Pascal Boivin

Bio: Pascal Boivin is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Soil water & Soil structure. The author has an hindex of 19, co-authored 56 publications receiving 1363 citations. Previous affiliations of Pascal Boivin include University of Applied Sciences Western Switzerland & Institut de recherche pour le développement.

Relationship between Clay Content, Clay Type, and Shrinkage Properties of Soil Samples

Abstract: The availability of methods for quasi-continuous measurements of soil shrinkage curves allowed the development of new models. The exponential (XP) model allows the calculation of the volume of two pore phases in the soil, namely macro and micropore volumes. The micropore volume is identified with the pore volume of the soil clay matrix according to the assumption that the maximum swelling of the clay matrix (MS) is the point of minimum water content of the structural shrinkage (Point D). This is discussed using undisturbed and repacked soil samples with various clay contents and clay types. The slope of the shrinkage curves as a function of equivalent saturated-pore radius show a transition in pore type around a 10-μm pore radius, where smaller and more deformable pores start to desaturate. This corresponds to the fitted D point and is close to the size of the largest pores in the clay matrix or clay–silt phase reported in the literature. The calculated micropore volume and micropore swelling properties are close to clay paste properties reported in the literature. At low water content, the specific micropore volume is independent from clay content. At Point D, the shrinking capacity of the specific micropore volume decreases with increasing clay content for clay contents below 40%. Our results show that Point D can be identified with the MS of the clay matrix, and that the XP model can be used to calculate the swelling properties of clays in the soil, without extraction.

Iron reduction and changes in cation exchange capacity in intermittently waterlogged soil

Abstract: Summary The long-term effects of intermittent flooding on soil properties were studied in field experiments on a Vertisol cropped with rice in Senegal. The dominant clay minerals were smectite and kaolinite. When the soil was reduced after flooding, its cation exchange capacity (CEC) increased to twice that of its oxidized, unflooded state. Mossbauer spectroscopy showed an increase in smectite structural FeII upon reduction, which explained a part of the increase in CEC. The rest of the increase was attributed to the removal of iron oxyhydroxide coatings by reductive dissolution. The reduction and dissolution of oxides under the field conditions were substantiated by analysis of the surfaces of vermiculites buried in the Ap horizons of the cropped and the non-cropped soils. The redox-induced CEC changes were found to be reversible after 22 cycles of rice cropping. Nevertheless, the structural Fe and free Fe contents of the rice field Ap horizon were less than those of soil in uncropped neighbouring land, suggesting that inundation induced weathering and eluviation of the minerals. The observed changes in CEC and related redox reactions may substantially modify proton, anion and cation balances in intermittently flooded soils.

Soil quality – A critical review

Abstract: Sampling and analysis or visual examination of soil to assess its status and use potential is widely practiced from plot to national scales. However, the choice of relevant soil attributes and interpretation of measurements are not straightforward, because of the complexity and site-specificity of soils, legacy effects of previous land use, and trade-offs between ecosystem services. Here we review soil quality and related concepts, in terms of definition, assessment approaches, and indicator selection and interpretation. We identify the most frequently used soil quality indicators under agricultural land use. We find that explicit evaluation of soil quality with respect to specific soil threats, soil functions and ecosystem services has rarely been implemented, and few approaches provide clear interpretation schemes of measured indicator values. This limits their adoption by land managers as well as policy. We also consider novel indicators that address currently neglected though important soil properties and processes, and we list the crucial steps in the development of a soil quality assessment procedure that is scientifically sound and supports management and policy decisions that account for the multi-functionality of soil. This requires the involvement of the pertinent actors, stakeholders and end-users to a much larger degree than practiced to date.

Restoring Soil Quality to Mitigate Soil Degradation

Abstract: Feeding the world population, 7.3 billion in 2015 and projected to increase to 9.5 billion by 2050, necessitates an increase in agricultural production of ~70% between 2005 and 2050. Soil degradation, characterized by decline in quality and decrease in ecosystem goods and services, is a major constraint to achieving the required increase in agricultural production. Soil is a non-renewable resource on human time scales with its vulnerability to degradation depending on complex interactions between processes, factors and causes occurring at a range of spatial and temporal scales. Among the major soil degradation processes are accelerated erosion, depletion of the soil organic carbon (SOC) pool and loss in biodiversity, loss of soil fertility and elemental imbalance, acidification and salinization. Soil degradation trends can be reversed by conversion to a restorative land use and adoption of recommended management practices. The strategy is to minimize soil erosion, create positive SOC and N budgets, enhance activity and species diversity of soil biota (micro, meso, and macro), and improve structural stability and pore geometry. Improving soil quality (i.e., increasing SOC pool, improving soil structure, enhancing soil fertility) can reduce risks of soil degradation (physical, chemical, biological and ecological) while improving the environment. Increasing the SOC pool to above the critical level (10 to 15 g/kg) is essential to set-in-motion the restorative trends. Site-specific techniques of restoring soil quality include conservation agriculture, integrated nutrient management, continuous vegetative cover such as residue mulch and cover cropping, and controlled grazing at appropriate stocking rates. The strategy is to produce “more from less” by reducing losses and increasing soil, water, and nutrient use efficiency.

A review of earthworm impact on soil function and ecosystem services

Abstract: Summary Biodiversity is responsible for the provision of many ecosystem services; human well-being is based on these services, and consequently on biodiversity. In soil, earthworms represent the largest component of the animal biomass and are commonly termed ‘ecosystem engineers’. This review considers the contribution of earthworms to ecosystem services through pedogenesis, development of soil structure, water regulation, nutrient cycling, primary production, climate regulation, pollution remediation and cultural services. Although there has been much research into the role of earthworms in soil ecology, this review demonstrates substantial gaps in our knowledge related in particular to difficulties in identifying the effects of species, land use and climate. The review aims to assist people involved in all aspects of land management, including conservation, agriculture, mining or other industries, to obtain a broad knowledge of earthworms and ecosystem services.