Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 1999
Publication Date: N/A
Interpretive Summary: Accurate estimates of cotton dry matter accumulation and nitrogen content are important for many reasons including soil and water management aspects of cotton production. However, the resources necessary to measure these values are costly. Therefore, it is important to know the cotton sample size necessary for acceptable estimates of cotton dry matter, lint yield, and shoot nitrogen. Three cotton cultivars were grown in a typical Coasta Plain soil. Cotton plots were sampled in different ways, and the remainder of the whole plot was subsequently measured. The methods of sampling were then compared to the values obtained by the more time consuming and costly measurement of the entire plot. In plots with 12 meters of row, a sample size of one meter of row was necessary for reliable results.
Technical Abstract: Accurate estimates of cotton (Gossypium hirsutum) dry matter accumulation and nitrogen content are important for many reasons including soil and water management aspects of cotton production. The objective of this investigation was to determine the cotton sample size necessary for acceptable estimates of cotton dry matter, lint yield, and shoot nitrogen per 100 kg of lint ratio (NLR) values. Three cotton cultivars ('DeltaPine 90', 'DeltaPine 5415', and 'Stoneville 474') were planted in 9.3 m**2-subplots on 13 May 1997 in an Eunola loamy sand (fine-loamy, siliceous, thermic Aquic Hapludult). Split plots were four sampling dates. Split-split plots were four sampling techniques [a) four randomly selected plants (4RP), b) 0.3 meter of row (0.3-m), c) one meter of row (1-m), and d) two meters of row (2-m)]. Each entire subplot was harvested on each sampling date after sampling by the four techniques. Shoot dry matter for the whole plot was 7.2 Mg/ha, and lint yield was 1.46 Mg/ha. Cotton shoot dry matter and NLRs were significantly overestimated by both the 4RP and 0.3-m techniques, but not by the 1- and 2-m techniques. The whole plot NLRs varied with cultivar from 9.1 to 11.4. The earliest maturing cultivar, Deltapine 90, had the lowest NLR and the latest cultivar, Stoneville 474, had the highest NLR. Accurate estimates of cotton dry matter accumulation and nitrogen content will likely require 1-m samples, and 2-m samples should further improve precision. The NLRs were in line with data (NLR < 15) that suggest 1.6 Mg/ha (3-bale/acre) cotton lint yields can be achieved with less than 250 kg/ha of shoot-accumulated N.