Joint International Conference on Long-term Experiments ...

concentration in the surface layer than moldboard plowed or chiseled plots. On the other
hand, carbon levels at lower depths are generally similar in both systems, or higher
under moldboard plow (Angers et al. 1997, Gal, 2005).
The actual effect of different tillage practices on soil carbon storage is highly
dependent on the crops produced in the field. Crop rotation contributes to increased
yield (Mitchell et al., 1991) and nitrogen contribution by legumes can be very
important. Crop rotation is known to increase soil microbial activity, which has the
direct effect of breaking down organic matter by the microbes. Residue quantity is the
main factor in determining soil organic carbon, for example lower soil organic carbon
level corresponds with sequences including soybean, but organic carbon increases as
soybean is not present or corn is present in a sequence according to Studdert et al.
(2000). However, the effect of residue amount is conditioned by several other factors.
Several studies have been conducted to determine the quantity and distribution of
organic carbon and total nitrogen under different tillage and rotation systems in longterm
studies (Kern and Johnson, 1993; Angers et al., 1997; VandenBygaart et al., 2002).
Gal et al. (2007) have found on the same experimental plots that while no-till clearly
resulted in more organic carbon and nitrogen accumulation in the surface 15 cm than
moldboard plow, the relative no-till advantage declined sharply witd depth. Indeed,
moldboard plow resulted in more organic carbon and total nitrogen int he 30-50 cm
depth interval. However, less is known about the relationship of OC and N stored in the
soil and the emission of CO2, and N2O from the soil over the crop production cycle. In
order to understand the effect of different tillage and rotation systems on carbon
sequestration - which is the long-term storage of carbon in soil and can help to stop the
increase of greenhouse gases in the atmosphere - we have to examine these processes
more in details. Extended knowledge of the factors influencing soil capacity to be a net
sink or source of greenhouse gases in the atmosphere is one of the most relevant and
urgent needs in agricultural policy making and also in extension.
The objective of the research was to compare the long-term effects of conservation
(no-till) and conventional (chisel plow and moldboard plow) tillage systems on soil
CO2, and N2O emission, in continuous corn and soybean-corn rotation.
MATERIALS AND METHODS
Research area
The sampling site chosen for the study is located at Purdue University (West Lafayette,
IN, USA), at the Agronomy Center for Research and Education. The soil is a poorly
drained Chalmers silty clay loam (Typic Haplaquoll according to the US Taxonomy)
dark, with approximately 4 % organic matter in the surface 30 cm, developed under
prairie vegetation (Vyn et al., 2000). The Long-Term tillage experiment has been
conducted for 30 years. Moldboard plow, chisel plow and no-till tillage treatments were
compared in continuous corn and soybean-corn rotation.
The experiment is a randomized complete block in a split-plot (small plots) design
with treatments replicated four times. Crop rotations are the main units, and the tillage
treatments the subunits. In the course of this experiment, starter N (36 kg N ha -1 as 34-0-
0) and side-dressed N (222 kg N ha -1 as 28% urea ammonium nitrate, UAN) were
applied.
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