Effects of nitrification inhibitor and agrochemicals on soil microorganisms and nitrogen cycling

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Xu, Zhihong

Wang, Weijin

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Teng, Ying

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2018-03
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Abstract

All societies are pressed to increase agricultural production – whether via enhancing crop yields in cultivated lands or via changing previous crop patterns into intensive agricultures, and the intensive agricultures are developing rapidly all over the world. Compared with the traditional agriculture, the intensive agriculture is under conditions of continuous production with high-intensity applications of fertilizers and other agrochemicals. Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a commercial agrochemical applied to enhance nitrogen (N) fertilizer utilization efficiency. To maintain crop yield and quality, fungicide iprodione or herbicides atrazine and glyphosate are also applied into the agricultural soils, but their inhibitory or toxic effects are not constrained to hazardous fungi or weeds only. Once being applied into agricultural soils, the agrochemicals alone or with their degradation metabolites, may have negative effects on the entire soil microorganisms, and thereby soil biogeochemistry and quality. Apart from severe soil contaminations, the growing public concerns of agrochemicals are also associated with their impacts on soil environment and greenhouse gas emission. Previous studies have generally focused on single iprodione application, whereas in intensive agriculture production, iprodione is repeatedly applied. The DMPP and iprodione may be applied into agriculture soils simultaneously, but there are limited studies focusing on the interactive effects of DMPP and iprodione applications. For sugarcane farming, the herbicides different functions are essential to ensure sugarcane yields. However, few studies were conducted to reveal the impacts of DMPP and herbicides on soil N transformation rates and greenhouse gas emissions under different soil moisture conditions. Traditional researches about soil microbial population commonly utilized the culturing methods. However, the uncultured microorganisms far exceed their cultured counterparts, and approximately 80% of soil microorganisms are not discovered due to the shortages or costs of culturing methods. The superiorities of high-throughput sequencing technology enable detections of detailed microbial community changes that have not been reported with culturing methods, and it vastly enlarges our scientific horizon and understanding of bacterial and fungal responses to agrochemical applications at different taxonomic levels. Moreover, identifications of N flow and loss mechanisms are essential to enhance N utilization efficiencies and modify fertilizer and agrochemical management practices. External 15N isotope tracing method enables to accurately trace the transformations of applied N. In existing agricultural systems where N fertilizer or commercial agrochemical practices have already been established for decades, it is beneficial to apply the external 15N isotope tracing method to quantify effects of agrochemicals on the fluxes of applied N fertilizers...

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Thesis (PhD Doctorate)

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Doctor of Philosophy (PhD)

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School of Environment and Sc

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The author owns the copyright in this thesis, unless stated otherwise.

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Subject

Nitrification inhibitor

Iprodione

Atrazine

Glyphosate

Soil microorganisms

N cycling

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