| Long-term continuous cropping of plants would have serious issues of continuous cropping obstacles,especially in Xinjiang,having long planting time and wide planting area.Therefore,breakthrough point of this study was to improve the farmland environment via reducing the chemical substances in the cotton field,and alleviating cotton continuous cropping obstacle.Four planting patterns were cultivated which included cotton?Gossypium herbaceum Linn.?and onion?Allium cepa Linn.?intercropping?C?O?,cotton and cumin?Cuminum cyminum Linn.?intercropping?C?C?,alfalfa?Medicago sativa Linn.?-cotton rotation?A?C?,and wheat?Triticum aestivum Linn.?-cotton rotation?W?C?.The allelopathic effects of cotton seed germination and seedling growth were determined by biological test method using aqueous extracts of cultivated four crops.The total phenolic content and soil enzyme activities were determined by chemical experiment method.High performance liquid chromatography?HPLC?was used to determine the different allelopathic compounds content of different planting patterns soil.The allelopathy of four crops on cotton was clarified.The reasons for improving long-term continuous soil bioactivity by intercropping and rotation were explained.This study laid the theoretical foundation for building a reasonable planting system improving farmland soil ecological environment.The conclusions were shown as follows:Wheat,onion and cumin extracts on cotton seed germination and seedling growth showed the allelopathic effect of promotion in low concentration and inhibition in high concentration.Their the maximum allelopathy indexes of aboveground fresh weight were 0.10,0.15,and 0.07,respectively.Under the same quality concentration,the inhibition effect of alfalfa extracts on cotton was stronger than that of wheat extracts,and the inhibition effect of cumin extracts was stronger than that of onion extracts.The allelopathic synthetic effect of 60 g·L-1 alfalfa extract on cotton was significantly inhibited,which of seed germination and seedling growth was-0.40 and-0.84,respectively.The activity of soil peroxidase activity and invertase activity in four planting patterns were lower than that of the control,and the rotation processing was significantly reduced.The activities of soil peroxidase and invertase were decreased by 7.59%and 28.46%in rotation wheat system,respectively.The activities of soil urease,neutral phosphatase and catalase were improved comparing the control,and urease and catalase activities in rotation treatment were significantly higher than that in control.Catalase and urease activities were the highest in wheat rotation cotton,while neutral phosphatase activity was the highest in cotton and alfalfa rotation.Cotton intercropped onion significantly increased the soil catalase activity,also intercropping improved the neutral phosphatase activity.In brief,peroxidase activity and catalase activity told that hydrogen peroxide,phenol and amine compounds were reduced in soil and soil resistance was enhanced.Intercropping and rotation promoted the conversion of nutrients in the soil,and improved the utilization of soil organic matter.In 30-year long-term continuous planting soil,soil total phenolic content increased 7.91%comparing that of 20-year continuous planting soil,moreover,significantly increased 10.53%comparing that of10-year continuous planting soil.Compared with 30-year continuous cropping,the method of using intercropping and rotation could reduce the soil total phenolics,in which cotton intercropped onion had the best effect,declined 20.44%of soil total phenolic content,and cotton intercropped cumin decreased by8.91%.Cotton rotation alfalfa and wheat could decrease 3.56%and 6.19%of total phenolics content,but there were no significant difference.In 30-year continuous cropped soil,the content of p-hydroxybenzoic acid was the highest,followed by vanillin,and finally was ferulic acid.In four different planting patterns and continuous cropping,the sum of three allelochemicals contents from large to small was in turn:30-year continuous cropped cotton>cotton intercropped cumin>alfalfa rotation cotton>wheat rotation cotton>cotton intercropped onion.Among them,three substances decreased by more than 50%in the cotton intercropped onion pattern.In cotton intercropped cumin,p-hydroxybenzoic acid content was decreased 31.45%,vanillin content was decreased 13.61%,however,ferulic acid content only decreased 5.26%,compared with control.The content of three phenolic acids in rotation was significantly lower than that of control,and the differences among different treatments were significant.In conclusion,low concentration of onion,cumin,wheat and wheat leaching solution promoted cotton germination and growth,but low concentration of alfalfa leaching solution slightly inhibit cotton.Along with the cropping years increasing,cotton soil total phenol content was increased.But it is a good way to reduce the soil phenolic content and regulate soil enzyme activity that using intercropping and rotation.In addition,it could also reduce the biological toxicity of soil,promote the transformation of mineral elements and alleviate the problems caused by long-term cotton planting. |
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