TABLE 2.

Relative content of phenolic acids from rhizosphere soils in fields with alfalfa continuous cropping.

CC yeara	Vanillic acidb	p-Hydroxybenzoic acidb	Ferulic acidb	p-Coumaric acidb
1	0.050 ± 0.008 a	0.127 ± 0.014 a	0.031 ± 0.004 a	0.056 ± 0.011 a
7	0.068 ± 0.007 b	0.171 ± 0.013 b	0.026 ± 0.004 a	0.079 ± 0.009 b
14	0.070 ± 0.006 b	0.212 ± 0.017 c	0.046 ± 0.012 b	0.097 ± 0.011 c

^aIndicates alfalfa continuous cropping (CC) for 1, 7, and 14 years. ^bDifferent letters in the column indicate significant difference according to Duncan’s multiple range test (P = 0.05).