| Continuous cropping is common in vegetable protected production, especially in some traditional producing areas, the increasing continuous cropping obstacles have restricted the sustainable development of protected vegetables. Using the nutrition medium made from crops straw and organic manure as the main raw materials instead of heavy continuous cropping soil in protected vegetable cultivation has become an effective way to solve vegetables continuous cropping obstacle. In this study, the 1～10 stubbles soil of cucumber continuous cropping were set as control, the effects of nutritiont medium continuous cropping cultivation on cucumber growth and development and the microenvironment at rhizosphere were studied, the alleviating effects and influence factors of nutrient medium cultivation on continuous cropping obstacle were clarified. Otherwise, mimicry acidifying test, high temperature heat treatment and biochar repair test in continuous cropping nutrition medium were employed to clarify the possible factors and adjustment measures of the way how nutrition medium alleviated continuous cropping obstacle, these experiments results will put forward in bid to provide technical support and theoretical basis for overcoming continuous cropping obstacles and pursuing application of nutritional medium in protected cultivation.The main results were as follows:1. Compared with soil cultivation, nutrition medium alleviated continuous cropping obstacles significantly, obvious reproductive disorders were shown on cucumbers after four stubbles of soil cultivation and ten stubbles of nutrition medium, respectively. In the same continuous cropping stubble, cucumber plant height, stem diameter, the weight of aerial parts and roots, leaf chlorophyll content and net photosynthetic rate of nutrient medium cultivation were higher than that of soil cultivation. The usage of nutrition medium raised cucumber plot yields by 30.0%,9.5% and 6.2% respectively, and decreased plant mortality by 21.0%,35.7% and 24.4%, which indicated the nutrition medium cultivation had obvious advantage compared to soil cultivations in promoting cucumber growth and yield formation in continuous cropping cultivations.2. Along with the increasing cucumber continuous cropping stubbles, the physiochemical properties of soil and nutrition medium showed a general pattern of continuous cropping obstacles, such as the increase of the bulk density, conductivity, organic matter, total nitrogen, total phosphorus, available nitrogen and available phosphorus, the decrease of total phosphorus and pH. However, within the same stubble times, bulk density and conductivity of nutrition medium were higher than that of soil, at the meantime, the water content, pH, organic matter, total nitrogen, total phosphorus, alkaline hydrolysis nitrogen, available phosphorus and available potassium were lower than that of soil, which declared each stubbles of nutrition medium shown a better physiochemical properties than soil, and improved nutrient absorption by roots.3. Besides sucrase in tenth stubble and neutral phosphatase in fourth stubble, within the same stubble times, sucrase, neutral phosphatase and urease activity of nutrition medium were higher than that of soil; fungi population was lower than that of soil, bacterial population in fourth stubble, the ration of bacteria to fungus were higher than that of soil. Denaturing gradient gel electrophoresis (DGGE) and stripe distribution of bacteria 16S rDNA and cluster analysis of bacterial community similitude showed, there were significant differences between the effects of nutrition medium and soil on bacterial community, the bacterial community and diversity of nutrition medium were much better than that of soil, the bacterial community in tenth nutrition medium was close to soil.4. Compared with continuous cropping soil and nutritional medium without heat treatment, cucumber growth were improved by heat treatment, but the improvement shown in different ways, for nutrition medium, plant height, dry and fresh weight of aerial part were increased, and for soil cultivation, every growth index was raised except for chlorophyll content, and the promotion in soil was more significant than that in nutrition medium. And the best biological effect heat treatment for continuous cropping soil and nutrition medium is 55 ℃ for 96 hours.5. The nutrients content and biological characteristics of continuous cropping soil and nutritional medium were changed after heat treatment. In soil after heat treatment, the content of organic matter, total nitrogen, alkali-hydrolyzale nitrogen, rapidly available potassium were significantly improved, while catalase, neutral phosphatase, sucrase activity, bacteria, actinomycetes population and B/F were increased, fungi population was decreased; in nutrition medium after heat treatment, bacteria and actinomycetes population and B/F were increased, fungi population was decreased, the microbial environment was improved, but at the meantime, the activity of catalase, sucrase and urease, the content of total nitrogen, alkali-hydrolyzale nitrogen, rapidly available potassium were declined. These indicated that the fast deterioration of physiochemical property and biological environment in continuous cropping soil is one of the main causes of continuous cropping obstacles.6. The results of acidification simulation test showed that during the decline of pH value from 6.5 to 5.5, nutrition medium showed its superiority in cucumber cultivation, plant height, fresh and dry weight of aerial part, fresh weight of roots and leaf chlorophyll content were significantly higher than that in soil, especially in pH5.5 treatment. However, with further easing of pH value, this cultivation advantage gradually faded away.7. During the decline of pH value, the content of organic matter, alkali-hydrolyzale nitrogen rapid available phosphorus and potassium in nutritional medium were maintained at a higher level. The failing pH value had little impact on enzyme activity of nutritional medium, but that of soil cultivation was significantly suppressed. Bacterial population and ratio of bacteria to fungus in nutrition medium were higher than that in soil when the pH value ranged from 5.0 to 6.0. Under the condition of pH5.5-6.5, the buffering capacity to acidification was stronger in nutritional medium, which concerned with higher content of organic matter and bigger cation exchange capacity in nutritional medium, this may be one of major factors for how nutritional medium alleviated continuous cropping obstacles compared to soil cultivation.8. adding biochar content of organic matter and rapid available potassium and pH value were increased, the growing environment of cucumber roots was improved, photosynthesis, SOD and POD activity in leaves were accelerated, yield and fruit soluble sugar were raised, the accumulation of nitrate was decreased, the most obvious effect was performed when adding 5% mass ratio biochar.To sum up, nutritiont medium showed a significantly alleviated continuous cropping obstacle compared with soil cultivation, the main influence factors can be summarized as the following two points:on the one hand, the better physiochemical property and biological characteristics in nutrition medium provides more nutrition and better the microenvironment at rhizosphere for cucumber growth; on the other hand, the slower deterioration of physiochemical property and biological characteristics in nutrition medium eases the impact of continuous cropping on cucumber growth. |
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