EFFECT OF SOURCE AND RATE OF N AND RATE OF K ON THE YIELD AND CHEMICAL COMPOSITION OF ALFALFA AND ORCHARDGRASS

Abstract

Alfalfa and orchardgrass were grown in hydroponic culture in the greenhouse with nutrient solutions containing K at concentrations of 10, 50, and 250 p.p.m., N at 50 and 250 p.p.m. with 12% and 75% of the N supplied as NH₄⁺ in a 3 × 2 × 2 factorial design. Alfalfa yields were higher with the 12% than with the 75% NH₄⁺ source of N. At 50 p.p.m. N, orchardgrass yields were higher with the 75% NH₄⁺ source but 12% NH₄⁺ was better at 250 p.p.m. N. The severe reduction in yield which occurred at 10 and 50 p.p.m. K with the 75% NH₄⁺ source (particularly with 250 p.p.m. N) was alleviated by the 250 p.p.m. rate of K. Yield was increased fivefold by increasing the K concentration from 10 to 250 p.p.m.The N and P content of the tissue, which was higher with the 75% NH₄⁺ source of N, decreased with increasing rates of K. Percent of total protein, non-protein, and organic (reduced) N fractions in the tissue were higher with the 75% NH₄⁺ source and only nitrate N was higher with the 12% NH₄⁺ source. While an increasing K supply generally caused a decrease in the total protein, non-protein, and organic N fractions, the total yield of protein N from three forage cuts was highest with 250 p.p.m. K for both sources of N. High rates of N, unless accompanied by adequate potassium, caused an accumulation of soluble nitrogen which reached a high of 1.95 and 2.28% for alfalfa and orchardgrass respectively with the 250 p.p.m. N, 10 p.p.m. K treatment.