Abstract:

To solve the problems of low planting density and yield decline caused by low temperature and cold climate damage at the early stage of cotton growth in Xinjiang, we took ‘Nongda Cotton No. 4’ as the material, and adopted the split plot experiment design. Two treatments were set for the planting density in the main area: 192000 plants /hm² (M1) and 144000 plants /hm² (M2), and four treatments were set for the spraying time in the sub-area: delaying 0 days (D0), 3 days (D3), 6 days (D6) and 9 days (D9). The effects of spraying time on photosynthetic characteristics and yield of cotton under different low densities were studied. The results showed that delaying the spraying time of DPC weakened its inhibitory effect on cotton growth, gave better play to the individual plant advantage of cotton, shaped different plant types, increased the leaf area index by 9.19%-45.34%, decreased the SPAD value by 1.28%-5.03%, decreased the net photosynthetic rate by 5.18%-15.75%, and increased the yield of pre-summer bolls by 4.66%-18.53%. The decrease of planting density reduced the leaf area index by 24.42%, increased the SPAD value by 2.66%, increased the net photosynthetic rate by 5.57%, increased the boll opening rate by 8.59% 20 days after DPC spraying, increased the number of bolls per plant by 22.98%, and the consequence of the yield of the seed cotton was D3>D6>D0>D9. Therefore, under the low density of 192000 plants /hm² and 144000 plants /hm², it is suggested that the spraying time of DPC should be delayed for 3 days and 6 days respectively, so as to give better play to the advantages of individual cotton plant, and achieve stable yield.

Key words: cotton, low density, DPC, spraying time, yield