Greenhouse evaluation of potassium application on selected soil and plant properties utilizing four Virginia ultisols

Three crops of corn (Zea mays L.) were grown on four Coastal Plain soils in a greenhouse study to determine the effects of increasing rates of Kon corn growth, elemental composition of corn tissue and soil nutrient levels. Plant height and production of dry matter were measured to determine the effect of K application on corn yield. Plant tissue concentrations of Ca, Mg and K were determined, as were NH₄OAc extractable soil Ca, Mg and K.

Potassium, as KCl, was applied at rates of 0, 100, 200, 300 and 400 ppm K to the first corn crop. Potassium application of 100 ppm increased corn yield on the Kenansville and Uchee soils, but no further increase or decrease in yield occurred at higher K rates. Increasing K rates caused an increase in plant tissue Kand a simultaneous decrease in plant tissue Mg. Plant tissue Ca was also reduced in plants grown on the Kenansville and Uchee soils. Magnesium deficiency symptoms were observed on corn plants grown at K rates greater than 100 ppm Kon the Goldsboro, Kenansville, and Uchee soils. Magnesium deficiency was confirmed by plant tissue analysis which revealed plant Mg levels as low as 0.07% on the Goldsboro soil.

A second corn crop was grown in the previously amended soil. Results were similar to the first crop with yield increasing with the application of 200 ppm K on the Kenansville and Uchee soils. Yields did not significantly increase or decrease at higher K rates. Plant tissue K increased with increasing K rates with a simultaneous decrease in plant tissue Mg in plants grown on three of the four soils.

Potassium, as K₂SO₄•2MgSO₄, was applied to a third corn crop at the same K rates as the first crop (ie. 0, 100, 200, 300, and 400 ppm K). Application of K₂SO₄•2MgSO₄ also supplied Mg at rates of 0, 60, 120, 180 and 240 ppm Mg.

Plant yield increased at the 100 ppm K application rate on the Kenansville and Uchee soils, but decreased at rates of 300 ppm Kor greater on the Kenansville and at rates of 200 ppm Kor greater on the Uchee soil. Plant tissue K increased in plants grown on all soils, and Mg increased in plants grown on three of the four soils. However, Ca levels in plant tissue were reduced with increasing Kand Mg application in plants grown on all soils. Reduction in yield on the Kenansville and Uchee soils coincided with Ca levels of 0.3% or less. These Ca levels are considered to be insufficient for proper plant growth and decreases in plant yield were attributed to Ca deficiency. Excessive rates of K as K₂SO₄•2MgSO₄ (300 and 400 ppm K) were necessary to induce Ca deficiency.