Samuel Abiven

Bio: Samuel Abiven is an academic researcher from University of Zurich. The author has contributed to research in topics: Soil water & Soil carbon. The author has an hindex of 31, co-authored 86 publications receiving 7434 citations. Previous affiliations of Samuel Abiven include Institut national de la recherche agronomique & École Normale Supérieure.

Persistence of soil organic matter as an ecosystem property

Abstract: Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

The effects of organic inputs over time on soil aggregate stability – a literature analysis

Abstract: Since the beginning of the last century, many studies have reported evidence describing the effects of organic inputs on soil aggregate stability. In 1965, Monnier proposed a conceptual model that considers different patterns of temporal effects on aggregate stability depending on the nature of the organic inputs: easily decomposable products have an intense and transient effect on aggregate stability while more recalcitrant products have a lower but longer term effect. We confronted this conceptual model with a literature review of experimental data from laboratory and field experiments. This literature analysis validated the conceptual model proposed by Monnier and pointed out gaps in our current knowledge concerning the relationships between aggregate stability and organic inputs. Noticeably, the experimental dataset confirmed the biological and temporal effects of organic inputs on aggregate stability as proposed in the model. Monnier's model also related the evolution of aggregate stability to different microbial decomposing agents, but this relationship was not made clear in this literature analysis. No direct or universal relationship was found between the aggregative factors induced by organic input decomposition (binding molecules or decomposers of biomass) and temporal aggregate stability dynamics. This suggests the existence of even more complex relationships. The model can be improved by considering (i) the direct abiotic effect of some organic products immediately after the inputs, (ii) the initial biochemical characteristics of the organic products and (iii) the effects of organic products on the various mechanisms of aggregate breakdown. For now, no trend is evident in the effect of the rate of organic inputs or the effect of the soil characteristics (essentially carbon and clay contents) on aggregate stability

Heterogeneous global crop yield response to biochar: a meta-regression analysis

Abstract: Biochar may contribute to climate change mitigation at negative cost by sequestering photosynthetically fixed carbon in soil while increasing crop yields. The magnitude of biochar's potential in this regard will depend on crop yield benefits, which have not been well-characterized across different soils and biochars. Using data from 84 studies, we employ meta-analytical, missing data, and semiparametric statistical methods to explain heterogeneity in crop yield responses across different soils, biochars, and agricultural management factors, and then estimate potential changes in yield across different soil environments globally. We find that soil cation exchange capacity and organic carbon were strong predictors of yield response, with low cation exchange and low carbon associated with positive response. We also find that yield response increases over time since initial application, compared to non-biochar controls. High reported soil clay content and low soil pH were weaker predictors of higher yield response. No biochar parameters in our dataset—biochar pH, percentage carbon content, or temperature of pyrolysis—were significant predictors of yield impacts. Projecting our fitted model onto a global soil database, we find the largest potential increases in areas with highly weathered soils, such as those characterizing much of the humid tropics. Richer soils characterizing much of the world's important agricultural areas appear to be less likely to benefit from biochar.

Climate Change 2007: Impacts, Adaptation and Vulnerability.

Abstract: Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

Abstract: This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

The contentious nature of soil organic matter

Abstract: Instead of containing stable and chemically unique ‘humic substances’, as has been widely accepted, soil organic matter is a mixture of progressively decomposing organic compounds; this has broad implications for soil science and its applications. The exchange of nutrients, energy and carbon between soil organic matter, the soil environment, aquatic systems and the atmosphere is important for agricultural productivity, water quality and climate. Long-standing theory suggests that soil organic matter is composed of inherently stable and chemically unique compounds. Here we argue that the available evidence does not support the formation of large-molecular-size and persistent ‘humic substances’ in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds. We discuss implications of this view of the nature of soil organic matter for aquatic health, soil carbon–climate interactions and land management. Soil organic matter contains a large portion of the world's carbon and plays an important role in maintaining productive soils and water quality. Nevertheless, a consensus on the nature of soil organic matter is lacking. Johannes Lehmann and Markus Kleber argue that soil organic matter should no longer be seen as large and persistent, chemically unique substances, but as a continuum of progressively decomposing organic compounds.