Effect Of Planting Densities On Cotton Yield Formation And Water Use Efficiency Under Limited Drip Irrigation

Water shortage is one of the major problems in cotton（Gossypium hirsutum L.）production in north-western in China. The aim of the study is find a new ways of water-saving and high-yield of cotton. Xin luzao 45 hao was used in this study. The planting method is drip irrigation under mulch. To explore the effects of drip irrigation patterns and planting densities on agronomic characters, canopy structure, canopy photosynthetic characteristics, dry matter production performance, yield, fiber quality and water use efficiency, split-plot experiment with two drip irrigation patterns(conventional drip irrigation(I₅₀₀), limited drip irrigation(I₄₂₅) and three levels of planting densities 12×104(D₁₂), 24×104(D₂₄), 36×104(D₃₆) was designed. The results showed that :1. The effect of drip irrigation patterns and planting densities on agronomic traits is significant. Limited drip irrigation pattern declined cotton plant height significantly, but has no effect on the number of main stem leaf, branch number and reproductive organ. Plant height, the number of main stem leaf, branch number and reproductive organ significantly decreased when planting density increasing. I₅₀₀D₁₂ had the maximum values of all above parameters.2. Compared with conventional drip irrigation pattern, limited drip irrigation pattern had higher LAI, increased the MTA and DIFN. All these result in light absorption rate increasing at the middle and below of canopy structure. In conventional drip irrigation pattern, the maximum LAI and LIR were observed in middle density. In limited drip irrigation pattern,high density had the maximum values of all above parameters. It indicated that I₅₀₀D₂₄ 、I₄₂₅D₃₆ can improve light absorption rate at the middle and below of canopy structure.3. Compared with conventional drip irrigation pattern, limited drip irrigation pattern had higher canopy apparent photosynthetic rate（CAP）, and can inclined the canopy respiration rate（CR）. CAP and CR increased when density increase. The interaction of drip irrigation pattern and planting density showed, before full boll stage, I₅₀₀D₃₆ had maximum CAP, the next was I₅₀₀D₂₄、I₄₂₅D₃₆; after full boll stage, I₅₀₀D₂₄、I₄₂₅D₃₆ had higher CAP. I₅₀₀D₃₆ had maximum CR during the whole growth stage. It indicated that I₅₀₀D₂₄、I₄₂₅D₃₆ had higher canopy photosynthetic capacity.4. Compared with conventional drip irrigation pattern, limited drip irrigation pattern increased the net assimilation rate（NAR） from full flowering stage to boll opening stage significantly. At I₅₀₀, the maximum crop growth rate（CGR）, boll growth rate（BGR）, NAR,total dry matter weight（TDW）, boll dry matter weight（BDW） and ratio of reproductive to vegetative organs（RVR） were observed under D₂₄. At I₄₂₅, all of the above parameters significantly increased with increasing planting density, and the maximum was D₃₆. The regression analysis showed that I₅₀₀D₂₄、I₄₂₅D₃₆ had the maximum the maximum theory valuesof biomass accumulation（Wm） and the fastest growth rate（Vm）, and the minimum rapid growth duration（T）. It showed that higher Wm and Vm, less T contributed to formation of higher dry matter.5. At I₅₀₀, the number of boll and yield increasing at first and then decreasing when density increasing, middle density had the maximum values. At I₄₂₅, the number of boll and yield increasing when density increasing, high density had the maximum values. Middle density in conventional drip irrigation and high density in limited irrigation had maximum the number of boll and yield. The other parameters of fiber quality of different treatments had no significant difference except that limited drip irrigation pattern increased micronaire.6. Limited drip irrigation pattern enhanced the water use efficiency（WUE） and irrigation water use efficiency（IWUE）. Planting density had no significant effect on WUE and IWUE. The interaction of drip irrigation patterns and planting densities showed, I₄₂₅D₃₆ had the maximum WUE and IWUE, the minimum was observed in I₅₀₀D₁₂. The seed yield and IWUE had significant positive correlation with BN and RVR. There was a significant positive correlation between IWUE and NAR. Therefore, it can achieve the goal of water-saving and high yield by high boll number per area, resulting from keeping large crop growth rate and capability of dry matter production.