Nitrogen (N) is often the nutrient applied in greatest quantity to cotton and the nutrient that is most chemically dynamic in the environment. While a standard N recommendation for cotton has been 50-55 lbs. N/480 lb. bale, small-seeded, modern cotton cultivars might require less N than did those previously grown. A common experiment was conducted in ten states for two years. The objectives were to determine the response of modern cotton cultivars to N rates, to evaluate the utility of pre-plant soil nitrate testing for determining optimum N application rates in arid to humid regions, and to assess the effect of N rates on cultivars with different sized seed.
At each location treatments included three locally-adapted cultivars with planting seed of different sizes, and four N rates, 0, 40, 80, and 120 lbs./acre. High levels of soil nitrate (NO3) in the top two feet of soil, > 81 lbs. nitrate nitrogen (NO3-N)/acre, were found at two western sites, and 40-65 lbs. NO3-N/acre were commonly found at locations in the Mid-South. Lint yields responded positively to fertilizer N at only 11 of 20 sites. Total N increased plant height and number of fruiting nodes, decreased relative crop maturity, and increased seed weight, lint yields, and fiber strength up to a maximum of 147 lbs. applied N + pre-plant soil NO3-N/acre.
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