Effects Of Irrigation Methods And Row Spacing Configuration On Photosynthetic Production And Defoliation Of Machine-harvested Cotton Under Mulch Drip Irrigation

In recent years,Xinjiang has achieved high and stable cotton yield after the combination of mulch drip irrigation and high density.However,the difficulty of cotton defoliation after high-density planting led to a higher impurities content by machine-harvest,which seriously reducing the quality of cotton fiber and unfavorable to textile processing.The low efficiency of water use efficiency in actual cotton production and the current water stress in farmland restrict the sustainable development of cotton in Xinjiang.In order to improve cotton quality and promote the development of machine-harvest cotton,two irrigation methods（one film with three tapes,MD-T₃ and one film with two tubes,MD-T₂）with four row spacing configurations(RS₆₆₊₁₀H,RS₇₆H,RS₇₆L and RS₆₆₊₁₀L)were used to study soil water distribution and water consumption patterns,population canopy structure characteristics,photosynthetic production capacity and changes in cotton defoliation and deflocculation from the perspective of efficient utilization of light,heat and water resources and suitable for mechanical harvesting.Through the research,we have screened out the most suitable field management mode for machine-harvest cotton to improve the efficient utilization of light,heat and water resources,which could provide theoretical basis and practical guidance for the further sustainable development of machine picking cotton.The main results of this paper are as follows:1.The effects of irrigation method and row spacing configuration on cotton growth and fertility processes.Our results showed that compared to MD-T₃,the same row spacing in MD-T₂ significantly accelerated the fertility process（especially after the three-leaf stage）and shortened the total fertility period by 4-9 d.However,after the first water（early June）irrigation,the growth rate of cotton plant height and main stem leaves in MD-T₂ was less than that of the same row spacing in MD-T₃,and the total boll number per unit area was significantly reduced by significantly lowering the boll formation rate of inner and outer boll in the middle and upper part of cotton（above the fourth fruiting branch）in the later stage of fertility,resulting in significantly lower seed and lint yields than the same row spacing in MD-T₃.Under the same irrigation method,low-density planting showed faster growth development after the three-leaf stage than high-density planting,especially in MD-T₃ where RS₇₆L shortened the total reproductive period by 4-5 d compared to RS₆₆₊₁₀H and RS₇₆H.And it also increased the boll setting rate at the first fruit node on the 1st-2nd and 7th-10th fruit branches and at the 2nd fruit node on the 1st-6th fruit branches in the middle and lower canopy;the increase in cotton boll weight compensated for the lack of total boll number and achieved the same yield level as RS₆₆₊₁₀H.2.The effects of irrigation method and row spacing on cotton canopy structure and population photosynthetic productivity.It was shown that the treatments in MD-T₂ improved the light exposure conditions of the lower and middle canopy leaves,but the lower LAI and the rapid decline of CAP in late reproduction led to a decrease in the population photosynthetic production capacity,which eventually limited the accumulation of cotton boll biomass and reduced the yield of machine-picked cotton,compared to the same plant spacing in MD-T₃.The reason why RS₇₆L obtained the same yield level as RS₆₆₊₁₀H in MD-T₃ in this research was mainly because:（1）the suitable LAI range and reasonable spatial distribution during the critical reproductive period ensured a higher FIPAR while increasing the DIFN in all parts of the canopy,improving the light interception rate and photosynthetic capacity of the lower and middle canopy leaves,which in turn improved the photosynthetic capacity of the population;（2）Higher CAP in the lower and middle canopies during late growth increased the proportion of boll biomass in the lower and middle canopies,which in turn increased the overall boll biomass,and significantly increased fiber length and break ratio strength and decreased the clonal value in the lower and middle canopies of cotton.Therefore,the one film with three tapes（conventional irrigation）and low-density equal row spacing can improve the photosynthetic capacity of the group by optimizing the canopy structure and improving the light distribution,thus maintaining a high yield level,and has the potential to improve the boll fiber quality in the lower and middle canopies.3.The effect of irrigation method and row spacing configuration on the load capacity of cotton leaves and roots.The results showed that cotton in MD-T₃ increased leaf loading in late reproduction relative to the same row spacing in MD-T₂,which lied in the higher chlorophyll content and leaf photosynthetic rate in each canopy position at late reproduction stage,thus maintaining a higher CAP_leaf.Compared with MD-T₂,the same row spacing in MD-T₃ significantly increased root length,root surface area,root mass and population root biomass in each soil layer,but reduced root shoot ratio therefore increased root load capacity.Under the same irrigation method,especially in MD-T₃,RS₇₆L significantly increased the root load carrying capacity in the middle and late growth stages;In addition,the higher leaf photosynthetic capacity and CAP_leafat the middle and late growth stages ensure the photosynthetic production capacity of leaf population,and improve the leaf area load capacity and leaf area boll load at the middle and late growth stages,compare to the higher-density plantings of RS₆₆₊₁₀H and RS₇₆H.4.Effects of irrigation method and row spacing configuration on water consumption and water use efficiency of cotton in the field.The distribution of water in the soil was altered by the irrigation method,which also affected the water consumption pattern,transpiration rate and water use efficiency of cotton.Compared with MD-T₃,the irrigation methods of the same row spacing in MD-T₂ were arranged in the middle of wide rows about 40 cm away from the cotton rows,and because of the low irrigation method,resulting in lower aboveground LAI level,which could not get high yield,although it significantly reduced transpiration water consumption and obtained higher WUE during the whole reproductive period.The ability of RS₇₆L under MD-T₃ to improve WUE with high cotton yield is due to the significant reduction in soil water consumption in the 20-80 cm soil layer at a horizontal distance of 19-38 cm from the cotton row compared to RS₆₆₊₁₀H and RS₇₆H,and the reduction in CAT and DWCI of the cotton population,which saved50-60 mm and 47-64 mm of soil water consumption during the whole reproductive period compared to RS₆₆₊₁₀H and RS₇₆H,respectively.The soil water consumption was reduced by 36-53 mm and 37-64 mm,and the WUE was increased by 5.6-8.3%and 7.5-9.4%compared with RS₆₆₊₁₀H and RS₇₆H,respectively.5.Regulation of cotton plant characteristics by irrigation method and row spacing configuration affected defoliation of cotton.Our research results showed that the fruit branch angle was significantly positively correlated with the rate of defoliation and boll opening,and negatively correlated with the number of hanging branches and ossified leaves.Compared with MD-T₂,the cotton of the same row spacing in MD-T₃significantly increased plant height,internode length of main stem,fruit branch length and number of fruit branches,reduced the fruit branch angle,and shaped a more compact plant type,thus reducing the efficiency of defoliation and boll opening.Under the same irrigation method,the RS₇₆L increased plant height,fruit branch length and fruit branch angle,main stem internode length decreased compared with high-density planting,and the number of hanging branch leaves and ossified leaves was the lowest,and defoliation accelerated ripening was the best.Considering the yield factor,RS₇₆L under MD-T₃ is the most suitable for high yield and defoliation influence in field production.It can be seen from the Xinxili test that increasing the spraying times or dividing the high concentration dilution into multiple spraying can significantly improve the effect of cotton defoliation and ripening,and reduce the impurity content of raw cotton.