Effects of Reduced Tillage on Soil Organic Carbon and Microbial Activity in a Clayey Soil

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 plough[2], 15 cm deep, followed by rotary harrow[3], 5 cm deep).

Fertilization Slurry alone versus manure compost and slurry (both systems at a level of 1.4 livestock units).

Biodynamic With versus without biodynamic compost and field preparations[4]
preparations (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 reduced-tillage 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 Corg, including under reduced tillage as in the experiment described. The high plant 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 ten-year 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%.

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.

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.

References

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Angers, D. A., N'dayegamiye, A., Côté, D. (1993): Tillage-induced differences in organic matter of particle-size fractions and microbial biomass. Soil Science Society of America Journal 57:512-516.

Hampl, U. (2005): Projekt Ökologischen Bodenbewirtschaftung. Zehn Jahre differenzierte Grundbodenbearbeitung im ökologischen Ackerbau. Abschlussbericht. Stiftung Ökologie & Landbau, Bad Dürkheim.

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[1] Research Institute of Organic Agriculture FiBL, Ackerstrasse, 5070 Frick, Switzerland, E-Mail Internet www.fibl.org

[2] WeCo-Dyn-System of the EcoDyn company, Schwanau, Germany

[3] Rotary harrow of the Rau company, Weilheim, Germany.

[4] see http://www.sciencemag.org/cgi/content/full/296/5573/1694/DC1