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Influence of K on the Yield and Chemical Composition of Grasses Grown in Hydroponic Culture with 12, 50, and 75% of the N Supplied as NH₄⁺¹

The role of K in NH₄⁺ utilization by three grasses harvested at the early vegetative, late vegetative, and early heading stages of development was studied in a greenhouse hydroponic experiment. Nitrogen was supplied at 250 ppm, with 12, 50, or 75% of the N in the form of NH₄⁺ in solutions containing 50 or 250 ppm K. Orchardgrass produced the highest dry matter yield followed by bromegrass and timothy. A high ammonium source (75%) with low K (50 ppm) resulted depression of yield, reduction in tillering, increased mortality, and significant changes in the percent K, Ca, Mg, P in the plant tissue. Provision of adequate K (250 ppm) improved NH₄⁺ utilization, increased the yield of forage and reduced the content of total, protein, and nonprotein N in the tissue. Potassium reduced the accumulation of tissue N in soluble or nonprotein form. Nonprotein nitrogen was the same at the late vegetative and early heading stages as at the early vegetative stage of development. The reduced nitrogen fraction which ranged from 0.3 to 0.8% with 50 ppm K was lowered to a range of 0.1 to 0.5% with 250 ppm K. Significant interaction effects for K and percent NH₄⁺ showed that K increased the utilization of NH₄⁺ nitrogen by grass and altered the percent of each nitrogen fraction present in the tissue.

² Head, Soils and Plant Nutrition Section, (present address: Experimental Farm, Charlottetown, P. E. I.) and Chief, Analytical Chemistry Research Service.

Received for publication June 14, 1965.