Study On Allelopathy Of Decomposing Material Of Tobacco Residues

Tobacco is the solanaceae crops avoiding continuous cropping. Continuous cropping obstacles in the production of tobacco have become the bottleneck of tobacco development in China. Many studies had showed that allelopathy caused by allelochemicals was the main reason for continuous cropping obstacle and allelochemicals mainly come from decomposition of the plants.With lettuce seeds and tobacco K326 as materials and by the methods of biological detection, hydroponic experiments and pot experiments, the existence of allelochemicals from decomposition of tobacco and its role of regulation had been detected Preliminarily. The main findings are as follows:1. Results from biological detection had showed that allelochemicals existed in the early decomposing of all tobacco residues and had activity of allelopathy under a wide rang of pH. The acid-soluble component in decomposition had effect of inhibition caused by allelopathy and neutral and alkali soluble component had weak inhibition. Low concentration of neutral and alkali soluble components in decomposition had a certain promoting role of allelopathy. The decomposition from different tobacco residues and its different components produced a certain effect of allelopathy on lettuce seeds and the effect of inhibition of allelopathy increased with the increase of the concentration. Low concentration for promotion but high for suppression had been found.2. Results from hydroponic experiments had showed that tobacco residue decomposition had an effect of inhibition on dry matters accumulation and with increase of the concentration of decomposition, the effect of inhibition increased but its role on the seedling chlorophyll content, root activity, nitrate reductase activity was not obvious. Tobacco residues decomposition could increase activity of POD in tobacco seedlings and content of MAD and the level of peroxidation injury increased with increase of time of treatment, indicating tobacco residues decomposition had autotoxicity on the growth of tobacco seedlings.3. Results from pot experiments had showed that decomposition from tobacco roots rich in nutrients, could significantly increase the soil fertility and had inhibition role on growth of pot tobacco in early stage with a strongest inhibition as highest concentration used, but its effect of inhibition became weak gradually as tobacco grew and even represented promotion, greatest at low concentrations and intermediate concentrations. Treatment by decomposition from tobacco roots increased content of MAD and protected activity of POD and the activity of growth-related enzymes was at first increased and then decreased. In addition, the early decomposition from tobacco roots may contain pathogenic factors that may increase the risk of tobacco susceptibility.In conclusion, allelochemicals that had negative influence on growth and development of tobacco could be released into soil in the early stage of tobacco decomposing and showed a serious impact on matter accumulation and antioxidant system of the tobacco and may increase the risk of tobacco susceptibility, leading to decreasing in yield and quality. Therefore, allelochemicals from decomposition of tobacco may contribute to continuous cropping obstacle and in production of tobacco, tobacco residues should be handled properly and prevent its decomposition in the field.