Review of the trends in the study of non-point source nitrogen in hydrological processes on farmland over irrigation district

The major driving force for non-point source nutrient losses from irrigated farm land comes from the natural rainfall-runoff process in the watershed.Study of the regularity in nutrient losses and the relevant modeling methodologies is thus important for the comprehensive pollution control of non point sourcen itrogen in China's irrigation districts.This paper reviews the trends and progresses in the study of non point source nitrogen in hydrological processes on farm lands,with emphasis on the aspects of the mechanism of nutrient losses and the influence factors,as well as the prediction methods.The scope and application of both black box model and mechanism dissection model are analyzed in detail.The advantage and disadvantage of the two models are also underlined.Based on the study,a prioritylist of promising research areas on the subject is proposed,including the selection of representa tive researchunits,the scale issues,and the coupling of farm land nutrient losses from different hydrologic flow pathways.