Residue incorporation by tillage—Interaction of mass and cover

The majority of farm plans written to meet conservation compliance requirements include surface residue as a major source of protection against excessive soil erosion. Expected residue levels at critical period in the crop rotation are predicted by applying residue retention factor values associated with specific tillage implements. Frequently, values for retention by fraction of mass and by fraction of cover are used interchangeably. A relationship between fraction of pretillage residue mass and fraction of pretillage residue cover retained as a function of a single area to mass residue characteristic and pretillage mass per unit area is developed in this paper. Cover and mass fraction retention values are similar only under very limited conditions. Conservationists and others designing farm plans must be aware of these differences in cover and mass fraction retention values and ensure that consistent procedures are followed in estimating the residue levels expected at critical erosive periods.