Abstract
In a field experiment on cotton, ammonium sulfate was applied to give 60, 120, and 180 kg N/ha, all in winter, early spring, and late spring applications. A check treatment was included. Soil samples to a depth of 120 cm were taken from time to time, and moisture and nitrate concentrations were measured. The early spring fertilization at the two lower levels of application produced higher yields than the two other application times, with a maximum at the 120-kg N/ha level. The highest level of application induced a yield depression. The early spring application produced a nitrate distribution in the soil profile with a peak in the 20โ40 cm depth. The yield results were partially explained by the nitrate distribution in the soil profile during the early growth period. A computer program simulated well, within experimental errors, the nitrate distribution in the soil profile. It was concluded that such a program could improve considerably nitrogen fertilizer requirements and timing predictions.
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