Effects of Mepiquat Chloride and Plant Density on Crop Growth of Intercropped Cotton

Cotton canopy structure is often determined not only by planting density and row structured (inter-)cropping but also by plant growth regulator e.g. mepiquat chloride (MC), which is widely used for control of excessive vegetative growth. The morphological growth of cotton influences crop light utilization, partitioning, and thereby biomass growth and yield. Cotton /wheat relay intercrops experiments were carried out in 2009 to 2012 to quantify the effects of MC and plant density on crop biomass growth, partitioning, canopy structure of cotton. Five MC treatments differing MC starting times from seedling to boll stages and dose, and four plant densities, e.g. 3.0, 4.5, 6.0 and 7.5 plants m^-2, were tested. The application of MC did not significantly affect dry matter production, while it was linearly increased with plant density. Applying MC increased partitioning ratio to reproductive organs over above ground dry matter, and also increased partitioning ratio to leaf over vegetative organs. However, those partitioning effects by plant density were inverse compared to MC. Plant height and length of fruit branch were significantly reduced by MC, resulting a short and compact canopy size. Application of MC and plant density significantly interacted with year. We concluded that optimising MC and PD application could achieve an adaptive canopy structure for improvement of yield, as well as for a optimal plant architecture for mechanical harvesting of cotton in intercropping system.