Table 1. Composition of C functional groups (%) estimated from relative integration values of ¹³C CPMAS NMR spectra of soil samples.

	Alkyl C (0–45ppm)	O-alkyl C (45–110 ppm)				Aromatic C (110–160 ppm)			Carbonyl C (160–210 ppm)
	Alkyl C	N-alkyl/methoxyl C	Carbohydrate C	di-O-alkyl C	Total	Aryl C	O- aryl C	Total	Carboxyl/amide C	Ketone C	Total
1989	11.1 abc	3.6 de	13.6 d	7.9 cdef	25.1 cde	27.4 def	7.8 cde	35.3 cdef	22.8 d	5.7 a	28.6 ab
1999
OM	9.5 abcd	6.2 a	16.8 abc	8.9 a	31.9 a	24.9 g	9.1 b	34.0 ef	22.3 de	2.2 bc	24.6 cd
1/2OM	9.7 abcd	6.3 a	18.8 a	8.8 ab	33.9 a	25.5 fg	7.9 cd	33.4 f	20.2 e	2.9 abc	23.1 d
NPK	9.9 abcd	4.9 bc	17.5 ab	8.3 abcd	30.7 ab	25.4 fg	7.9 cd	33.3 f	23.1 cd	3.0 abc	26.1 abcd
NP	8.9 bcd	3.8 cde	13.6 d	7.1 gh	24.5 cde	29.1 bcd	8.5 bc	37.6 abc	25.6 ab	3.5 abc	29.1 a
PK	10.6 abc	4.7bcd	14.6 bcd	7.8 defg	27.1 cd	29.1 bcd	7.3 de	36.4 bcde	24.5 abcd	1.4 c	25.9 abcd
NK	11.9 a	3.7 de	12.8 d	6.8 h	23.2 e	31.4 ab	7.3 de	38.7 ab	22.9 cd	3.3 abc	26.2 abcd
CK	11.8 a	5.8 ab	14.3 cd	7.0 gh	27.1 cd	29.1 bcd	6.8 e	35.9 bcdef	23.2 bcd	2.0 bc	25.2 bcd
2009
OM	7.8 d	4.7 bcd	14.6 cd	8.6 abc	27.8 bc	26.6 efg	10.6 a	37.2 bcd	24.8 abcd	2.5 bc	27.2 abc
1/2OM	8.7 cd	4.6 cd	14.5 cd	8.2 abcd	27.3 bcd	28.1 cde	9.4 b	37.4 abc	24.1 abcd	2.4 bc	26.5 abc
NPK	10.1 abcd	4.4 cd	15.4 bcd	7.2 fgh	27.0 cd	28.0 cde	7.6 cde	35.6 cdef	25.3 abc	2.1 bc	27.3 abc
NP	11.4 ab	4.9 bc	14.3 cd	8.0 bcde	27.2 cd	28.3 cde	7.7 cde	36.1 bcdef	22.6 de	2.8 abc	25.4 bcd
PK	11.3 abc	4.7 bcd	13.7 d	7.9 cde	26.4 cde	26.5 efg	7.8 cde	34.3 def	23.1 cd	4.9 ab	28.0 abc
NK	7.9 d	3.0 e	13.6 d	7.3 efgh	23.9 de	32.4 a	7.9 cd	40.3 a	25.9 a	2.0 bc	27.9 abc
CK	9.7 abc	3.9 cde	14.8 bcd	7.6 defgh	26.2 cde	30.4 abc	7.8 cde	38.2 abc	23.0 cd	2.9 abc	25.9 bcd

Treatments followed by different letters in a column are significantly different at p < 0.05 (Tukey test, n = 3).