Nebraska soils are “mineral” soils, which implies that these soils were formed from minerals such as feldspar, mica, hornblends, etc., and secondary minerals and clays. Because different minerals contain varying amounts of potassium, and since all soils are not formed from the same minerals, it is important to note that soils differ in their ability to supply potassium to a growing crop. Evidence of this variability is shown in Table 6.1.

The most commonly used chemical extracting agent to estimate exchangeable and solution potassium is 1/10 molar ammonium acetate at pH 7. However, this test does not measure total potassium in the soil. The reported value from the chemical analysis is an index of the soil’s ability to supply potassium to different crops. Table 6.1 indicates the difference in exchangeable potassium, as determined by the potassium soil test for soils found in various parts of the Midwest. It can be seen that soils vary in their ability to provide extractable potassium to the crops being grown.

  soil type and location    
  Clarion silt loam Story County, Iowa Hall silt loam Dawson County, Nebraska Thurman loamy sand Merrick County, Nebraska
soil depth inches Exchangeable potassium (lbs/acre 6 inches)2 Exchangeable potassium (lbs/acre 6 inches)2 Exchangeable potassium (lbs/acre 6 inches)2
0 - 6 143 1,488 247
6 - 12 97 992 156
12 - 18 61 725 87
18 - 24 33 712 72
24 - 30 30 1,020 71
30 - 36 33 1,358 89
total 397 6,295 722

Table 6.1 Soil type and location