Relationship of soil organic matter dynamics to physical protection and tillage

Tillage has been reported to reduce organic matter concentrations and incre ase organic matter turnover rates to a variable extent. The change of soil climate and the incorporation of aboveground C inputs within the soil lead to no unique effect on biodegradation rates, because of their strong intera ction with the regional climate and the soil physical properties. The perio dical perturbation of soil structure by tools and the subsequent drying-rew etting cycles may be the major factor increasing organic matter decompositi on rates by exposing the organic matter that is physically protected in mic roaggregates to biodegradation. This paper reviews the assessed effects of tillage on organic matter, the scale, extent and mechanisms of physical pro tection of organic matter in soils. (C) 2000 Elsevier Science B.V. All righ ts reserved.