The relative values of individual crops in different sequences have also been found.

Conservation workers in the Corn Belt and the Northeastern States have used tables of soil-loss factors reflecting these variables to evaluate conservation cropping systems. The tables serve as guides to help farmers select combinations of rotations and practices for their soils that will reduce soil losses to within the allowable limits.

The above values are based on good management. For a high management level, multiply the factors by 0.7.

The table opposite is based on data from soil and water conservation experiment stations in that region. It shows the average annual soil losses from the standard 3-year rotation (R O H) on soils have an credibility factor of 1.0 with different slopes and practices.

The table above presents combined soil-loss factors for common rotations on soils of different erodibilities. When the basic soil losses in the first table are multiplied by these factors, the results are the estimated soil losses from corresponding slopes and practices with different rotations on different soils.

For example, to estimate the soil loss from an R R O H H rotation on a soil that has an credibility factor of 1.25 and a 6-percent slope 300 feet long that is contoured, first find the basic soil loss figure in the first table for the slope and practice specified. It is 4.7 tons per acre. This figure multiplied by the combined soil loss factor from the second table (1.55) gives 7.3 tons an acre as the expected average annual soil loss under the conditions described.

If the allowable annual soil loss for this soil is 4 tons an acre, this rotation with contouring is not an adequate conservation system. Either a more effective rotation must be used or the land must be stripcropped or terraced to bring the expected soil loss down to the allowable figure. Other calculations with the two tables will indicate which combinations of crops and practices will do that.