Dry Matter Accumulation by Upland and Pima Cotton

B. L. Unruh, J. C. Silvertooth, A. J. Steger, and E. R. Norton


Several investigations of dry matter accumulation and patterns of dry matter partitioning by Upland cotton (Gossypium hirsutum L.) under dryland production have been conducted in the southeast, but few of these types of studies have been conducted under irrigation in more arid environments, with Upland cotton. There have even been extensive investigations to compare dry matter partitioning between obsolete and improved Upland varieties. However, none of these types of experiments have been conducted with American Pima cotton (G. barbadense L.). In addition, there has been a shift in production management of cotton from scheduled operations on a calendar basis (or days after planting, DAP) to the use of heat unit (HU) accumulations to project cotton growth and development. For these reasons, we conducted a study to describe the dry matter accumulation and the partitioning into various plant parts for Upland and Pima cotton. Heat unit accumulations were used to describe (model) the accumulation and partitioning of dry matter over time throughout the development of the plant.

This study was conducted throughout the growing seasons of 1990 through 1992 at two locations in southern Arizona (six site years of data). All locations received adequate moisture via flood irrigation and N, P, and K fertility were maintained throughout, including in-season additions of N as needed (based on petiole feedback and crop monitoring). Both Upland (var. DPL 90) and Pima (var. S-6) cotton were grown each year at each location. Beginning 14 to 20 d after emergence, whole cotton plants were removed from a 1-m section of row (1-m rows) within two replications of each study. This was continued on approximately 14 d intervals until maturity. Cotton plants were then separated into stems, leaves (including petioles), and fruiting forms (mature and immature bolls). Mature bolls were separated into lint, seeds, and burs (carpel walls). The bur fraction, as denoted in the results, included squares, flowers, immature bolls, and burs from mature bolls. The dry weight of each fraction (leaf, stem, bur, seed, and lint) was determined. Cotton yields at each location were determined at maturity by mechanically picking the center four rows of each eight row plot. All plant samples were removed from the four rows which were not harvested. Basic plant measurements, including height-to-node ratios and nodes above the top white bloom (NAWB, first or second fruiting site on mainstem fruiting branches) were made, on 14 d intervals. Heat unit accumulations after planting (HUAP, 30/13 C thresholds) were obtained from weather stations at each location. Regression analyses was used to model dry matter accumulation as a function of both DAP and HUAP. A stepwise procedure was used that would not allow a variable to remain in the model unless it produced an F statistic significant at an value of 0.05 or less.

Regression analyses indicated that HUAP was equally good, and in most cases superior to using DAP to model dry matter accumulation and partitioning within both Upland and Pima cotton. The general patterns of dry matter partitioning for Upland and Pima cotton are similar. However, Upland and Pima differ in the relative amount of dry matter incorporated into reproductive (bur, seed, and lint) and vegetative (leaf and stem) structures. Pima incorporated more dry matter into reproductive structures than Upland, at least prior to peak bloom. However, from peak bloom (i.e., NAWB at 7 to 8) through cut-out (i.e., NAWB <5) Upland cotton incorporated about 83% of its dry matter compared to 70% for Pima into reproductive structures at physiological maturity. Upland was also more efficient at partitioning lint dry matter within the total dry matter of the reproductive structures. At maturity, 23% of the dry matter incorporated into reproductive structures was lint for Upland, compared to only 14% lint in Pima cotton. In summary, Upland placed more total dry matter into reproductive structures at maturity, and of the amount placed into reproductive structures, a greater proportion was incorporated into lint, when compared to Pima cotton.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1334
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998