Fluxes and mechanisms of permanent nitrogen removal and N2O production in a heavy nitrogen loaded regions of China (FluxCHINA)
Knowledge on the fate of the massive loading with reactive N from agriculture in the Yangtze River Delta Region in China is poor but needed to develop strategies for effective solutions. In this project we target this gap by developing and applying improved methods to study emissions of dinitrogen and other N gases.
The massive increase in reactive nitrogen (N) use in agricultural soils has led to a cascade of detrimental environmental consequences including emission of the greenhouse gas nitrous oxide (N2O) via biological processes including denitrification and nitrification. In addition, there is great uncertainty about the fate of applied N as we suspect a large proportion might be lost as dinitrogen (N2) through denitrification. We certainly need to improve current techniques to quantify N2 losses from agricultural soils to better understand the N cycle in various agricultural systems which is needed for optimizing N management.
The Yangtze River Delta Region is one of the most densely populated and economically developed areas in China and being one of the heaviest N loading regions in the world. The research team led by Prof. Xiaoyuan Yan at the Institute of Soil Science at CAS conducted intensive monitoring of N fluxes at watershed scale in the delta region of Yangtze River. By budget calculation it was found that more than half of the N input was permanently removed from terrestrial ecosystems, likely through N2 production, either through denitrification and anaerobic oxidation of ammonium. However, such budget calculation is an indirect method and the results are imprecise, resulting from the cumulated uncertainties of the various N fluxes, each with their respective uncertainty.
In this project, we study soils from three common Chinese agricultural management systems (paddy rice, fruit and vegetable fields) with new robust methods to i) precisely quantify direct N2 and N2O fluxes under different land-use, ii) distinguish the production pathways of N2O for estimating the processes governing N removal, iii) and to understand driving forces of N2O production and reduction processes.
The research team at the Thünen Institute investigates N cycling in the biosphere and processes governing N2O turnover, with special emphasis in using stable isotope tools to study N transformations in soils and aquifers. A major focus has been the development of methods to measure denitrification at lab and field scales. We enhanced the N2O isotopomer approach to determine N2O producing processes in agricultural soils to use it also for calculating N2O reduction during denitrification.
In this project, we will: a) develop robotized continuous flow soil incubation system to study direct N2 and other N gas fluxes, b) conduct laboratory experiments to validate the N2O isotopomer approach that is used to determine N2O production processes; c) apply the N2O isotopomer approach also to determine the N2O/(N2+N2O ) product ratio; and d) cooperate with CAS work packages to characterize the tempo-spatial variation of denitrification, N2O emission, N2O/(N2O+N2) product ratio and their key controlling factors under field conditions. A fully automated robotized soil incubation system will be established at both, Thünen Institute and Chinese Academy of Sciences (CAS, China), to set up parallel incubation trials for direct N2 measurements and for the calibration of N2O isotopomer approaches.
The goals of our work package are::
2.2017 - 12.2020
Project funding number: WE 1904-12/1
Project status: finished