| One significant symbol of modern agriculture is to the soil artificially imposed a number of technical measures, in particular putting in a lot of chemical fertilizers, pesticides and other chemicals to improve production conditions, to achieve the purpose of access to grain yield. However, due to the excessive use of land, giving the soil a large number of inputs and the use of chemical substances year after year, and giving up the use of organic fertilizers, soil quality is gradually losing bio-technology, and then to chemical technology, the quality of the soil physical and biological quality of place changes significantly affect the crop yield and quality and seriously restricts the sustainable development of agricultural production. Therefore, under the conditions of modern production levels, human activities on soil quality, seeking to restore and improve the soil quality has become one of the important tasks of scientific research workers in soil science.At present, work on restoration of soil quality on the theoretical foundation and technical measures at home and abroad is very rich, including the restoration of soil biological quality as the main objective of the research is important content and task in soil science, restoration ecology. Based on academic developments, combined with the actual production, developing the technology to restore soil biological quality seems especially urgent.In this study, micro-organisms with nitrogen fixation ability were filtered and separated from 70 different environment, different land use types and the different management levels soil , and in an attempt to propagation through training, applied to soil to improve soil nitrogen supply, promote the healthy growth of plants, gradually reduce the use of chemical fertilizer. Study yielded the following results:1. A total 38 isolates were selectively obtained from 70 soil samples. These isolates were separated based on their growth on nitrogen-free medium. These isolates were tested for their nitrogenase activity using acetylene reduction assay (ARA). The result suggested that 35 isolates showed nitrogenase activity, The nitrogenase activities of one isolates was significantly higher than the reference strain (Azotobocter chroococcum), this isolate was GD66-2; The rape was inoculated with 38 isolates , the results indicated that one isolate with higher yield on potted rape, and this isolate is GD92-3. Second, from the 70 tested soil 38 strains of nitrogen-fixing bacteria were screened from 18 soil samples, soil isolated strains only account1 / 4 for the total number of tested soil, and this indicating a long-term heavy use of inorganic nitrogen fertilizer, nitrogen-fixing bacteria in the soil itself is not conducive to breeding, soil biological systems suffer a great damage and crops have to rely on making a lot of fertilizer to use nutritional supplements which increased agricultural costs and environmental risk. Restoration of agricultural biological systems and cultivate their nutritional function becomes extremely urgent.2. On nitrogenase activity and obtain a yield significant taxonomic identification of strains were initially identified their taxonomic status. Given to the one on the high nitrogenase activity strains and a high yield strain for morphological, physiological and biochemical characterization, using 16S rDNA sequence analysis techniques to identify the nitrogen-fixing bacteria, GD66-2 was identified as Paenibacillus sp. Isolates GD92-3 was identified as Rhizobium.3. Isolates were inoculated to the test of soil fertility , in order to get the further identification of their biological effects and transformation in the soil material. Product of treated domestic sludge applicated for base fertilizer, The pakchoi was inoculated with GD66-2,GD92-3 bacteria solution,the results showed that: GD66-2 can significantly increase the fresh weight of pakchoi; pakchoi treated with GD66-2,GD92-3 had a same level total P compared to chemical fertilizer treatment, and GD92-3 can significantly increase total Vc content compared to chemical fertilizer treatment.Quality index of soil matrix also significantly changed, GD66-2 decreased pH and soil bulk density of surface soil, meanwhile it increased soil porosity and nutrient content.Soil biological quality was improved, pakchoi rhizosphere microorganisms have improved, soil enzyme activity significantly changed. GD66-2 increased the numbers of bacteria, nitrogen-fixing bacteria and cellulose-decomposing microorganism in rhizosphere soil, GD92-3 significantly increased actinomycetes number; soil enzyme activity with GD66-2 treatment had no obvious improve, GD92-3 significantly decreased activity of xylanase, pectinase. |
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