Comprehensive Evaluation Of The Effect Of Bioactive Humic Substances On Soil Environment Of Xinjiang Glycyrrhiza Uralensis Production Area

The total area of Xinjiang desertified land is 7.96×10⁵km², which takes up 47.7% of Xinjiang total area. Desertification has become the main presentation of Xinjiang soil degradation, which needs immediate restoration. Furthermore, Xinjiang is one of the most important Glycyrrhiza uralensis production areas in China. Improving the yield and modifying the production environment to prevent soil degradation and desertification have great social, economical and environmental profits. The in-house restoration effect verification test of bio-active humic substances (BHS) was first conducted, which verified the marvelous restoration effect of BHS on the desertification-caused degraded soil and made it relatively clear the relationship between humic acids and microorganisms. The effects of BHS at different rates on the soil quality of Glycyrrhiza uralensis production area were systematically studied through in-situ restoration test in Xinjiang. The dynamic changes of the soil mechanical composition, main nutrients, humus composition, enzymatic activities and microbial indices were analyzed and the restoration effects of BHS were verified. Systematic evaluation of the restoration effect was conducted through principal component and cluster analysis, and the comprehensive evaluation system fitting for evaluating the soil quality of Xinjiang Glycyrrhiza uralensis production area was established. The following conclusions were mainly drawn:1. In-house BHS restoration effect verification testThe quality of the BHS-treated soil has been greatly improved. The content of soil organic matter, the quantity of soil microbes and the biomass of Medicago sativa L. have rapidly and significantly increased. The relationship between humic acid and microbes and their respective contributions to the restoration were analyzed: the restoration effect was not obvious if microbes acted by itself.The humic acid itself played a more important role in restoration and microbes significantly improved the restoration effect of humic acid.The bio-active humic substances, as a whole, had the best restoration effect .2. In-situ restoration test of Xinjiang Glycyrrhiza uralensis production area(1) The height, aboveground fresh weight per plant and yield were examined to evaluate the effect of BHS at different rates on the growth status of Glycyrrhiza uralensis. The results showed that the effects of BHS were significantly different due to their rates. Medium and low rates of BHS contributed more to the increase of plant height and the aboveground fresh weight per plant. The former reached 80.8cm and 79.4cm and increased by 8.2% and 6.3%,respectively,the latter reached 137.5g and 134.7g and increased by 6.9%å’Œ4.7%,respectively,while the treatment of high rates of BHS showed little difference compared with the control. The yield reached 18412.95kg·hm^-2·dry weight and 16666.05kg·hm^-2·dry weight with the application of medium and high rates of BHS, respectively, increased by 29.1% and 16.9%,while the yield under the treatment of low rates of BHS was lower than the control with no BHS incorporation.(2)The soil texture was significantly promoted with the application of BHS,compared with the control with no BHS incorporation. The contents of coarse and fine sand decreased sharply with the increasing rates of BHS, while the silt and clay content increased significantly. During the first 150 days after application of BHS, soil pH showed little change and was in the range of 8.53-8.92.From the 150th to 190th day, the soil pH dropped obviously and fluctuated in the range of 7.80-8.19.The pH of the soil treated by BHS was slightly higher than that of the control. The contents of soil total nitrogen and organic carbon were significantly improved with the application of BHS and the best application rate was 450kg·hm^-2, at which the contents at the190th day increased by 21.6%, from 0.758g·kg-1 to 0.922g·kg-1 and 15.9%, from 7.55 g·kg-1 to 8.75 g·kg-1, respectively. There was an increasing trend for total phosphorus content and a descending trend for the total potassium.(3) The contents of extractable humus carbon(EH-C), fulvic acid carbon(FA-C) and humic acid carbon(HA-C) were greatly improved with the application of BHS, especially at the rate of 450kg·hm^-2,which reached 4.15g·kg-1, 2.16g·kg-1 and 1.99g·kg-1, respectively and increased by 21.0%, 17.4% and 20.1% correspondingly, compared with the control.(4)The soil urease, alkaline phosphatase and catalase activity were significantly improved after application of BHS. The best rate was 450kg·hm^-2 and the soil urease, alkaline phosphatase, catalase activities reached 187.12 mg·kg-1·3h-1, 26.33 mg·kg-1·h-1 and 3.62 mL 0.1mol·L-1KMnO4·g-1·20min-1, respectively and increased by 57.6%, 20.3% and 11.9%, compared with the control.(5) The numbers of soil bacteria, actinomycetes, total cultivatable microbes,ammonia-oxidizing bacteria and azotobacter, microbial biomass carbon content and microbial quotient were significantly improved after application of BHS and basically the application rate 450 kg·hm^-2 was the best, at which the strains separated from the plates at the 130th day were identified based on the 16SrDNA sequences.The results showed that the prevailing bacteria were Bacillus sp and the strains were identified as Bacillus pumilus, Bacillus amyloliquefaciens, Bacillus gibsonii, Bacillus simplex, endogenous Bacillus, Bacillus megaterium, Bacillus subtilis,Georgenia ferrireducens and Kocuria sp.(6) Correlation analysis showed that the indices were best correlated at the 190th day.Generally, the soil clay and silt content (<0.005mm), clay content (<0.002mm), total nitrogen, available nitrogen, available phosphorus, available potassium, organic carbon, extractable humus carbon, fulvic acid carbon, humic acid carbon, soil enzyme activity and microbial indices with the exception of fungi presented significant or extremely significant positive correlation, which indicated that the BHS had much influence on soil physical, chemical,biochemical and microbial indicators. There was positive correlation between the yield and other soil indices (except soil fungi), especially the microbial biomass carbon and microbial quotient,which presented significant positive correlation. The improvement of soil quality was the comprehensive embodiment of various soil characters. Combined with the indices analyzed above and the data of the yield, 450kg·hm^-2 was defined as the best application rate.(7)The original, principal component and principal component comprehensive score of soil physical, chemical, biochemical and microbial indices were used to conduct cluster analysis. The objective soils were well classified according to the restoration effects, which were as follows: 450kg·hm^-2>750 kg·hm^-2> 600 kg·hm^-2>300 kg·hm^-2> 150 kg·hm^-2> control.According to the changes of indices after application of BHS and the result of principal component and cluster analysis, The soil quality evaluation system for Xinjiang Glycyrrhiza uralensis production area was established. The specific indices consist of soil mechanical composition, total nitrogen, available nitrogen, available phosphorus, available potassium, organic carbon, C/N ratio, extractable humus carbon, fulvic acid carbon, humic acid carbon, activities of urease, alkaline phosphatase and catalase, numbers of bacteria, actinomycetes and fungi, numbers of ammonia-oxidizing bacteria and azotobacter, total numbers of cultivatable microorganisms, microbial biomass carbon and microbial quotient.