Effect of varying quantities of dicyandiamide on the utilization of nitrogen by several crops from sodium nitrate and ammonium sulphate

Abstract

Coastal Bermuda grass tolerated the highest rate (16·7 p.p.m. N) of dicyandiamide with no decrease in growth although mild toxicity symptoms were observed. The data in Tables 1 and 2 show that with a constant rate of sodium nitrate and increasing rates of dicyandiamide the yields of maize, oats and wheat gradually decreased. The effect must be direct toxicity of dicyandiamide as plants receiving ammonium sulphate were not injured to any greater extent than those receiving sodium nitrate. The author's observations are in agreement with the Coastal Bermuda grass tolerated high rates of dicyandiamide; oats, wheat, maize and cotton were moderately injured and tomatoes were severely injured by the higher rate (16·7 p.p.m. N) of dicyandiamide. With a constant rate of sodium nitrate and increasing rates of dicyandiamide the yields of maize, oats and wheat gradually decreased indicating that the toxicity of dicyandiamide was a direct injury. Visible toxicity symptoms were observed on plants receiving 6·7 p.p.m. N or more of dicyandiamide in the soil. The highest rate (16·7 p.p.m. N) caused progressive withering of leaves from the tip and subsequently depressed the growth of cotton, oats and tomatoes. However, a low content of dicyandiamide (not exceeding 15 lb./A) in nitrogen fertilizers may benefit plant growth.