Cotton Growth And Development And Field Ecology At Different Film Removal Times During The Early Stage

Object: The removal of mulch in the bud stage can control the increment of residual film pollution.Removing the film will inevitably change the soil environment,thus affecting cotton growth.This study aimed to reveal the potential mechanism of mulch film removal during different periods with respect to the aboveground response to soil microenvironment and root growth dynamic and spatial configuration changes.To address the above question,the regulation mechanism of cotton physiology,field ecology and root system characteristics is revealed.The results of this study will provide a scientific basis and theoretical guidance for high-yield cultivation of cotton and mulch film residue control in arid and semiarid cotton growing regions.Methods: A field experiment was conducted in the No.2 experimental plot(44.3108° N,85.986° E,altitude: 460 m)of the Xinjiang Academy of Agricultural and Reclamation Science,Shihezi,Xinjiang,China during 2015-2016.A split-plot experimental design was used with differing cotton varieties in the main plots and differing film-removal time in the sub–plot.This experiment was conducted to examine the influence of mulch film removal time(10 and 1 d before the first irrigation(T10 and T1,respectively)and 1 d before the second irrigation(E1)after emergence)on cotton growth and farmland ecosystem,i.e.the spatial and temporal variation of nutrients in soil profile,the spatial configuration of cotton root system,the relationship between nutrient uptake of cotton and soil nutrient supply,the physiological parameters,photosynthetic characteristics,canopy structure and yield,quality and water utilization efficiency.The control group(CK)was film mulched throughout the growth stage.The first irrigation time during 2015-2017 was 30 days,35 days and 43 days after emergence respectively.The test material was a variety of Gossypium hirsutum L.,that is,Xinluzao 42(XLZ42)and Xluzao 45(XLZ45).On the basis of the above research,the influence mechanism of the film-removal on the root system construction and yield formation was revealed.At the same time,the effects of different irrigation water amount(the amount of water was increase by 10%(W1)and 30%(W3)in each irrigated time than T1 during the growth stage after emergence.T1 was the same water amount as CK in each irrigated time)on the cotton growth and yield were studied.Results:1.Soil temperature,moisture and salinity at different film removal timesThe soil temperature in each 0-30 cm soil layer of the film-removal treatment groups was lower than that in CK 50 d after emergence,but the difference gradually declined until film-removal treatment groups soil temperature was less than CK.The effect of the film-removal on soil moisture in more rainfall years was not obvious,while in normal years,the soil moisture content of 0-60 cm layer was decreased.Film-removal promoted soil salt accumulation in the more rainfall year(2016,the rainfall in May and September was 120.2mm),while in normal years(2017,the rainfall in May and September was 96.5mm),it has the effect of inhibiting salt accumulation,and the more obvious this trend is in the later growth period.2.Soil nutrient changes and cotton nutrient absorption at different film removal timesFilm-removal treatments increased the content of organic matter at the end of the growth stage,increased the total nitrogen content of 0-10 cm soil layer and 40-50 cm soil layer in 2015-2016,increased the total phosphorus content of 0-50 cm soil layer,and also increased the content of hydrolyzed nitrogen in 0-10 cm soil layer and the content of instant potassium in every soil layer.The peak of N and P nutrients accumulation in normal year(2017)and N,P,K nutrients accumulation in the rainy year(2016)film-removal treatments were moved backwards,however,the time of rapid accumulation of nutrients is longer and the maximum accumulation of nutrients is larger in those film-removal treatments in 2016 and 2017,whereas opposite results were obtained of N,P,K nutrients accumulation in dry years(2015)and K nutrients accumulation in 2017.The maximum accumulation rate of N,P,K nutrients in 2015-2016 and K nutrients in 2017 in film-removal treatments was lower than than in CK treatment.In a normal rainfall year,film-removal treatments were not conducive to the accumulation of nitrogen,phosphorus and potassium in different organs,in the rainy season,film-removal treatments increased the accumulation of nitrogen,phosphorus,potassium in the root and the boll,and increased the accumulation of phosphorus and potassium in the leaf.Compared with normal years,the rainy year is not conducive to the absorption of phosphorus in cotton.3.Cotton root morphology and dry matter accumulation at different film removal timesIn initial flowering stage,film removal at an appropriate time can increase RLD,RSD,and RVD.The root dry weight density(RDWD)was significantly(even to a very significant level of difference)higher than the CK in the soil layer below 10 cm.The cotton root-shoot ratio(R/T)was higher in the film-removal treatments than in CK in both years.E1 showed the highest proportion of hair roots thinner than 1.0 mm during any stage in both years except for 2015 BBFS.Film removal is conducive to the accumulation of root dry matter only in yearswith lower rainfall.4.Cotton Photosynthetic physiology at different film removal timesFilm-removal treatments can improve the net photosynthetic rate in cotton later flowering stage,improve the transpiration rate in middle and later flowering stage.Film-removal treatments improved the actual electron transport rate(ETR)and the maximum electron transfer rate(ETRmax)between the cotton photosystem,improve the electron transfer activity of PS ? except late flowering stage in 2016.Film-removal treatments can improve the efficiency of light energy conversion in early and middle flowering stage in 2016 and middle and late flowering stage in 2017,and reduce the efficiency of light energy conversion of early flowering stage in 2017.It can increase the tolerance of plants to strong light,especially in the early flowering stage of more rainfall years,the trend is more pronounced.Leaf area index(LAI)and leaf area duration(LAD)were reduced in film-removal treatment,the net assimilation rate(NAR)of film-removal treatment was higher than CK in most periods.The value of the mean tilt angle(MTA),diffuse none-interceptance(DIFN)and light leakage reflectivity(LLR)of film-removal treatments were higher than CK's,but the light interception rate(LIR)of film-removal treatments was lower than CK's.In addition to the year of drought(2015),the maximum accumulation of dry matter of film-removal treatments was the highest.Under the condition of removed the mulch film,compared to the CK,Tmax(the time when the root or shoot dry matter accumulation rate reached a maximum)and t1(starting time of linear accumulation of dry matters)appeared earlier and t of(days of linear accumulation of dry matters)was longer,dry matter accumulation in linear accumulation stage were more.Film-removal treatments can promote the distribution of dry matter to reproductive organs in normal years.Film-removal treatment increased the content of proline(Pro)and superoxide dismutase(SOD)activity in the late growth stage.5.The effect of increasing irrigation water after film-removal on the growth of cotton.Under the condition of increasing the amount of irrigation water after removed the mulch film,the structure of the canopy and the interception rate of light energy were improved.In the normal year of rainfall,the LAI was improved,and the DIFN was reduced,the NAR was significantly improved,the LAD was reduced,and photosynthetic performance was improved in late growth stage,water use efficiency(WUE)was reduced,intrinsic WUE(WUEi)and limiting value of stomata(Ls)were promote In normal years,the accumulation of dry matter in organs can be increased,and the proportion of the assimilation products to the reproductive organs is reduced.6.Seed cotton yield and fiber quality at different film removal timesThe film-removal reduces lint cotton yield in dry years and increases lint cotton yield in the remaining years.The film-removal can improve the fiber quality to a certain extent,and the earlier the film-removal time,the more obvious the trend.The lint cotton yield decreased and utilization efficiency of irrigation water decreased significantly under the condition of increasing the amount of irrigation water after removed the mulch film.The upper half mean length was lower,and the macron value and elongation percentage increased.Appropriate increase the amount of irrigation water(W1)in normal years can improve the specific breaking strength and uniformity index,and reduce the short fiber index.Conclusion: Cotton for improving soil temperature and conserving soil water content effect of film mulch needs to maintain at least 50 d after emergence,before this,film removal will seriously affect the cotton growth and development,in the aftermath,removal the film according to the climate in every year before the first or the second irrigation after the emergence.It is beneficial to the construction of root system and photosynthesis in the late stage after early stress exercise.More distribution of photosynthetic products to reproductive organs and cotton production were increased.The structure of the canopy can improved by increase irrigation water after removal film,but the yield and utilization efficiency of irrigation water were not improved.