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Abstract
Measurement of total and mineral nitrogen (N), resulted by the presence of soil organic matter, would make the more precise determination of N fertilization possible with respect to the amounts of N absorbed by crop grains. Such a test requires a wide range of soil properties and observations. Accordingly, in a three-year experiment, grain N uptake and soil total and mineral N were determined using different analytical methods (standard laboratory and the N-Trak quick method). The other experimental treatments consisted of sampling time (seeding and postseeding where plants were about 30 cm tall), sampling depths (0–30 and 30–60 cm) as well as the condition of samples (wet or dry). Using regression equations the effects of N fertilization and soil total and mineral N on the uptake of grain N was investigated. Accordingly, the proposed N test predicted the optimum N fertilizer amounts of 236 to 271 kg ha−1 for corn production.
ACKNOWLEDGMENTS
We would like to thank very much Peter, Khosro, Ken, Philip and Mark for their great help in the field and laboratory.