Effect of Nitrogen Fertilizer on Corn Yield and Soil Nitrates

Abstract

Corn growers in southern Minnesota have become accustomed to using high rates of nitrogen fertilizer. Regardle- ss of their experience, there were still questions about proper rates for maximum yields and profits. Also, questions related to nitrate movement out of the rooting zone and possible effect on ground water were unanswered. HISTORICAL REVIEW In the 1940's, nitrogen costs were high compared to the value of corn, thus nitrogen use was unpopular. Knowledge of nitrogen use was also limited. Ammonium sulfate was a popular form at first, then ammonium nitrate became the chief form of nitrogen. During the early 1950's, anhydrous ammonia was introduced and its direct application became popular. Along with this nitrogen form came many new questions. In the 1960's, nitrogen prices dropped to as low as 3% cents per pound and rates per acre climbed accordingly. In the 1970's, shortages occurred and prices rose sharply. Recommended rates again needed study. By the late 1960's, concern was increasing over nitrogen's ·downward movement to the underground water This was· accompanied with a consistent increase in nitrogen use throughout the state. Table 1 shows that nitrogen use increased from 1,500 tons in 1945 to the present figure of over 560,000 tons.