The paper presents the results of a scientific project focused on limiting nutrient losses from farms by introducing measures to apply fertilizers in a more sustainable way. It is a case study of selected aspects of farm management, focussing on the issue of sustainable agriculture and their tools. The main aim of the study was to analyse and evaluate farmers’ knowledge of the fertilizing process and its aspects, as well as applying sustainable agricultural activities on farms. The study emphasised the importance of nutrient management, as very important for sustainable farming. Also, the links between farmers’ opinions and their activities were analysed. The important issue concerned measures for sustainable farm management introduced on the farms, as well as measures to limit nutrient leaching into groundwater. Twenty-eight farmers from two regions in Poland were interviewed about their perceptions for the case study. In general, the farmers considered their farm activities to be more sustainable than in the past. They demonstrated an understanding of the general idea of sustainable agriculture. However, many farmers still demonstrated a poor grasp of nutrient flows and nutrient balances on farms. Their knowledge and perception was based on general, rather than specific knowledge gleaned from an academic/vocational course. The farmers demonstrated a realization that there were some new, or low-cost measures that could be introduced to make management more sustainable and pro-environmental, but there was still a need for wider adoption of sustainable agricultural practices.

With growing urbanization cities become hotspots for nutrients. Food items are imported, and food residues, including excreta and not-eaten food, are often exported to landfill sites and water bodies. However, urban sanitation systems can be designed to achieve a high degree of nutrient recovery and food security while counteracting current nutrient resources depletion, environmental degradation, and wasteful energy use. This article illustrates how an extended solid waste hierarchy also including human excreta and wastewater can guide actions to save and recover phosphorus (P) by the three sectors: food industry, households, and waste utilities. P use in diets and agricultural production is not part of the analysis, despite the potential to save P. Novel systems thinking and material flow analysis show that waste prevention can replace over 40% of mined P presently used for making fertilizers. Reuse and recycling of P in excreta and food waste can replace another 15–30%, depending on P efficiency from mine to plate. Keeping excreta separated from other wastewater facilitates such measure. Incineration and land filling are deemed the least appropriate measures since mainly P is recovered in the ashes. The European Union (EU) waste management policy is analyzed for real barriers and opportunities for this approach. The EU Parliament policy guidelines were watered down in the EU Commission’s Directives, and today most biowastes are still being landfilled or incinerated instead of recovered. An anticipated overcapacity of incineration plants in Europe threatens to attract all combustible materials and therefore, irrevocably, reduce nutrient recovery. On the other hand, reduced generation and enhanced recovery can delay exhaustion of P resources by several centuries and simultaneously reduce environmental degradation.

Urban growth leads to geographically concentrated demand for water and food – and to growing volumes of wastewater and organic waste. Left unattended by city authorities, both local and planetary resources boundaries for water and nutrients will be transgressed. A novel partly dynamic ‘flexible water balance’ is developed to explore ways to address a looming water crisis. A systems-based flow chart shows how rainwater, groundwater and recycled water interact. Measures from supply-, demand-, and reuse management are combined to manipulate the water flows. Water management in Bangalore, India, focused on supply management over the period 1964 to 2015, tapping distant rivers. This mind-set was challenged by a Water Disputes Tribunal and international financiers. Residents and industry were losing faith in the erratic water supply, and met part or all their water needs by digging or drilling wells. The ‘flexible water balance’ is tested on Bangalore for the year 2050 when the population has increased from 8 to 20 million. New housing complexes can provide opportunities for effective arrangements to recycle water and nutrients, save energy, and reduce water pollution and air emissions. The ‘flexible water balance’ indicates that Bangaloreans can get enough household water without tapping river water and still recharge groundwater.

The urban world population will increase from 3 to 8.5 thousand million in the 21st century. Cities become hot spots of both demand for water and global food and for disposed used water and nutrients. Sustainability requires that resource flows through our cities are co-managed and connected to agriculture. Reduced use of harmful chemicals in consumer products facilitates treatment to a quality that allows reuse/recycling of water and nutrients. A solid and liquid waste hierarchy can assist in ordering measures. A novel flexible water balance can guide city infrastructure and keep toilet water separate. New water-saving equipment can substantially reduce water use without losing personal comfort. The combination of these new approaches ascertains access to safe urban water, and that recovered nutrients from cities can substitute half of chemical fertilisers needed in food production. Now, thousands of new cities and suburbs provide unique opportunities to develop resource-smart and sustainable flows.

As global consumption expands, the world is increasingly facing threats to resource availability and food security. To meet future food demands, agricultural resource efficiency needs to be optimized for both water and nutrients. Policy makers should start to radically rethink nutrient management across the entire food chain. Closing the food loop by recycling nutrients in food waste and excreta is an important way of limiting the use of mineral nutrients, as well as improving national and global food security. This article presents a framework for sustainable nutrient management and discusses the responsibility of four key stakeholder groups—agriculture, the food industry, consumers, and waste management—for achieving an effective food loop. In particular, we suggest a number of criteria, policy actions, and supporting strategies based on a cross-sectoral application of the waste hierarchy.