Effect Of Organic Nutritiveadditives On Soil Micro-ecological Restoration And Its Mechanism.

Soil health is based on soil microbe diversification, and healthy soil is the foundation for plant healthy development. Soil micro-ecological niche and microbial diversity could be changed by crop system, fertilizer and pesticides and some other factors in different levels. Continuous-cropping, excessive chemical fertilizer and pesticides are the main factors that depraving soil healthy, aggravating plant diseases. Application of organic additives is possibly effective pathway for restoring soil microbial diversity and inhibiting succession cropping obstacle.In this study, the affects of continuous-cropping on soil microbial diversity was measured firstly. Then, three kinds of organic carbon sources, e.g. biochar, corn starch, chitin, and four kinds of organic nitrogen sources, e.g. bone meal, bean flour, tryptone, humic acid, and organic 8-hydroxy quinoline were tested on potted Nicotiana tobaccum. Meanwhile, the microbial diversity restoration was analyzed by culture-dependent method and culture-independent PCR-DGGE method. This study aims at exploring ecological techniques for restoring soil micro-ecology, and underlying the foundation of tobacco healthy cultivation. The main contents and results were as follows:1.The varieties of microorganisms were reduced observably in the soli which had be used for continuous cropping tobacco for several years and were damaged by tobacco diseaseWe found that the bacteria levels from three and five years'continuous tobacco cropping field were reduced observably along the increasing of continuous cropping year. And the same time, actinomycetes and fungi levels of the soil did not varied distinctly and declined generally, which were also correlated with the degree of tobacco diseases.2. By using organic additives, the soil microbial diversity was enriched and tobacco plant development was also improved.(1) In the single-factor test, straw carbon and corn starch, of the tested carbon source, had a significant enrichment of soil bacteria, fungi and actinomycetes, also promoting tobacco leaves'growth and roots development. Among them, 6g/plant of straw carbon showed the best effect, 3g/L of corn starch was the better. There was some effect on soil microbial enrichment by using chitin (400 dilution ), with slightly effect on tobacco growth. Humic acid, bone meal (2.5%) and bean flour (90g/L) as nitrogen sources can significantly enrich soil bacteria, fungi and actinomycetes population, which also promoted tobacco leaf and roots'development. Humic acid in 4g/plant significantly affected the developments of tobacco. Eight hydroxyquinoline in 2.5g/L also dramatically enriched soil bacteria and actinomycetes population, however it had little effect on the fungi and tobacco growth.(2) The multi-factor test showed that different organic C sources and organic N sources had different effect. On root fresh weight, the importance order was humic acid> bone meal>bean flour> biochar; On stem and leaf fresh weight, the importance order was humic acid> biochar> bean flour>bone meal>; On soil bacteria, the importance order was biochar> bone meal >humic acid>bean flour; On soil fungi, the importance order was bone meal> biochar > bean flour> humic acid; On soil actinomyces, the importance order was humic acid> bone meal>bean flour> biochar.(3)Consisting with potted trial, PCR-DGGE analysis showed some single factor and combination treatment more significantly enriched the diversity of soil bacteria.In general, the soil microbial diversity can be reduced significantly by continuous cropping, and then tobacco disease became severe and severe yearly. Addition of organic nutriments had a positive effect on soil microbial diversity and benefiting soil bacteria, fungi and actinomyces, that restored soil micro-ecology and improved tobacco growth.