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Tillage Effects on Soil Respiration in Swedish Arable Soils
Veera Kainiemi Faculty of Natural Resources and Agricultural Sciences
Department of Soil and Environment Uppsala
Doctoral Thesis Swedish University of Agricultural Sciences
Acta Universitatis Agriculturae Sueciae 2014:2
ISSN 1652-6880 ISBN (print version) 978-91-576-7952-2 ISBN (electronic version) 978-91-576-7953-6 © 2014 Veera Kainiemi, Uppsala Print: SLU Service/Repro, Uppsala 2014
Tillage Effects on Soil Respiration in Swedish Arable Soils
Abstract The amount of carbon (C) present in soil is greater than the sum of C present in
terrestrial vegetation and the atmosphere combined. Small changes in soils can therefore affect atmospheric CO2 levels and ultimately the global climate. Soil C is also one of the main soil properties involved in several soil functions critical for soil productivity. Mechanical disturbance of the soil, e.g. through tillage, can influence soil C and has been the focus of much research. However, the mechanisms behind C mineralisation are still not completely understood and research results vary. Tillage affects the availability of organic material for decomposers, the soil structure and the activity of soil organisms, which are also affected by changes in soil moisture and temperature.
This thesis examined the effects of different tillage practices on short-term soil respiration and changes in soil structure, moisture and temperature and the effects on C mineralisation in soils. It also quantified potential soil respiration resulting from mechanical disturbance in different Swedish arable soils. In order to unravel the mechanisms involved, experiments were carried out in the field and under controlled conditions in the laboratory. The response of soil respiration to different tillage treatments and plant residue managements was measured in the field and changes in soil structure, moisture and temperature were recorded and related to soil respiration. In the laboratory, soils of different textures were subjected to mechanical disturbance at different water contents and potential soil respiration was measured.
The field studies showed that mouldboard ploughing decreased soil respiration by up to 340 kg ha-1 compared with no tillage and 140 kg ha-1 compared with shallow tillage during the 10 days following tillage, after which the differences were negligible. Soil temperature and water content did not significantly affect soil respiration in the field. Furthermore, mouldboard ploughing produced most large aggregates (>64 mm), corresponding to about 90% of soil mass in the tilled layer and resulted also in the lowest soil respiration. The potential soil respiration following physical disturbance at a controlled water content and temperature resulted in C losses of up to 74 kg ha-1 in the laboratory, indicating that increasing clay content and water content can increase the risk of C losses from soils due to mechanical disturbance. However, under field conditions, the mechanisms behind C mineralisation following tillage are primarily determined by residue management rather than by soil structure or changes in soil moisture and temperature.
Keywords: Tillage, soil respiration, plant residues, organic matter decomposition, soil structure, physical protection, aggregates, soil water content, soil temperature
Author’s address: Veera Kainiemi, SLU, Department of Soil and Environment, P.O. Box 7014, 75007 Uppsala, Sweden E-mail: Veera.Kainiemi@slu.se
To my grandmother Sanni.
Contents List of Publications 9
1 Introduction 13
2 Aim 15
3 Background 17 3.1 Soil Tillage 17
3.1.1 Tillage – The Plant Residue Manager 18 3.1.2 Tillage – The Soil Architect 19
3.2 Carbon Cycling in Arable Systems 21 3.2.1 Abiotic Factors Controlling SOM Decomposition 22 3.2.2 Biological Activity of Soil Aggregates 23
3.3 Soil Respiration – Quantifying C Mineralisation 25 3.4 Outlining Tillage Effects on C Mineralisation 26
4 Materials and Methods 29 4.1 Soil Respiration Measurements 29
4.1.1 Infrared Gas Analyser (IRGA) 29 4.1.2 Automated Respiration Analysis (Respicond IV) 30
4.2 Field Studies (Paper I & II) 31 4.2.1 Soils and Sites 31 4.2.2 Experimental Plan 32 4.2.3 Soil Respiration, Moisture and Temperature Measurements 32
4.3 Soil Aggregates and Respiration (Paper II) 33 4.3.1 Site and Soil Sampling 33 4.3.2 Experimental Plan 34
4.4 Physical Disturbance Induced Respiration (DIR) (Paper III) 36 4.4.1 Soils and Sampling 36 4.4.2 Pre-incubation and basal soil respiration rate (RES) 37 4.4.3 Physical Disruption Method and DIR 37
4.5 Basic Soil Properties 38 4.6 Statistical Analyses 39
4.6.1 Physical Properties and Respiration in the Field (Paper I and II) 39 4.6.2 Soil Respiration in Different Aggregates (Paper II) 39
4.6.3 Mechanical Disturbance Effects on Respiration - Physical Properties and Soil Texture (Paper III) 39
5 Results and Discussion 41 5.1 Soil Respiration Response to Different Tillage Practices in the Field 41 5.2 Linking Soil Structure and Biological Activity in Response to Tillage 45 5.3 Tillage Retarded Soil Respiration – A Residue Incorporation Effect? 49 5.4 Potential Short-Term C Mineralisation due to Physical Disturbance 51
6 Conclusions 57
List of Publications This thesis is based on the work contained in the following papers, referred to by Roman numerals in the text:
I Kainiemi, V., Arvidsson, J., Kätterer, T. (2013). Short-term organic matter mineralisation following different types of tillage on a Swedish arable soil. Biology and Fertility of Soils 49(5), 495-504.
II Kainiemi, V., Arvidsson, J., Kätterer, T. Effects of autumn tillage and residue management on soil respiration in a Swedish long-term field experiment. (manuscript).
III Kainiemi, V., Kirchmann, H., Kätterer, T. Respiration response to physical disturbance in arable soils of differing texture under controlled conditions. (manuscript).
Paper I is reproduced with the permission of the publishers.
The contribution of Veera Kainiemi to the papers included in this thesis was as follows:
I Planned the experimental work with the co-authors. Performed the practical work, with some assistance. Performed data analyses and wrote the main part with some assistance from the co-authors.
II Planned the experimental work with the co-authors. Performed the practical work, with some assistance. Performed data analyses and wrote the main part with some assistance from the co-authors.
III Planned the experimental work with the co-authors. Performed the practical work, with some assistance. Performed data analyses and wrote the main part with some assistance from the co-authors.
Abbreviations C carbon CO2 carbon dioxide DIR physical disturbance induced respiration GHG green house gas KOH potassium hydroxide MP mouldboard ploughing to 20 cm NT no-till RES basal soil respiration SOC soil organic carbon SOM soil organic matter ST shallow tillage to 5 cm W gravimetric water content volumetric water content water potential
1 Introduction The amount of carbon (C) present in soils is greater than the sum of C present in living biomass and the atmosphere. Any change in soil organic carbon (SOC) affects atmospheric CO2 and has an impact on climate change. Loss of SOC is one of the main threats to soils and its protection is listed as one of the main goals in soil protection by the FAO (Bot & Benites, 2005) and the European Commission (Van-Camp et al., 2004; Blum, 2008). A decrease in SOC affects the soil structure, making the soil more sensitive to e.g. compaction and reducing its capacity to retain water and nutrients. Moreover, soils provide substrates and habitat for a quarter of all species in the world (Turbé et al., 2010). Anthropogenic influences such land use changes and agricultural management can increase or decrease SOC (Kätterer et al., 2012).
Zero or no tillage and reduced tillage practices have been applied for decades, especially in the USA after the Dust Bowl in the 1930s, where large areas were ploughed and left fallow, contributing to significant wind erosion and enormous losses of topsoil. In Northern Europe, where long wet winters are the norm, autumn tillage and winter fallow periods have long been the predominant management practices on clay soils. However, reduced tillage practices are now attracting increasing interest due to the lower work load and fuel costs (Maraseni & Cockfield, 2011) and increased SOC content in the surface soil layers compared with conventional tillage (Franzluebbers, 2008; Virto et al., 2012). In cold temperate regions, the effect of no tillage on C sequestration is small, in contrast to in warm and dry areas (Govaerts et al., 2009; Regina & Alakukku, 2010). Soane et al. (2012) reviewed tillage effects on GHG emissions and concluded that the mechanisms behind C mineralisation in relation to tillage are not completely understood.
Tillage modifies soil architecture and thereby changes soil moisture and temperature conditions, but it also cuts up and buries plant residues in the cultivated