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How do animals help make soil?
An introduction to the ways in which \"some animals break down dead plants to creat new soil, while others spread nutrients around\"--Page 4 of cover.
Book
Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy
Background Oxidation-reduction and acid-base reactions are essential for the maintenance of all living organisms. However, redox potential (Eh) has received little attention in agronomy, unlike pH, which is regarded as a master variable. Agronomists are probably depriving themselves of a key factor in crop and soil science which could be a useful integrative tool. Scope This paper reviews the existing literature on Eh in various disciplines connected to agronomy, whether associated or not with pH, and then integrates this knowledge within a composite framework. Conclusions This transdisciplinary review offers evidence that Eh and pH are respectively and jointly major drivers of soil/plant/microorganism systems. Information on the roles of Eh and pH in plant and microorganism physiology and in soil genesis converges to form an operational framework for further studies of soil/plant/microorganism functioning. This framework is based on the hypothesis that plants physiologically function within a specific internal Eh-pH range and that, along with microorganisms, they alter Eh and pH in the rhizosphere to ensure homeostasis at the cell level. This new perspective could help in bridging several disciplines related to agronomy, and across micro and macro-scales. It should help to improve cropping systems design and management, in conventional, organic, and conservation agriculture.
Journal Article
Celebrating soil : discovering soils and landscapes
\"This richly illustrated book celebrates the diversity, importance, and intrinsic beauty of soils around the world and helps the reader to understand the ways that soils are related to the landscapes in which they form. The book unravels the complex bond between humans and soils and the importance of soils in our cultures and everyday lives. Soil is critical to terrestrial life on earth. It underpins human food supply and provides materials on which we build our lives. Soil is out of sight and often out of mind, thus easy to overlook. Yet soil has tremendous variety and intrinsic beauty for those who care to look. Soil contains a memory of the events that have shaped the landscape and the environment. With help you can look at a soil and understand the stories that it has to tell. Written in a reader-friendly way, Celebrating Soil is a wonderful resource for farmers, horticulturalists, naturalists, students and others who are concerned about how soils are formed, work and are used.\"--Provided by publisher.
Book
Multiple factors influence the role of arbuscular mycorrhizal fungi in soil aggregation—a meta-analysis
Background and aims Soil aggregation is a crucial aspect of ecosystem functioning in terrestrial ecosystems. Arbuscular mycorrhizal fungi (AMF) play a key role in soil aggregate formation and stabilization. Here we quantitatively analyzed the importance of experimental settings as well as biotic and abiotic factors for the effectiveness of AMF to stabilize soil macroaggregates. Methods We gathered 35 studies on AMF and soil aggregation and tested 13 predictor variables for their relevance with a boosted regression tree analysis and performed a meta-analysis, fitting individual random effects models for each variable. Results and conclusions The overall mean effect of inoculation with AMF on soil aggregation was positive and predictor variable means were all in the range of beneficial effects. Pot studies and studies with sterilized sandy soil, near neutral soil pH, a pot size smaller than 2.5 kg and a duration between 2.2 and 5 months were more likely to result in stronger effects of AMF on soil aggregation than experiments in the field, with non-sterilized or fine textured soil or an acidic pH. This is the first study to quantitatively show that the effect of AMF inoculation on soil aggregation is positive and context dependent. Our findings can help to improve the use of this important ecosystem process, e.g. for inoculum application in restoration sites.
Journal Article
Deep soil organic matter—a key but poorly understood component of terrestrial C cycle
Despite their low carbon (C) content, most subsoil horizons contribute to more than half of the total soil C stocks, and therefore need to be considered in the global C cycle. Until recently, the properties and dynamics of C in deep soils was largely ignored. The aim of this review is to synthesize literature concerning the sources, composition, mechanisms of stabilisation and destabilization of soil organic matter (SOM) stored in subsoil horizons. Organic C input into subsoils occurs in dissolved form (DOC) following preferential flow pathways, as aboveground or root litter and exudates along root channels and/or through bioturbation. The relative importance of these inputs for subsoil C distribution and dynamics still needs to be evaluated. Generally, C in deep soil horizons is characterized by high mean residence times of up to several thousand years. With few exceptions, the carbon-to-nitrogen (C/N) ratio is decreasing with soil depth, while the stable C and N isotope ratios of SOM are increasing, indicating that organic matter (OM) in deep soil horizons is highly processed. Several studies suggest that SOM in subsoils is enriched in microbial-derived C compounds and depleted in energy-rich plant material compared to topsoil SOM. However, the chemical composition of SOM in subsoils is soil-type specific and greatly influenced by pedological processes. Interaction with the mineral phase, in particular amorphous iron (Fe) and aluminum (Al) oxides was reported to be the main stabilization mechanism in acid and near neutral soils. In addition, occlusion within soil aggregates has been identified to account for a great proportion of SOM preserved in subsoils. Laboratory studies have shown that the decomposition of subsoil C with high residence times could be stimulated by addition of labile C. Other mechanisms leading to destabilisation of SOM in subsoils include disruption of the physical structure and nutrient supply to soil microorganisms. One of the most important factors leading to protection of SOM in subsoils may be the spatial separation of SOM, microorganisms and extracellular enzyme activity possibly related to the heterogeneity of C input. As a result of the different processes, stabilized SOM in subsoils is horizontally stratified. In order to better understand deep SOM dynamics and to include them into soil C models, quantitative information about C fluxes resulting from C input, stabilization and destabilization processes at the field scale are necessary.
Journal Article
Dirt : the erosion of civilizations
An engaging natural and cultural history of soil that sweeps from ancient civilisations to modern times, 'Dirt' explores the compelling idea that we are - and have long been - using up Earth's soil.
Book
Does biochar influence soil physical properties and soil water availability?
AIMS: This study aims to (i) determine the effects of incorporating 47 Mg ha⁻¹ acacia green waste biochar on soil physical properties and water relations, and (ii) to explore the different mechanisms by which biochar influences soil porosity. METHODS: The pore size distribution of the biochar was determined by scanning electron microscope and mercury porosimetry. Soil physical properties and water relations were determined by in situ tension infiltrometers, desorption and evaporative flux on intact cores, pressure chamber analysis at −1,500 kPa, and wet aggregate sieving. RESULTS: Thirty months after incorporation, biochar application had no significant effect on soil moisture content, drainable porosity between –1.0 and −10 kPa, field capacity, plant available water capacity, the van Genuchten soil water retention parameters, aggregate stability, nor the permanent wilting point. However, the biochar-amended soil had significantly higher near-saturated hydraulic conductivity, soil water content at −0.1 kPa, and significantly lower bulk density than the unamended control. Differences were attributed to the formation of large macropores (>1,200 μm) resulting from greater earthworm burrowing in the biochar-amended soil. CONCLUSION: We found no evidence to suggest application of biochar influenced soil porosity by either direct pore contribution, creation of accommodation pores, or improved aggregate stability.
Journal Article
Soil pH - nutrient relationships: the diagram
The pH of the soil in relation to the availability of plant nutrients has been an important research topic in soil fertility and plant nutrition. In the 1930 and 1940 s, a diagram was proposed that showed how the availability of major and minor nutrients was affected by the pH. This conceptual diagram, developed by Emil Truog based on earlier work, included 11 nutrients. The width of the band at any pH value indicated the relative availability of the plant nutrient. The band did not present the actual amount, as that was affected by other factors such as the type of crop, soil and fertilization. For the 11 nutrients on the diagram, a pH of around 6.5 was considered most favorable. The diagram has been often published in text books and soil extension material and continues to be reproduced. This paper reviews how the diagram was developed, and what its limitations are. In recent decades, research in soil fertility and plant nutrition has focused on the biological transformations of plant nutrients in the soil and it has been recognized that the soil pH influences solubility, concentration in soil solution, ionic form, and adsorption and mobility of most plant nutrients. Nutrients interact and different plants respond differently to a change in pH. The soil pH cannot be used to predict or estimate plant nutrient availability, and the diagram should not be used as it suffers from numerous exceptions and barely represents any rules.
Journal Article