AN ASSESSMENT OF NITROGEN UTILIZATION IN CONTINUOUS CORN (NEBRASKA)

A continuous corn rotation study was initiated in 1912 at Scottsbluff, Nebraska, on a Tripp very fine sandy loam (Aridic Haplustoll). In 1942, manuring was started on half of the plot area and has continued to the present at a rate of 27 metric tons/ha. In 1953, N fertilization of both manured and non-manured treatments began at 5 rates (0, 45, 90, 135, and 180 kg N/ha as NH(,4)NO(,3)). In the spring of 1980, depleted N-15 fertilizer N was applied. Soil samples were collected to a depth of 15 m to determine leaching losses of NO(,3)(\u27-)-N. Soil samples were also collected for the top 300 mm for characterization. Plant samples were taken at the six leaf and silking stages and at harvest to determine N uptake and N fertilizer use efficiency (NFUE). Balance sheets for 1980 and the period 1942 to 1980 were developed for both manured and non-manured treatments. Unaccounted for N losses varied from 0 to 48% of the applied fertilizer and manure N and was assumed to be primarily due to gaseous losses. Several N availability indexes were compared and the correlations with N uptake and grain yield were determined. It was determined that a model with autoclave-mineralizable N and soil NO(,3)(\u27-)-N level (1800 mm depth) was the best predictor of both N uptake ad grain yield. Approximately 89 to 100% of the laboratory derived mineralizable N value was taken up by the corn crop in 1980