effects of base and topdressing nitrogen fertilizerswith different ratios on the physiological characteristics of functional axial leaves and yield of hybrid cotton

To investigate the effects of base and topdressing nitrogen fertilizers on the photosynthetic biochemical characteristic of functional leaves of hybrid cotton in Nanjiang,fertilizers with three different compositional ratios( base vs. topdressing fertilizers of N1,N2,and N3 were 0∶ 10,2∶ 8,N3,and 4∶ 6,respectively) were employedusing Zhaofeng 1 and Lumianyan 30. Results showed that when equal amounts of total nitrogen were applied,with the reduction of topdressing nitrogen,the physiological indexesof the main functional stem leaves tended to increase first and then became decreased. According to additional analysesof the related indexes,zero base fertilizer treatment had significantly reduced the LAI and SPAD values of the main functional stem leaves,and the activities of nitrate reductase and soluble proteins,peak values of which appeared 20 daysearlier,resulting in an earlysenescence process. With N3 treatment,SPAD value,NR activity and SP content at the post-flower-boll stagehad decreased quickly,reaching the levels of 31. 08% ~ 32. 04%,57. 12% ~ 74. 55%,and 78. 53% ~80. 79%,respectively. Additionally,at the boll opening stage,the photosynthetic rate was reduced approximately 66% fromthe maximum,minimizing the transfer of the photosynthetic products to the bolls. It was further found that when Zhaofeng 1 and Lumianyan 30 were treated with the 2∶ 8 fertilizer,the indexes of the main functional stem leaves seemed to be balanced,increasing 5. 04% ~25. 44% of leaf chlorophyll content,improving the performance of photosynthesis,extending the functional period of leaves,postponing senescence of the leaves at the middle and the lower portions,and enhancing the weight per boll and the lint yield to 4 389. 89 kg·hm- 2. Lint yield of Zhaofeng1 was lower than that of Lumianyan30,which was found to be significantly different with N2 and N3 treatments but not N1.