Abstract
Seasonal growth characteristics and shading ability of six sugarcane varieties were compared during the second production year. For each variety, trend analysis of data showed a significant linear trend. Differences in shoot emergence among the varieties were observed beginning in early April and as the season progressed, shoot production and shoot height increased for ‘L 97-128’, ‘Ho 95-988’, ‘L 99-226’, and ‘L 99-233’ but lagged for ‘HoCP 96-540’ and ‘LCP 85-384’. Beginning in mid-April ground cover increased most rapidly for L 99-233. In late May ground cover was around 60% for LCP 85-384 and HoCP 96-540; around 70% for L 97-128, Ho 95-988, and L 99-233; and was approaching 90% for L 99-226. Sugarcane canopy height across the growing season was consistently greater for L 97-128 and L 99-233 and averaged 21% more than for the other varieties in early June and 15% more in mid-July. Based on photosynthetically active radiation (PAR) data collected in the row middles, sunlight in the sugarcane canopy at ground level was reduced an average of 61% in early June for L 97-128 and L 99-226 compared with 29% for LCP 85-384 and HoCP 96-540. By late July PAR reduction was equal and averaged 90% for L 97-128, Ho 95-988, L 99-226 and L 99-233 compared with 78% for LCP 85-384 and HoCP 96-540. Shade studies were conducted in fields with natural infestations of bermudagrass and johnsongrass using enclosures (0.61 x 0.61 x 0.61m) covered with shade cloth providing 30, 50, 70 and 90% shade. At 55 days, bermudagrass ground cover under full sunlight was 88% compared with 10% for 90% shade; above ground biomass for 90% shade was reduced 95%. Exposure to 90% shade for 35 days decreased johnsongrass plant population 86% and above ground biomass 90%. With 30% shade, dry weight of bermudagrass was reduced 30% and johnsongrass biomass was reduced 45%. Based on this research the varieties L 97-128, L 99-226, and L 99-233 should be competitive with bermudagrass and johnsongrass. In contrast, the open canopy of HoCP 96-540 would be conducive to weed reinfestation.
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