| Summary: | In 2005 only did statistical analysis indicate a significant cotton density effect with respect to soybean yield. Means separation analysis indicated a lower soybean yield for only the highest cotton density of 5.25 plants /row m-1 when compared to other cotton densities. In 2004 and 2005, statistical analysis indicated no significant cotton interference interval effect on soybean height nor yield in 2004. A significant linear relationship between cotton interference period and soybean yield was observed in 2005. Based on best fit regression equation, a soybean yield reduction for an interference interval of 8 wk would equate to a minimal yield decrease of only 3.3% when calculated from the intercept value.
With respect to cotton height, a linear relationship with soybean density was observed both years in Louisiana but not in North Carolina. Based on results at St. Joseph in 2004, height reductions of 6, 3, 1.2, and 0.6% can be expected following season-long competition with soybean densities of 3.3 plants/row m-1, 1.6 plants/row m-1, 0.7 plants/row m-1, and 0.3 plants/row m-1, respectively. Based on 2005 St. Joseph results, expected height reduction was 0, 10.6, 11.3, and 7% for these respective densities. At North Carolina, there was not a significant height effect was not observed. Based on results at St. Joseph in 2004, seed cotton yield reduction of 30, 15, 6, and 3% can be expected at the respective densities. Based on 2005 Louisiana and North Carolina results, expected yield reduction for these densities were similar at 37, 19, 7, and 4% and 21, 11, 4, and 2% respectively. At St. Joseph in 2004, a significant linear relationship between interference period and cotton height was observed. Soybean interference for 4 and 8 wk would result in an expected cotton height reduction of 3 and 5%, respectively. Based on 2004 results in Louisiana and North Carolina, a seed cotton yield reduction greater than 4% can be expected beginning with 4 wk soybean interference, however, in 2005 in Louisiana a similar yield reduction can be expected beginning at 2 wk.
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