Effect Of Reduced Amount Drip Irrigation During The Flowering And Boll-Forming On The Development Of Cotton Boll And Its Leaf Photosynthetic Characteristics

With the warming and humidification of climate in northern Xinjiang in recent years,the frequency of short-term heavy rainfall in the cotton areas of northern Xinjiang has increased,and peaked during the cotton blooming and boll period.The water demand of cotton has generally declined in each growth period,and the decline in the flowering and boll period is the most obvious.Therefore,the restrictive factors of the drought on the cotton fields in northern Xinjiang have been weakened.However,cotton’s high-efficiency water-saving technology is not yet perfect,and the problem of water shortage still exists.Therefore,set three different drip irrigation rates during flowering and boll-forming stage:2450m³·hm^-2（CK）,2050m³·hm^-2（W₁）,1650m³·hm^-2（W₂）for this experiment,among them,CK is the local conventional drip irrigation rate.Two test varieties:Xinluzao 50（not drought-tolerant）and Xinluzao 73（drought-tolerant）were selected.To study the changes of cotton yield and quality,cotton boll development and leaf photosynthetic characteristics under different drip irrigation during the flowering and boll stage,in order to provide a feasible amount of drip irrigation during the flowering and boll period when the water supply of the cotton field is insufficient.the main research results are as follows:1.The effect of soil moisture of cotton field and cotton yield and quality under reduced drip irrigation application during flowering and boll-forming stage.The formation of cotton yield and quality were affected under reduced drip irrigation application during flowering and boll-forming stage,while moderately reduced the drip irrigation（W₁）cotton yield had a small decline and can improve water use efficiency.The soil moisture content of each soil layer of the two varieties of cotton fields under reduced drip irrigation reached the largest decline in the prophase full-bolling stage,but decreased in the later full-bolling stage,and the soil moisture content of each soil layer has little difference.Under the W₁ treatment,the water use efficiency of the two varieties was 3.08%～4.38%and 1.88%～3.85%higher than that of the CK and W₂ treatments,respectively.Under the W₂treatment,the soil moisture content of the 20-60 cm soil layer of Xinluzao 50 decreased significantly in the late stage of the boll,and the biomass of the reproductive organs increased.Under the W₁ and W₂treatments,the number of fruit branches and bolls in each part of the two varieties decreased,and the yield of whole seed cotton decreased by 6.27%～7.77%and 19.28%～21.75%.Among them,the number of upper fruit branches and the yield decreased the most.In addition,the micronaire value dropped significantly of the two varieties,the micronaire values of the lower and upper fruit branches decreased by7.66%～15.97%and 1.14%～13.45%,respectively.Under the treatments W₁ and W₂,the decreasing amplitude in soil water content,reproductive organ biomass and yield of Xinluzao 50 were greater than those of Xinluzao 73,indicating that reduced drip irrigation had a greater impact on Xinluzao 50.2.The effect of growth and development of cotton buds and bolls under reduced drip irrigation application during flowering and boll-forming stage.Under the W₁ and W₂ treatments,the buds and bolls number of the two varieties decreased;and the cotton fiber and cotton seed dry weight decreased.The upper fruit branches were the most obvious.The shedding rate of buds and bolls on the same part fruit branch of the two varieties was W₂>W₁>CK,the shedding rate of upper fruit buds of Xinluzao 50 was significantly higher than that of Xinluzao 73（P<0.05）.The numbers of buds and bolls on the middle and lower branches were W₁>CK>W₂,but the numbers of buds and bolls on the upper fruit branches were CK>W₁>W₂.The length,diameter,volume,cotton fiber and cotton seed dry weight of the two varieties of cotton bolls were CK>W₁>W₂,while the boll shell dry weight was the opposite.It is found that the decrease of the length of the two varieties of cotton bells is not significant,and the reduction of the volume of the cotton boll was mainly caused by the decline of the cotton boll.Compared with the control,the maximum theoretical value and the maximum accumulation rate of cottonseed and cotton fiber dry matter decreased after the reduced drip irrigation treatment,and the cotton fiber decreased greatly.Among them,the upper fruiting branch cotton boll suffers from drought stress for a long time,and the export of boll shell and cottonseed sucrose is blocked,which makes the fiber dry matter quality decrease significantly.Under the treatments W₁ and W₂,the cotton fiber and cotton seed dry weight of Xinluzao 50 decreased by 8.65%,18.11%,4.47%and 19.46%,respectively,which were higher than those of Xinluzao 73.3.Effect of photosynthesis and rapid chlorophyll fluorescence characteristics of cotton leaves under reduced drip irrigation application during flowering and boll-forming stage.For 33 to 45 days post-flowering treatment,under W₁ and W₂ treatments,the leaves of two cotton varieties intercellular CO₂ concentration（C_i）and stomatal conductance（G_s）decreased at the same time,indicating that the main reason for the decrease in the net photosynthetic rate（P_n）was the stoma factor,indicating that the decrease in drip irrigation did not cause the two cotton fields severe drought.In the rapid chlorophyll fluorescence induction kinetic curve（OJIP）of the two cultivars,W₂>W₁>CK before point J,and CK>W₁>W₂ after point I.Under W₂ treatment,the two varieties of variable fluorescence curves（ΔV_t）at K point（300μs）-I point（30 ms）,the amplitude ofΔK-ΔJ value and Wk value were all higher than those of W₁ treatment.It indicated that under the W₂ treatment,the photosystemⅡcomplex（PSⅡ）donor side oxygen-evolving complex（OEC）of the two varieties of leaves were obviously damaged,the photosynthetic apparatus of cotton leaves and the electron transfer were inhibited,and Xinluzao 50 was more affected.W₂ treatment also caused a decrease inψo,φPo,φEo,PI_ABS,total,Fv,Fv/Fm,Fv/Fo and an increase in TRo/RC and DIo/RC.It shows that the performance of the electron transport chain in the PSⅡreaction center and the electron transport activity between photosystems are reduced,the production of the cell reactive oxygen（ROS）decreased.Decreasing the amount of drip irrigation during flowering and boll-forming stage allowed cotton leaves to relieve the pressure caused by excess light energy by increasing heat dissipation,resulting in a decrease in light energy utilization,the W₂ treatment was more obvious.In summary,When the total drip irrigation application was 3 350m³·hm^-2,the drip irrigation application during flowering and boll-forming stage of cotton fields in northern Xinjiang was 2 050m³·hm^-2（W₁）,the water use efficiency was higher.,the decreasing amplitude of the performance of electron transport chain in the PSⅡreaction centerand light energy utilization relatively small,In addition to the accumulation of photosynthetic products in the middle and lower fruits,cotton overall yield decreased by 6.27%～7.77%,and the water use efficiency was higher,Therefore,it can be used as a reference when water resources are scarce in cotton field in northern Xinjiang.Among varieties,Xinluzao73 is more suitable for planting when water supply is insufficient in cotton fields of northern Xinjiang.