Agriculture Reference
In-Depth Information
over time and that they are resistant to C mineralization even when the conditions promoting
C loss are prevalent.
Table 1. Effect of soil amended with crop residues (CR), and cattle manure (CM) on
total organic carbon (TOC),
δ
13
C of TOC, and on C,
δ
13
C and COOH groups of humic
acids with respect to the control unamended (C
0
) at the start of the experiment and after
30 yrs. of trials
Treatments
CM
30
Soil
C
0
C
30
CR
30
TOC (%)
0.82 ± 0.01a
0.63 ± 0.005
0.74 ± 0.005
0.85 ± 0.003a
-
- 23.1
- 9.8
+ 3.7
Δ(%)†
δ
13
C (‰)
-24.1 ± 0.2
-22.0 ± 0.5a
-22.0 ± 0.1a
-22.4 ± 0.2a
Humic acid
C (% d.m)
38.0 ± 0.05
40.2 ± 0.02
44.0 ± 0.03
45.7 ± 0.03
-
+ 6
+ 16
+ 20
Δ(%)†
δ
13
C (‰)
-24.6 ± 0.1a
-24.5 ± 0.07a
-23.4 ± 0.3
-24.3 ± 0.1a
COOH
meq/100g
560 ± 2.0
468 ± 2.5
520 ± 3.2
590 ± 1.6
Amendants
Wheat straw
Manure
C (% d.m)
42.0 ± 0.17
23.02 ± 0.35
δ
13
C (‰)
-24.0 ± 0.10
-20.75 ± 0.30
Means followed in the same row by the same letter are not statistically different at
P
< 0.05 according
to Duncan's test.
†Δ (%) percentage change = [(TOC
1972
- TOC
2002
)/TOC
1972
] x 100
± standard error
The quantification of HA carboxylic acids (COOH) is shown in Table 1. Our data shows
a statistically significant increase (
P
<0.05) in COOH groups in plots amended with CM and a
net loss of these groups of about 16% and 7%, in C
30
and CR
30
, respectively. These results are
generally in agreement with previous findings on HS from several amendment trials [38].
Moreover, it is generally accepted that the carboxylic groups increase in organic matter
during humification [5], therefore, the higher the amount of COOH groups in CM
30
, the
greater the chemical reactivity towards xenobiotic compounds and the better the soil buffer
activity.
