NITROGEN-FERTILIZATION AND PLANT DEVELOPMENT OF COTTON AS DETERMINED BY NODES ABOVE WHITE FLOWER

Early maturation is very beneficial in successfully harvesting a high-quality, high-yielding cotton (Gossypium hirstum L.) crop. If harvest is delayed until inclement weather patterns are established, both yield and fiber quality may be lost. The objective of these studies was to determine the maturity differences that occur in cotton differentially fertilized with nitrogen (N). Field experiments with irrigated cotton were conducted in 1990 and 1991 in three locations to study the effects of soil applied N rates on cotton maturity as estimated by nodes above white flower (NAWF) measurements. The test sites and soils were a production field near Manila, AR, on a Dundee sandy loam (fine-silty, mixed, thermic Aeric Ochraqualfs), the Southeast Branch Experiment Station (SEBES) near Rohwer, AR, on an Hebert silt loam (fine-silty, mixed, thermic Aeric Ochraqualfs), and the Northeast Research and Extension Center (NEREC) near Keiser, AR, on a Sharkey silty clay (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquepts). Criteria used as indicators of crop maturity and earliness in these studies were the time in days after planting (DAP) and the accumulated heat units (HU) for the crop to reach NAWF=5. Increasing N rates delayed maturity at SEBES both years and at Manila in 1991 but not at NEREC either year. Differences in maturity between N treatments of 168 and 224 kg N/ha were minimal at all locations both years. Smaller differences in time for the plants to achieve NAWF=5 were observed in the cotton grown at Manila in 1990 and at NEREC both years. The smaller differences at Manila are assumed to be due to high levels of residual N from previous crops. Early-season vegetative growth was indicated by NAWF extrapolated to first flower (60 DAP or 945 HU). A trend of higher NAWF at the extrapolated first flower stage with increasing N rate was observed, but generally differences were minimal. The NAWF values at DAP=60 were lower in 1991 than in 1990 for all locations.