Better Yields Without Cation Ratios

By Scout Nelson

Base saturation and cation ratios have sparked interest in crop nutrient management. These concepts suggest maintaining specific ratios of potassium, calcium, and magnesium will improve yield. However, decades of research say otherwise.

Base saturation refers to the percentage of the soil’s cation exchange capacity (CEC) occupied by key nutrients. While the idea of an "optimal" cation ratio exists, evidence doesn’t support its use for improving yield or fertilizer planning. Soil cation levels fluctuate and are influenced by factors such as nutrient application and soil type.

Potassium is the most discussed nutrient in base saturation. Some claim that a potassium base saturation below 4% means crops will suffer, but research says otherwise. In Minnesota trials, yields remained high even when potassium saturation was under 2%. Achieving 4% saturation in high clay soils is difficult and unnecessary. For example, loamy soils require very high potassium levels to meet this ratio—levels that rarely provide yield gains.

Another problem is that many soil labs overestimate CEC using the “cation summation method,” especially in high-pH soils. This leads to misleadingly low potassium saturation readings.

Current research shows that standard potassium soil tests are more effective for determining crop needs. Soil tests from mid-June showed a clear relationship between potassium levels and corn yield. High yields often occurred at 80 ppm or more in field-moist samples.

“In the end, K base saturation is just another way to look at your soil test and provides no better information than the soil test alone.”

Farmers should aim for potassium levels near 200 ppm in high clay soils and 100–160 ppm in low CEC soils instead of targeting cation ratios.

Photo Credit:gettyimages-dmytro-diedov