Global changes in soil stocks of carbon, nitrogen, phosphorus, and sulphur as influenced by long-term agricultural production

Quantifying changes in stocks of C, N, P, and S in agricultural soils is important not only for managing these soils sustainably as required to feed a growing human population, but for C and N, they are also important for understanding fluxes of greenhouse gases from the soil environment. In a global meta-analysis, 102 studies were examined to investigate changes in soil stocks of organic C, total N, total P, and total S associated with long-term land-use changes. Conversion of native vegetation to cropping resulted in substantial losses of C (-1.6 kg m(-2), -43%), N (-0.15 kg m(-2), -42%), P (-0.029 kg m(-2), -27%), and S (-0.015 kg m(-2), -33%). The subsequent conversion of conventional cropping systems to no-till, organic agriculture, or organic amendment systems subsequently increased stocks, but the magnitude of this increase (average of +0.47 kg m(-2) for C and +0.051 kg m(-2) for N) was small relative to the initial decrease. We also examined the conversion of native vegetation to pasture, with changes in C (-11%), N (+4.1%), and P (+25%) generally being modest relative to changes caused by conversion to cropping. The C: N ratio remained relatively constant irrespective of changes in land use, whilst in contrast, the C: S ratio decreased by 21% in soils converted to cropping - this suggesting that biochemical mineralization is of importance for S. The data presented here will assist in the assessment of different agricultural production systems on soil stocks of C, N, P, and S -this information assisting not only in quantifying the effects of existing agricultural production on these stocks, but also allowing for informed decision-making regarding the potential effects of future land-use changes.