Spectral and Photosynthetic Characteristics of Cotton under Chemical-controlled Topping Technology

Bing Chen,Jing Wang,Qifeng Wu*,Gang Wang,Jing Zhao,Huanyong Han,Fangyong Wang

1.Xinjiang Academy of Agricultural and Reclamation Sciences/Key Laboratory of Biology and Genetics and Breeding of Northwest Inland Cotton,Ministry of Agriculture,Shihezi 832000,China;2.Institute of Water Conservation and Architectural Engineering,Xinjiang Shihezi Vocational College,Shihezi 832003,China

Abstract[Objective]The paper was to study the effect of chemical-controlled topping technology on spectral and photosynthetic characteristics of cotton.[Method]Two row spacing configurations and four topping treatments were set in the experiment field,and the spectral and photosynthetic characteristics of cotton under different configurations and topping treatments were analyzed.[Result]There was no significant difference in spectral reflectance of cotton leaves and canopy among all treatments(T1-T8)before topping.After topping,the spectral reflectance of cotton leaves showed little difference in visible light band,but significant differences in near-infrared light band under two row spacing configurations (T2-T4,T6-T8).And in near-infrared band,compared with CK (T1,T5),the reflectance increased and then decreased under close planting with equal row spacing configurations(T2-T4)and narrow row dense planting configurations (T6-T8).However,the change of cotton canopy reflectance in short infrared bands increased first and then decreased under close planting with equal row spacing configuration,and increased constantly under narrow row dense planting configuration.The photosynthetic capacity of leaves increased,and the net photosynthetic rate(A),stomatal conductance(GH2O),transpirationrate(E)and intercellular CO2concentration(Ci)significantly increased by controlling the top with chemicals,and differences were observed between two configurations.After topping treatments,the leaf area of apical leaf increased,and chemical-controlled topping treatments had significant difference with the control.The apical cotton leaves were shrunk internally,and the plant height increased gradually by 7-15 cm;the number of fruit branches increased by 2-4,and the area of apical leaves decreased significantly in chemical-controlled topping treatments.[Conclusion]After topping with chemicals,the spectral characteristics of cotton change,the photosynthetic capacity of leaves is improved,and the growth of apical leaves and apex of cotton is inhibited.

Keywords Chemical-controlled topping;Cotton;Reflectance;Photosynthetic;Growth characteristics

At present,the leading importance of Xinjiang cotton in national cotton is increasingly prominent.The National Bureau of Statistics released announcement on cotton production in 2020:the national cotton planting area in 2020 was 3 169.9 km2,and the output reached 5.91 million t.Among them,the cotton planting area in Xinjiang was 2 501.9 khm2,and the yield reached 5.16 million t.The cotton area and yield of Xinjiang accounted for 78.9% and 87.3% of the whole country,respectively[1-2].In recent years,the cotton mechanization level of Xinjiang Corps has reached more than 90%,and the control of cotton diseases and insect pests,machine picking and defoliation,chemical control and foliar fertilizer application have all been fully mechanized.Only topping technology has not been fully mechanized,which is the last bottleneck in the whole process of cotton mechanization[3-4].Cotton topping in Xinjiang mainly relies on manual topping,which is time-and labor-consuming,with high cost and high labor intensity[5].There are also attempts of mechanical topping.However,due to high requirements of land leveling and cotton growth uniformity,as well as technical problems such as mechanical damage of cotton plants,overtopping and missed topping,mechanical topping still needs to be further improved,and has not been applied in a large area[6].The emerging chemical-controlled topping technology is characterized by integration of cotton shaping and topping,high efficiency,low cost,less labor,low labor intensity and all-weather operation,etc.,which opens up a new method for cotton topping technology and provides a solution for realizing whole process mechanization of cotton production[7-8].At present,improving the quality and efficiency of cotton in Xinjiang has become the key link and top priority restricting cotton production,and cotton chemical-controlled topping technology is an important measure to improve the quality and efficiency[9].Therefore,it is urgent to actively promote the maturity and application of this technology.

Scholars at home and abroad have carried out a series of studies on cotton chemical-controlled topping technology,most of which focused on defoliation and boll opening effect of cotton chemicalcontrolled topping technology,and a few studies analyzed the growth and development of cotton plants after chemical-controlled topping,while very few studied the changes in physiological characteristics of cotton after chemical-controlled topping[10].Su et al.[11]studied the effect of spraying different concentrations of fluorine on cotton instead of artificial topping,and found that cotton plants had vigorous growth,lowered plant height,smaller apical leaf,and increased single boll weight and seed cotton weight,but there was no obvious change in quality.Zhao et al.[12]studied the similarities and differences of cotton agronomic traits,canopy characteristics,boll spatial distribution,yield traits and fiber quality under chemical topping and manual topping.Ji[13]carried out field test of spraying topping agent and manual topping,and found that chemical topping not only saved labor and time,but also reduced the cost of cotton planting while controlling cotton plant height.Chen et al.[14]studied the influence of chemical detopping Toyouta on the agronomic traits,yield and fiber quality of cotton,and suggested that low concentration of topping treatment(400 and 600 mL/hm2)received better topping effect and basically had no effect on cotton quality.Zhang et al.[15]analyzed the comprehensive benefits of chemical topping based on the survey data in the 134 corps,and concluded that the comprehensive benefits of chemical topping were better than that of manual topping.Therefore,chemical topping saves cost and increases efficiency remarkably,effectively improves labor efficiency and reduces labor intensity,and can significantly improve the timeliness of cotton topping, which has good application prospect.Scholars at home and abroad have also done some research on photosynthetic characteristics of cotton growth regulation.Shahbaz et al.[16]put forward that the application of Mepiquat chloride significantly reduced carbohydrate metabolism and leaf photosynthesis of late-planted cotton by 1%-28%,and decreased lint yield by 6%-29%.Cetin et al.[17]tested the effects of fertigation frequency in Anatolia,Turkey,and found that fertigation frequency had little impact on lint yield and chlorophyll content,but improved lint quality.Scholars at home and abroad have also studied the spectral characteristics of cotton growth.Tian et al.[18]analyzed the canopy hyperspectral data and leaf net photosynthetic rate of"Xinluzao 33"in four key growth periods under different water treatments,and found that RVI could better predict the net photosynthetic rate of cotton leaves.Qi et al.[19]studied canopy hyperspectral reflectance in different growth stages of cotton,and established quantitative models of canopy characteristic information such as leaf area index,fresh biomass and dry biomass of cotton field based on hyperspectral normalized vegetation index and vegetation index,and the determination coefficients were all higher than 0.8.Priscila et al.[20]reduced the spectral range from 1 000-2 500 nm to 1 000-1 381 nm by using near-infrared hyperspectral imaging technology and linear discriminant analysis,to classify and identify the pathogen of cotton anthracnose.

In summary,scholars at home and abroad have studied cotton chemical-controlled topping technology,photosynthetic characteristics and spectral characteristics of cotton growth regulation respectively,but few efforts have been dedicated to the relationship between chemical-controlled topping technology and physiological characteristics.The hyperspectral and photosynthetic characteristics after chemical topping under different configurations have not been systematically studied.The effects of chemical-controlled topping on spectral and photosynthetic characteristics of cotton were analyzed in the paper,in order to provide the theoretical support for the popularization of chemical-controlled topping technology.

1 Materials and Methods

1.1 Planting condition and experimental design In 2018,plot test was performed in No.3-13 and No.2-6 plots with medium fertility in the agricultural trial field of Xinjiang Academy of Agricultural and Reclamation Science(Table 1).Using randomized block design,each treatment was repeated three times,and each repeat covered an area of about 23 m2(10 m×2.3 m).The two test plots were adjacent to each other,and the cotton variety tested was"Jinken 86-29".No.3-13 plots were close planting with equal row spacing configuration of one film and three rows(row spacing 76 cm and row spacing 5.6 cm);No.3-6 plots were narrow row dense planting configuration of one film and six rows[row spacing (10+66)cm and row spacing 9.5 cm].Seeds were sown from April 17 to April 20,with hill-seeding above mulch and drip irrigation under mulch.The irrigation amount in the growth period was 5 000 m3/hm2.The 150 kg/hm2of basal fertilizer triammonium phosphate,600 kg/hm2of topdressing urea and 450 kg/hm2of potassium dihydrogen were applied with water droplets.Water was dropped 11 times once every 9-10 d during the whole growth period.Other management measures followed local high-yield cultivation mode.The tested agent was chemical detopping Toyouta AS(Henan Donglixin Bioengineering Co.,Ltd.).Two row spacing configurations and four topping control treatments were set in the test.Four treatments were set in plots 3-13,including T1,artificial topping control(CK);T2,450 mL/hm2;T3,750 mL/hm2;T4:1 050 mL/hm2.Four treatments were set in plots 2-6,including T5,artificial topping control(CK);T6,450 mL/hm2;T7,750 mL/hm2;T8,1 050 mL/hm2.Each treatment was under consistent field management measures.On July 8,2018,disease-free sample points with robust cotton plants and consistent uniformity were selected, and agents were artificially sprayed with knapsack sprayer.

Table1 Distribution of different treatments in experimental plots

1.2 Measurement items and methods

1.2.1 Determination of agronomic traits.Ten plants with uniform growth were selected from each plot(five plants in each inner and outer row)and labeled.The agronomic character indexes including plant height,number of bolls per plant,number of bolls on the top forth branch,leaf age,number of fruit branches and apical leaf area were measured at 1 d prior to topping,and 5,10 and 20 d post topping.

1.2.2 Spectrometric determination.The spectrum of canopy was measured by a portable ASD Fieldspec ProFR2500 spectrometer,and the spectrum of cotton leaf was coupling-measured by a portable ASD Fieldspec ProFR2500 spectrometer and ASD Leaf Clip test clip.The determination method referred to the reference[21-22].The spectra of cotton leaves were measured on July 8 and August 12,respectively.The spectra of canopy were measured on July 8,July 21 and August 3,respectively.

1.2.3 Photosynthetic measurement.Photosynthesis was determined by GFS-3000 portable photosynthetic meter manufactured by Walz(Germany),and the detailed determination method referred to the reference[23].Photosynthetic parameters were determined on July 21 and August 3.In the spectral and photosynthetic determination,three pieces of top second leaf and top third leaf were tested,respectively,and the average value was calculated.

1.3 Data analysis Reflectance spectral data of single leaf and canopy were obtained from ViewSpecprogram software provided by ASD Company,and spectral reflectance curve was plotted.Data collation and variance analysis(Student-Newman-Keuls multiple comparison method)were carried out using Excel 2013 and SPASS 22.0 software.

2 Results and Analysis

2.1 Effects of different topping treatments on spectral characteristics of cotton leaves and canopy As shown in Fig.1,the spectra of cotton leaves in different topping treatments(T1-T8)changed greatly before and after topping.Compared with the control(T1,T5),the spectral reflectance and spectral curves of cotton leaves in different topping treatments(T2-T4,T6-T8)had no significant changes in the whole band(400-2 500 nm)before spraying(July 8),regardless of the configuration mode.Compared with the control(T1,T5),the spectral reflectance of cotton leaves in different topping treatments(T2-T4,T6-T8)in most spectral bands was greater than that of the control leaves(lower in the red valley)after spraying(August 12).There was no significant difference in reflectance between different topping treatments,but they had significant difference with control(T1,T5)(P＜0.05).The spectral reflectance of different chemical-controlled topping treatments(T2-T4)under close planting with equal row spacing had little changes in the visible band,but had significant changes in near-infrared band(700-1 300 nm)and short-wave infrared band(1 300-2 500 nm)(P＜0.05),which first increased and then decreased.The spectral reflectance of different chemicalcontrolled topping treatments (T6-T8)under narrow row dense planting had significant changes in visible and nearinfrared light bands (P＜0.05),which first increased and then decreased,while that in short-wave infrared band constantly increased.

Fig.1 Spectral reflectance characteristics of cotton leaf in different topping treatments

As shown in Fig.2,the spectra of cotton canopy in different topping treatments changed before and after topping.The spectral reflectance of canopy in the control decreased gradually with the passage of time,especially in near-infrared band.Regardless of configuration mode,compared with the control,the spectral reflectance and spectral curve of cotton canopy in different topping treatments had no significant changes in the whole band before chemical-controlled topping(July 8).The spectral reflectance of cotton canopy in different topping treatments changed greatly in the whole spectral band after chemical-controlled topping treatment(July 21,August 3).With passage of time,the reflectance of different topping treatments(T2-T4,T6-T8)showed no significant changes in visible light band,but showed significant differences in near-infrared to short-wave infrared bands(P＜0.05).In near infrared band,the reflectance of cotton canopy under equal row spacing and close planting configuration in low concentration treatments(T2,T3)were higher than that in the control,while those in high concentration treatments (T4)was lower than that in the control at 10 d post spraying,showing the trend of increasing first and then decreasing.At 20 d post spraying,the reflectance of cotton canopy in different topping treatments(T2-T4)were higher than that in the control,showing the trend of gradually increasing.At 10 d post spraying,the reflectance of cotton canopy under narrow row dense planting configuration in different chemical-controlled topping treatments(T6-T8)were higher than that in the control(T5),showing the trend of increasing first and then decreasing.At 20 d post spraying,the reflectance of cotton canopy in low concentration treatments(T6,T7)were lower than that in the control,while that in high concentration treatment(T8)was higher than that in the control,showing the overall trend of decreasing first and then increasing.The changes of two configurations were basically consistent in visible light band,but the differences were great in near infrared light band.The spectral characteristics under close planting with equal row spacing configuration increased with the increase of spraying concentration,while that under narrow row dense planting configuration first decreased and then increased.

Fig.2 Spectral reflectance characteristics of cotton canopy in different topping treatments

2.2 Effects of different topping treatments on photosynthetic performance of cotton leaves The net photosynthetic rate (A),transpiration rate (E),stomatal conductance(GH2O)and intercellular CO2concentration(Ci)of cotton leaves in different topping treatments(T1-T8)changed significantly before and after topping(Fig.3).Compared with the control(T1,T5),the net photosynthetic rates of cotton leaves in different topping treatments(T2-T4,T6-T8)were increased after spraying under two configuration modes;there was no significant difference at 12 d post spraying(except T2),but there were significant differences at 25 d post spraying(P＜0.05),and the variation was less than 4.3 μmol/(m2·s).The increase of net photosynthetic rate under close planting with equal row spacing configuration was greater than that under narrow row dense planting configuration.The transpiration rate of cotton leaves was increased by all chemicalcontrolled topping treatments.The transpiration rate of cotton leaves in different topping treatments were 0.4-2.2 mmol/(m2·s)higher than that in the control under close planting with equal row spacing configuration(P＜0.05),while those under narrow row dense planting configuration were 1.7-3.2 mmol/(m2·s)higher than that in the control(P＜0.05).The increase of transpiration rate under close planting with equal row spacing configuration was smaller than that under narrow row dense planting configuration.The chemical-controlled topping treatments had great impact on GH2O,which all increased the GH2O of leaves.The GH2O in different topping treatments under close planting with equal row spacing configuration were 32.71-126.50 mmol/(m2·s)higher than that in the control(P＜0.05).The GH2O in different topping treatments under narrow row dense planting configuration were 51.92-214.58 mmol/(m2·s)higher than that in the control(P＜0.05).The increase of GH2O under close planting with equal row spacing configuration was smaller than that under narrow row dense planting configuration.Spraying treatments greatly increased the intercellular CO2concentration of cotton leaves.The intercellular CO2concentrations in different topping treatments under close planting with equal row spacing configuration were 7.3-33 ppm higher than that in the control(P＜0.05).The intercellular CO2concentrations in different topping treatments under narrow row dense planting configuration were 17.1-25.4 ppm higher than that in the control(P＜0.05).The increase of intercellular CO2concentration under close planting with equal row spacing configuration was smaller than that under narrow row dense planting configuration(Table 2).

Fig.3 Photosynthetic performance of cotton leaves in different topping treatments

Table 2 Photosynthetic performance of cotton leaves in different topping treatments

2.3 Effects of different topping treatments on cotton growth and development As shown in Table 3,with the advance of time,the apical leaf area and plant height in all topping treatments increased constantly,but the number of bolls per plant and number of fruit branches changed slightly.There were significant differences among T5-T8 on July 26,but no significant differences were observed at other periods.The number of bolls on the top forth branch changed very little,and the difference was not significant.Compared with the control,there was no significant difference in the apical leaf area before and after topping,and the apical leaf area of all treatments increased after topping.The apical leaf area in topping treatments(T2-T4,T6-T8)had significant difference with that in the control(T1,T5)(P＜0.05).The plant height in the control was basically unchanged,and the plant heights in chemical-controlled topping treatments gradually increased.The plant height in chemicalcontrolled topping treatments had little difference with that in the control before spraying,and the difference between most treatments was less than 1 cm(P＞0.05).At 10 d post spraying,the plant height in chemical-controlled topping treatments still increased,and the plant heights in low and medium concentration treatments(T3,T6,T7)were greatly increased by 5-9 cm(P＜0.05).The plant height in high concentration treatments(T4,T8)increased little,and the difference was not significant.At 20 d post spraying,the plant heights in chemical-controlled topping treatments were increased by 3-9 cm(P＜0.05).Compared with the control,the number of fruit branches in chemical-controlled topping treatments did not change before topping and at 10 d post topping,and there was no significant difference among treatments.However,the number of fruit branches were increased by 2-4 at 20 d post topping(P＜0.05).The number of bolls on the top forth branch first increased then decreased,and there was no significant difference among topping treatments.The apical cotton leaves raised with inconcentric contraction after chemical-controlled topping treatments.

Table 3 Cotton growth and development under different topping treatments

3 Discussion

The spectral characteristics,photosynthetic characteristics,growth and development of cotton in different topping treatments under different configuration modes were discussed in the paper.The results showed that the spectra of leaves in different chemical-controlled topping treatments (T2-T4 and T6-T8)under two configuration modes were greater than that in the control(T1,T5),but there were slight difference among different bands.The spectra of cotton leaves in visible light band changed smaller under close planting with equal row spacing configuration,which changed greatly in infrared and short-wave infrared light band,but the spectra of cotton leaves under narrow row dense planting configuration varied greatly in the whole wave band.Chen et al.[24]found that the leaf spectral reflectance in the visible light band was mainly influenced by chlorophyll content;the higher the chlorophyll content,the more the light absorption,and the low the reflectivity;the chlorophyll content per unit area on disinfected leaves was low,so the leaves absorbed less light,with higher reflectivity.And in near infrared and shortwave infrared bands,the spectral reflectance of simple leaf was mainly affected by chlorophyll,water content per unit area of leaf,dry matter content and internal structure of leaves.Under the two configuration modes,the leaves in different chemical-controlled topping treatments were damaged by agents;the chlorophyll content in leaves reduced,the water content per unit area of leaves decreased,and the dry matter content and internal structure of leaves were all affected,resulting in the greater spectra of leaves in most bands than the control.In addition,the individual growth of cotton plants was vigorous under close planting with equal row spacing configuration,with strong individual advantage;the plant height before chemical-controlled topping was large,and the leaf area of the same position at the top was large.After topping,agents were absorbed slowly,the internal structure of leaves was damaged slowly,and the leaf water content per unit area decreased,so the spectra of leaves changed greatly in infrared and short-wave infrared band.In contrast,the growth of cotton plants under narrow row dense planting configuration was relatively weak before chemical-controlled topping,with weak advantages,and the leaf area of the same position at the top was small.After topping,agents were absorbed quickly,and the internal structure of leaves was damaged quickly,so the spectra of leaves had greater changes in infrared and shortwave infrared band.

The reflectance of cotton canopy had different variation trends after chemical-controlled topping under two configuration modes.The reflectance of cotton canopy in different topping treatments(T2-T4)under close planting with equal row spacing configuration showed different trends at 10 d post spraying,which was higher than that in the control at 20 d post spraying.The reflectance of cotton canopy in different topping treatments(T6-T8)under narrow row dense planting configuration were higher than that in the control(T5)at 10 d post spraying,but showed different trends at 20 d post spraying.After topping,the plants in the control reacted quickly within 10 d post spraying,and the apical dominance was instantly impressed,so the vegetative growth slowed down and the reproductive growth accelerated,and the vegetative growth quickly transformed to reproductive growth[25-27].Because apical dominance was artificially removed,the number of bolls no longer increased,and the number of bolls on the top forth branch first increased.At20 d post spraying,the growth tended to be stable,and the number of bolls on the top forth branch gradually decreased,and the canopy spectra changed little.However,after chemical-controlled topping,it took some time for cotton plants absorbing agents,and cotton plants still grew within 10 d;the number of fruit branches increased,and the number of bolls on the top forth branch increased as well.At 20 d post spraying,the growth tended to be stable;the number of bolls on the top forth branch decreased,and the canopy spectrum changed greatly.The differences in individual cotton development under different configuration modes led to the differences among groups.The cotton individuals under narrow row dense planting configuration were weak,but the group was strong;the drug control was weak within a short term after spraying,so the group continued to increase;the number of fruit branches increased,the number of bolls on the top forth branch increased,and the reflectivity increased rapidly.At this time,the control reacted quickly,and the apical dominance was instantly inhibited,with slow growth and basically consistent reflectivity.Therefore,the reflectance of cotton canopy in different topping treatments(T6-T8)was higher than that in the control(T5).After spraying agent for a long time,the control of agents to the group gradually enhanced at low concentration,and the group was basically controlled with the reflectivity no longer increased.The control of agents to the group was strong at high concentration,and the group had two times of growth phenomenon when the efficacy was reduced;the number of fruit branches continued to increase,the number of bolls on the top forth branch increased,and the reflectivity increased rapidly,so the reflectivity in the control slightly increased.Therefore,the reflectance at low concentration(T6,T7)was lower than the control,and that at high concentration(T8)was higher than the control.The variation trend of cotton plants under close planting with equal row spacing configuration was similar to that under narrow row dense planting configuration after topping.The obvious spectral changes of cotton leaf and canopy in different topping treatments under two configuration modes indicated that they had great influence on the spectrum.The process of topping of different chemical agents could be analyzed through the changes of spectral characteristics.

From the perspective of photosynthetic physiology,the net photosynthetic rate(A),stomatal conductance(GH2O),transpiration rate(E)and intercellular CO2concentration(Ci)of cotton leaves were all increased by topping,which improved the photosynthetic capacity of cotton leaves.The results of this study are similar to those of Yang et al.[28]and Cui et al.[29].Yang et al.[28]studied the photosynthetic rate of cotton group under chemical-controlled topping,and found that the photosynthetic rate of cotton group under chemical-controlled topping was higher than that of artificial topping,with larger leaf area index and longer duration.Since the plant growth was inhibited after artificial topping,especially the growth of apical leaves was inhibited,the photosynthetic capacity was weakened.The plants still grew after chemical-controlled topping,especially the growth of leaves still continued within a short term,and the photosynthetic capacity was strong.As the agents were absorbed by plants,the apical leaves were slowly inhibited,and the photosynthetic capacity began to decrease.However,compared with artificial topping,chemical-controlled topping improved the photosynthetic capacity of the top second and third leaves,while A,GH2O,E and Ciwere all significantly increased,and there were slight differences among different configurations.The cotton apical leaf area and plant height increased the most in T2-T7 topping treatments,the number of bolls per plant and the number of fruit branches was large,while the number of bolls on the top forth branches changed small.The two configuration modes basically had the same impact on the growth and development of cotton,indicating that chemical-controlled topping had consistent impact on the growth and development of plants under different configuration modes.After spraying,the apical cotton leaves were wrinkled and necrotic under two configuration modes,indicating that chemical-controlled topping caused certain damage to cotton leaves.The results suggested that chemical-controlled topping inhibited the apex growth of cotton plants under different configuration modes,but it needed a long-term process,and secondary growth might occur in the late stage,leading to the increase of spectral reflectance and photosynthetic capacity in the short term,which was in good agreement with the changes of spectral characteristics and photosynthetic parameters.

4 Conclusions

Compared with the control,the spectral reflectance and spectral curve of cotton leaves and canopy in different topping treatments under two configuration modes had no significant changes in the whole wave band before spraying.After spraying,the spectral reflectance of cotton leaves in different topping treatments had the same changing trends in different bands,but there were significant differences in spectra,which were significantly greater than the control in most bands(P＜0.05).The spectral reflectance of cotton canopy in different topping treatments varied in different bands,the concentration of agents was different under different configuration modes,and the spectral reflectance of different durations after spraying was higher or lower than that in the control.The results demonstrated that different topping treatments had impacts on cotton leaves and canopy,which were consistent at leaf level and were not affected by configuration modes,but were inconsistent at canopy level and were greatly affected by configuration modes.

Compared to the control,different topping treatments under two configuration modes improved the photosynthetic rate,transpiration rate,intercellular CO2concentration and stomatal conductance of leaves,indicating that chemical-controlled topping improved the photosynthetic capacity of cotton leaves,and improved the growth of apical cotton leaves.

Compared with the control,the plant height in different topping treatments under two configuration modes gradually increased until the growth stopped,and the number of fruit branches increased by 2-4;the number of bolls on the top forth branch first increased then decreased,and the apical cotton leaves raised,with inconcentric contraction.The results suggested that chemical-controlled topping had good inhibition effect on cotton apex,which could control the top effect.Meantime,it could increase the growth of reproductive organ and improve the yield of cotton in the late stage.