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Thu Nga Do, Kei Nishida (2014).

A nitrogen cycle model in paddy fields to improve material flow analysis: the Day-Nhue River Basin case studyNutrient Cycling in Agroecosystems, 100(2), pp. 215–226, DOI 10.1007/s10705-014-9639-4


Abstracts
Material flow analysis (MFA) hasbeenapplied to assess the environmental impact of humanactivities on nutrient flows at the river basin scale. Thispaper reports the enhancement of the MFA model byincorporating a nitrogen cycle model for the paddyprocess in the Day-Nhue River Basin, Vietnam. Dynamic transport and transformation of nitrogen inthe paddy soil were quantified using the results fromprevious studies. All nitrogen inputs to a paddy wereconsidered. The primary nitrogen inputs were classified as nitrate, ammonium, and organic nitrogen. Themodified MFA model was used to quantify nitrogenloads from paddy fields to atmosphere, surface water,and soil/groundwater using the classified nitrogeninputs and corresponding nitrogen loss rates. Thisrestructured paddy process significantly influenced theestimated nitrogen loads to the environment. Nitrogenloads to the air and soil/groundwater increased by 18and 64 % in spring fields and by 0 and 25 % insummer fields, respectively. Compared with MFA thatdid not apply the nitrogen cycle, nitrogen load tosurface water remarkably increased; it was 39 timeshigher for spring fields and 29 times higher forsummer fields. The estimated runoff loads for the tworice seasons were in the range of measured valuesreported in previous studies. As a result of thesecalculations, it was proposed that the application ofchemical fertilizer could be reduced by 50 % in bothseasons to control environmental impacts without impacting rice production. The inclusion of thisdetailed paddy nitrogen cycle significantly enhancedthe quality of the MFA model.
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