| Facility agriculture is an efficient agricultural production mode and plays an important role in the out-of-season and trans-regional cultivation of vegetables and other important economic crops. However, the temperature is usually high in greenhouses and there is little rain to flush the salinity of greenhouse soil, besides, agricultural production is usually under a status in which multiple cropping index is high and fertilizer is largely used. It results in the aggravation of secondary salinization, continuous cropping obstacles, soil compaction, soil acidification and increasement of harmful gas. Secondary salinization seriously affects the outputs and quality of crops and poses a grave threat to groundwater safety and human health. At present, there are kinds of disadvantages in the traditional methods of improving greenhouse soil, such as high cost, long periods and easily to form secondary pollution. So it is necessary to conduct further researches.This research is established in the situation that nitrate accumulates heavily and microbial biomass reduces largely in greenhouse soil. We screen salt resistance microbes that can make use of nitrate efficiently and add them into greenhouse soil combined with organic materials such as flour, straw and organic fertilizer. We expect to reduce the extent of secondary salinization through the immobilization of nitrate and finally achieve the goal that soil improvement consists with reuse of agricultural wastes. Main conclusions are as follows:i) The study on soils sampled from different ages of greenhouse shows that, pH reduces with the increase of greenhouse age, while EC and salinity increase on the contrary. When greenhouse is used over 15 years, pH in the surface soil reduces by 1.33 units compared to outdoor soil, while EC and salinity reach 8920μS·cm-1 and 0.54% respectively, which are 85.4 and 54.0 times that of outdoor soil respectively. The content of NO3--N, NH4+-N, NO2--N and SON increase with greenhouse age. NO3--N is the main form of mineral nitrogen and increases rapidly with greenhouse age. When greenhouse is used over 15 years, the content of NO3--N, NH4+-N, NO2--N and SON in surface soil reaches 2868.4,35.4,1.54 and 971.9 mg-kg-1 respectively, which is 121.1, 9.5,7.1, and 33.7 times that of outdoor soil.Protease, sucrase and glutamine synthetase activities are inhibited by the increase of greenhouse age; nitrate reductase activity is promoted by the increase of greenhouse age; the effect of greenhouse age on urea enzyme activity is not obvious.Bacteria is the main kind of microbes in facilities soil (about 70%-90%). Low-age-greenhouse is suitable for the growth of microbes, while high-age-greenhouse significantly inhibit the growth of microbes. Fungus and actinomycetes adapt the accumulation of salt better than bacteria.Correlation analysis shows that correlation between the content of nitrogen and salinity is significantly positive (P<0.05,n=6); correlation between Protease activity and salinity is significantly negative (P<0.05,n=6), while correlation between nitrate reductase activity and salinity is significantly positive (P<0.05,n=6); correlation between microbe amount and salinity is not significant.ii) When glucose is added, mineral nitrogen is immobilized quickly at first and then mineralized slowly. There is a significant positive relationship between C/N and utilization rate of mineral nitrogen, C/N and microbial biomass nitrogen (MBN) as well (P<0.05,n=4). The time when utilization rate is highest is brought forward with the increase of C/N.When there is no glucose and C/N is low (C/N=10), the utilization rate of NH4+-N by NCT-2 is higher than that of NO3--N, the difference is significant at 0.01 level. When C/N is medium (C/N=25) and high (C/N=40), the difference is not so significant as former. When no glucose is added, N03--N is immobilized after about 14 d, while NH4+-N is immobizized without delay period. When glucose is added, the utilization rate of NO3--N reaches highest after 3-4 d, while NH4+-N after 7 d.iii) Wheat stalk of which C/N is higher is in favour of the immobilization of NO3--N compared with flour, soy bean stalk, and decomposed organic fertilizer. It is more obvious when it is added combined with NCT-2. |
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