Distribution and Nitrification of Anhydrous Ammonia in a Nicollet Sandy Clay Loam

Abstract

Abstract A roughly cylindrical distribution of NH 3 centered at the knife openings was found when anhydrous ammonia was applied with a field applicator at a depth of 4 inches, by sampling an 8‐ by 8‐ by 2‐inch cross section perpendicular to the applicator row. NH 4 ‐N, NO 3 ‐N and pH were determined on each 1‐inch square subsample. NH 4 ‐N decreased from a maximum concentration of 1,300 to 2,000 ppm. (pH 9.5) at the center to less than 200 ppm. (pH 8) in the area about 1½ inches away from the center of the retention zone. After 2 weeks, the maximum concentration of NH 4 ‐N was about 800 ppm. (pH 8.8) in the center decreasing to less than 100 ppm. (pH 7.0) in the area about 2½ inches away from the center of the retention zone. Nitrification initially proceeded more rapidly in the outside 2 inches of the retention zone where the concentration of NH 4 ‐N was less than 400 ppm. Later in the original ammonia retention zone, nitrification appeared to be limited by low pH and nitrate concentration; at the end of 4 weeks the pH had decreased to a value of 5.0 to 5.5 and NO 3 ‐N had increased until 200 to 300 ppm. were present. Ammonia applied in November just prior to freezing showed little nitrification by March. Rapid nitrification began in mid‐April when soil temperatures rose above 40° F. Approximately 8 weeks were required to completely nitrify the ammonia.