Yield and Fiber Quality in Relation to Mepiquat Chloride and Plant Population Density in Cotton (Gossypium hirsutum)

Mepiquat chloride (MC), a chemical regulator for modifying plant growth and architecture, is commonly used in cotton production in China. However, users have difficulties determining the correct dosage and timing of application, especially in relation to plant population density (PPD) which also affects plant growth and architecture. Studies were carried out at the Yellow River cotton area in China from 2009 to 2010, in order to find the optimal combination of MC application dosage, application timing, and PPD. Eleven MC treatments with different amount (0 to 129 g ha^-1) differed in starting and ending time of application. Four plant population densities were tested (3.0, 4.5, 6.0 and 7.5 plants m^-2). A low amount of MC (6 g ha^-1) at early stage (seedling stage) and a higher amount of MC (45, 60, 105 g ha^-1) after first flower stage did not affect cotton yield significantly. However, the application of MC at square stage significantly decreased cotton yield, regardless of whether or not it was applied at other stages, which was probably related to a severe drought during square period in both years. Increasing plant population density to more than 3.0 plants m^-2 increased lint yield. The fiber length, strength and uniformity were significantly improved by applying MC. The micronaire was significantly decreased (improved) by applying MC. Increasing plant density also significantly improved cotton fiber quality. We did not find a significant interaction between MC and PPD, while the yearly variation was significant. We conclude that cotton yield was not increased by MC application generally, but fiber quality was significant improved. Applications of MC in proper strategies with taking MC amount, PPD and climatic factors into account, is considered a desirable management tool to control crop growth for high yield and quality.