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Farm size plays a critical role in agricultural sustainability. This may have far-reaching consequences for the economic and environmental performance of agricultural production, resulting, for instance, in an excessive use of mineral fertilizers. However, the magnitude of such effects and their main causes are not well understood, while being essential for effective policy development, especially for countries like China where the agricultural sector is still largely dominated by smallholder farms. In this paper, we review the current understanding of how farm size affects agricultural sustainability using China's crop farming as an example from economic, environment and social aspects. We analyze impacts from both a Chinese and a global perspective to identify intervention points to improve agricultural performance. We found that increasing farm size has a positive impact on farmer's net profit, as well as economic, technical and labor efficiency with mean coefficients 0.005, 0.02 and 2.25 in economic performance, respectively. Nevertheless, the relationships between farm size and overall productivity, total factor productivity and allocative efficiency are still not well understood and therefore require more research. Meanwhile, increase in farm size is associated with statistically significant decrease in fertilizer and pesticide use per hectare, showing clear benefits for environmental protection. In line with the experiences documented for the evolution of agricultural practices in developed countries, the expansion of large-scale farming is a critical path for modernizing agricultural production and ensuring sustainable food production from the social perspective. Measures concerning farm size should be implemented in an interaction between farmers and the government to promote the green development of agriculture.

'Commentary' paper. Increasing amounts of nitrogen fertilizer have been used in agriculture during the last decades to boost food production for the increasing global human population. The marked increase in reactive nitrogen use has also contributed to severe nitrogen pollution and multiple impacts on human and ecosystems' health. Nitrogen is an important precursor to air pollution (e.g., fine particulate matter, near-surface ozone), water pollution (algal blooms, nitrate contamination), biodiversity loss (nitrogen deposition and eutrophication), soil acidification (ammonium fertilizer use), and global warming (nitrous oxide). Agricultural nitrogen pollution has decreased in some high-income countries, such as those in the European Union (EU), during the last decades, but the remaining nitrogen pollution still causes serious damage. The societal cost of nitrogen pollution by agriculture in the EU has been estimated to range from €35 to €230 billion per year and this cost appears to be greater than the farm profits from nitrogen fertilizer use, which range from €20 to €80 billion per year. Socioeconomic trade-offs between farmers and society need to be introduced to decrease nitrogen pollution.

Western diets are characterised by a high intake of meat, dairy products and eggs, causing an intake of saturated fat and red meat in quantities that exceed dietary recommendations. The associated livestock production requires large areas of land and lead to high nitrogen and greenhouse gas emission levels. Although several studies have examined the potential impact of dietary changes on greenhouse gas emissions and land use, those on health, the agricultural system and other environmental aspects (such as nitrogen emissions) have only been studied to a limited extent. By using biophysical models and methods, we examined the large-scale consequences in the European Union of replacing 25–50% of animal-derived foods with plant-based foods on a dietary energy basis, assuming corresponding changes in production. We tested the effects of these alternative diets and found that halving the consumption of meat, dairy products and eggs in the European Union would achieve a 40% reduction in nitrogen emissions, 25–40% reduction in greenhouse gas emissions and 23% per capita less use of cropland for food production. In addition, the dietary changes would also lower health risks. The European Union would become a net exporter of cereals, while the use of soymeal would be reduced by 75%. The nitrogen use efficiency (NUE) of the food system would increase from the current 18% to between 41% and 47%, depending on choices made regarding land use. As agriculture is the major source of nitrogen pollution, this is expected to result in a significant improvement in both air and water quality in the EU. The resulting 40% reduction in the intake of saturated fat would lead to a reduction in cardiovascular mortality. These diet-led changes in food production patterns would have a large economic impact on livestock farmers and associated supply-chain actors, such as the feed industry and meat-processing sector.

Australia is a warm country with well-developed agriculture and a highly urbanized population. How these specific features impact the nitrogen cycle, emissions, and consequently affect environmental and human health is not well understood. Here, we find that the ratio of reactive nitrogen () losses to air over losses to water in Australia is 1.6 as compared to values less than 1.1 in the USA, the European Union, and China. Australian emissions to air increased by more than 70% between 1961 and 2013, from 1.2 Tg N yr-1 to 2.1 Tg N yr-1. Previous emissions were substantially underestimated mainly due to neglecting the warming climate. The estimated health cost from atmospheric emissions in Australia is 4.6 billion US dollars per year. Emissions of to the environment are closely correlated with economic growth, and reduction of losses to air is a priority for sustainable development in Australia.

As a potent greenhouse gas and contributor to stratospheric ozone depletion, nitrous oxide (N2O) represents a global pollutant of growing concern. We use the N2O example to consider the potential for Green Economy thinking to promote sustainability through emission reduction. A fundamental barrier to change arises from the distinction between 'Sector View' (green actions consistent with improved profit) and 'Societal View' (incorporating the value of all externalities). Bringing these views closer together requires a long-term perspective, while counting all co-benefits of taking action. N2O control should be considered within the context of the wider nitrogen cycle, with an emphasis on improving full-chain nitrogen use efficiency (NUEfc), exploiting a combination of technical measures in agriculture, industry, transport, waste water management and other combustion sources. Avoiding excessive meat and dairy consumption by citizens in developed countries can substantially reduce N2O emissions. These measures offer many options for low-cost control of N2O emissions, while reducing the health and ecosystem threats of other N pollution forms. In order to bring the 'nitrogen green economy' forward, a much stronger public profile is needed to motivate citizens' actions and to encourage investment in bringing new technologies to profitability. A recent estimate suggests that improving global NUEfc by 20% would provide a N-saving worth ~23 billion USD to business, plus health and environmental benefits worth ~160 billion USD. The value of externalities highlights the green economy case for governments to develop a suite of instruments to go further in controlling N2O emissions than the Sector View would typically allow.

Australia is a warm country with well-developed agriculture and a highly urbanized population. How these specific features impact the nitrogen cycle, emissions, and consequently affect environmental and human health is not well understood. Here, we find that the ratio of reactive nitrogen (N(r)) losses to air over losses to water in Australia is 1.6 as compared to values less than 1.1 in the USA, the European Union, and China. Australian N(r) emissions to air increased by more than 70% between 1961 and 2013, from 1.2 Tg N yr(−1) to 2.1 Tg N yr(−1). Previous emissions were substantially underestimated mainly due to neglecting the warming climate. The estimated health cost from atmospheric N(r) emissions in Australia is 4.6 billion US dollars per year. Emissions of N(r) to the environment are closely correlated with economic growth, and reduction of N(r) losses to air is a priority for sustainable development in Australia.