Drought, high yields can lead to soil potassium deficiency
Drought in many areas of the Midwest this year could yield some surprising results in soil tests: Lower than expected levels of soil potassium.
"Potassium becomes tightly fixed between clay layers under dry soil conditions and does not become available until water moves through the soil again," says Dan Wiersma, livestock information manager for Dupont Pioneer.
And the potassium accumulated by corn plant residue from the previous year won’t be released until rainfall allows microbial breakdown of the residue and movement of the potassium back into the soil profile, he says.
Dairy farmers and their crop consultants can prevent potassium deficiencies in alfalfa and corn by calculating potassium removal by the preceding year’s crop. For example, every ton of alfalfa harvested will remove 60 lb. of potassium. So a 10-ton yield will remove 600 lb. per acre of potassium.
To replenish established alfalfa fields, potassium should be applied twice each year. The first application should occur after first cutting and the second after the last summer harvest.
"For new seedings of alfalfa, it is important to build up soil potassium to the optimum or high range before seeding because this is the only opportunity during the life of the stand to mix nutrients throughout the top soil," Wiersma says.
Corn silage will remove 8 to 9 lb. of potassium per ton and corn grain will remove 0.3 lb. of potassium per bushel. As a result, a 25 to 30 ton per acre yield of corn silage will remove 225 lb. to 270 lb. per acre; and a 200 bu. to 230 bu. per acre corn yield will remove 60 lb. to 70 lb. per acre, Wiersma says.
For corn, potassium should be applied prior to planting and then worked into the soil for optimal crop uptake.