There is a narrow window of optimum nitrogen fertilizer rates for cotton production. The optimum rate varies with the year, the yield potential, and the amount of residual soil nitrogen which is available throughout the growing season. Typical rates of nitrogen fertilization vary between 75 and 200 lbs/ac, with tradition and experience being the primary method of determining the specific rate for a field.

Insufficient nitrogen will reduce lint yields and excess nitrogen can cause difficulties in defoliation, harvest, and a reduction in lint yield. Excess nitrogen can also lead to pollution of the groundwater if water is applied in excess of crop requirements. Growers typically spend between $25 and $100 dollars/ac for nitrogen fertilizer, and the development of a soil test which would assist in the selection of the optimum fertilizer rate would be beneficial from many standpoints.

Many growers use petiole sampling as a guide in fertilization, but by the time a representative petiole sampling can be obtained, water running the nitrogen fertilizer is usually the only method of application available. Therefore, a soil test for residual soil nitrogen, which could be taken early in the growing season would be of added value in determining the optimum rate of fertilizer at a time when a choice of application methods is still available.