A field and laboratory study was conducted to determine the long-term effects of varying rates of nitrogen (N) on soil properties that affect cotton nutrition. Nitrogen was applied for cotton in the same plots for 12 years at rates of 0, 25, 50, 75, 100, 125 and 150 pounds per acre. After the twelfth crop was harvested, soil samples were collected from each plot to a depth of 36 inches in 6-inch increments and were analyzed by standard University of Arkansas soil test procedures.

Where N rates exceeded plant utilization as indicated by seedcotton yields, several soil test properties were affected significantly. The higher rates of N increased soil nitrates and organic matter and decreased pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfates. There was also a reduction in plant population where excess nitrates accumulated in the soil profile.

These results indicate that the application of excessive rates of N can cause long-term changes in soil properties that impact cotton yields and modify direct response to fertilizer.