P Factor 

P is the support practice factor. The RUSLE P-factor reflects the impact of support practices an the average annual erosion rate. It is the ratio of soil loss with contouring and/or stripcropping to that with straight row farming up-and-down slope.

As with the other factors, the P-factor differentiates between cropland and rangeland or permanent pasture. Both options allow for terracing or contouring, but the cropland option contains a stripcropping routine whereas the rangeland/permanent-pasture option contains an "other mechanical disturbance" routine. For the purpose of this factor, the rangeland/permanent-pasture option is based on the support operation being performed infrequently, whereas in the cropland option the support operation is part of the annual management practice.

From Technical Guide to RUSLE use in Michigan, NRCS-USDA State Office of Michigan.

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