J. Six

J. Six
ETH Zurich | ETH Zürich · Department of Environmental Systems Science

PhD in Soil Science

About

579
Publications
342,757
Reads
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52,827
Citations
Introduction
Dr. Six received his PhD in Soil Science in 1998 from CSU; was a Research Scientist at CSU from 1998 until 2002; and a professor at UCDavis from 2002 till 2012. Currently, he is a professor at ETH-Zurich. He studies the complex interactions between soil (e.g, structure, texture and mineralogy), plants (e.g., diversity, nutrient uptake), soil biota, and the carbon and nitrogen cycles in terrestrial ecosystems, especially agroecosystems. His general approach is to conduct experimental work from the micro- to landscape scale and subsequently integrate it with modeling to interpolate and extrapolate it to the regional and global scale. Bio-economic modeling is conducted in collaboration with economic and social scientist to holistically assess the sustainability and resilience of agriculture
Additional affiliations
June 2002 - December 2012
University of California, Davis
Position
  • Professor in Agroecology
September 1995 - June 2002
Colorado State University
Position
  • Researcher

Publications

Publications (579)
Article
Under the United Nations Framework Convention on Climate Change (UNFCCC), industrialized countries and countries with economies in transition (so called Annex 1 countries) are encouraged to move towards more sophisticated approaches for national greenhouse gas reporting. To develop a model-based approach for estimating nitrous oxide (N2O) emissions...
Article
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Cassava (Manihot esculenta Crantz) is an important staple crop in Nigeria. It provides approximately 80 % of the caloric intake in Nigeria. High starch content and fresh root yields are important for the commercialization of cassava. Cassava is a perennial crop, and it can be produced all year round. However, cassava fresh root yield and starch con...
Article
The intensification of agricultural systems has caused a noticeable impact on agro-ecosystem services. Thus, the adoption of more sustainable agricultural practices such as crop diversification and reduction of external inputs represent an alternative strategy to minimize the impacts of intensive agricultural systems to the environment. This study...
Article
Freshwater aquaculture ponds constitute one of the important anthropogenic sources of atmospheric methane (CH4). Nevertheless, estimates of global CH4 emissions from freshwater aquaculture have large uncertainties due to a lack of data from different aquaculture types. Furthermore, despite that ebullition is a major pathway of CH4 in aquatic system...
Article
Nitrous oxide (N2O) is an important trace gas contributing to global warming and depletion of ozone in the stratosphere. Its increasing abundance is caused mainly by anthropogenic sources, such as application of fertilizers in agriculture or emissions from industry. To understand the N2O global budget, its sources and sinks need to be well-describe...
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Secondary forests constitute an increasingly important component of tropical forests worldwide. Although cycling of essential nutrients affects recovery trajectories of secondary forests, the effect of nutrient limitation on forest regrowth is poorly constrained. Here we use three lines of evidence from secondary forest succession sequences in cent...
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Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N 2 O. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and N 2...
Article
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Efficient utilization of incident solar radiation and rainwater conservation in rain-fed smallholder cropping systems require the development and adoption of cropping systems with high resource use efficiency. Due to the popularity of cassava-maize intercropping and the food security and economic importance of both crops in Nigeria, we investigated...
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Long-term nutrient mining of soil hampers agricultural production across Africa. However, emerging sanitation technologies afford a hygienically safe and ecologically sustainable solution to this development challenge by providing fertilizers derived from human excreta that could facilitate a socio-technical transition toward a more sustainable foo...
Article
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In Morocco, droughts are an increasing threat affecting water availability, agricultural production and producers' livelihoods. Moreover, water demand for irrigation has led to overexploitation of the groundwater table causing significant natural resource management challenges. The combination of groundwater changes and increasing drought risk rais...
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Aquatic losses of nutrients are important loss vectors in the nutrient budgets of tropical forests. Traditionally, research has focused mainly on losses of inorganic nutrient forms, whereas the potential contribution of organic and particulate losses to the total nutrient export budget is much less constrained. In this study, we quantified full aqu...
Article
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Agricultural intensification and forest conservation are often seen as incompatible. Agricultural interventions can help boost food security for poor rural communities but in certain cases can exacerbate deforestation, known as the rebound effect. We tested whether coupling agricultural interventions with participatory forest zoning could improve f...
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The Congo and Amazon are the two largest rivers on Earth and serve as major sources of dissolved organic carbon to the ocean. We compared the dissolved organic matter (DOM) composition of both rivers using Fourier‐transform ion cyclotron resonance mass spectrometry to investigate seasonal and regional differences in DOM composition exported to the...
Conference Paper
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With climate and land use changes, it is becoming increasingly important to understand not only how much carbon is and will be stored in soils, but also how long this C will remain in soils. Estimates of C age can provide useful information about the timescales on which C will respond to such changes. It is generally accepted that the interaction o...
Article
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Background Across the tropics, the share of secondary versus primary forests is strongly increasing. The high rate of biomass accumulation during this secondary succession relies on the availability of essential nutrients, such as nitrogen (N). Nitrogen primarily limits many young secondary forests in the tropics. However, recent studies have shown...
Preprint
Carbon is a key element for the functioning and productivity of tropical soils. While the impact of organic inputs on carbon storage in these soils is known, little is known about the contribution of non-cultivated trees. In this study, we measured carbon content in non-cultivated trees (VC), soil organic carbon (SOC) and soil total nitrogen (TN) i...
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Rivers act as a natural source of greenhouse gases (GHGs). However, anthropogenic activities can largely alter the chemical composition and microbial communities of rivers, consequently affecting their GHG production. To investigate these impacts, we assessed the accumulation of CO2, CH4, and N2O in an urban river system (Cuenca, Ecuador). High var...
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We have read with interest an opinion paper recently published in the European Journal of Soil Science (Berthelin et al., 2022). This paper presents some interesting considerations, at least one of which is already well known to soil scientists working on soil organic carbon (SOC), i.e. a large portion (80-90%) of fresh carbon inputs to soil is sub...
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With climate change and an increasing global human population, the concept of agroforestry is gaining economic and environmental interest. The practice of growing trees and crops on the same land is mainly applied in (sub)tropical climate and rarer in temperate areas where farmers fear decreased understorey crop yields due to competition with trees...
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Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we...
Article
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Diversified farming systems are promoted to improve ecosystem services in agriculture while maintaining productivity. Intercropping could improve soil quality, the stability of yields and climate resilience. Whether direct emissions of greenhouse gases from soil are reduced as well, depends on the specific measures of diversification. Here, we dete...
Preprint
Background Across the tropics, the share of secondary versus primary forests is strongly increasing. The high rate of biomass accumulation during this secondary succession relies on the availability of essential nutrients, such as nitrogen (N). Nitrogen primarily limits many young secondary forests in the tropics. However, recent studies have shown...
Article
The degradation of soil from agricultural land is a major threat to food security and a driver of global changes. Soil conservation systems are thus being promoted and/or adopted worldwide. In this on-farm study conducted in Switzerland, we compared the effect of three cropping systems – conventional with tillage, conventional without tillage (i.e....
Article
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Soil compaction caused by highly mechanized agriculture can constrain soil microbial diversity and functioning. Physical pressure on the soil decreases macropores and thereby limits oxygen diffusion. The associated shift from aerobic to anaerobic conditions can reduce nitrification and promote denitrification processes, leading to nitrogen (N) loss...
Article
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Root architectural and anatomical phenotypes are highly diverse. Specific root phenotypes can be associated with better plant growth under low nutrient and water availability. Therefore, root ideotypes have been proposed as breeding targets for more stress-resilient and resource-efficient crops. For example, root phenotypes that correspond to the T...
Article
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Food insecurity is a pressing problem in many regions across the world. Drivers of food insecurity are becoming increasingly embedded in sociocultural and economic processes that transcendent multiple spatial and temporal scales. This is due to the increasingly globalized interconnections of places and people. Understanding this complexity is essen...
Article
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Cassava is a perennial crop that can adapt to periods of drought at different times in a growing season, which permits scheduling planting and harvest to develop production systems supplying roots continuously. However, farmers plant and harvest cassava at the onset of rains which creates glut and results in unattractive root prices. Thus, farmers...
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We need measurements of soil water retention (SWR) and available water capacity (AWC) to assess and model soil functions, but methods are time‐consuming and expensive. Our aim here was to investigate the modelling of AWC and SWR with visible–near‐infrared spectra (vis–NIR) and the machine‐learning method cubist. We used soils from 54 locations acro...
Article
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Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (N 2 O) and sink for methane (CH 4). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ N 2 O and CH 4 flux measurements are scarce. Here, we provide multi-year...
Preprint
Full-text available
The acceleration of erosion, transport and burial of soil organic carbon (C) in response to agricultural expansion represents a significant perturbation of the terrestrial C cycle. Recent model advances now enable improved representation of the relationships between sedimentary processes and C cycling and this has led to substantially revised asses...
Article
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Sustainability certification has been posited as a key governance mechanism to enhance the climate resilience of smallholder farmers. Whilst many certifications now include climate resilience in their standards, their ability to deliver this for smallholders remains untested. We take the case of the 2015-16 drought-shock to cocoa production in Ghan...
Article
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Trees within farmers’ fields can enhance systems’ longer-term productivity, for example, via nutrient amelioration, which is indispensable to attain sustainable agroecosystems. While arbuscular mycorrhizal fungi (AMF) are known to improve plant access to soil nutrients, the potential of AMF to mediate nutrient uptake of tree-derived nitrogen (N) by...
Article
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CONTEXT Most Western-European countries exceed the critical loads for nitrogen (N) losses. High nitrogen (N) inputs make agriculture one of the largest contributors to N pollution. There might be a potential to reduce this losses with an output tax on animal products, as they have low N use efficiency and a tax has the potential to reduce the consu...
Preprint
Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N2O. Despite their importance, changes in terrestrial N loss pathways driven by global change and spatial redistribution of N inputs are highly uncertain. We present a novel coupled soil-atmosphere isotope model (IsoTONE) to...
Article
Full-text available
Soil compaction affects many soil functions, but we have little information on the resistance and resilience of soil microorganisms to this disturbance. Here, we present data on the response of soil microbial diversity to a single compaction event and its temporal evolution under different agricultural management systems during four growing seasons...
Article
Agroforestry is often proposed as a ‘climate smart’ strategy for allowing agriculture to both adapt to and mitigate climate change and sustainably increase agricultural production. This is because shade trees in agroforests may buffer growing conditions by creating favorable microclimates (climate-change adaptation), and because shade trees can seq...
Article
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Climate change is a growing concern for farmers and food systems across the globe, raising interest in their resilience to climate change. Thus, exploring farm resilience in various contexts may help understand its prerequisites and build context and scale-specific strategies. Using an adaptive cycle framework through a survey-based assessment of t...
Article
Studies on sediment export from tropical forest watersheds are scarce. Of the assessments that do exist, most are of larger rivers or are model-based and lack validation with measured data. Understanding the mechanisms of sediment export dynamics in forested headwaters is important for assessing downstream effects and as a baseline for net impacts...
Article
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Low soil fertility is challenging the sustainable production of yam and other staple crops in the yam belt of West Africa. Quantitative soil measures are needed to assess soil fertility decline and to improve crop nutrient supply in the region. We developed and tested a mid-infrared (mid-IR) soil spectral library to enable timely and cost-efficient...
Article
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Information on soil properties is crucial for soil preservation, the improvement of food security, and the provision of ecosystem services. In particular, for the African continent, spatially explicit information on soils and their ability to sustain these services is still scarce. To address data gaps, infrared spectroscopy has achieved great succ...
Article
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Sequestering carbon (C) into stable soil pools has potential to mitigate increasing atmospheric carbon dioxide concentrations. Carbon accrues in grassland soil restored from cultivation, but the amount of physically protected C (here measured as microaggregate-within-macroaggregate C) and predominant mechanisms of accrual are not well understood. W...
Article
Rare earth oxides (REOs) as tracers track aggregate formation and breakdown pathways. However, investigations on the impacts of residue quality and soil texture on aggregation pathways are lacking. In this study, easily, moderately and slowly decomposable residues with different qualities (milk vetch, C/N = 16.7; maize, C/N = 35.5; and decomposed m...
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Agricultural-food production systems are facing the challenging task to provide food and socio-economic welfare while preserving natural resources in the long-term. In Morocco, the Green Moroccan Plan steered the promotion of groundwater-based drip irrigation. Over the last decade, the Plan encouraged producers to shift to cash crop production. Thi...
Article
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Cassava-maize intercropping is a common practice among smallholder farmers in Southern Nigeria. It provides food security and early access to income from the maize component. However, yields of both crops are commonly low in farmers’ fields. Multi-locational trials were conducted in Southern Nigeria in 2016 and 2017 to investigate options to increa...
Article
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Modern agricultural and sanitation systems depend on linear, one-way resource flows. However, these models are resource-intensive and wasteful. To address this problem equitably and sustainably, the RUNRES project seeks to link the dual development challenges of agriculture and sanitation by creating circular resource flows in four African city reg...
Article
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Food production systems can contribute to the degradation of the environment; thereby endangering the very resource, they depend on. However, while overall large, the environmental impacts of individual agricultural products are disparate. Therefore, in order to gain a better understanding of the impact different food production systems have on the...
Article
Retaining trees in low-input agroecosystems could be key to maintain mycelia of arbuscular mycorrhizal fungi (AMF) and hence, improve soil fertility and crop performance. We assessed the impact of faidherbia (Faidherbia albida, Fabaceae) and mango (Mangifera indica, Anacardiaceae) trees on AMF and soil fertility in smallholder farmers’ maize fields...
Article
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The Congo Basin's rapidly growing population still largely depends on shifting cultivation for both energy and food security. This nexus of population growth and ecological impact will continue to exacerbate landscape degradation in the coming decades. To quantify the effects of land-use intensity on soil nutrient stocks and the functional composit...
Article
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Information on soils' composition and physical, chemical and biological properties is paramount to elucidate agroecosystem functioning in space and over time. For this purpose, we developed a national Swiss soil spectral library (SSL; n=4374) in the mid-infrared (mid-IR), calibrating 16 properties from legacy measurements on soils from the Swiss Bi...
Article
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Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanism...
Article
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Meeting future global staple crop demand requires continual productivity improvement. Many performance indicators have been proposed to track and measure the increase in productivity while minimizing environmental degradation. However, their use has lagged behind theory, and has not been uniform across crops in different geographies. The consequenc...
Article
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CONTEXT The effective control of Fusarium head blight (FHB) in wheat, mainly caused by the toxigenic fungus Fusarium graminearum, has a significant impact on food safety worldwide. As maize is one of the main hosts of F. graminearum, the risk of infection by this plant pathogen is highest when wheat is grown after maize and infected crop residues a...
Article
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Ecosystems provide multiple services to humans. However, agricultural systems are usually evaluated on their productivity and economic performance, and a systematic and quantitative assessment of the multifunctionality of agroecosystems including environmental services is missing. Using a long-term farming system experiment, we evaluated and compar...