| Growing conditions in the Xinjiang Uyghur Autonomous Region are ideal for the production of processing tomatoes. However, tomato yield have declined in recent years due to the widespread use of continuous cropping practices. This paper includes results from both pot and field experiments. The objective of the pot experiment was to assay allelopathic potential in extracts from processing tomato plants and fruit. The objective of the field experiment was to determine the effect of continuous cultivation on the growth, photosynthetic activity, metabolic enzyme activity, dry matter production, and yield of processing tomatoes. The study increases understanding about allelopathy and auto-toxicity in continuously cropped processing tomatoes. The results can be used to develop recommendations for increasing tomato production in Xinjiang Province.Long-term continuous cropping of processing tomato had negative effects on the soil nutrient balance and the obstacles of continuous cropping were obvious. Soil pH increased as the duration of continuous cropping increased. Total P concentrations, available P concentrations and total K concentrations increased during the first three years of continuous cropping and then decreased, while soil bulk density didn’t change significantly. Soil organic matter content, total N concentrations and available K concentrations during seven years of continuous cropping decreased by 8%, 21% and 29%, respective.Long-term continuous cropping of processing tomato significantly inhibited the activity of soil microbial activity. Compared with soil microbial biomass P(SMBP), Soil microbial quotient(qMB), soil microbial biomass N(SMBN) and microbial biomass C(SMBC) significantly decreased as the duration of continuous cropping increased. After seven years of continuous cropping, the SMBC content, the SMBN content and the microbial quotient(qMB) decreased by 48.2%, 78.8%, 52.3%, respectively. Continuous cropping significantly increased soil catalase activity, whereas the opposite trend was observed for sucrase activity, phosphatase activity., polyphenoloxidase activity and urease activity. Correlation analysis showed that there was significant correlation among soil pH, soil microbial biomass, qMB, soil enzyme activities and soil nutrients. These results indicate that soil microbial biomass and activity combining reflect changes in soil quality and thus can be used as biological indices in the evaluation of soil fertility.Continuous cropping of processing tomato significantly increased the PLFA of fungi, whereas the opposite trend was observed for the total PLFAs biomass, bacteria, and the ratios of bacteria and fungi, but the PLFA of actinomycetes have on change in the law. In the expanding stage, the PLFA of bacteria and actinomycetes presented the highest. The PLFA of fungi presented the highest in the maturity stage. The total PLFAs biomass presented the highest in the expanding stage, followed by the maturity stage, and then in the flowering fruit bearing stage. Therefore,There were different influences on soil microbial at each growth stage of processing tomato in different years of continuous cropping, and fungi were better adapted to the nutrient poor conditions compared to bacteria. Based on the diversity index analysis, shannon-wiener index, simpson indenx, brillouin index and pielou index increased first and then decreased with the continuous cropping years of processing tomato increasing. Soil microbial diversity index reached the highest in three years of continuous cropping, while the seven years of continuous cropping of processing tomato was the lowest. The result could be concluded that the microbial community diversity and uniformity were decreased with the increasing of the plant years. Correlation analysis showed that there was significant correlation among the PLFA of bacteria, fungi and actinomycetes, the total PLFAs biomass, soil microbial biomass and soil fertility factors. The result indicates that the soil microbial biomass was highly related with the soil fertility and thus can be used as biological indices in the evaluation of soil fertility. The above results revealed that with the increase of continuous cropping years, the microbial community structure in processing tomato soils occurred in a great change, which would lead to a decline of soil microbial biomass. Finally, the obstacles of continuous cropping were the result of the comprehensive effect of soil micro-ecological system and environmental factor.Compared with the bacteria, the shannon-wiener index and richness index of fungal in rhizosphere soil decreased with the increasing years of processing tomato, and those indexes in maturity stage higher than in flowering fruit bearing stage. The bacterial and fungal pielou indexes were not sensitive to continuous cropping years of processing tomato, which indicats that soil microbial distributes uniformly in different treatments. Soil indigenous bacterial community structure was significantly influenced by continuous cropping of processing tomato, and the number of some dominant populations of soil indigenous bacteria decreased or disappeared. The dominant fungi were more different in the fields with different continuous cropping years,continuous cropping significantly increased the number of some fungi,meanwhile, the number of some other fungi was significantly decreased or disappeared. Most dominant fungi populations were enriched in soil with processing tomato continuous cropping years of 5,and which number was quite different with the non-dominant fungi populations. The change of soil bacteria and fungi population balance that caused by continuous cropping of processing tomato maybe one of the important reasons for its continuous cropping obstacle. Sequencing analysis of prominent electrophoretic bands showed that the dominant bacteria of soil sample belong to Pseudomonas sp., Arthrobacter ramosus, Alpha-proteobacterium, Uncultured alpha proteobacterium and Uncultured bacterium, while the dominant fungus belong to Uncultured fungus, Geosmithia putterillii, Amylomyces rouxii, Candida tropicalis and Myrothecium sp..Fruit numbers, fruit weights and yields of processing tomato significantly decreased as the duration of continuous cropping increased at maturity. There was a significant negative correlation between yield and continuous cropping years, and y=?26.261x+520.55(r=0.9746**). After seven years of continuous cropping, the fruit numbers, the fruit weights and yields decreased by 17.1%, 20.2% and 33.9%, respectively.In summary, long-term continuous cropping of processing tomato significantly changed soil microflora, decreased soil microbial activity, even caused the imbalance of soil nutrient ratio, and finally showed continuous cropping obstacle. Therefore, in agricultural production, it’s best to use cereal crops and processing tomato to take reasonable rotation, but avoid making peppers, eggplant and other solanaceae crops as previous crops. This study suggests that continuous cropping of processing tomato preferably not more than 3 years. After processing tomato harvest, it must purge all of diseased plants and residual bodies, and do autumn ploughing and winter irrigation early. Moreover, it must strengthen the prevention and treatment of field diseases at expanding stage to maturity in particularly. |
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