Effects Of Planting Density With Nitrogen Rate On Yield And Fiber Quality Of Direct Seeding Cotton After Wheat Harvest,and Regulation Of Nitrogen Utilization,Plant Type And Physiological Activity

In order to clarify the effect of planting density and nitrogen rate on the yield,fiber quality and its related mechanism for direct seeding cotton after wheat harvest(DSCWH),the combined application of different planting density and nitrogen rate were designed to investigate the yield formation,nitrogen absorption and utilization,plant type and physiological activity of carbon and nitrogen metabolism.The main results were as follows.1.High planting density with medium nitrogen rate were beneficial to obtain high yield and improve fiber quality for DSCWH.Under the planting density of 12×104 plants· hm-2 with the nitrogen application of 150kg·hm-2,DSCWH was easier to achieve high yield,and the seed cotton yield reached at 4147.8 to 5119.2 kg·hm-2.The number of squares reached at 111.0 to 126.1×104·hm-2,the number of bolls reached at 87.7 to 95.3×104·hm-2,the number of fruiting nodes reached at 300.4 to 302.4×104·hm-2,and the dry weight accumulation of reproductive organs was at 1922.6 to 1955.5 kg·hm-2,which accounted for more than 50%of total dry weight.Meanwhile,the power of bud setting and boll setting were high.High planting density with medium nitrogen rate was beneficial to obtain the good fiber quality for DSCWH.The micronaire value was at 4 to 4.2,the fiber length was at 29.98 to 30.20 mm,and the fiber strength was at 29.87 to 32.18 CN/tex.Therefore,the planting density of 12×104 plants·hm-2 with the nitrogen application of 150kg·hm-2 could achieve high yield and good fiber quality for DSCWH.2.High planting density with medium nitrogen rate was beneficial to the absorption and utilization of nitrogen for DSCWH.The planting density of 12×104 plants·hm-2 combined with 150 kg·hm-2 nitrogen application was beneficial to promote the nitrogen absorption and high efficient utilization for DSCWH.Nitrogen recovery efficiency(NRE)reached at 44%to 54%,Agronomic nitrogen use efficiency(aNUE)reached at 7.16 to 8.72 kg/(kg N),Physiological nitrogen use efficiency(pNUE)reached at 15.79 to 19.16 kg/(kg N),Partial productivity of nitrogen fertilizer(NPP)reached at 21.12 to 32.00 kg/(kg N),Internal nitrogen use efficiency(iNUE)reached at 10.40 to 10.86 kg/(kg N).3.High planting density with medium nitrogen rate was beneficial to construct ideal plant type for high photosynthetic efficiency.Under high planting density with mediU1m nitrogen rate(12×14 plants·hm-2 combined with 150 kg·hm-2 nitrogen),plant height was at 72 to77cm,the increased plant height daily was the fastest at the squaring stage,which was maintained at 1.0 to 3.0cm·d-1.The ratio of fruiting nodes to fruiting branches was at 2.23 to 2.79.The fruit branch lengths for upper,middle and lower were kept at about 9 to 15 cm,16 to 20 cm and 25 to 29 cm respectively.The main stem internode diameter for upper,middle and lower were kept at 0.4 to 0.6 cm,0.5 to 0.7 cm and 0.8 to 0.9 cm,respectively.The main stem internode lengths for upper,middle and lower were kept at 2 to 5 cm,5 to 8 cm and 4 to 6 cm respectively.The internode diameters of fruiting node were kept at 4.5 to 4.6 mm,3.0 to 3.8 mm,2.8 to 3.3 mm and 2.1 to 3.0 mm respectively as the fruiting node position extension on the fruiting branch.In addition,the bending degree was the smallest,and the direction value of fruiting branches was the highest,4.High planting density with medium nitrogen rate could maintain suitable nitrogen metabolism level and high carbon metabolism intensity,which provide coordinated physiological basis of carbon and nitrogen metabolism for high yield and good fiber quality.The planting density of 12×104 plants·hm-2 combined with 150 kg·hm-2 nitrogen application was beneficial to increase chlorophyll content and free amino acid content,soluble protein content and GPT activity were kept at suitable level;and the net photosynthetic rate,stomatal conductance and intercellular CO2 concentration of functional leave were high.Regression analysis showed that there were significant linear positive correlation between the contents of chlorophyll,free amino acids and seed cotton yield,fiber length and strength respectively;showDownward parabola relationships were detected between soluble protein content,GPT activity and seed cotton yield,fiber length and strength respectively.These results indicated that high planting density with medium nitrogen rate was beneficial to maintain high carbon metabolism intensity and moderate nitrogen metabolism level for DSCWH,which provided a reasonable carbon and nitrogen physiological metabolism basis for the formation of high yield and good quality fiber.