Soil Potassium Availability

The Roles of Manure, Irrigation and Potassium Feldspar

Why do Nebraska soils tend to have high potassium (K) availability, even with high yields and often without fertilizer K application? Why are yield responses to fertilizer-K infrequent (Figure 1)? The answers lie in the K applied in manure and irrigation water, and soil mineralogy.

There is much application of manure to cropland in Nebraska. A 25-ton/ac application of feedlot manure may supply 500 lb/ac K2O, which is equal to removal in about 2400 bu of corn grain.

The K concentration in irrigation water varies across counties and across wells within counties. In a 1200-sample UNL survey of water quality, the average K2O content per ac-ft of irrigation water was 39 lb/ac but county averages per ac-ft ranged from 13 lb in Gage County to 216 lb K20 /ac-ft in Grant County. The average K2O contents in lb/ac-ft varied by region of the state and were 30 lb for northeast, 31 lb for north central, 37 lb for south central, 39 lb for southeast, 44 lb for west, and 68 lb for west central. For comparison, the removal in a 250 bu corn harvest is about 52 lb K2O. Again, there was much variation across wells and irrigation water should be tested for concentrations of K and other nutrients.

This article was originally published by the University of Nebraska – Lincoln’s Institute of Agriculture and Natural Resources | Original Story