The amount of phosphorus-based mineral and organic fertiliser used on grassland across the world must increase four-fold by 2050 in order to meet future food demands, finds a study in Nature Communications. Unless phosphorus inputs are more closely managed, loss of grassland and cropland productivity could threaten the sustainability of global food production if the population continues to grow at its current rate.
Phosphorus is a key component of grassland productivity, but may be lost from livestock-grazed grassland soils when manure is collected and then used to fertilise arable cropland. If these lost nutrients are not replaced, the productivity of grazing grassland, on which meat and dairy products rely, is likely to be severely compromised.
Martin van Ittersum and colleagues use data collected between the years 1975 and 2005 by the Food and Agriculture Organisation of the United Nations (FAO) in order to build the first global model of phosphorus budgets in grasslands, using these values to estimate future agricultural requirements up to the year 2050. They find that the phosphorus budgets of most grasslands around the world are currently negative (more is being lost than added), and that four times more mineral fertilisers will need to be applied (totalling 24 megatonnes per year) in order to avoid loss of soil fertility and productivity and in order to meet expected future food demands of the worlds’ population.
Regionally, they find that Asia is responsible for the largest transfer of phosphorus from grasslands to croplands via manure-based fertilisers, accounting for 44% of the global total, whereas North America and Eastern Europe were the only regions to show a net transfer in the other direction (from croplands to grasslands) during the same time period. Improved management of global nutrient inputs will therefore be required in order to avoid widespread expansion of agricultural land in the future.