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Influence of Sample Size on Cotton Shoot Nitrogen Accumulation: Lint Yield Ratios

P.G. Hunt, T.A. Matheny and P.J. Bauer


Accurate samples of cotton vegetation and nitrogen content are important for investigation of both erosion and nitrogen management. The objectives of this investigation were to a) determine if cotton dry matter was upwardly biased and highly variable in small samples and b) determine if the shoot nitrogen per 100 kg of lint (NLR)values were affected by sample size. Three cotton cultivars were planted in four replications on 13 May. Each entire subplot (9.5 m2) was harvested after sampling by four techniques 1) four randomly selected plants (4RP); 2) randomly selected 0.3 meter of row (0.3-m); 3) randomly selected one meter of row (1-m); and 4) randomly selected two meters of row (2-m). Shoot dry matter for the whole plot yielded 7.2 Mg ha-1, and lint yields were good, >1.35 Mg ha-1. Cotton shoot dry matter was significantly overestimated by both the 4RP and 0.3-m methods, but not by the 1- and 2-m methods. The whole plot mean for the NLR was 10.1. The NLR for the 4RP and 0.3-m methods were significantly greater than the whole plot while the 1- and 2-m methods were not significantly different. A 1-m sample would seem to be necessary, and a 2-m sample is likely desirable to reduce both the bias and the variation. These NLRs are substantially lower than those generally reported for nonirrigated cotton. Nonetheless, these NLRs are in line with data that suggest 1.6 Mg ha-1 (3-bale/acre) cotton requires less than 200 kg ha-1 of shoot-accumulated N.

Reprinted from Proceedings of the 1998 Beltwide Cotton Conferences pp. 675 - 678
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998