Effect And Mechanism Of Intercropping Garlic Or Green Garlic On Alleviating The Continuous Cropping Obstacles Of Cucumber Grown In Plastic Tunnel

Continuous cropping obstacles are becoming more and more serious. It has restrictedsustainable production of cucumber in protected cultivation. In this study, garlic or greengarlic was continuously intercropped with cucumber to investigate the effect and mechanismof intercropping alleviating continuous cropping obstacles of cucumber in plastic tunnel. Thegrowth and development, physiological changes, disease incidence, yield and quality ofcucumber, and microbial feature, nutrient status, pH and EC value of the soil was analysed.The objective of this study is to provide a theoretical and technical basis to the establishmentof the efficient and sustainable intercropping patterns of garlic and green garlic withcucumber. The main results summarized as follows:（1） Except cultivar G064, intercropping with other cultivars of garlic significantlyimproved the growth of cucumber plant height and stem diameter. Conversely, intercroppingwith green garlic inhibited cucumber growth in the first intercropping year. The intercroppedgarlic and green garlic significantly enhanced the plant height, stem diameter, number offemale flowers and total number of leaves, and the leaf area of the fifth functional leaf ofcucumber in the second and third cropping year. Compared with monocropping, intercroppingwith garlic and green garlic significantly increased chlorophyll content, decreased MDAcontent, SOD, POD and CAT activity of cucumber leaves.（2） Since spring cultivation of the first intercropping year, yield advantages ofintercropping with garlic and green garlic started to appear, compared with monocropping. Inspring cultivation of the first year, garlic cultivar G005increased cucumber yield by13.4%;in autumn cultivation of the second year, green garlic increased cucumber yield by11.9%.There was no significant difference of cucumber yield between intercropping andmonocropping in the third year. In autumn cultivation of the first intercropping year, differentcultivars of garlic and green garlic had no significant effect on cucumber fruit quality. In spring cultivation of the first year, intercropping treatment significantly increased Vc contentof cucumber fruit. Dry matter, soluble protein and Vc content were significantly improved byintercropping in the second year. Intercopping with garlic and green garlic significantlyincreased the content of dry matter, soluble protein, Vc and soluble sugar of cucumber fruit inthe third year.（3） The inhibitory effect of cultivar G064and green garlic among treatments was better.With continuous cropping increasing, the incidence rate of cucumber fusarium wilt and rotknot nematode disease was increasing in monocropping. Intercropping treatmentssignificantly inhibited the incidence rate of cucumber fusarium wilt and the nematode, and thegreen garlic showed stronger inhibitory effect. Intercropping with garlic and green garlicsignificantly increased the amount of soil bacteria and actinomyteces, while decreased theamount of soil fungi, compared with monocropping. In the first year, soil microbial speciesand amount was related to the dynamic sampling date and garlic cultivar. The previous trendwas not stable. In the second and third year, the effect trend of intercropping with garlic andgreen garlic on the soil microbe was stable. With the planting year increasing, the amount ofbacteria and actinomyteces was first decreasing slowly, then increasing rapidly and lastdecreasing; the amount of fungi was increasing as “M” dynamic change. Intercropping withgarlic and green garlic significantly influenced the activities of soil enzymes, which werevaried with enzyme species and intercropping years. Except autumn cultivation in the firstyear and spring cultivation in the third cropping year, intercropping significantly improvedsoil catalase activity. In the autumn cultivation of the first year, intercropping systemssignificantly reduced soil invertase and urease activities. Subsequently, intercroppingtreatment significantly improved enzymes activities. In the three continuous intercroppingyears, intercropping systems significantly improved soil alkaline phosphatase activity.（4） Intercropping with garlic and green garlic significantly increased soil available Ncontent, compared with monocropping. In autumn cultivation each intercropping year,intercropping treatments increased soil available P and K at the early growth stage ofcucumber. However, with the garlic and green garlic growing, the available P and K contentdecreased in intercropping systems. Up to the spring cultivation in the next year, the availableP and K content in the intercropping systems was no difference or higher than themonocropping after garlic and green garlic harvest. With the planting year increasing, soil pHvalue was gradually declining in monocropping. Intercropping treatment first reduced thenenhanced soil pH value, stabilizing soil acidity. From the second to the third intercroppingyear, intercropping treatments significantly reduced the soil EC value. It demonstratedintercropping treatments alleviated replant soil secondary salinization. （5） The harvest time of garlic in the intercropping systems planting in plastic tunnel was30⁴0days earlier than in the open field. Green garlic was continuously cut for four times inthe autumn season and had good commercial character. By productivity benefit analysis,intercropping garlic and green garlic significantly increase net output each planting year andarea in plastic tunnel. In the first year, intercropping with garlic cultivar G005, G064andG087increased the net output by15.6%,17.2%and19.6%, respectively; green garlicincreased the net output by33.6%. In the second year, the net output was increased by19.0%and38.1%when intercropping with garlic and green garlic. In the third year, the net outputwas increased by14.7%and28.3%in garlic-cucumber and green garlic-cucumberintercropping system, respectively.（6） Pot experiment was carried out to investigate the effect of intercropping withdifferent amounts of green garlic on nutrient uptake and soil microbial community structure.The results demonstrated that intercropping with green garlic significantly increasedcucumber biomass, N, P, K, Ca and Mn content, while decreased Mg, Zn and Fe content.Moreover, intercropping improved soil organic matter content and balance the proportion ofN, P and K. Intercropping with green garlic significantly increased population of soil bacteria,actinomycetes, AM fungi, Protozoa and B/F ratio, while decreased population of total fungi.Intercropping make soil from a more bacterial dominated to a more fungal communitystructure. Intercropping with moderate amounts of green garlic （300g,450g and600g garlicbulbs for each cucumber） showed better effect.（7） Antibacterial test in vitro was carried out to investigate inhibitory effect of garlic rootexudates and green garlic volatiles on growth of soil-borne and leaf disease. The resultsshowed that garlic root exudates significantly inhibited mycelial growth and sporegermination of cucumber fusarium wilt, and the effect was increasing with the concentions ofgarlic root exudates increasing. Inhibition rate of mycelial growth and spore germination was40.0%and60.4%when the concentration was0.28mg·ml^-1. Green garlic volatilessignificantly inhibited mycelial growth and spore germination of cucumber target spot.Inhibition rate of mycelial growth and spore germination was55.3%and93.3%when theconcentration was2.50mg·ml^-1. Mycelial morphology and structure observed by scanningand transmission electron microscopy demonstrated that treated mycelium was ruga, wizenedand easy to breakage; had thinner cell wall, more cavity, nonuniform cytoplast andunconspicuous nucleus zone.The experiment of continuous intercropping in three years demonstrated thatintercropping with garlic or green garlic alleviated continuous cropping obstacles ofcucumber. The mechanism were related to the allelopathy regulating effect of garlic root exudat and live volatile matter on the growth and physiology of cucumber, the incidence ofroot and leaf diseases, the microbial population and community structure, the soil enzymesactivities and soil nutrient availability. Intercropping garlic or green garlic with cucumber is aefficient and sustainable productive pattern.