Plant and yield responses to skips in upland cotton

Abstract

The objectives of this research were to study plant responses to skips in Deltapine and TAMCOT cultivars and to develop models for yield adjustment utilizing seven skip treatments in the 1979 and 1980 seasons at Texas A&M University Farm. Skips were established by removing a prescribed number of plants in the center and data were taken from plants adjoining and opposite to skips. Skips within a row had no consistent effect on height of adjoining plants. Deltapine cultivars showed significant increases in vegetative and fruiting branches beginning at a 60 cm skip; a significant response was noted in TAMCOT SP-37 at 75 cm skip. In 1980, a significant response in TAMCOT SP-37H was not detected until skip length reached 150 cm. In 1979, seed cotton yield from the 1st and 2nd plants adjacent to a skip significantly increased in both cultivars; yield responses beyond that position were inconsistent. In 1980, yield compensation was significantly only for plants immediately adjacent to skips. A significant increase was observed in plants opposite to a skip in the second year. In 1979, number of bolls produced by the 1st, 2nd, 3rd, and 4th plants adjacent to a skip increased as length of skip increased, but significance was noted only for the 2nd and 4th. In 1980, no plants in those positions showed significant increases. Number of bolls on plants opposite to skips significantly in TAMCOT SP-37H with 180 and 210 cm skips. In one-row plots 6 m long, a 25% reduction in stand significantly reduced boll numbers. Yield reduction was noted after stand loss reached 30 and 35% in Deltapine 61 and TAMCOT SP-37H, respectively. Significant yield reduction did not occur in 2 or 3-row plots in which skips were imposed in only one of the rows. The equation Y(,c) = Y(,o)/(1 + l) was used as a yield correction formula in the presence of skip(s); Y(,c), Y(,o), and l represent the corrected yield, the observed yield, and percent yield gain from a plot with skips. Yield gain models for 1, 2, and 3-row plots were developed using length of skips, yield of plants surrounding skips, and other skip variables. The 1979 models were applied to the 1980 data, and vice versa, to test their validity. A yield gain model developed from 1979 data suggested that effectiveness of replanting with stand loss of 30% or less is questionable, but 40% stand loss appears to justify replanting.