| Pool-culture and pot experiments were used to study the effect of continuous cropping on the growth, development and quality of flue-cured tobacco, and the physics and chemistry character of soil planting tobacco. And the improvement effect of microbial agents on the tobacco growth, development and quality of continuous cropping flue-cured tobacco, and the physics and chemistry character of continuous cropping soil were investigated. The experiment was designed to evaluate the harm on growth, quality and the physics and the soil chemistry character of continuous cropping caused by continuous cropping in Chongqing tobacco areas, and the role of microbial agents in continuous cropping soil repair. So it will offer some effective technologies for the abatement technology of continuous cropping of flue-cured tobacco, while the sustainable development of the tobacco produces in Chongqing tobacco areas. The main results are as follows:1 Effect of continuous cropping on tobacco in Chongqing tobacco areas1.1 The effects of different years of continuous cropping on growth and development were different. The plant height, pitch, leaf width, leaf length, dry weight, and the N, P, K nutrients accumulation, the contents of total sugar, reducing sugar and K of different organs of 8 years cropping were significantly lower than what of normal cropping and 3 years cropping, and the content of nicotine was significantly higher than what of normal cropping and 3 years cropping. And in this study, the trends of the yield and value of flue-cured tobacco were first increased and then decreased, along with the continuous cropping years increasing, and the ratio of mid-high grade leaves and average price of tobacco, all their trends were downward trend, along with continuous cropping years increasing.1.2 Tobacco cropping could increase the soil available N, P, K content, even appeared serious accumulation. Their content increased with cropping years'increasing, the accumulation of available P was most serious. And the available P average content of cropping 8 years in the tobacco growing season were higher than normal and 3 years cropping, increasing by 79.41%, 55.10%. And the soil organic matter content was first increased and then decreased with the extension of tobacco continuous cropping year. different elements content also increased with cropping years'increasing, the contents of cropping 8 years were more than CK's, by 1.2 times Same time, the study also found that the organic matter, available N, available P, available K content of cropping tobacco soil showed a strong regularity with the advanced of tobacco growing period, and the trends were "up-down-up-down". And there had two peak values at 65d and 98d after transplanting.1.3 Number of soil bacteria and actinomycetes were first increased and then decreased with the continuous cropping years increasing. But the number of soil fungi decreased with continuous cropping years increasing. Therefore, the trend of actinomycetes number, and the unease, phosphatase, invertase and catalase activities of each treatment was "up-down-up-down", along with the flue-cured tobacco growing, and it was the same as the trends of soil enzyme activities. But, the trends of soil fungi and actinomycetes were not obvious, along with the variation of flue-cured tobacco growth period.1.4 The difference of different years of continuous on the chlorophyll and carotenoids of different leaf parts were different in growth peak period. the content of and quite different. The chlorophyll and carotenoids of middle and lower leaves of normal cropping were the larger (except for the chlorophyll b of the lower leaves). While, all these of cropping 8 years were the minimum, and there were significant difference of chlorophyll and carotenoids among different treatments. Tobacco cropping could cause the activities of CAT and NR decreased, and MDA content increased. And the CAT, NR activities and MDA content of different leaf positions were different, but all of them of upper leaves were maximum, while the lower leaves were minimum. 2 The effect of microbial agents on continuous cropping of tobacco2.1 Microbial agents could significantly increase the agronomic traits of tobacco cropping, and microbial agents had he most obvious role in the plant height, leaf number and maximum leaf area , and its values were higher than CK, and their were significant differences with CK(except for treatment 4). But Microbial agents had little effect on the stem circumference. The differences of deferent microbial agents on the agronomic traits were different. And the promotion effect of treatment 1, treatment 2 and treatment 3 were optimal, but the promotion effect of treatment 4 was less. Meanwhile, the study also found that microbial agents were significantly promoted on the dry matter accumulation, nutrient accumulation rate, chemical composition and economic traits of tobacco, and also promote the chemical composition of flue-cured tobacco more suitable and coordination.2.2 Microbial agents could be significantly improved the contents of soil organic matter and available NPK in continuous cropping soil. Which may be due to microbial agents improved the number of the soil, so improved the abilities of transformation and cycling of soil organic matter and nutrient. In this study, except for the 65d after transplanting of treatment 3, 45d after transplanting of treatment 4, the soil organic matter content of the other were significantly higher than that of CK, and there are significant differences among the treatments. and the effect of treatment 1 were the best, This depend on microbe-manure had a large number of beneficial bacteria what accelerate the transformation of soil organic matter and also contains large amounts of organic matter; Except for treatment 2 and treatment 4, the soil available P contents of the other treatments were significantly higher than CK, and there were significant differences among the treatments. and the effect of treatment 3 was the best; Except for 75 and 113ds of treatment 1, the soil available K content of other treatments all higher than CK; The soil nitrogen content of each treatment was higher than CK, and there were significant differences among the treatments, and the effect of treatment 1 was the most significant.2.3 In the flue-cured tobacco growth period, the change trends of the quantity of bacteria and fungi were same as the change trends of the soil enzyme activities, and showed that "up-down-up-down" trend. Microbial agents could promote the quantity of bacteria, fungi and actinomycetes. The quantity of bacteria of each period were significantly higher than CK, microbial agents on the number of bacteria, and the number of actinomycetes during the growing season averages were higher than CK. The study also found that the number of microbial agents in the promotion of soil, and significantly contributed to the increase of microbial biomass carbon and nitrogen. In this study, four kinds of microbial agents on microbial biomass carbon and nitrogen were significantly higher than CK, and except for treatment 4, the other treatments were significantly different with CK.2.5 treatment 1, treatment 2 and treatment 4 treatments improved the activities of these four soil enzymes. However, treatment 3 treatment only improved the activities of urease, phosphatase and catalase. Based on the improvement effects, treatment 1 and 2 were the most efficient, and that of treatment 3 and 4 were the second. This showed that microbial agents could to create a good soil biochemical environment for the production of quality tobacco.2.6 Microbial agents could significantly improve the chlorophyll and carotenoid contents of tobacco leaves, and the effect of treatment 1 on the chlorophyll and carotenoid contents of the lower and upper leaves were most obvious, the effect of treatment 2 on the chlorophyll and carotenoid contents of the lower and middle leaves were most obvious. The change trends of CAT and NR activities and MDA content between the different variations of the same leaf were same, and the upper leaves were the largest, the lower leaves were minimal. Microbial agents could improve CAT and NR activities and decrease MDA content of cropping tobacco leaf, and the effect of treatment 2 on CAT activity and MDA content were greater, while the effect of treatment 3 on NR activity was with greater. |
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