Moisture Deficit Effects on Cotton Lint Yield, Yield Components, and Boll Distribution

Understanding how moisture deficit stress alters cotton (Gossypium hirsutum L.) reproductive growth and yield component development would provide insight into the current yield stagnation problem plaguing U.S. cotton producers. Objectives were to document the effects of moisture deficit stress on reproductive growth, lint yield, yield components, boll distribution, and fiber quality. Field studies were conducted from 1998 through 2001 utilizing eight diverse genotypes, which were grown under both dryland and irrigated conditions. Weekly white bloom counts, nodes above white bloom, lint yield, yield components, end-of-season plant mapping, and fiber quality data were collected. Genotypes responded similarly to the two soil moisture regimes for all of the parameters evaluated. Irrigation delayed cutout, the slowing of vegetative growth due to strong reproductive demand for assimilate, an average of 6 d. This delayed maturity enabled those plants to sustain flowering later in the growing season compared with dryland plants. During the years when sufficient moisture deficits occurred, the lint yield of dryland plants was reduced 25%, primarily because of a 19% reduction in number of bolls. Irrigated plants produced more bolls at higher plant nodes (>Node 10) and at the more distal positions (≥2) on the sympodial branches than did the dryland plants. Irrigation did not affect most fiber traits, but 3 out of 4 yr of irrigation produced approximately 2% longer fiber. Production of more bolls higher up the plant and further out the fruiting branch with irrigation indicates that these areas on the plant are where high yields need to be stabilized.