Effects Of Different Cropping Patterns On The Cotton Growth And Soil Microorganism Of Continuous Cropping Cotton

Xinjiang is a major cotton producing area in China.Its cotton planting has excellent natural conditions and advanced technology,and its output and quality are ahead of other cotton areas.In 2017,the cotton planting area in Xinjiang accounted for 63% of the country's total.Due to the large planting area,under the conditions of limited arable land resources in Xinjiang,the continuous long-term continuous cropping of cotton is common,and the phenomenon of continuous cropping for 20 or even 30 years is more common,causing Xinjiang cotton planting to face continuous cropping obstacles.In order to promote the sustainable development of Xinjiang cotton,it is of great significance to explore scientific and rational planting methods to alleviate the continuous cropping obstacles in cotton.Therefore,based on the soil of cotton field after 30 years of continuous cropping,this study explored five planting patterns: cotton continuous cropping(CK),cotton intercropping onion,cotton intercropping cumin,rotation of 2 years alfalfa and rotation of wheat after planting cotton.The effects of different cropping patterns on cotton growth and development and soil microbial communities in cotton rhizosphere were studied in order to reveal the remediation effects of different intercropping and rotation patterns on continuous cropping cotton fields.The results of the study are as follows:1.Effects of different planting patterns on the growth and photosynthetic characteristics of cotton shoot.The effects of different treatments on the shoot growth and photosynthetic rate of cotton were not significantly different from those of the control at seedling stage.Intercropping onion,rotation wheat and alfalfa from budding stage to flowering stage could promote the growth of cotton shoot.To improve the chlorophyll content and photosynthetic rate of cotton,the comprehensive performance between treatments was: rotation of wheat > intercropping onion > rotation of alfalfa.The intercropping cumin had no effect on the aboveground biomass and photosynthetic rate of cotton compared with the control.2.The intercropping and rotation treatments could promote the development of cotton root system,which showed that the cotton root length,root surface area and root volume increased,and there were differences among different treatments.The cotton intercropping onion,wheat rotation and alfalfa rotation had better effects.There was no significant difference between intercropping cumin and control.Different intercropping and rotation treatments could increase the root activity,antioxidant protective enzyme activity and soluble protein content of cotton roots,and decrease the content of MDA.The results showed that intercropping onion > wheat rotation > alfalfa rotation > cumin intercropping.3.Effects of different planting patterns on soil microbial Community structure of Cotton Rhizosphere.We proved by dilution curve that the results of the experiment can reflect the microbial community of soil samples.The ACE,Chao1,Simpson and Shannon indices of soil microbes were analyzed.The results showed that the abundance of rhizosphere bacterial communities treated with onion,cumin and wheat rotation in cotton competition zone was higher than that in cotton continuous cropping.The bacterial diversity of rotation wheat treatment was also greater than that of cotton continuous cropping treatment,and the richness of bacterial community was increased by intercropping onion treatment compared with cotton continuous cropping treatment in cotton non-competitive area.Intercropping onion,intercropping cumin,alfalfa rotation and wheat rotation increased the diversity of bacterial community,but intercropping onion decreased the soil fungal diversity of cotton rhizosphere.The microbial cluster analysis at OTUs level showed that the intercropping treatments(intercropping cumin and intercropping onion)were separated from other treatments in the bacterial community,but only in the non-competitive areas in the fungal community.According to the abundance and PCA analysis of soil microbial phylum in rhizosphere,it was concluded that the main categories in the competitive and non-competitive regions had no change but the richness had changed.The difference between intercropping(intercropping onion and cumin)and cotton continuous treatment was greater than that between rotation(alfalfa rotation and wheat rotation)and cotton continuous cropping.The richness of the main genera showed that there was no difference between the main components of bacteria in the competitive region and the non-competitive region,but the main components of fungi changed,and there were significant differences in the richness of some genera among the treatments.The following conclusions are drawn: the improvement of cotton rhizosphere soil by four planting patterns is as follows: intercropping onion > intercropping cumin > rotation wheat > rotation alfalfa,and the cotton rhizosphere soil in non-competitive area is better than that in competitive area.Conclusion: cotton intercropping onion,cumin,wheat rotation and alfalfa rotation can improve soil microbial structure,increase bacterial diversity and richness,promote cotton root development and increase physiological metabolic enzyme activity.Leaf photosynthetic rate and plant biomass were also increased.There were differences among different treatments.Intercropping onion,rotation wheat and alfalfa rotation had better effect on alleviating continuous cropping obstacle in continuous cropping cotton field,but the effect of intercropping cumin was not obvious.