Crop growth, light utilization and yield of relay intercropped cotton as affected by plant density and a plant growth regulator

Modern cotton cultivation requires high plant densities and compact plants. Here we study planting density and growth regulator effects on plant structure and production of cotton when the cotton is grown in a relay intercrop with wheat, a cultivation system that is widespread in China. Field experiments were carried out in 2010, 2011 and 2012 in Anyang, Henan province, China. Plant densities (PD) were 3.0, 4.5, 6.0 and 7.5 plants m−2, and growth regulator mepiquat chloride (MC) was applied in four different schedules. Plant density significantly affected cotton biomass, but MC did not. Aboveground biomass was linearly associated with plant density. Increasing plant density significantly increased crop light use efficiency, especially during the reproductive phase. This effect was attributed to a better light distribution in the canopy, resulting in higher crop photosynthesis. MC increased the partitioning to leaves, expressed as leaf/shoot ratio. Plant height and length of fruit branches were significantly reduced by MC, resulting in a more compact canopy. Maximum leaf area index was slightly lowered at higher MC dose, but MC did not significantly affect light interception. Plant density and MC showed a significant interaction effect on crop height, but not on leaf growth, biomass or lint yield. At high plant densities, 3–4 consecutive applications of MC improved plant architecture, resulting in a higher LUE and yield. Lint yields were about 10% higher with MC applied at a high cumulative dose with high plant densities compared to MC free control.