Effects Of Intercropping Leafy Vegetables On Biological And Soil Chemical Properties And Enzymatic Activities Of Continuous Cropping Cucumber Under Plastic Tunnel Cultivation

Continuous cropping obstacle has become a bottleneck restricting the sustainable development of our country’s facility cucumber industry.Reasonable intercropping and filling with crops are one of the effective means to overcome the continuous cropping obstacle of facility vegetables.For common leafy vegetables,there are problems such as low economic value or relatively single species,and there are some limitations to reducing the obstacles to continuous cropping of cucumbers by building a diverse intercropping and filling system.In this study,through positioning experiments,the use of high economic value or salt-tolerant leafy vegetables,such as Mesembryanthemum crystallinum L.,Tetragonia tetragonioides（Pall.）Kuntze,cluster mallow（Malva verticillata L.）,Basella rubra L.,water spinach（Ipomoea aquatica Forsk.）,amaranth（Amaranthus tricolor L.）,etc.,and plastic tunnel cucumber intercropping and summer filling with planting,respectively,from the growth and development of cucumber,yield,quality,soil chemical properties,soil enzyme activity,leafy vegetable yield and total net income,etc.,systematic study on the mechanism of these cultivation modes to reduce the continuous cropping obstacles of cucumber,which can enrich the system of cucumber intercropping and summer filling and build a sustainable development model,and also could provide theoretical and technical basis for cucumber industry development.The main results are as follows:1.Biological effects of intercropping of different leafy vegetables and cucumbers in springIn the spring stubble of 2019,the results of growth indicators such as plant height and maximum leaf area of cucumbers at different developmental stages showed that the growth of cucumbers intercropped with M.crystallinum,T.tetragonioides and green garlic were inhibited to a certain extent.The results of the cucumber yield of intercropping with different leafy vegetables showed that there was no significant difference between the M.crystallinum/cucumber treatment and the single crop,while the yield of the green garlic/cucumber,T.tetragonioides/cucumber treatment were significantly lower than the single crop,besides cluster mallow,B.rubra,amaranth,water spinach were significantly higher than the single crop.But in terms of the total net income,except for the green garlic/cucumber treatment,the total net income of other intercropping treatments was significantly higher than the single cropping treatment,among which the M.crystallinum/cucumber treatment was the highest,followed by T.tetragonioides/cucumber,cluster mallow/cucumber,B.rubra/cucumber,water spinach/cucumber and amaranth/cucumber.In the spring stubble of 2020,the yield and total net income of intercropping between cucumber and different leafy vegetables showed that,except for B.rubra,amaranth,and green garlic intercropping,the yields of cucumber were not significantly different from the single crop,and the yield of other intercropped cucumbers was significantly higher than the single crop,the highest total net gain is M.crystallinum/cucumber and T.tetragonioides/cucumber.Overall,there was no significant difference in the nutritional quality of cucumbers between the two spring stubble intercropping treatments and single cropping.Comprehensive field management,cucumber yield and the total net income,etc.,the results show that:the best intercropping mode is M.crystallinum/cucumber and T.tetragonioides/cucumber in spring.The suitable plant number ratio of cucumber and M.crystallinum was 1:1 and the row spacing of M.crystallinum was 33 cm×40 cm.The suitable plant number ratio of cucumber and T.tetragonioides was 1:0.5～1:0.6,the ratio of row number was 2:1,and the plant spacing of T.tetragonioides was 30 cm.In terms of management,cucumbers are the mainstay,and M.crystallinum and T.tetragonioides are also considered.2.Biological effects of different leafy vegetables and cucumber intercropping in autumnIn the autumn stubble of 2019,the growth and development results of the intercropping of cucumber and different leafy vegetables showed that compared with the single crop,except for the cucumber stem thickness that had no significant difference in each treatment,the other morphological indicators had no obvious regular changes;the intercropping treatments failed to significantly reduce disease index of cucumber fusarium wilt and root-knot nematode.The results of yield and total net income of different treatments showed that the yield of M.crystallinum/cucumber and T.tetragonioides/cucumber treatment was significantly higher than the single crop;except for the M.crystallinum/cucumber treatment,the total net benefit of the T.tetragonioides/cucumber and the B.rubra/cucumber treatment was significantly higher than other treatments.Compared with the spring crops of 2019 and2020,the yield of autumn leafy vegetables was significantly reduced,indicating that autumn cucumbers were not suitable for intercropping with leafy vegetables,but the intercropping of autumn B.rubra/cucumbers still had certain value.3.Soil chemical properties and enzymatic activities of different leafy vegetables and cucumber intercropping treatments in spring and autumnCompared with single crop,the intercropping treatments in spring and autumn had no significant effect on soil p H（except for very individual treatment）and content of Mg²⁺.After three consecutive intercroppings,the soil organic matter content in the intercropping treatments of prickly pear,T.tetragonioides,M.crystallinum,and green garlic increased significantly;almost all intercropping treatments significantly decreased the content of total nitrogen（except green garlic）,total phosphorus（except B.rubra）,total potassium（except for amaranth,M.crystallinum and green garlic）decreased significantly.Among all leafy vegetable intercropping treatments,the spring stubble water spinach/cucumber,T.tetragonioides/cucumber and M.crystallinum/cucumber treatments have the best effect on reducing soil soluble salt.After three consecutive intercroppings,the intercropping of water spinach and T.tetragonioides significantly increased the activity of soil neutral phosphatase,and the intercropping of T.tetragonioides,green garlic,M.crystallinum,and cluster mallow significantly increased the activity of soil sucrase.The intercropping of M.crystallinum and cluster mallow treatments significantly enhanced the activity of soil dehydrogenase,but there was no significant difference in soil catalase activity among the treatments.In improving the soil quality of continuous cropping of cucumber in greenhouse,spring intercropping was significantly stronger than autumn intercropping.The effect of spring intercropping on improving the soil quality of continuous cropping is in descending order:T.tetragonioides/cucumber,M.crystallinum/cucumber,water spinach/cucumber,cluster mallow/cucumber,B.rubra/cucumber,amaranth/cucumber,green garlic/cucumber.4.Soil chemical properties and enzymatic activities of different leafy vegetables in summer fillingThe results of the summer filling experiment showed that all treatments had no significant effect on soil p H and Mg²⁺,and all treatments significantly increased the soil organic matter content and significantly reduced the soil electrical conductivity,especially in the spring intercropping of T.tetragonioides and newly-sown amaranth.The contents of total nitrogen,total phosphorus,total potassium,Ca²⁺and Cl^-in the soil were significantly reduced by each summer filling treatment.Except for winter cluster mallow,other summer filling treatments significantly reduced the soil content of Na⁺.At the end of the filling period,the soil dehydrogenase activity of each treatment was significantly increased,and the soil catalase activity（except the newly planted T.tetragonioides）and the neutral phosphatase activity of most of the treatments（except spring intercropping T.tetragonioides）were significantly increased,while soil sucrase activity decreased significantly（except for spring intercropping B.rubra and T.tetragonioides）.In addition,the soil urease activity of water spinach and amaranth were significantly enhanced at the end of the filling period.Combining the yield,net income and improvement of continuous cropping soil quality of leafy vegetables in summer,it is the most economical and ecological benefit to use spring stubble intercropping of T.tetragonioides and spring stubble intercropping of B.rubra for summer filling.