| Along with the exploitation and utilization of the resource of iron ore, lots of iron tailings was produced, which occupied vast land, destoried vegetation and polluted environment seriously. Therefore, it is high time to conduct revegetation to improve the eco-environment. Alfalfa is a well adapted, high yield and high protein content legume, the root of alfalfa can form nitrogen fixing system with rhizobium, and it has an excellent effect on improving the physicochemical and biological properties of soil, because of these reasons, alfalfa is the preferred plant to produce and revegetate the deserted or degraded soil and the metallic tailings. However, because of the poor physicochemical properties and few microorganism, it is too hard for alfalfa to plant on iron tailings. In order to search an effective approach to improve the physicochemical and biological properties of iron tailings, and promote the growth and improve the quality of alfalfa, the study using pot experiment in outdoors, taking iron tailings as matrix, setting N0(5kg iron tailings)?N1(4.95 kg iron tailings + 0.05 kg organic manure)?N2(4.875 kg iron tailings + 0.125 kg organic manure) and N3(4.75 kg iron tailings + 0.25 kg organic manure), four fertilization levels, using A0(inoculate nothing), A1(inoculate rhizobium No.17512), A2(inoculate rhizobium No.17513) and A3(inoculate rhizobium No.17676), four inoculation ways and taking split-plot design, discussed the effects of different fertilization levels and inoculating different rhizobiums on the growth of alfalfa and the physicochemical and biological properties of iron tailings, furthermore, screening the best combination of rhizobium strain and organic manure level, then on this basis, the effects of growth years on the improvement effect of iron tailings and the effects of fertilizer levels on the content of crude protein of alfalfa and key enzymes activities of nitrogen metabolism were studied. The main results were as follows:(1) Inoculation of rhizobium significantly promoted the increase of the height, root length, fresh weight aboveground, root fresh weight, total biomass and fresh nodule weight of alfalfa. The most effective rhizobium strain was the No.17676 in all strains provided. However, inoculation of rhizobium had no significant effects on the physicochemical properties of iron tailings, including volume-weight, p H, field capacity, total porosity, and the contents of organic matter, available nitrogen, available phosphorus and available potassium. Because of inoculating rhizobium, the quantity of bacteria and the enzymatic activities were significantly promoted, and the No.17676 strain was the most effective.(2) Fertilization markedly promoted alfalfa growth. With the fertilization level raising, the plant height, shoot fresh weight and total biomass of alfalfa gradually increased and reached maximum under N3 fertilization level. Moreover, the significant differences in the plant height, shoot fresh weight and total biomass were observed between N3 and N2 or N1 fertilization level. N2 fertilization level gave the best result for increasing root nodule weight. Fertilization significantly promoted the decrease of volume-weight and p H, and the increase of field capacity, total porosity, organic matter, available nitrogen, available phosphorus, and available potassium. The effects of N3 fertilization level on the decrement of volume-weight and p H and the increment of the content of organic matters, available phosphorus and available potassium in the iron tailings were more significant than those of N1 or N2 level; Fertilization markedly increased the quantity of fungi and actinomycetes, but didn't show significant difference on bacteria, each fertilization level achieved significant difference on the effects of enzymatic activities, and the N3 fertilization level was the most effective.(3) The effects of growth years of alfalfa on improving the iron tailings were studied on the condition of the best combination between rhizobium and fertilization level. The results showed that, along with the increase of alfalfa's planting year, volume weight and p H of iron tailings decreased gradually, field capacity, total porosity, the content of organic matter, available nitrogen, available phosphorus and available potassium increased gradually.Compared with the fertilized but no inoculated treatment, the effects of the first year's alfalfa on total porosity achieved significant difference, and had markedly significant difference on volume weight and field capacity, the effects on p H, organic matter, available nitrogen and available phosphorus had no significant influence, but the effect on available potassium had markedly significant difference, and the effects on the quantity of microorganism and soil enzyme activities reached markedly significant difference;Compared with the fertilized but no inoculated treatment, the effects of the second year's alfalfa on total porosity achieved significant difference, and had markedly significant difference on volume weight and field capacity, the effects on organic matter and available nitrogen had no significant influence, but had significant difference on available phosphorus and had markedly significant difference on p H and available potassium, and the effects on the quantity of microorganism and soil enzyme activities reached markedly significant difference;Compared with the first year's alfalfa, the effects of the second year's alfalfa on total porosity had no significant difference, but achieved markedly significant difference on volume weight and field capacity, the effects on organic matter and available nitrogen had no significant influence, but had significant difference on available phosphorus and had markedly significant difference on p H and available potassium, and the effects on the quantity of microorganism and soil enzyme activities reached markedly significant difference.(4) It was investigated that the effects of fertilization level on the content of crude protein and activities of key enzymes of nitrogen metabolism of alfalfa, planted in iron tailings, at different growth stages by outdoor pot experiment in this paper. The results showed that the content of crude protein and the activities of nitrate reductase(NR) increased gradually with the fertilization level increasing, and reached maximum at initial bloom stage and decreased gradually afterwards. There was significantly positive correlation between the fertilization level and content of crude protein. The significantly positive correlation was also found between the content of crude protein and activities of NR in stalk and root of alfalfa. The activities of GS and GDH was improved with suitable fertilization level application(N1, N2), but decreased when excessive fertilization(N3) was used. Fertilization level did not affect the changing tendency of the activities of enzymes of nitrogen metabolism in different organs in the process of alfalfa growth and development.(4) Compared with CK, the effects of the first year's alfalfa on p H, organic matter, available nitrogen and available phosphorus had no significant influence, but the effect on available potassium had markedly significant difference; the effects of the second year's alfalfa on organic matter and available nitrogen had no significant influence, but had significant influence on available phosphorus and markedly significant influence on p H and available potassium; Compared with the first year's alfalfa, the effects of the second year's alfalfa on organic matter and available nitrogen had no significant influence, but had significant influence on available phosphorus and markedly significant influence on p H and available potassium. |
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