Cotton Has Modest Nitrogen Needs
July 21, 2014
Research identifies minimum nitrogen requirements to optimize yield and minimize environmental impacts
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. Large seed size was associated with increased fiber strength and decreased gin turn out. No significant interactions of seed size and N rate were found for yield. Results of this research are reported more fully in Main et al. 2013 Effects of Nitrogen and Planting Seed Size on Cotton Growth, Development and Yield. Agronomy Journal 105 (6): 1853-1859.
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