ABSTRACT

Cotton (Gossypium spp.) was planted in 1990, 1991, and 1992, respectively, to determine the effect of nitrogen rate on crop growth rate, yield, and boll characteristics when produced on a Red River alluvial soil (Norwood silt loam, pH near 8.0) in central Louisiana. Seven rates of N ranging from 0 to 168 kg/ha in 28-kg increments were applied prior to planting in a randomized complete block design. The optimum N rate in 1990 was 124 kg/ha. Relevant results were not obtained in 1991 due to rainfall. The optimum rate in 1992 was 140 kg N/ha. The average optimum rate for the two representative years was 132 kg/ha which is nearly twice that commonly recommended. Increasing N rates resulted in higher concentrations of N, Ca, Fe, Mg, Mn, and Na. There was a clear decrease in concentration of S as N increased above 56 kg/ha. Boron and potassium decreased by over 40% between the lowest and highest N rates. The effect of N on Zn was significant but inconclusive. There was no effect of N rate on Al, Cu, Ni, or P.