Crop Growth And Yield Affected By Plant Density And Mepiquat Chloride In Relay Intercropped Cotton

Relay intercropping of cotton with winter wheat is an important farming system in the Yellow River Region. However, with the shortage of labor and the rise of labor cost, the demand of mechanized harvest has become the inevitable trend of cotton production in China. Because of the high rainfall in cotton growing season and indeterminate growth of cotton, the plant structure was used to be qualitatively regulated by the application of Mepiquat Chloride (MC), But the suitable canopy structure limited the process of mechanical harvesting in this area. Therefore, it is a critical question to quantify the heterogeneous canopies in relation to different cultivation measures. Three years field experiments were conducted at the experimental station of Cotton Research Institute of the Chinese Academy of Agricultural Sciences in Anyang city, Henan province, China in2010to2012. The objectives of present study were to identify influence of plant density and use of MC on cotton yield, quality, light use, dry matter accumulation and partitioning of intercropped cotton, and to assess the distribution and light capture induced by different cotton canopies under various agronomy practice, providing the mechanisms behind overyielding in intercropped cotton systems. The main results were as follows:(1) Higher density and multiple application of MC increased lint yield in the relay intercropped cotton, which mainly derived from the changes of spatial distribution of harvestable boll. Lint yield increased40.7%when plant density increased from3.0to7.5plants m-2, and enhanced7.9%by applying MC four times compared to MC free control. Applying MC four times not only slightly increased total harvestable boll number (0.6-11.5%) in the plant, but also modified the distribution of the harvestable bolls, compared to the MC free treatment. The total harvestable boll number at lower and inside positions increased25.6%for all plant densities by applying MC four times as compared to MC-free control. Yield of harvestable bolls at low and middle fruit branches increased by on average28.6%by applying MC four times across four plant densities, comparing the MC free control; where boll density increased by on average14.3%. High plant density also increased yields and boll density from low and middle fruit branches increased74.1%and66.4%, respectively.(2) Plant density and MC produced compact canopy and improved light use in the relay intercropped cotton. Plant height was reduced by the higher dose of MC at higher density. Fruit branch length was shortened by30-50%at lower and middle positions. Specific leaf weight(SLW) decreased with a rise in plant density at lower density, but increased at plant density above6.0plants m-2with MC. Leave area index were reduced by MC, but the reduction of leaf area index was compensated at higher plant density. High density had a higher (a difference of30%) light use efficiency compared to lowest density. Applying more MC increased light use efficiency by6.5%.(3) Plant density and MC optimized dry matter accumulation and partitioning in the relay intercropped cotton."The beta growth function" was used to simulate the dynamics of cotton dry matter and quantify daily partitioning ratio in cotton growth season. Applying MC did not alter the above-ground dry matter accumulation, while MC adjusted dry matter of each organ,(decreasing dry matter accumulation of stem and increasing dry matter of fruit). Dry matter accumulation of each part increased when plant density increased from3.0to7.5plants m-2. The dry matter partitioning to fruit increased (the maximum ratio was0.53) by applying MC four times as compared to MC-free control, but the partitioning ratio of leaf and boll decreased with higher density.(4) Based on CottonXL, we explored the distribution and interception of light under different configuration and plant density. We found that strip intercropping with a relative lower plant density appeared appropriate for sufficient light interception and had more potential to capture light comparing to mono stands. In terms of light interception, currently practiced plant densities used in sole cotton crops in the Yellow River region (around4.5plants m-2) are likely suboptimal for light interception and could be increased. We also found the vertical light distribution in intercropped cotton was more heterogeneous than in a sole crop with the same number of rows, due to gaps in the canopy that allowed light penetration to deeper canopy layers. Intercropped cotton had potential to reduce boll abscission rates on lower branches and improve yield.