| As aquatic resources have been rich in China, so has massive production of wastes from processing of fishes, which are not further utilized. These fish wastes still contain abundant proteins and mineral substrates, which were often turned into wasteful resource and economic losses and shall not be utilized for the moment because of the poor extraction process. Amino acids play the crucial role in ecological functions, with few contents in soil. Additional supplement is needed to meet the surge of amino acids in global demand. Fish wastes could be turned into amino acid fertilizer using enzymatic technique. And if this shall be applied to cultivated soil, it can improve soil quality owing to amino acids supplying and also can provide an alternative approach for utilization of fish wastes and development of sustainable agriculture. Hence, the effects of amino acids produced from fish waste hydrolysis on soil quality were discussed and compared with traditional manure and chemical fertilizers along nutritional gradient in this paper, for the assurance that the amino acid fertilizer hydrolyzed from fish wastes would be in great benefits on agricultural soils.The most noticeable effects on soil physicochemical characteristics were found in the soils applied by fertilizer produced from fish wastes(FW). FW could alleviate soil acidity and salinity significantly. Besides, contents of TC, TN, OC, AP, MBC and MBN and value of C/N in soil were significantly increased when amended with organic fertilizers, especially in M treatment. And contents of AK did not change along all the treatments. However, soil inorganic N concentrations including NH4+-N and NO3—N were higher in chemical treatments, particularly when amended with unbalanced chemical fertilizers. Whereas application of FW tended to lower their concentrations, relieving the negative effects of inorganic N on soil ecosystem health.In the measure of soil microbial activities, FW and M could significantly improve the activities of peroxidase and C cycling related enzyme including β-glucosidase and sucrase, while inorganic fertilizers decreased enzyme activities involving in C cycling. Changes of N cycling related enzyme activities including protease and urease were not consistent along the treatments. The negative effect of chemical fertilizer on protease occurred while it tended to increase with organic fertilizers added, especially in M. With relatively higher variation scope, urease was IV found most active in FW and there was no significant difference in other fertilization treatments. In addition, acid and alkali phosphatase activities, representing P cycling capability in soil, were obviously high, followed by FW, with relatively low in mineral treatments. Redundancy analysis showed that microbial biomass indicated by MBC and MBN were positively correlated to the increases in all enzyme activities. Meanwhile soil AP, to a certain extent, contributed to enhancement of soil enzyme activities. Activities of protease and C-cycling enzymes were associated with TC and C/N, but negatively related with NH4+-N contents. Moreover, activities of urease and N-cycling enzymes were correlated with p H and OC, and P-cycling enzyme activities also showed positive correlation with most soil physicochemical properties.The microbial population diversity based on phospholipid fatty acids(PLFA) analysis indicated that abundance of Gram positive, Gram negative bacteria, actinomycetes and fungi was remarkably high in organic fertilization, with highest amounts in M, while chemical amendments put dumps on their populations. Principle component analysis was applied in order to clearly assess the variation in soil microbial community structure caused by different fertilization. And it turned out that most of measured PLFA profiles increased significantly in M, followed by FW, but they were distinctly separated in the score plots, which might be explained by different responses of various microbial groups to the two organic inputs. Despite the distinct consumption and ingredient in mineral treatments, no obvious difference in microbial community compositions was observed among chemical fertilization. Redundancy analysis elucidated that soil microbial populations measured in our study were positively associated with AP, OC, TN, TC concentrations and C/N value, which were greatly improved by FW and M. In addition, despite no marked relationship with any measured soil environmental variable, fungi/bacteria(F/B) value reached its maximum in FW.The experimental results indicated that FW could significantly improve soil acidity and salinity, and increase the contents of most soil physicochemical properties, despite the lower contents in comparison with M. Also FW could enhanced soil enzyme activities significantly, especially the urease activity. Both the organic fertilization showed obvious benefits on microbial populations, but they differed in soil microbial community structure from each other based on principle component analysis. In addition, redundancy analysis showed that accumulation of inorganic nitrogen can be themain constrain on microbial growth and activities, while FW fertilization can counterbalance and lower the contents of inorganic nitrogen. Therefore, application of FW has proved its exploitable value in improvement of agricultural soils. |
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