Effects of Potassium Management on Chloride Cycling and Corn Yield and Element Uptake

Corn production covers a vast area in Minnesota, and large quantities of potassium (K) fertilizer are applied to this crop each year when a need is indicated by a soil test. The most common K fertilizer is potassium chloride (KCl, 0-0-60-48Cl). With KCl, the application of large amounts of K implies the application of large amounts of chloride (Cl-). Cl- is an essential plant nutrient, but excessive soil Cl- can impact crop yields. Due mostly to increasing use of road salt, Cl- contamination of surface waters is a growing problem. However, the use of KCl as a K source potentially contributes to this issue. Any costs or benefits of applying Cl- to corn as KCl would be eliminated by substituting a non-Cl- K source such as potassium sulfate (K2SO4). To evaluate the effects of the Cl- fraction of KCl on corn crop health and soil water Cl- concentrations, nine treatments were applied to plots of DeKalb 4375 corn at the Rosemount Research and Outreach Center in Rosemount, MN: (1) a check treatment receiving no K or Cl-; (2, 4, and 6) KCl applied at 50, 100, and 150 lbs/ac K2O, respectively; (3, 5, and 7) K2SO4 applied at the same K rates; (8) liquid dairy manure applied at 150 lbs/ac K2O and 68 lbs/ac Cl-, and (9) CaCl2 applied at 75 lbs/ac Cl-. Grain yield was unrelated to treatment. Unexpectedly, the treatment receiving 100 lbs/ac K2O as KCl had higher stover dry yield than any other treatment. The concentrations of K, Cl, and S in grain were unrelated to treatment. In contrast, the concentrations of K and Cl in stover increased with their application rates. Although the application rate of S was held constant across all treatments except the manure treatment by applying gypsum (CaSO4) as needed to bring the rate to 51 lbs/ac S, stover concentrations of S increased with the application rate of K2SO4. Results for grain and stover element uptake, considered separately, were similar to those for their respective element concentrations, except that high stover yield in the treatment receiving 100 lbs/ac K2O as KCl resulted in a significant quadratic response for K and Cl uptake. Elemental uptake into grain and stover combined showed similar patterns to those seen in stover alone, except that combined S uptake was unrelated to treatment. Soil water Cl- concentrations at a depth of six feet were unrelated to treatment. In contrast, end-of-season soil K to a depth of six inches and soil Cl- to a depth of two feet were related to the application rates of K and Cl-, respectively. These results suggest that the Cl- supplied by KCl was neither beneficial nor harmful to the corn crop in this study, and that, in this dry year, Cl- did not leach to a depth of six feet into the soil. Furthermore, The S content of K2SO4 was apparently more available to the crop than that of gypsum.