Agriculture Reference
In-Depth Information
The addition of manure, did not induce a preferential accumulation of corn-derived C in
HA in spite of the increase in HA-C content and although with this treatment the greatest
proportion of corn-derived C was found in SOC. Nevertheless this treatment caused the
highest C sequestration in the HA fraction that was not only due to increased yields of roots
residues, but also to higher humification rate and the direct application of organic matter
through the manure itself. Moreover we measured a very slow turnover rate of the old C
3
-C in
the plots treated with manure, that might be due to slower breakdown rate.
C
ONCLUSION
Long-term field experiments where a change in vegetation from C
3
to C
4
plant species
has occurred and where plots of C
3
species are maintained have a great worth for the study of
C dynamics. The agricultural management practices are crucial for the maintenance of the
SOC level over long time periods and our results indicate that the mineral fertilization and the
addition of manure are both able to reduce the C loss or even to increase the SOC over years.
The addition of manure had the most positive effect on C sequestration as a result of several
factors, in particular the supply of organic matter through the manure itself, but also other
more general benefits related to the microbial activity and physical conditions of soil (Kundu
et al., 2007). Both treatments, however, positively affected soil C sequestration, by inducing
an increase in the amount of corn-derived C in SOC compared to the control and by slowing
down the turnover rate of the old C
3
-C.
When we considered the humic fraction, being one of the most important pools of SOC
involved in C sequestration, we found that both treatments were able to significantly increase
this pool compared to the unfertilized control, but the mechanism involved was mainly a
preservation of the old C
3
-C from degradation process, not an increase in the proportion of
new C
4
-C in the humic pool. This proportion was actually similar for the control and the two
treatments, but the turnover rate of the C
3
-C from the treated plots was threefold and fivefold
slower for Min and Org treatments respectively suggesting that the annual supply of mineral
fertilizers and even more of manure, can significantly increase the preservation of old C in the
humic C pool.
A
KNOWLEDGEMENTS
The authors would like to thank Profs. Giovanni Toderi, and Guido Baldoni and Dr.
Gianni Giordani for kindly providing the historical soil samples, as well as soil data and
management information. This research has been funded by University of Bologna ex quota
60%.
R
EFERENCES
Angers D.A., R.P. Voroney, and D. Cote. 1995. Dynamics of soil organic matter and corn
residues affected by tillage practices.
Soil Sci. Soc. Am. J.
59:1311-1315
