We are wasting a mineral essential for our food security. A mineral without which crops and grass cannot grow, i.e. phosphorus. Our food system is by far the largest user of phosphorus. Phosphorus is a mineral mined from phosphate rock. However, natural reserves of phosphate rock are limited and only occur on a few places on earth. Depletion of phosphate rock reserves poses, therefore, a threat to global food security. Yet we are still wasting large amounts of phosphorus in our food system. To keep the system going, this waste is currently replenished with phosphate rock. In fact, we are in a downward spiral which eventually will undermine global food production.

To reduce phosphorus waste in the food system, we need insights into the effect of 1) waste prevention and recycling strategies, and of 2) changes in the level of animal protein in human diets. These insights require a systems approach in which crop production, animal production, human consumption and waste management are integrated.

To show the principles of reducing phosphorus waste in the food system, we modelled a hypothetical food system designed to produce sufficient food for a fixed population with a minimum input requirement of phosphate rock. The model includes representative crop products and animal products (milk and associated beef, and pork) and was parameterised with data from the Netherlands. The principles in our model, however, also hold for food systems in other countries with different farming practices and environmental conditions.

Phosphorus is, among others, lost through wasting human excreta. The crops we consume, either directly or indirectly through animal products, have taken up phosphorus from the soil. By harvesting these crops, the phosphorus ends up on our plates, and, eventually, in our excreta. In our current society, human excreta is wasted, while it should instead be recycled as crop fertiliser to avoid soil depletion. Recycling human excreta is particularly relevant when the human diet contains phosphorus rich products, such as dairy products.

Phosphorus is also lost through wasting animal meal, made from the non-edible animal parts, such as bones and skin. However, recycling of animal meal in European food systems is currently hindered by legislation, as a measure to prevent the spread of diseases. If we were able to safely recycle animal meal as feed or crop fertiliser, we should be able to prevent this unwanted waste of valuable minerals.

Eventually, we also analysed two other recycling and prevention strategies. An important insight gained from the modelling exercise is that the optimal consumption level of animal protein depends on the applied (combination of) waste reduction strategies. The most promising combination of strategies reduced phosphorus losses by 90%. Achieving this reduction would require technological innovation, changes in legislation and increased awareness among all actors in the chain.

 

This article is freely available for one month: ‘Closing the phosphorus cycle in a food system: insights from a modelling exercise

Authors: H. R. J. van Kernebeek, S. J. Oosting, M. K. van Ittersum, R. Ripoll-Bosch

To view the special topic in the August issue, visit: Livestock production evolving to contribute to sustainable societies

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