Obvious but overlooked: soil erosion neglect in the global phosphorus cycle

Phosphorus (P) as a key element in DNA, RNA as well as ATP and phospholipids is essential for the growth, functioning and reproduction of all life on earth. However, if fertilization with animal wastes or human excreta is not available or not organized, P fertilizers stem from nonrenewable geological P deposits, which are an increasingly limited resource. The potential threats of a global P limitation due to “peak phosphorus” have been discussed intensively in the recent past  including the socio economic as well as political consequences which will be dramatic. While a deficit in available soil P leads to a loss of agricultural yield, an excess of total P in soils triggers aquatic eutrophication, loss in biodiversity and wildlife habitat in surrounding water bodies in other regions of the world.

We calculated global soil P balances considering input from atmosphere and plant management (as sum of manure and residue input minus plant uptake) versus depletion due to soil erosion in coupling P fluxes from (Ringeval et al., 2017) with soil erosion rates from (Borrelli et al., 2017).

The world’s soils are currently being depleted in P in spite of high chemical fertilizer input. Considering the current high chemical fertilizer inputs most continents result in slightly positive P balances (e.g. net P input to soils). Exception are Africa with very low chemical fertilizer input of 1.7 kg ha^-1yr^-1 paired with high losses due to soil erosion of 2 kg ha^-1yr^-1 and Europe (the latter is the average for the geographic Europe including eastern European countries with very low chemical fertilizer input). Results indicate negative balances globally as well as for all continents (depletion between 4 and 19 kg P ha^-1yr^-1 ) if input of chemical fertilizers is neglected.

Parallel to the distribution pattern and dynamics of global soil erosion by water (Borrelli et al., 2017), P losses from soils due to water erosion are most dramatic in countries and regions with intensive agriculture and/or extreme climates (e.g., high frequencies of heavy rain storm or droughts followed by significant rain events).

References

Borrelli, P., Robinson, D.A., Fleischer, L.R., Lugato, E., Ballabio, C., Alewell, C., Meusburger, K., Modugno, S., Schütt, B., Ferro, V., Bagarello, V., Oost, K.V., Montanarella, L. and Panagos, P., 2017. An assessment of the global impact of 21st century land use change on soil erosion. Nature Communications, 8(1): 2013.

Ringeval, B., Augusto, L., Monod, H., van Apeldoorn, D., Bouwman, L., Yang, X., Achat, D.L., Chini, L.P., Van Oost, K., Guenet, B., Wang, R., Decharme, B., Nesme, T. and Pellerin, S., 2017. Phosphorus in agricultural soils: drivers of its distribution at the global scale. Global Change Biology