Row spacing effects on the canopy light extinction coefficient of upland cotton

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Steglich, Evelyn Marie
Texas A&M University
agronomy.; Major agronomy.
thesis / dissertation description
Field experiments were conducted in 1998 and 1999 at the Stiles Farm, Thrall, Texas and the Blackland Research Center, Temple, Texas, respectively, to characterize the influence of row spacing, plant density and time of day on the extinction coefficient (k) in cotton (Gossypium hirsutum). Treatments consisted of four row spacings (0.19-m, 0.38-m, 0.76-m, and 1.00-m) and four plant densities [148, 222, 296, 445 (1998) and 371 (1999) thousand plants ha-1] with each treatment replicated three times. Experimental design was a split-plot randomized complete block design. Main plots were row spacings, and subplots were plant densities. Light interception measurements were taken on square meter areas approximately two weeks apart beginning at pinhead square at 0900h, 1030h and 1230h. Above-canopy-incoming, above-canopy-reflected and below-canopy-transmitted photosynthetically active radiation were measured on each date and time. Leaf area index, plant height and main stem node number (1999) were also recorded for each area measured. Plant density had no influence on leaf area indices, plant height, main stem node number, or k during both years. Time of day showed to significantly influence the extinction coefficient. Light extinction coefficient values were lowest at solar noon, suggesting that daily light interception based solely on solar noon values may underestimate the total daily light interception of a canopy. Results from 1998 indicated that the ultra-narrow row spacings (0.19-m) had greater leaf area indices throughout the season. In 1999 the ultra-narrow row spacings (0.19-m) accumulated LAI faster than the wide rows (>0.76-m), but as the season progressed the wide rows surpassed the narrow rows due to interplant competition in the narrow rows. Row spacing had no effect on the number of main stem nodes per plant. Row spacing had a significant influence on k during both years. In 1998 the extinction coefficient increased slightly as the row spacing increased, contradictory to previously published material. However, in 1999, similar to other estimations of k for cotton, the extinction coefficient increased as row spacing decreased.