Nitrogen Requirements of Contemporary Cotton Cultivars.

Nitrogen (N) is often the nutrient applied in greatest quantity to cotton (Gossypium hirsutum) and the nutrient most subject to transformation in the environment. While a standard N recommendation for cotton has been 110 kg. N per Mg lint, we hypothesized that small-seeded, contemporary cotton cultivars might require less N than did those previously grown. A common experiment was done in AR, AZ, KS, MS, NC, OK, SC, TN, TX(2) for two years to determine the response of modern cotton cultivars to N rates, to evaluate the utility of pre-plant soil nitrate testing in arid and humid regions, and to assess the effect of N rates on cultivars with different sized seed. Treatments were cultivars with planting seed of different weight ranges, and four N rates, 0, 45, 90, and 134 kg/ha. Only half of the sites responded to applied N. High levels of soil nitrate (> 91 N-NO₃ kg/ha) were found a two western sites, and 45-73 kg N-NO₃/ha. was found at locations in the Mid-South. N increased plant height and number of fruiting nodes, decreased crop maturity, and increased seed weight and lint yields up to a maximum rate of 84-121 kg. total available N/ha. Considering only sites that responded to N, maximum lint yields were achieved with 90 kg total available N/ Mg lint produced. Cultivars with large and medium seed had higher yields in response N that did small-seeded cultivars. Large seed size increased fiber length, strength, fiber length uniformity and decreased micronaire. No significant interactions of seed size and N rate were found.