To the Editor

In a recent Commentary, Obersteiner and colleagues1 correctly highlight the conflicting priorities of phosphorus-producing nations, rich phosphorus-consuming nations, and poor nations that continue to manage soils under severe phosphorus deficiency. We agree with their point that a reduction in phosphorus wastage in the developed world, where phosphate waste streams are largest2, offers significant opportunities for phosphorus recycling — which, in turn, could ultimately make phosphorus more affordable for everyone. We argue, however, that developing countries that lack mineable phosphorus reserves could achieve greater autonomy by recycling the phosphorus contained in agricultural waste products.

One insufficiently explored example in this respect is the phosphorous stored in animal bones. Animal bone products (derived from the grinding or thermal treatment of raw bone) contain a greater concentration of plant-available phosphorus than commercial phosphate rock fertilizer3,4. For instance, between 2008 and 2011 the livestock herd in Ethiopia comprised more than 50 million cattle, 23 million sheep and 22 million goats5, and would have yielded approximately 192,000 to 330,000 tonnes of bone waste annually6 (Table 1). Recycling of these bones would have yielded around 28 to 58% of annual phosphorus fertilizer supplies to Ethiopia over the same period7. Importing an equivalent amount of phosphorus fertilizer costs approximately US$ 50 to 104 million.

Table 1 Total phosphorus in annual bone residues from slaughtered animals in Ethiopia

Taking the Ethiopian livestock herd as an example, we argue that developing countries already have access to an indigenous supply of phosphate fertilizer, in the form of organic waste products. We suggest that by tapping into this resource, these countries can secure a significant fraction of their phosphorus demands without relying on international markets or the benevolence of rich countries.