Without industrially produced ammonia from atmospheric nitrogen, there would not be enough nitrogen to feed the current world population.  However, most nitrogen used in food production is lost to the environment, causing a multitude of negative impacts. This paper illustrates how people’s diets, both in type and amount of protein, control the nitrogen’s losses to the environment.  Our findings highlight the substantial increase in nitrogen use over time and the potential for dietary changes to reduce losses in the future.

Nitrogen (N) inputs exceed outputs over the Australian continent, mainly because of biological N-fixation by permanent pastures, but the surplus is partly offset by the N-mining of dryland crops. Fertiliser N application is increasing rapidly but still contributes less than mineralised N from soil reserves to production and to environmental problems. Nitrogen use efficiency by crops is relatively low and we propose research on improved methods of fertiliser application.

Animal production systems provide nutritious food to humans and income to farmers, but also contribute to human health issues and environmental pollution. Global animal production increased threefold during the past 50 years, which led to increased air and water pollution through nitrogen and phosphorus losses. Joint efforts of science, industry and governments are needed to markedly improve the environmental performance of landless industrial animal production systems in particular.

The economics of nitrogen are of central importance to the management of nitrogen fertiliser and its regulation by policy. Key economic findings include that factors determining optimal nitrogen rates are as much socio-economic as they are bio-physical, that farm profit is often highly insensitive to changes in the nitrogen fertiliser rate over a wide range of rates, and that the cost of reducing fertiliser rates is initially very low but escalates as the degree of reduction increases.

N performance indicators such as N use efficiency (NUE) or N surplus can help evaluate optimum N use for agricultural production while minimising the risk of environmental losses. We reviewed NUE and N surplus values for dairy production systems to assess realistic global goals for these indicators. Our results showed that there is no ‘one-size-fits-all’ for global NUE and N surplus targets and that standardisation of methods for estimating these indicators is required.

Quantifying excreted N loads is required to improve N management on grazing system dairy farms. Excreted N (437 g cow^–1 day^–1; 69% of N imports) accumulated in parts of farms close to the dairy shed (overnight paddocks, feedpads and holding areas) and loading rates to the ‘night’ paddocks were greater than fertiliser N applied. Regression relationships developed between excreted and intake N can be used to improve within-farm N management.

Application of animal manures to land affects the supply and losses of plant nutrients, including nitrogen, over many years. We developed a simple model that can predict the release of nitrogen from manures in the years after application. The model can be used to better predict residual effects of manure on both the nitrogen supply for crops and the risks of nitrate leaching.

Chinese agriculture is challenged by the need to feed 1.3 billion people while reducing environmental pollution. Currently, losses of synthetic fertiliser and animal manure to the environment are high. ‘Double High Agriculture’ (DHA) is a form of agriculture assuming that food can be produced at a lower environmental cost. DHA can be combined with recycling of animal manure back to arable lands, which will lead to lower nutrient enrichment in Chinese seas. Herein we model the environmental benefits in terms of coastal eutrophication that can be achieved by implementing such changes in the future.

Under elevated CO₂ (eCO₂; 550 µmol mol^–1), applying 100 kg N fertiliser ha^–1 to wheat at sowing doubled the grain yield response compared with the response observed under ambient CO₂ (aCO₂; 390 µmol mol^–1). Grain protein concentration (GPC) did not significantly increase under eCO₂ for different N management strategies assessed in the present study, with the exception of 100 kg N ha^–1 applied, suggesting that it is not practical to increase GPC using N fertiliser alone.

Competition between plants and soil microbes to obtain nitrogen from soils, when carbon is added, is related to plant productivity. Microbial community structure changes when nitrogen and carbon are added to soils are not well understood. In the present study, we found that soil management history (organic vs conventional) influenced these changes – microbial usage of nitrogen when carbon is added to soils has a strong impact on fertiliser efficiency. Our finding could provide some basic information in understanding the mechanisms behind this.

This study showed that emissions of the greenhouse gas, nitrous oxide, from celery cropping are amongst the highest recorded globally. These emissions, however, could be dramatically lowered by using a nitrification inhibitor, particularly when applied on manures. This provides growers with an excellent cropping practice to reduce the negative effect of excess nitrogen on the environment and to avoid the overuse of fertilisers and manures in vegetable crops.

Chemical inhibitors that impair nitrification, such as 3,4-dimethylpyrazole phosphate (DMPP), have been shown to lower nitrous oxide (N₂O) emissions from agricultural soils in temperate environments. We investigated N₂O emissions from aerobic rice crops grown in the wet subtropics and found no consistent mitigation of cumulative seasonal N₂O emissions with a commercial DMPP-urea product compared to standard urea. These results suggest that the efficacy of DMPP may be substantially lower in warm, wet subtropical environments than in temperate environments.

Fertiliser nitrogen (N) losses are detrimental for the environment and the profitability of food production. Nitrification inhibitors (e.g. 3,4,-dimethylpyrazole phosphate (DMPP)) slow the conversion of ammonia (NH₄⁺) to nitrate (NO₃^–), which has the potential to reduce N losses and increase crop accumulation of N. This study demonstrates that although DMPP can slow the conversion of NH₄⁺ to NO₃^–, nitrification inhibitors are unlikely to facilitate large yield increases in broadacre crops grown in Australian Mediterranean environments.

Increasing nitrogen fertiliser inputs to pastures can increase production and also lead to greater environmental impacts. Using data from 920 Australian field experiments, we developed a mathematical model that predicts increases in pasture production from added nitrogen fertiliser. These predictions are useful for economic analysis and determination of optimum nitrogen fertiliser application rates for Australian pastures in different regions and seasons.

Inappropriate fertiliser applications have caused a series of environmental problems and threaten the sustainable production of rice in China. Nutrient Expert, a new scientific approach for rice fertiliser recommendation, was proved that it could balance nutrient application and improve grain yield, nutrient uptake, and fertiliser use efficiency under field conditions in the main rice-growing regions of China. And it could be used as a practicable tool to make fertiliser recommendation for rice.

NBudget is a Microsoft (Armonk, NY, USA) Excel-based decision support tool developed primarily to assist farmers and/or advisors in Australia’s northern grains region manage N. It does not rely on soil testing; instead, it uses simple paddock descriptions and crop history plus rule-of-thumb values and stand-alone or linked algorithms describing, among other things, legume N₂ fixation and rates of mineralisation of background soil organic N and fresh residue N. The tool accurately predicted sowing soil nitrate levels but not when the soil was flooded or heavily waterlogged.

Soil and crop N data from 33 legume crops in 16 dryland cropping experiments conducted in eastern Australia between 1989 and 2016 identified relationships that can assist farmer decision-making by benchmarking the expected improvements in the availability of soil mineral N after legumes and estimating the relative value of legume N for a subsequent wheat crop.