The Science of 4R Nutrient Stewardship for Phosphorus Management across Latitudes.

When phosphorus (P) fertilizers were introduced, the main goals were to increase the productivity and profitability of agricultural crop production. Over time, other goals have been added: to minimize losses affecting water quality, to increase recycling, to reduce consumption of the limited resource, to improve soil health, and to enhance biodiversity. The science of 4R nutrient stewardship addresses these multiple goals. Across latitudes, temperate and tropical soils differ in their chemical reactivity with P. Legacies of cumulative P surplus, however, differ more widely across longitudes than latitudes. As of 2016, the ratio of cumulative P surplus to current crop P removal ranged from 18 in the United States to 31 in Brazil to 63 in western Europe. The opportunity to use these legacies to improve P use efficiency-and to reduce risk of harm to water quality-in all three regions depends on the improvement of tools to assess the availability of soil P to crops. Science focused on balanced crop nutrition and systematic analysis of crop response has the opportunity to improve farm-level tools to guide responsible management of P. Transitions in 4R practice depend on engagement between science and industry not only at the farm level but along the full agricultural value chain. Whole-system changes may be necessary to enable practitioners to implement 4R nutrient stewardship strategies that can in turn result in major improvements to full-chain use efficiency of the earth's P resources.