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Soil erosion represents a primary threat to soil systems with adverse implications for ecosystem services, crop production, potable water and carbon storage. While numerous studies have quantified the spatial distribution of aboveground Biomass (AGB), soil erosion and soil organic carbon (SOC) in the Yangtze River Basin (YRB), limited attention has been given to assessing the contributions of different land use types and especially crop types to AGB, soil erosion and SOC. In most studies, cropland is taken as a land use class, while detailed crop types and rotation patterns, and their effect on soil erosion and SOC, vary significantly. In this study, we used the Metronamica model to generate a detailed crop rotation and distribution map across the YRB and subsequently employed the Pan‐European Soil Erosion Risk Assessment (PESERA) model to simulate the spatial distribution of AGB, soil erosion and SOC on a monthly basis. PESERA model simulations indicate an average soil erosion rate across the entire YRB of 7.7 ton/ha/yr, with erosion hotspots concentrated in the Sichuan Basin and the central‐southern regions. The southwestern region and western Sichuan show elevated levels of AGB and SOC, while the eastern plains display lower levels. Erosion rates are lowest in areas designated as artificial land, pasture and grassland, whereas croplands and fruit tree plantations experience the highest erosion rates. In terms of crop types, the highest erosion rates and lowest AGB are observed under fallow and potato cultivation, while the lowest erosion rates and highest AGB are found in rice‐wheat rotation fields. To the best of our knowledge, this is the first study taking detailed crop types and patterns into account while evaluating their effect at a relatively large scale (i.e., YRB). These findings can help to develop sustainable soil management and (cropping) conservation strategies. [ABSTRACT FROM AUTHOR]

The volatilization of ammonia (NH 3) from fertilizer application and livestock wastes is an overwhelmingly important pathway of nitrogen losses in agricultural ecosystems and constitutes the largest source of atmospheric NH 3. The volatilization of NH 3 highly depends on environmental and meteorological conditions, however, this phenomenon is poorly described in current emission inventory and atmospheric models. Here, we develop a dynamic NH 3 emission model capable of calculating the NH 3 emission rate interactively with temporal- and spatial-varying meteorological and soil conditions. The NH 3 flux parameterization relies on several meteorological factors and anthropogenic activity including fertilizer application, livestock waste, traffic, residential, and industrial sectors. The model is then embedded into a regional WRF–Chem model and is evaluated against field measurements of NH 3 concentrations, emission flux, and satellite retrievals of column loading. The evaluation shows a substantial improvement in the model performance of NH 3 flux and ambient concentration in China. The model represents the spatial and temporal variations of ambient NH 3 concentration well, indicating the highest emission in the North China Plain (NCP) and Sichuan Basin, especially during summertime. Compared with normal simulations using fixed emission inventory input, this model features superior capability in simulating NH 3 emission flux and concentration during drastic weather changes like frontal activities and precipitation. Such advances in emission quantification also improve the model performance of secondary inorganic aerosol on synoptic scales. While more laboratory and field measurements are still needed for better parameterization of NH 3 volatilization, the seamless coupling of soil emission with meteorology provides a better understanding of NH 3 emission evolution and its contribution to atmospheric chemistry. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) is the most important alkaline gas in the atmosphere, which has negative effects on biodiversity, ecosystems, soil acidification and human health. China has the largest NH 3 emissions globally, mainly associated with agricultural sources including nitrogen fertilizer and livestock. However, there is still a limited number of ground monitoring sites in China, hindering our understanding of both surface NH 3 concentrations and emissions. In this study, using the polar-orbiting satellite (Infrared Atmospheric Sounding Interferometer – IASI) and Fengyun-4A Geostationary Interferometric Infrared Sounder (GIIRS), we analyzed the changes in hourly NH 3 concentrations and estimated surface NH 3 concentrations and NH 3 emissions in China. GIIRS-derived NH 3 concentrations in the daytime were generally higher than those at night, with high values during 10:00–16:00 local time. Satellite-derived surface NH 3 concentrations were generally consistent with the ground observations, with R -square at 0.72 and slope equal to 1.03. Satellite-based NH 3 emissions ranged from 12.17 to 17.77 Tg N yr -1 during 2008–2019. Spatially, high values of NH 3 emissions mainly occurred in the North China Plain, Northeast China and the Sichuan Basin, while low values were mainly distributed in West China (Qinghai–Tibet Plateau). Our study shows a high predictive power of using satellite data to estimate surface NH 3 concentrations and NH 3 emissions over multiple temporal and spatial scales, which provides an important reference for understanding NH 3 changes over China. [ABSTRACT FROM AUTHOR]

The losses of excessive reactive nitrogen (N) from agricultural production pose detrimental impacts on water, air and land. However, N budgets of agroecosystems are still poorly quantified, presenting a barrier to understand the N turnover in agriculture. Agricultural ammonia (NH 3) volatilization has been recognized as a crucial contribution to the pollution of fine particulate matters over China through reacting with acid gases. Building on these challenges, the first national-scale model analysis was constructed on the N budgets to gain an overall insight into the current status of N flows in Chinese dryland systems towards sustainable N management. Total inputs of soil N in Chinese dryland soils were estimated at 121 kg N ha−1 in 2010, considering all pathways including N manure, fertilizer, atmospheric deposition and litter from crop residues. Atmospheric N deposition accounted for 25% of N fertilizer plus N manure in Chinese dryland soils, suggesting that N deposition could not be ignored when estimating total N inputs to Chinese dryland soils. The highest ratio of NH 3 volatilization to total N outputs was found at 43 kg N ha−1 (∼21%) in Northern China, followed by 41 kg N ha−1 (∼20%) in Sichuan Basin and 25 kg N ha−1 (∼26%) in Northeastern China. The modeling results indicated that, if a 20% decrease in N fertilizer plus N manure was achieved, it would lead to a 24% (7–49%) reduction in NH 3 volatilization. Substantial reductions of NH 3 volatilization would also be achieved by making an improvement in changing management practices (controlled release fertilizer and full irrigation). The results would give an overall insight into N budgets in Chinese dryland soils. The constructed N budgets assisted with understanding agricultural N flows and NH 3 pollution, and evaluated the impacts of human activities on N cycle towards a precise way to regulate agricultural management. Image 1 • N deposition accounted for 25% of N fertilizer in dryland soils. • NH 3 volatilizations were identified as the major pathways of soil N outputs. • NH 3 volatilizations can be reduced by appropriate fertilizer and irrigation. [ABSTRACT FROM AUTHOR]