Table 5. Stepwise regression with the dominant factors against alfalfa productivity based on field trial data collected from 1983 to 2008

Parameter	Standardized coefficient	p-value	VIF	R2 change	R2
Factor 1	0.633	0.000	1.002	0.379	0.602
Factor 2	0.485	0.000	1.001	0.210
Factor 3	0.115	0.012	1.001	0.013

VIF, variance inflation factors.