across soil series, the soil-test K levels, and soil conditions related to drainage and moisture content cycles.” Even though the dried and ground method is easier to perform, “There is no numerical factor that can be used to transform test results between moist and dried testing procedures. “
The recommendations for dried ground Potassium levels were also updated, to account for the fact that response to applied K has been observed when dried ground tests for K are as high as 240 ppm. The ISU researchers note that:
Although the new interpretations improve the performance of the dry K test, we encourage use of the moist test for K.”
A summary of the new guideline for potassium is as follows:
More details can be found in the updated PM 1688 guideline, which can be downloaded or ordered here.