Study On The Effect Of Cotton Defoliation Under Different Machine-harvested Planting Patterns

For mechanically harvested cotton planting,the wide and narrow row planting mode with one film and six rows(66+10)cm is generally adopted at present.Because the growing population is too large,it is not conducive to the defoliation of cotton harvesting,resulting in a serious decline in the quality of cotton.Planting through the variety and machine-planting mode is one of the most effective ways to improve the defoliation effect of cotton and solve the problem of the quality of machine-cut cotton.In this experiment,Xinluzao 57,a loose cotton variety,and Xinluzao 48,a compact cotton variety,were used as test materials.The growth and development,yield and quality,canopy structure,photosynthetic characteristics and antioxidant enzyme system of cotton under machine-harvested planting patterns before and after the application of defoliant were studied,and the differences of defoliation effects under different planting modes were compared.It also reveals the inherent mechanism of the differences,explores the key factors affecting the effect of cotton defoliation,establishes the optimal cotton planting mode suitable for mechanical harvesting in North Xinjiang,and provides a scientific basis for improving the technology of cotton defoliation and the integration of high-quality and high-efficiency technology of mechanical harvesting.The main results are as follows:1.The growth period of cotton with 3 rows of 1 film was 2-6 days earlier than that with 4 rows of 1 film and 6 rows of 1 film.The effect of defoliation and flocculation was better,and the yield increased significantly.It was more suitable for mechanical harvesting.At the same time,the cotton with 3 rows of 1 film was severely branched because of the small plant spacing.The fiber quality of cotton is closely related to the genetic characteristics of cotton varieties,and the effect of mechanically harvested planting mode on it is small.The effect of mechanical harvesting on loose cotton is more prominent than that of compact cotton.In the aspect of leaf defoliation rate,cotton plant height was positively correlated with it(r=0.97),growth period days,total leaves and leaf area were negatively correlated with it,and the correlation coefficients were-0.86,-0.59 and-0.59,respectively.In the aspect of leaf branching rate,cotton petiole length,boll number per plant,fruit branch length and leaf thickness were positively correlated with it,and the correlation coefficients were 0.89,0.88,0.64 and 0.61,respectively.2.1 film and 3 rows of cotton had good canopy transparency.When the defoliant was sprayed,it was beneficial to uniform medication in the middle and lower leaves of the canopy,as well as to the development of medicinal properties.The canopy permeability of compact cotton was better than that of loose cotton,which provided a good environment for spraying defoliant.Xinluzao 57 had the highest sensitivity to defoliants under the 1 film 3 rows model,followed by 4 rows and 6 rows models;Xinluzao 48 had little difference in sensitivity to defoliants under the 1 film 3 rows and 1 film 4 rows models,but was significantly stronger than that under the 1 film 6 rows model;among varieties,Xinluzao 48 was more sensitive to defoliants than Xinluzao 57.3.Relative water content(LRWC)of cotton leaves decreased after defoliant spraying.The activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in cotton leaves increased first and then decreased.The content of malondialdehyde(MDA)increased with the application time.The changes of antioxidant enzymes in Cotton Leaves under 1 film 3 rows were less than that under 1 film 4 rows and 1 film 6 rows,which indicated that the cotton leaf cells in this pattern did not have the sensitive ability to regulate the enzymes activity.The membrane structure of cotton leaf cells was easily damaged by defoliant spraying.Among cotton varieties,Xinluzao 57 had stronger resistance to defoliant than Xinluzao 48,which was not conducive to defoliation.In summary,the cotton varieties under the mode of 1 film and 3 rows are sensitive to defoliant,which is beneficial to defoliation.At the same time,the cotton varieties under the mode of 1 film and 3 rows have excellent yield performance and good suitability for mechanical harvesting.On the whole,the mode of 1 film and 3 rows is suitable for popularization and application in cotton production in Northern Xinjiang.