Planting and irrigation termination timing effects on the yield of Upland and Pima cotton

There have been conflicting results reported about the effect on cotton (Gossypium spp.) lint yield of altering planting and irrigation termination (IT) timing. The objectives of this study were to identify a planting window (PW), on a heat unit (HU) basis, and IT timing, as a function of crop growth stage, for optimum yield potential of Upland (G. hirsutum L.) and American Pima (G. babadense L.) cotton. Two PWs of Upland 'Deltapine 90' (DPL 90), Pima 'S-6', and IT treatments were included in field experiments for 11 site-years. Planting windows were defined as PW1 and PW2 for plantings prior to and following 600 HU accumulated after 1 January, respectively. Two IT treatments were imposed for each planting. Irrigation termination in the desert Southwest generally results in cessation of growth (crop termination). The first IT treatment (IT1), was imposed to ensure full development of bolls set up to cutout, and the second (IT2) was after two additional irrigations. From covariate analysis, there was no evidence of interaction between PW and IT, indicating that these treatments responded the same across the different environments for both cotton species. There were, however, differences in lint yields among treatments. For DPL 90, PW1 IT2 yielded 83 and 97 lb/acre more than PW1 IT1 and PW2 IT2; and for Pima S-6, PW1 IT2 was 118 and 204 lb/acre more than PW1 IT1 and PW2 IT2, respectively. Early planting is necessary for optimum yield potential of full-season cotton varieties; with the greatest yield coming from early planting and termination after the development of a second fruiting cycle (PW1 IT2). However, if a reduction in input costs and the avoidance of late-season insect pests are important considerations then cotton should be planted early (300 to 600 HU after 1 Jan) and terminated at the end of the first fruiting cycle (approximately 600 HU past cutout) to maintain the lint yield potential of full-season maturity types of Upland and Pima cotton.