RUSLE2 computes residue at maximum canopy as a linear function of yield.  The result is that the typical residue to yield ratio increases as yield decreases.
	Key point: It is the residue at maximum canopy that is described.  Not residue at harvest.  RUSLE2 computes residue at harvest.
	Two data points are entered to describe relationship.
	One check is to consider the residue at zero yield.
	Vegetation like corn can have residue at zero yield.
	Vegetation like grass would not have a residue at zero yield.