The Influence of Nitrogen Fertilization on Crop Production and Ecohydrology in an Endorheic River Basin

Nitrogen fertilization is extensively applied in agricultural activities to boost food production, which changes the local hydrologic and carbon cycles. Quantitative evaluation of nitrogen fertilization on carbon and hydrologic dynamics remains challenging due to the complex linkage between hydrologic and biogeochemical processes during irrigation. To address the challenge, we utilized the Community Land Model 5 (CLM5) with activated crop module (CLM5-Crop) to investigate the response of crop yield, gross primary production (GPP), evapotranspi-ration (ET), and water use efficiency (WUE) to nitrogen fertilization in the cropland area of the Heihe River Basin (HRB) in northwestern China. Two batches of numerical experiments (irrigation and non-irrigation) with different nitrogen fertilization rates (0, 5, 10, 15, and 20 gN m(-2), respectively) during 2000-2012 were designed to gain insights into the feedback of agricultural production and ecohydrological response to fertilization. As a result, the crop yield is significantly promoted by similar to 120% with the nitrogen fertilization rate increasing from 0 to 20 gN m(-2) under irrigation conditions. Unlike the crop yield, a clear peak of GPP is observed at the nitrogen fertilization rate of 5 gN m(-2) under irrigation conditions, while higher nitrogen fertilization rates have no further promotion on GPP. ET shows a weak response to the nitrogen fertilization but a good correlation with irrigation. Different crops show different patterns of WUE under different nitrogen fertilization rates. Overall, our study demonstrates that the different influence of nitrogen fertilization on crop yield and hydrologic dynamics in a large endorheic river basin and such a finding should be taken into consideration in the future agricultural activities for the balance between food production and carbon neutrality.