The spatial and temporal distribution of nitrogen flow in the agricultural system and green development assessment of the Yellow River Basin

The Yellow River Basin (YRB) is an important agricultural production area with diverse of Agri-ecological functional units in northwest China. Through data collection and Nutrient Flows in Food chain, Environment and Resources Use (NUFER) and NUFER-AGD model, present study aimed to explore the spatial and temporal flows of nitrogen (N) in the cropping and animal farming systems of the YRB from 1999 to 2019; and to evaluate the developing status and restrictive factors for the green development in this area. The total N input of the area increased from 2.10 x 10(7) t in 1999-3.66 x 10(7) t in 2019, mainly originated from fertilizer (53%, 2019) and fodder (39%, 2019) input. The total N output increased from 8.27 x 10(6) t in 1999-13.77 x 10(6) t in 2019, and the main pathway of N loss was ammonia volatilization, accounting for 53.5% in 1999 and 53.1% in 2019 of the total losses. Based on the N input and loss per unit area in 2019, the upper reaches of the YRB were low-input and high-emission; the middle reaches were high-input and high-emission; the lower reaches were high-input and low-emission. Fifty variables of five dimensions, society development, economy growth, agricultural production, resources input and ecological environment were selected to assess whole YRB for the green development index, the results show that 36% variables reached the green level, and the parameters of the agricultural production and ecological environment among all variables were the key factors of limiting green development of the YRB area. These founding are of great importance to provide scientific support for sustainable agricultural development and ecological protection at regional scale.