“K” Deficiencies in Corn Increase

In the past several years there has been an increasing number of potassium deficiencies reported in field corn in South Dakota and southwestern Minnesota. Recent research by Gelderman, Gerwing and Bly at South Dakota State University is looking for some answers to this problem.

Historically, the native soil potassium levels in South Dakota soils are very high, with only a small percentage of the soil samples testing medium or lower in potassium. The reports of potassium deficiency in corn have been more common in the northeastern part of the state. In many of these situations, the composite soil sample from the field is above 160 ppm, but separate samples from the affected areas has been below 100 ppm. Many of these affected areas are large enough to warrant special fertilizer treatments.

The situations where these potassium problems commonly occur are usually related to coarse textured soils, steeper slopes, areas with a shallow topsoil and wet soil conditions. There has also been more potassium symptoms observed under no-till situations compared to conventional tillage. Additional stresses such as compaction, too dry or too loose soil conditions, too wet and other nutrient problems tend to make the “K” deficiency worse.

Influence of Broadcast Potassium (KCL) on Corn
SDSU, Brookings, SD 1999-2000
K20
Rate
1999
Site A
2000
Site A
2000
Site B
2000
Site C
2000
Site D
lb/a ————— bu/a, 15% grain —————
0 99 134 127 100 81
60 112 148 122 119 86
120 124 149 137 117 83
240 122 156 134 115 80
—————- Soil K – ppm —————-
Soil K 106(M) 127(M) 152(H) 114(M) 141(H)

Research from 1999 & 2000 has shown that 30 lb/a K2O in a band or 90-120 lb/a broadcast under conventional tillage systems will maximize early growth and yield (see figure). Limited data indicates that “K” guidelines may need to be increased for soil testing 120 to 160 ppm. Research is ongoing to determine calibration for both conventional and no-till cropping systems for corn.

In the meantime, the best answer to this problem is to first identify fields in your area with this problem. In many cases, you already know which fields have this problem. Soil test the affected fields first, to determine the level of “K”. Another way to determine where these areas are is to soil test the fields in zones or grids. (This article was written with information presented at the North Central Soil Fertility Conference, November 15-16, St. Louis Missouri).