Effects Of Different Cropping Patterns On Soil Biological Properties And Quality Of Tobacco In Tobacco Growing Areas Of Shandong Province

The field experiment was carried out in Yishui County of Linyi City, Shandong Province from 2008 to 2009. Different tobacco planting systems (green moanure-tobacco with crop rotation, monoculture-tobacco, wheat-tobacco with crop-rotation and inter-cropping) were studyed to invistigate the effects of different cropping patterns on soil biological properties and quality of tobacco. The results showed that:1. In this study, there were no significantly difference of soil catalase, sucrase and urase activity in plowed layers (0~25cm) under different planting systems, however, these three soil enzymes activities varied with tobacco growth stages. In terms of different soil layers, the activities of catalase and urase increased with soil depth in the plowed layers; while sucrase activity was increased first and then dramatically decreased. In the whole growth period of flue-cured tobacco, the temporal variability of three soil enzymes was also analyzed. Soil urase got the largest temporal variation coefficient, which showed that it was impacted by the external environment largestly in the whole tobacco growth period; Soil sucrase took the second place, soil catalase had the smallest temporal variation coefficient, with the most stable seasonal variation.2. The ammonification intensity increased with time in plowed layer (0~25cm) under different treatments. The ammonification intensity varied with soil depth, it decreased with the soil depth in monoculture-tobacco and green manure-tobacco with crop rotation treatments; in wheat-tobacco with crop-rotation treatment, it reached the maximum in 15~25cm soil layer; while it showed no significant difference in different soil layers under wheat-tobacco with inter-croping treatment. However, the nitrification intensity varied with different growth stages in different treatments: The nitrification intensity decreased with time under monoculture-tobacco treatment; there were stable nitrification intensities in 0~5cm and 5~15cm soil layers in the other treatments; the nitrification intensity decreased before the rosette stage, and then show a stable intensity in growing and mature stages in 15~25cm soil layer.The nitrification intensity increased with soil depth in green manure-tobacco with crop rotation, wheat-tobacco with crop-rotation and inter-cropping treatments: while there were no significant differece in different plowed layers under monoculture-tobacco treatment.3. The number of main soil microbial flora in the study showed that soil bacteria content were the most, followed by fungi and the actinomycetes was least in tobacco soil plowed layer. The content of soil gram-negative bacteria was much higher than the gram-positive bacteria, whereas there were no significant differences between the content of soil aerobic and anaerobic bacteria. The content of soil microorganisms were most in green manure-tobacco with crop rotation treatment, less content in monoculture-tobacco treatment and the least content was in wheat-tobacco with crop-rotation and inter-cropping treatments. The content of main soil microbial flora were inconsistency in different growth stages, soil bacteria content decreased with time in different treatments; in 0~5cm soil layer, there were less fungi content in rosette stage and in growing stage, more content in mature stage. It was decreased in 5~15cm soil layer, while increased in 15~25cm soil layer; actinomycetes content decreased both in 0-5cm and in 5~15cm soil layers under different planting systems. However, there was no significant difference in actinomycetes content in other treatments, besides the high content of actinomycetes at the stage of before transplanting of monoculture-tobacco treatment or at growing stage of wheat-tobacco with crop-rotation treatment in 15~25cm plowed layers..4. In the four tobacco planting systems, there were higher total nitrogen content and total plant alkaloid content of leaves, yet lower leaf sugar content and sugar to nicotine ratio in green manure-tobacco with crop rotation treatment compared with other treatments,; in wheat-tobacco with crop-rotation treatment, there were high content of leaf sugar content and high potassium chloride ratio, yet low total nitrogen and total plant alkaloid contents; the highest potassium content was found in wheat-tobacco with crop-rotation treatment, while the lowest content was in monoculture-tobacco treatment among all the tobacco planting systems.5. The tobacco yield and output value were highest in the green manure-tobacco with crop rotation treatment, followed by the wheat-tobacco with inter-cropping treatment, and the lowest value were both in monoculture-tobacco and wheat-tobacco with crop-rotation treatments. In general, the soil microbial community and biomass was highest in green manure-tobacco with crop rotation treatment. After green manure plowing, it supplied numerous nutrients to soil, which contributed to the improvement of tobacco yield and output value, but negative to the leaf quality due to the high content of leaf total nitrogen content and total plant alkaloid. In wheat-tobacco with crop-rotation and inter-cropping treatments, the soil microbial community and biomass were always at a low level. The decomposite rate was slow after straw returned to field. Moreover, straw decompostion could fix part of soil nitrogen, accordingly, the content of leaf total nitrogen content and total plant alkaloid was relatively low. Furthermore, it had a relatively short growth period of the wheat-tobacco with crop-rotation treatment, which was the main reason for low tobacco yield and output value. But wheat harvest could aslo increase the income. So we could achieve relatively high consolidated income in the wheat-tobacco with inter-cropping planting.