『Abstract
Soil management may affect C and N dynamics in soils, but the
underlying processes are not well understood. Our objective was
to quantify the impact of different tillage treatments on the
amount and distribution of free and occluded light fractions (fLF
and oLF, respectively), on the water-stable macro-aggregate (>250μm)
contents, and on organic carbon (Corg) storage.
Four long-term tillage trials were carried out on loess soils
in Germany with sugar beet followed by two years of winter wheat
as crop rotations. The different tillage treatments trialled were
regular conventional tillage (CT, to 30 cm), mulch tillage (MT,
to 10 cm) and no-tillage (NT). Soils were sampled in 0-5 cm, 5-25
cm and 25-40cm depth after 18-25 years of the different tillage
treatments. These four long-term tillage trials on plots differing
in soil texture and climatic conditions revealed consistent results
between them. Average crop yields of sugar beet and winter wheat
from 2004 to 2010 were higher under CT and MT than under NT. The
NT and MT treatments produced significantly higher Corg
contents than the CT treatment in 0-5 cm soil depth. The Corg stocks in the sampled profile, based on the
equivalent soil mass approach (CT: 0-40, MT: 0-38, NT: 0-36 cm),
were significantly higher for the MT treatment than for the CT
and NT treatments. The fLF, oLF, and macro-aggregate contents
were significantly higher for the NT and MT treatments than for
the CT treatment in the top 5 cm, whereas in 5-25 cm depth, the
oLF contents were significantly higher for the CT and MT treatments.
The correlation of the macro-aggregate content against the fLF
and oLF contents suggested that the macro-aggregate content is
not directly influenced by the different tillage treatments but
by the contents of available biomass, presumably due to the higher
biomass input via higher crop yields under CT and MT and the vertical
distribution of the residue input by mulching and plowing. Stepwise
multiple linear regression analysis suggested that the Corg content was the most important factor influencing
the macro-aggregate content in the soils of the four long-term
trials, whereas the contents of fLF and silt were negatively related
to the macro-aggregate content.
Keywords: Density fractionation; Aggregate fractionation; Tillage;
Carbon stocks; Sugar beet; Winter wheat』
1. Introduction
2. Material and methods
2.1. Experimental sites and treatments
2.2. soil sampling and soil properties
2.3. Water-stable aggregate fractionation
2.4. Density fractionation
2.5. Water extractable organic carbon
2.6. Statistical evaluation
3. Results
3.1. Crop yields, organic carbon contents and stocks under
different tillage treatments
3.2. Density fractions
3.3. Distribution of water-stable macro-aggregates over soil
depth
3.4. Correlation between organic carbon, macro-aggregates and
light fraction
4. Discussion
4.1. Crop yields, organic carbon contents and stocks under
different tillage treatments
4.2. Water extractable organic carbon contents under different
tillage treatments
4.3. Density fractions
4.4. Distribution of water-stable macro-aggregates and correlation
between organic carbon, macro-aggregates and light fraction
5. Conclusions
Acknowledgments
References