Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns Edvaldo Sagrilo Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns Edvaldo Sagrilo Thesis committee Promotors Prof. Dr T.W. Kuyper Personal chair at the Department of Soil Quality Wageningen University Prof. Dr E. Hoffland Personal chair at the Department of Soil Quality Wageningen University Other members Prof. Dr P.C. Struik, Wageningen University Prof. Dr B. Glaser, University of Bayreuth, Germany Dr L. Mommer, Wageningen University Prof. Dr W. de Vries, Wageningen University This research was conducted under the auspices of the C.T. de Wit Graduate School for Production Ecology and Resource Conservation Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns Edvaldo Sagrilo Thesis submitted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. Dr M.J. Kropff, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Tuesday 9 December 2014 at 1:30 p.m. in the Aula. E. Sagrilo Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns 128 pages. PhD thesis, Wageningen University, Wageningen, NL (2014) With references, with summaries in English, Dutch and Portuguese ISBN: 978-94-6257-167-9 To Monica Abstract Soil amendment with pyrogenic organic matter (PyOM) can sequester carbon, increase mutualistic root symbioses with arbuscular mycorrhizal fungi and nitrogen-fixing rhizobia, and hence improve crop yield. However, there is still a gap in our knowledge about the effects of PyOM over longer temporal scales, especially in field experiments that last longer than one cropping cycle. This thesis aims to study interactions between PyOM and soil organic carbon (SOC) and symbiotic patterns in soybean (Glycine max) under tropical field conditions in a sandy ferralsol in northeast Brazil. Data from a meta-analysis indicated that PyOM additions significantly increase CO2 emissions at PyOM-C (PyC):SOC ratios >2, suggesting that such increases are derived from the labile fractions of PyOM rather than from SOC. They also indicated that positive priming is not a main driver of increased CO2 emissions in PyOM-amended soils. Results from a field experiment using 13C isotopic data confirmed the lack of positive priming of SOC over four cropping cycles. Data demonstrated that decomposition of traditionally produced PyOM was faster than stated in the literature, and depended on the PyOM application rate. We found a significant PyOM × cropping cycle interaction for mycorrhizal root colonization, with a linear decrease in the first cropping cycle with increasing PyOM rates, in contrast to a linear increase in colonization in the fourth cropping cycle. Grain yield was highest at high PyOM rates in phosphorus-fertilized treatments in the fourth cropping cycle. Path analysis indicated a lack of pH and phosphorus-mediated effects on root colonization by arbuscular mycorrhizal fungi, suggesting interference in signaling processes as the likely mechanism for PyOM effects on the mycorrhizal symbiosis over time. Cropping cycle had a major effect on biological nitrogen fixation, but no effects of PyOM were observed. Alleviation of micronutrient deficiency at the fourth cycle enhanced positive effects of phosphorus fertilizer and increased biological nitrogen fixation, suggesting that under adequate management, PyOM does not increase nitrogen fixation in soybean. In this thesis I demonstrated that stability of PyOM can be influenced by the soil environment and provide indications that mycorrhizal activity may play a role in this stability in the long- term. I also showed that the main beneficial effects of PyOM on AMF and crop yield develop with time, but in well-managed soils, increased crop yield is not a direct consequence of PyOM addition. Contents Chapter 1 General introduction ............................................................................. 1 Chapter 2 Emission of CO2 from biochar-amended soils and implications for soil organic carbon .................................................................................... 15 Chapter 3 Biochar decomposition under field conditions depends on its application rate ................................................................................... 37 Chapter 4 Mechanisms affecting mycorrhizal dynamics in soils amended with pyrogenic organic matter .................................................................... 49 Chapter 5 Does pyrogenic organic matter enhance biological nitrogen fixation in well-managed soybean cropping systems? ......................................... 69 Chapter 6 General discussion ............................................................................... 83 References ........................................................................................... 97 Summary ............................................................................................ 109 Samenvatting ...……………………………………………………..113 Sumário ...…………………………………………………………..119 Acknowledgements .......……………………………………………123 Current affiliation of authors ............................................................. 113 PE&RC Training and Educational Statement ………………………127 x Abbreviations ADE Amazonian Dark Earth AMF Arbuscular Mycorrhizal Fungi ANOVA Analysis of variance BC Black carbon BNF Biological nitrogen fixation CC Cropping cycle CEC Cation exchange capacity CI Confidence interval CO2 Carbon dioxide CS Cropping season d.f. Degrees of freedom DHG Dehydrogenase FDA Fluescein diacetate IRGA Infrared gas analyser Ndfa Nitrogen derived from air PE Priming effect PET Potential evapotranspiration PyC Pyrogenic carbon PyOM Pyrogenic organic matter RR Response ratio SD Standard deviation SE Standard error SOC Soil organic carbon SOM Soil organic matter TTF Triphenyltetrazoliumformazan ix Chapter 1 General introduction Edvaldo Sagrilo General introduction 1.1 Introduction The use of pyrogenic organic matter (PyOM), also named biochar, as a soil amendment was inspired by the dyscovery of anthropogenic soils in the Amazon basin, called “Amazonian Dark Earths” (ADE - Terra Preta de Índio). These soils are more fertile and contain larger amounts of PyOM than the surrounding soils (Glaser et al., 2001). The high amount of PyOM is considered one of the main reasons for the high fertility of ADE (Glaser et al., 2002). Soil additions of PyOM have been shown to improve soil fertility and crop yields (Jeffery et al., 2011), while also providing other environmental services. These environmental services include PyOM’s capacity to increase the recalcitrant soil organic carbon (SOC) pool (Lehmann et al., 2006; Knicker et al., 2013), contributing to offset CO2 emissions. The combination of increased nutrient availability and crop yields, with a larger SOC pool suggests that the “carbon dilemma” (Janzen, 2006) could be solved by adding PyOM to the soil. Solving this dilemma would imply that crops could benefit from SOC decomposition and nutrient release, concomitantly with increases in SOC stocks. However, Jeffery et al. (2013) demonstrated that in many instances, it is not possible for all benefits to be simultaneously maximized in PyOM- amended soils, due to trade-offs between two or more “wins”, for instance, between soil fertility and C sequestration. Currently there is growing interest in research on PyOM (Fig. 1.1) and several areas have been emphasized in particular, for instance SOC and PyOM stability in PyOM-amended soils (Verheijen et al., 2014). Effects of PyOM on soil fertility and crop yield have also received attention of researchers, especially in tropical countries such as Brazil (Maia et al., 2011). In such environments, high temperature and soil moisture favour SOC decomposition (Tiessen et al, 1994). Therefore, soil amendment with PyOM is of particular interest in tropical agro- ecosystems, where the management of SOC represents one of the main challenges for sustainable use of soil. Soil organic matter (SOM) is essential as a source of important nutrients such as P and N, which become available when SOM is decomposed (Tiessen et al., 1994). It is also essential for microbial activity as SOM provides the fuel for the “engine” that drives soil quality (Balota et al., 2004; Causarano et al., 2008). Changes in soil microbiota following PyOM addition may have direct or indirect effects on plant growth through changes in nutrient cycles or soil structure (Lehmann et al., 2011). Modification of soil microbial assemblages following PyOM addition with special emphasis on microbial functionality (e.g. mutualistic root symbioses) is also a major topic for research (for instance, Warnock et al., 2007; Rondon et al., 2007; Mia et al., 2014). The use of PyOM can enhance plant associations with symbiotic microorganisms as arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria (rhizobia). However, the role of PyOM on modifying root symbioses has received much less attention compared to PyOM effects on SOC (Fig. 1.1). 3 Chapter 1 600 1 - 500 Biochar 400 Biochar + SOC Biochar + symbiosis 300 200 100 Number of publications year publicationsof Number 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year Figure 1.1. Number of publications in scientific journals (Web of ScienceTM) between 2005 and 2014. Blue bars represent total number of publications using only biochar as keyword.