Machine-picked Cotton Population Shaping and Yield under Mulch Drip Irrigation with Different Spatial Distribution of Water and Nitrogen

【Objective】 The spatial regulation of water and nitrogen has great benefits to shape the ideal machine-picked cotton population. 【Method】 Xinluzhong 66 was taken as the tested variety, the split-zone test design was adopted with three drip irrigation belt layouts of 2,3 and 5（marked as G₂, G₃ and G₅, respectively） in the main zone and four nitrogen fertilizer topdressing strategies of 0, 238, 317 and 396 kg/hm^2（marked as N₀, N₁, N₂ and N₃, respectively） in the sub -zone. Effects of different treatments on population index, leaf area index, dry matter accumulation, yield and agronomic effects of N fertilizer in cotton growth period were analyzed. 【Results】 Nitrogen application rate had a significant effect on the molding of machine-picked cotton population, and the number of drip irrigation belt arrangement had a significant effect on stem diameter and the height of fruit branch beginning. The leaf area index（LAI） of machine-picked cotton was increased by increasing the number of tubes and nitrogen application, and was significantly affected in the middle and late growth period. Above-ground dry matter accumulation, boll number per plant, boll weight per plant, lint percentage and seed cotton yield of machine-picked cotton showed a single-peak trend with the increase of nitrogen application rate, and had the maximum value at N₂ level. The interaction between the number of drip irrigation strips and nitrogen application rate had significant effects on the initial height of fruit branches, dry matter accumulation at the beginning of boll opening and yield. 【Conclusion】 Machine-picked cotton population shaping and yield are significantly affected by spatial regulation of water and nitrogen. As for “10 cm-66 cm-10 cm-66 cm-10 cm” machine-picked cotton mode, the recommended combination of water and nitrogen is G₅N₂. Considering the planting cost, G₃N₂ combination can also be selected, but the irrigation frequency should be appropriately increased and the irrigation quota should be correspondingly reduced.