Nitrogen effect on position of harvestable bolls in cotton

Abstract

Nitrogen (N) affects the number, size, disposition, and distribution of cotton (Gossypium spp.) bolls. Mapping cotton plants for boll number and position may help explain yield responses to N. Cotton was planted in central Louisiana on a Norwood silt loam soil [fine‐silty, mixed (calcareous), thermic Typic Udifluvent] in 1990 and 1992 and fertilized with N at seven rates ranging from 0 to 168 kg ha^‐1 in 28‐kg increments. Plants were harvested from plots at maturity and bolls were mapped. Yield fit to a quadratic curve both years and increased with N to a maximum between 120 and 150 kg ha^‐1 and then decreased. The number of fruiting branches generally coincided with yield in response to N both years. Total boll counts increased with N to a maximum and then decreased. Most harvestable bolls were in the middle portion of the cotton plant in both years. In 1990, there were more bolls in the lower part of the plant than in the upper while the reverse was true in 1992. In 1990, the percentage of bolls at the first fruiting position was inversely related to yield, compensated in part by an increase in percentage of bolls at fruiting position three or greater. There was no effect of N on boll percentages at any fruiting position in 1992. It appears that the increase in seedcotton yields due to N was mainly attributed to an increase in the number of fruiting branches and not to a change in percentage of cotton bolls in a specific horizon or at a specific fruiting position.