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In 1985 three cotton (Gossypium hirsutum L*) cultivars (Deltapine 30, Stoneville 506, and Arizona 107) were planted on four dates (April 16, May 3, May 24, and June 18) at two row spacings (40" and 30") in large irrigated borders at the University of Arizona's Maricopa Agricultural Center in Maricopa, Arizona. Plants were observed for time of emergence, daily flowering, boll maturation period, and lint yield. A heat unit (HU) computer accumulated 5 types of HU'5 during the growing season (low/high temperature cutoffs of 55/86, 55/88, 55/90, 55/92, and 60/86 F). All 5 types of HU's related well to stages of flowering and could be used to model cumulative flowers per unit area versus HU with Gompertz curves derived from experimental data. As flowers were tagged at later dates in boll maturation studies, a decline in accumulated HU during the boll maturation period (BMP) was noted. A crude way to equalize the HU's accumulated throughout the range of BMP's in our studies was to impose an upper limit on the hourly HU accumulation rate, so that bolls maturing in warmer BMP's would not accumulate "excess" HU's. Sequential hand-harvesting of open cotton in small plots within the test area did not reveal any consistent advantage in earliness at either row spacing. Machine-picked lint yields of 40" rows showed a pronounced decline in yields with delay in planting date, but this was not found in the case of the 30" cotton. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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