| Xinjiang has relatively rich light and heat resources,and its agricultural production belongs to irrigated agriculture.Cotton(Gossypium hirsutum L.)is the most important cash crop in Xinjiang.However,the lack of water resources has seriously restricted the sustainable development of the cotton production in Xinjiang.The use of water-saving irrigation technology is the fundamental way out for the development of cotton in Xinjiang.In the 1990 s,mulched drip irrigation was first established in Xinjiang,which significantly improved cotton yield and water use efficiency.Compared with traditional flood irrigation,the physiological and ecological mechanism of how mulched drip irrigation controls water supply and achieves water-saving and high yield of cotton is still unclear.There are few reports on the biological mechanism of water saving and high yield of cotton under mulched drip irrigation.In view of the above problems,mulched drip irrigation(conventional drip irrigation and excessive drip irrigation)and traditional flood irrigation(reduced flood irrigation and conventional flood irrigation)were used in this experiment under field conditions.Traditional flood irrigation was used as the control group.Soil environmental factors,root morphology and physiology,leaf photosynthesis,water consumption characteristics,relationship between root and shoot,yield and water use efficiency under different irrigation methods were studied.The main research results are as follows:1.The effects of different irrigation methods on soil environmental factors were studied.Compared with traditional flood irrigation,mulched drip irrigation increased the soil water content in 0-60 cm soil layer in vertical and horizontal directions(wide row and narrow row)and reduced the fluctuation range of soil water content at flowering and boll stage.Mulched drip irrigation formed a local wet and dry area.The local wetting zone of mulched drip irrigation could make the cotton root system located in the wetting zone with alternating boundary between dry and wet.Mulched drip irrigation reduced the soil bulk density in the 0-40 cm soil layer and increased the total soil porosity in the 0-40 cm soil layer,which made the shallow soil loose with a large number of pores and improved the soil water and air conditions.This indicated that mulched drip irrigation was better than traditional flood irrigation in maintaining shallow soil structure.2.The effects of different irrigation methods on root growth,root distribution and photosynthetic product accumulation were studied.The higher soil water content in the 0-40 cm vertical soil layer with a distance of 20 cm on both sides of the drip line under mulched drip irrigation increased the fine root length and fine root biomass in this area,and shaped a shallow fine root system.However,excessive drip irrigation was not conducive to the distribution of fine roots in the shallow soil layer.The fine root length and biomass of cotton under traditional flood irrigation were mainly distributed in the 0-40 cm and 60-100 cm soil layers,and the fine root distribution in the shallow layer was less than that in mulched drip irrigation.Further analysis showed that the higher root biomass in 0-40 cm soil layer under mulched drip irrigation was beneficial to the improvement of biomass per plant.3.The effects of different irrigation methods on the growth of white fibrous roots,physiological functions of roots and leaves and yield water use efficiency were studied.Compared with traditional flood irrigation,mulched drip irrigation increased the length,surface area and volume of white fibrous roots in the 0-60 cm soil layer at full flowering stage and prophase full boll stage of cotton and reduced the mortality rates of white fibrous roots.Mulched drip irrigation enhanced SOD activity,reduced MDA content,and improved physiological function of roots in the 0-60 cm soil layer,thus promoting the absorption of water and nutrients in the 0-60 cm soil layer.The leaves of mulched drip irrigation had high relative water content at full flowering stage and prophase full boll stage,which reduced the content of MDA,improved the physiological function of the leaves,and increased total biomass at prophase full boll stage.Small water consumption of conventional drip irrigation at prophase full boll stage significantly increased the total biomass water use efficiency at prophase full boll stage and thus increased the yield water use efficiency by 55.37%~59.59%.Excessive irrigation(600 mm)led to the decrease in total biomass water use efficiency of excessive drip irrigation at prophase full boll stage and thus reduced the yield water use efficiency.4.The effects of water consumption characteristics of cotton and water supply characteristics of soil on leaf photosynthesis under different irrigation methods were studied.In one irrigation cycle,the cotton plant of mulched drip irrigation mainly consumed the soil water storage in the 0-40 cm soil layer,but less in the deep layer.The shallow soil layer had a stable water supply capacity.Traditional flood irrigation mainly consumed the soil water storage in the 0-40 cm soil layer in the early stage of the irrigation cycle,and consumed the soil water storage in the 60-80 cm soil layer in the late stage.This meant that the depth of soil water supply in traditional flood irrigation fluctuated greatly.Compared with traditional flood irrigation,the stable water supply capacity in the 0-40 cm soil layer under mulched drip irrigation improved the stomatal conductance and transpiration rate of leaves,increased the net photosynthetic rate during the flowering and boll-setting stage,and thus increased the biological yield and biological yield water use efficiency and had the potential of high yield and high efficiency.5.The effects of different irrigation methods on the relationship between root and shoot and yield formation of cotton were studied.Compared with traditional flood irrigation,the higher soil water content under mulched drip irrigation increased the specific root length(SRL),which promoted the growth of fine root length and biomass at full flowering stage and prophase full boll stage.The growth of fine roots increased the root-shoot ratio(R/S)of mulched drip irrigation,and then inhibited the excessive vegetative growth of the aboveground parts.When entering the late full boll stage and boll opening stage,the fine root biomass and fine root mass fraction decreased rapidly under mulched drip irrigation,resulting in a lower R/S.The smaller R/S of mulched drip irrigation facilitated the distribution of photosynthetic products to reproductive organs,which increased the boll number per plant by 7.30%~25.10% and boll loading of fine root system by 32.84%~70.82%,thus increasing seed cotton yield.However,compared with conventional drip irrigation,over irrigation led to excessive vegetative growth of cotton under excessive drip irrigation,which resulted in the decrease of boll opening rate and seed cotton yield by 8.71%~17.19% and 14.14%~24.27%,respectively.Therefore,mulched drip irrigation promoted the root growth of cotton and inhibited the vigorous vegetative growth of shoot before the prophase full boll stage,and then reduced the growth redundancy of root and increased the productive capacity of the fine root system after the prophase full boll stage,which increased boll number per plant and yield.However,only under the appropriate irrigation amount(390 mm),mulched drip irrigation can increase both yield and yield water use efficiency.To sum up,it could be seen that when cotton planting mode was changed from traditional flood irrigation to mulched drip irrigation,mulched drip irrigation improved the shallow soil environment and optimized the distribution of cotton fine roots and shaped the shallow fine root system by changing the soil moisture area.The water absorption capacity of shallow fine root system under mulched drip irrigation was coupled with the stable water supply capacity of the soil,which promoted the growth of white fibrous roots and fine roots,and enhanced the water and nutrient absorption capacity.The physiological function of leaves under mulched drip irrigation was improved,which was helpful to increase photosynthetic capacity of leaves and biomass per plant.Furthermore,mulched drip irrigation reduced the redundant growth of roots in the late growth period,increased the distribution of assimilation products to reproductive organs,promoted the increase of boll number per plant and productive capacity of the fine root system,and thus increased the yield.However,excessive irrigation amount(600 mm)decreased boll opening rate and seed cotton yield of cotton under mulched drip irrigation,and increase the water consumption of cotton in the whole growth period,and thus reduced the water use efficiency.Therefore,under the appropriate irrigation amount(390 mm),mulched drip irrigation realized the cooperative development of roots and shoots through the effective regulation of water and roots,thus achieving the goal of water-saving and high-yield cultivation. |
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