New approach combining food value with nutrient budgeting provides insights into the value of alternative farming systems

Sustainable farming systems provide food for humans while balancing nutrient management. Inclusion or exclusion of livestock has nutrient management implications, as livestock produce food from otherwise inedible crops and their manure is a valuable soil conditioner. However, plant-based diets are becoming more widespread due to perceived environmental benefits. We measure both food production in terms of nourishment to humans (in this study measured by protein, fat, starch and sugar production) and nutrient sustainability in terms of fertiliser use of six rotational farming systems with differences in nutrient management approaches. The arable practices included were the application of synthetic fertilisers, a range of organic amendments, incorporation of crop residues and legume cultivation. Livestock and associated products were included in some systems but excluded in others. The production of protein, fat, starch and sugar was combined with the balance of nitrogen (N), phosphorus (P) and potassium (K) into an overall measure of nutrient use efficiency of human macronutrient production. Across all systems considered, N use efficiency (5-13 kg protein/kg applied N) was lower than P (84-772 kg protein/kg applied P) or K (63-2060 kg protein/kg applied K), and combining synthetic fertiliser use with organic amendment applications raised production significantly while balancing P and K management, regardless of which organic amendment was used. Legume-supported rotations without livestock produced more protein, starch and sugar per unit area than those with livestock. Nutrient balances and nutrient use efficiencies were more sensitive to management changes than purely food production. Using this approach allowed us to identify areas for improvement in food production based on the specific nutritional value of offtakes as opposed to yield overall.