Our long-term food security depends on finding a sustainable alternative to the finite and unevenly distributed rock phosphate deposits that are used to make the vast majority of our phosphorus (P) fertilisers, on which global food production relies. More urgently, there is a need to reduce the quantities of phosphate that are released into the environment and which are reported to have exceeded the limits of sustainability. Furthermore, over 2 billion people worldwide are currently affected by micronutrient deficiencies, and crop concentrations of essential minerals are declining. There is unlikely to be a single solution to these issues at a global scale, and so a range of solutions are required.
This paper examines whether a novel, recycled, multi-element fertiliser can contribute towards solving these problems by producing crop yields comparable to conventional rock phosphate derived fertilisers, and have an additional benefit of increasing essential mineral concentrations. This fertiliser is produced from abattoir and recycled industrial by-products, and as part of its novel production process, it increases the quantity of human edible protein recovered from a single animal by around 15%, compared to typical carcass processing.
It was tested against conventional mineral fertilisers in a pot trial with wheat and grass. In soil, yields were comparable between the fertiliser types, but, in a low nutrient substrate, it showed a yield benefit. Elemental concentrations in the plant material typically reflected the relative concentrations in the fertiliser, and plants fertilised by it contained significantly more of some essential elements, such as selenium and zinc. Furthermore, concentrations of the toxic element cadmium were significantly lower in crops fertilised by this new fertiliser. Among the fertilisers, manganese concentrations were greatest in the new recycled fertiliser, but within the fertilised plants, they were greatest under the mineral fertiliser, showing the complexity of assessing whether nutrients will be taken up by crops. This may have been due to how bioavailable the manganese in the fertiliser was, or due to negative interactions (antagonism) with other elements.
In summary, fertilisers from livestock waste have the potential to improve wheat and grass concentrations of essential elements while maintaining yields. Their ability to make a significant impact on the fertiliser market is frequently questioned, but if all global beef cattle by-products were processed in this way, it is estimated that 50 million tons per annum of fertiliser could be produced, representing ca.20% of the current global fertiliser use.