16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12303
Effects of reduced tillage on soil organic carbon and microbial
activity in a clayey soil
A. Berner 1, A. Fließbach1, B. Nietlispach1 and P. Mäder1
Key words: soil fertility; cultivation; soil organic matter; crop farming; reduced tillage
Abstract
In a long-term field trial recently launched (2002-2011), located in Frick (878 mm
mean annual precipitation) near Basle, Switzerland, the effect of reduced tillage on
soil fertility indicators and crop yield was studied in a heavy soil (45% clay) in a crop
rotation under organic farming conditions. We present the results of soil analyses after
three cropping years (2002-2005). Soil organic carbon (Corg) increased over that
period by 7.4% (+1.5 g Corg kg-1 soil) in the 0-10 cm soil layer in the reduced tillage
plots, while it remained constant in the ploughed plots. Soil microbial carbon (Cmic) and
dehydrogenase activity (DHA, TTC-reduction) were 28% higher in reduced-tillage
plots in this soil layer. Biological soil quality as calculated by Cmic to Corg was 15%
enhanced under reduced tillage. In the 10-20 cm soil layer no significant Corg, Cmic, Cmic
to Corg and DHA differences between the tillage schemes were found. It is suggested
that reduced tillage improves important indicators of soil fertility during the conversion
period. Long-term aspects of soil fertility, crop yield and weed infestation need
investigation over a prolonged experimental period.
Introduction
Reduced tillage diminishes soil erosion and enhances soil fertility. In organic farming,
problems remain to be solved with respect to weed competition, slug control and plant
nutrition (Peigné et al., 2007). Long-term experiments have revealed that soil turning
with a plough is necessary after several years in order to gain satisfactory yields
(Hampl, 2005; Kainz et al., 2005; Pekrun et al., 2003). By turning the soil layers,
however, the benefits of reduced tillage may vanish within a year (Stockfisch et al.,
1999). The experiment on a clayey soil presented here seeks to broaden the available
experience with reduced tillage under organic conditions. Tillage, fertilization and the
use of biodynamic preparations were combined, mimicking different agricultural
organic farming systems.
Materials and methods
In autumn 2002, we established in Frick, Switzerland, a field experiment comprising
the following factors, each at two levels:
Soil tillage
Ploughing system (mouldboard plough, 15 cm deep, followed by
rotary harrow, 5 cm deep) versus reduced tillage system (chisel
plough2, 15 cm deep, followed by rotary harrow3, 5 cm deep).
1 Research Institute of Organic Agriculture FiBL, Ackerstrasse, 5070 Frick, Switzerland, E-Mail
alfred.berner@fibl.org Internet www.fibl.org
2 WeCo-Dyn-System of the EcoDyn company, Schwanau, Germany
3 Rotary harrow of the Rau company, Weilheim, Germany.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12303
Fertilization
Slurry alone versus manure compost and slurry (both systems at a
level of 1.4 livestock units).
Biodynamic
preparations
With versus without biodynamic compost and field preparations4
(the latter applied three times a year).
The three factors – tillage, fertilization, preparations – were fully factorized. This
resulted in eight treatments, each replicated four times. The 32 plots were arranged in
a split-plot design. Plot size was 12 x 12 m, allowing the use of common-size farming
equipment.
Soil cores were taken at the beginning in autumn 2002, and again in spring 2005 (n =
32). The clay soil at the experimental site initially contained mean levels of 2.2%
organic carbon (Corg) and 45% clay, and had a pH of 7.1 (H2O). Corg was analysed by
wet oxidation, microbial biomass (Cmic, Nmic) by chloroform fumigation extraction and
dehydrogenase activity by TTC reduction. The mean annual precipitation in the
experimental period was 878 mm.
Before the experiment started, the field site was uniformly planted with silage maize in
2002. The crop rotation in the first three years (2002-2005), being the period to which
the results presented here refer, was winter wheat, oat-clover intercropping, sunflower
and spelt. Two years of grass-clover were planted in 2006-2007. Wheat grains and
straw were harvested and removed from the field.
Data were analysed by three-way analysis of variance (ANOVA). In this paper, first
results of the soil analyses from 2005 are presented.
Results
Within three years, Corg levels in the 0-10 cm soil layer rose in reduced-tillage soils by
7.4% (+1.5 g Corg kg-1 soil) as compared to the ploughed soils (Fig. 1a). Microbial
biomass (Cmic, Nmic) and DHA were 26-28% higher in reduced tillage at the same soil
depth (Fig. 1b). The Cmic to Corg ratio was increased by 15% under reduced tillage. For
these parameters, we found no significant interactions between the factors of tillage,
fertilization and biodynamic preparations. In the 10-20 cm soil layer no significant
differences in soil properties were found.
The yields of the cereals wheat and spelt were 14% and 8% lower in reduced-tillage
plots compared to ploughed plots. Sunflower yield was slightly higher in reducedtillage plots. Application of slurry only delivered a 5% higher grain yield with wheat.
The biodynamic preparations had no effects on yield.
Discussion
The increase of Corg under reduced tillage in our experiment can be explained by large
amounts of carbon contained in the roots of the crops, and especially in the biomass
of the sunflower residues which were incorporated into the soil. This matches the
findings of Alvarez (2005), Ogle et al. (2005) and Teasdale et al. (2007). In other
experiments, a reduction of Corg in deeper soil layers compensated the enhancement
of Corg in the upper soil layers (Wright et al., 2005). Angers et al. (1993) reported that a
sufficient amount of plant biomass incorporation is a prerequisite for enhanced C org,
including under reduced tillage as in the experiment described. The high plant
4 see http://www.sciencemag.org/cgi/content/full/296/5573/1694/DC1
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12303
biomass input in our experiment resulted in increased microbial biomass in the 0-10
cm top soil layer. Weber and Emmerling (2005) studied soil microbial activity in a tenyear tillage experiment, finding soil microbial activity to be enhanced by 30% following
layer cultivation with a chisel plough and by 21% following two-layer ploughing in the
0-15 cm surface layer.
Yield reduction in reduced tillage plots in our experiment was substantially lower than
that found in various comparable studies, e.g. the results reported by Kainz et al.
(2005) where crop yields dropped by up to 35%.
a)
Plough
Reduced tillage
-0.008
***
0.149
Slurry
0.065
0.076
Manure compost / Slurry
Without bd preparations
With bd preparation
ns
0.086
ns
0.054
-0.1
0
0.1
0.2
Δ % Corg
b)
Plough
Reduced tillage
780
***
996
883
893
ns
Manure compost / Slurry
Slurry
Without bd preparations
With bd preparation
895
882
ns
0
500
1000
1500
-1
mg Cmic kg Soil DM
Figure 1: (a) Development in Corg between 2002-2005. Zero line means no change
of Corg in the three experimental years. Note that 0.1 % Corg change corresponds
to 1 mg Corg kg-1 soil. (b) Microbial biomass (Cmic) 2005 at 0-10 cm soil depth. A
three-way ANOVA was calculated for Corg and Cmic for the three factors tillage,
fertilization and biodynamic preparations at two levels each (n = 16).
Conclusions
Based on the results obtained, we can conclude that reduced tillage is viable under
organic farming conditions in the conversion phase, even on a clay soil.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/12303
Furthermore, the results suggest that reduced tillage is feasible both with manure
compost and slurry fertilization. Since there were no interactions between the three
factors of tillage, fertilization and biodynamic preparations, neither for yields nor for
soil fertility indicators, we are unable to suggest any combinations of these farming
practices for optimal conversion to reduced tillage under organic farming conditions.
The long-term effects of the reduced tillage system need to be assessed to elucidate
their impact on soil fertility indicators and yield performance from the point of view of
carbon sequestration and weed competition.
Acknowledgments
This work was funded by the Swiss Federal Office for Agriculture and the following
institutions: Dutch BD-Vereniging, Stiftung zur Pflege von Mensch, Mitwelt und Erde,
Sampo Verein für Anthroposophische Forschung und Kunst, Software AG Stiftung and
Evidenzgesellschaft.
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