Agriculture Reference
In-Depth Information
Table 2. Proportion of new corn-derived C in SOC and HA and half-life of old C
3
-C in
SOC and HA measured in the control and in the plots treated consecutively over 30
years with mineral fertilizers (Min) and manure (Org)
Soil
HA
Proportion of
corn-derived C
Half-life of old
C
3
-C
Proportion of
corn-derived C
Half-life of
old C
3
- C
Treatment
%
yr
%
yr
Control
19.4 ± 0.56
55
26.4 ± 0.08
29
Min
23.9 ± 0.16
65
23.7 ± 0.62
100
Org
29.8 ± 0.88
86
26.4 ± 0.37
156
Mean
± standard error, n=6 replicates
Relic C
The turnover of the old C
3
-C was significantly affected by the treatments (Table 2). The
half-life of the previous C
3
-C in the total SOC pool increased in the following order: control,
Min, Org treatment, meaning that both treatments, but especially the Org one, were able to
slow down the turnover of the relic C.
The half-life of HA C
3
-C was shorter than that of SOC in the control, but significantly
longer than SOC with both treatments. The C
3
-C turnover time in the control was about 30
years, whereas the treatments increased the half-life of C
3
-C by three fold with repeated
mineral fertilization and by five fold with the addition of manure.
D
ISCUSSION
Total Organic C and Humic C
The absence of nutrient addition in the control emphasized the effect of the plant species
on the SOC content and dynamics. In the long-term field experiment at Halle, Germany, that
had rye as a reference plot, Flessa et al., 2000, measured a higher value of SOC concentration
in the rye plot compared to the corn plot although in this experiment the plots got mineral
fertilization. Our results showed that the addition of mineral fertilizer had a positive effect on
the TOC of the control with both plant species. By comparing the values of TOC
concentration of the treated and no-treated plots in 2002, we found that the mineral
fertilization produced the greatest positive effect on C storage in the corn plots than in the
wheat plots (Table1). Our results are not in agreement with those of literature demonstrating
that this effect on C storage is a complex phenomenon not well understood. In fact . in a long-
term field experiment with two levels of mineral fertilization, Wilts et al., 2004 observed an
overall decrease in SOC during continuous corn production with moldboard tillage. Similar
results were obtained by Reicosky et al., 2002 and by Clapp et al., 2000.
