Is air-drying of soil samples an appropriate step in determining plant available potassium for corn?

Abstract

Potassium (K) fertilizer recommendations are mainly based on air -dried soil samples which can lead to over-or under-estimation of plant available soil K. Three on-farm trials were conducted in North Dakota and Minnesota to determine the variation of soil test-K between air-dried (K Dry ) and field moist (K Moist ) soil samples. The differences between K Dry and K Moist decreased exponentially as soil K increased, but increased linearly with increasing soil moisture. Use of K Moist as yield predictor variable instead of K Dry improved the correlation coefficient from 0.83 to 0.92 at only one site. Soil drying influenced the plant available soil K-test value, producing higher K values compared to the moist soil K. It is unclear based on these initial experiments which method might produce a more predictable K critical value to aid in directing K application for corn in this region.