In cotton production, a plant growth regulator is a management tool used to limit excessive cotton (Gossypium hirsutum L.) vegetative growth, but over-application can promote early cut-out and potentially decrease yield. Specific information on how different plant growth regulator application strategies perform in a conservation tillage system is limited. The objective of this research was to compare how different plant growth regulator strategies affected plant growth and yield across two N rates in a conservation tillage system during the 2006 to 2008 growing seasons in Alabama. Treatments were arranged in a randomized complete block design with a split-plot treatment restriction and four replications across five site-years. Main plots were two N rates (101 and 134 kg N/ha), and subplots were six mepiquat chloride application strategies. The 134 kg N/ha rate increased plant height two out of three years, but the most effective strategy to control plant height varied across growing season. No clear application strategy was identified that consistently minimized height to node ratios. Whole plant biomass decreased with a high mepiquat chloride application rate and late application, but only for one site-year out of five. Yield responses to mepiquat chloride application were inconsistent across growing seasons and varied from a 16% yield decrease to a 9% yield increase. Variable environmental conditions occurred across growing seasons that likely resulted in inconsistent cotton yield response to mepiquat chloride application. Although variable, our results suggest that cotton, grown in a conservation system, responded comparably to mepiquat chloride applications in conventional systems.
