DOCSLIB.ORG

Soil Biodiversity

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Soil Biodiversity ISSN 1018-5593 The mission of the JRC is to provide customer-driven scientific and technical support for the conception, develop- LB-NA-23759-EN-C ment, implementation and monitoring of EU policies. As a service of the European Commission, the JRC functions as a reference centre of science and technology for the Union. Close to the policy-making process, it serves the com- mon interest of the Member States, while being independent of special interests, whether private or national. Soil Biodiversity Ciro Gardi and Simon Jeffery EUR 23759 EN Soil Biodiversity Ciro Gardi and Simon Jeffery The mission of the JRC-IES is to provide scientific-technical support to the European Union’s policies for the protection and sustainable development of the European and global environment. European Commission Joint Research Centre Institute for Environment and Sustainability Land Management & Natural Hazards Unit Authors: Ciro Gardi, Simon Jeffery Design: José-Joaquín Blasco Address: Via Enrico Fermi, 2749 I-21027 Ispra (VA) E-mail: [email protected] / [email protected] Tel.: +39 0332 783682 Fax: +39 0332 786394 http://ies.jrc.ec.europa.eu/ http://www.jrc.ec.europa.eu/ Legal Notice Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of this publication. Europe Direct is a service to help you find answers to your questions about the European Union Freephone number (*): 00 800 6 7 8 9 10 11 (*) Certain mobile telephone operators do not allow access to 00 800 numbers or these calls may be billed. A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server http://europa.eu/ PUBSY JRC50304 EUR 23759 EN ISBN 978-92-79-11289-8 ISSN 1018-5593 DOI 10.2788/7831 Luxembourg: Office for Official Publications of the European Communities © European Communities, 2009 Reproduction is authorised provided the source is acknowledged Printed in Italy Table of contents Soil Biodiversity 5 Measures of soil biodiversity 5 Organisms of the Soil 6 The Functions of Soil Biodiversity 7 Nutrient cycling 7 Soil formation and weathering 8 Waste recycling 8 Home for other organisms 9 Functional redundancy 9 Resistance vs. Resilience 10 The Economics of Soil Biodiversity 11 Soil Biodiversity and Sustainable Agriculture 13 Organic matter cycling and humification 13 Fertility regulation and nutrient uptake 14 Pest and disease control 14 Soil structure and soil-water relationships 14 Pollination 15 Soil Biodiversity and Biotechnology 16 Bioremediation 16 Antibiotics 16 Antibiotic resistance 17 Biocontrol of pests 17 Soil Biodiversity at the Extreme 19 Temperature 19 Hot 19 Cold 19 Dry 19 Solar Radiation 20 Mechanisms for coping with extremes 20 Cryptobiosis 20 Use of proteins 20 Cyst formation 20 Soil Biodiversity and Climate Change 21 The Impact of Soil Biodiversity on CO2 21 The Impact of Soil Biodiversity on other Greenhouse Gases 22 References 23 Soil Biodiversity What is biodiversity? Biodiversity has different mean- • Species evenness, normally denoted “E”, which is ings depending on the situation being discussed and a measure of how similar the abundances of different the target audience. For example, the Oxford English species are in a community. Species evenness ranges Dictionary defines biodiversity as being “The variety from zero to one. When evenness is close to zero, it in- of plant and animal life in the world or in a particular dicates that distribution of organisms within the com- habitat”. This is definition is clearly sufficient for non- munity is not even, i.e. most of the individuals belong specialists. However, when looking more specifically at to one, or a few, species or taxa. When evenness is biodiversity, it becomes evident that thought needs to close to one, it indicates that the distribution of organ- be given to other groups such as fungi, bacteria and isms within the community is even, i.e. each species or archea. As soil is such as diverse system when consid- taxa consist of a similar number of individuals. ered biologically (as well as physically or chemically) Clearly, these two measures of biodiversity are much it is necessary to include all taxonomic groups. There- more informative when combined than when used fore, throughout this booklet, when referring to “soil alone. biodiversity” it will be in reference to the variety of all living organisms found within the soil system. Other methods which are of the used to quantify biodi- versity in an ecosystem are: The soil system is dynamic, highly heterogeneous and extremely complex. Soil itself consists of a mineral por- Simpson’s index (D) gives the probability that two tion containing mainly silica and a mixture of trace met- randomly selected individuals belong to two different als, and an organic matter portion containing a large species/categories. It is often used to quantify the bio- variety of different organic compounds, as well as water diversity of a given habitat and takes into account both and vast array of different organisms. Soil can exist as a the number of species and the relative abundance of variety of textures; with the texture being a product of each species present. changes in the relative proportions of sand, silt and clay. Simpson’s index is calculated as follows: It can contain areas of relative dryness, and includes mi- cropores which are almost always water filled apart from in times of extreme drought. The proportion and type of organic matter varies both with depth, and spatially. Where S is the number of species, This high level of heterogeneity means that soil con- N is the total percentage cover or total number tains an extremely large number of ecological niches of organisms, which have given rise to a staggering array of biodiver- n is the percentage cover of a species or number sity. Using a taxonomic approach to measure biodiver- of organisms of a species. sity, it is often said that more than half the world’s es- timated 10 million species of plant, animal and insects It has been noted that the Simpson Index can, in some live in the tropical rainforests. However, when this situations, provide misleading results with some areas approach is applied to the soil, the level of diversity which clearly have low levels of biodiversity having a is often quoted as being in the range of hundreds of disproportionately higher index. This situation is un- thousands to possibly millions of species living in just common, however, and the Simpson Index normally 1 handful of soil! provides a realistic measure of biodiversity with a low index equating to a relatively high level of biodiversity Measures of soil biodiversity and a high index relating to a relatively lot level of bio- Measurements of the level of soil biodiversity in a given diversity. area are important as a high level of species diversity Shannon-Wiener index (H1) (also often referred to as is thought to indicate a healthy environment. No spe- the Shannon Index) is a measure of the order or disor- cific indices exist, or need to be developed for the soil der in a particular system which can be used and ap- system as biodiversity indices are applicable across plied to ecological systems. When applied in ecology, the entire range of ecosystems without the need for in order to quantify levels of biodiversity, the Shannon modification. However, each has its own strengths and index takes into account both species richness and weaknesses. the proportion of each species within a zone. A higher The simplest measures of biodiversity are: index is an indication that either there are a relatively high number of unique species or that there is relative- • normally denoted “S”, which is Species richness, ly high species evenness. the total number of species found in an ecosystem or sample. The Shannon index is calculated as follows: 5 Organisms of the soil As previously stated, the soil environment is home to an incredible diversity of organisms. Added to that, the p is the relative abundance of each species. This is i organisms which are found there are also often exist calculated as the proportion of individuals in a spe- at astonishingly high levels of abundance. The level cies compared to the total number of individuals in the of abundance and diversity varies from soil to soil, community: depending on factors such as organic matter content, soil texture, pH and soil management practices. Below is the approximate abundance and diversity of organ- n is the number of individuals in species i. i isms divided into groupings according to size, typically N is the total number of all individuals found in a handful of temperate grassland soil. S is the number of species. Microfauna Mesofauna Megafauna Size range: 1-100 mm Size range: 100 mm-2 mm Size range: ‹ 2 mm Bacteria Tardigrades Earthworms 100 billion cells from 10.000 species Fungi Collemobla Ants 50 km of hyphae from 500’s of species Protozoa Mites Woodlice 100.000 cells from 100’s of species Nematodes Combined 1.000’s individuals Combined 100’s individuals 10.000 individuals from 100’s of species from 10’s of species from 100’s of species Smaller size > larger size The reason that such as large abundance of organisms or extreme drought. The surface area of this pore space can be found in just one handful of soil is due to the can exceed 24,000 m2 in 1 g of clay soils, with the total pore space found within soil which is where the organ- surface area decreasing with increasing silt and sand isms live. While it may appear to be solid, soil normally content.
Load more

Recommended publications
  • Basic Soil Science W
    Basic Soil Science W. Lee Daniels See http://pubs.ext.vt.edu/430/430-350/430-350_pdf.pdf for more information on basic soils! [email protected]; 540-231-7175 http://www.cses.vt.edu/revegetation/ Well weathered A Horizon -- Topsoil (red, clayey) soil from the Piedmont of Virginia. This soil has formed from B Horizon - Subsoil long term weathering of granite into soil like materials. C Horizon (deeper) Native Forest Soil Leaf litter and roots (> 5 T/Ac/year are “bio- processed” to form humus, which is the dark black material seen in this topsoil layer. In the process, nutrients and energy are released to plant uptake and the higher food chain. These are the “natural soil cycles” that we attempt to manage today. Soil Profiles Soil profiles are two-dimensional slices or exposures of soils like we can view from a road cut or a soil pit. Soil profiles reveal soil horizons, which are fundamental genetic layers, weathered into underlying parent materials, in response to leaching and organic matter decomposition. Fig. 1.12 -- Soils develop horizons due to the combined process of (1) organic matter deposition and decomposition and (2) illuviation of clays, oxides and other mobile compounds downward with the wetting front. In moist environments (e.g. Virginia) free salts (Cl and SO4 ) are leached completely out of the profile, but they accumulate in desert soils. Master Horizons O A • O horizon E • A horizon • E horizon B • B horizon • C horizon C • R horizon R Master Horizons • O horizon o predominantly organic matter (litter and humus) • A horizon o organic carbon accumulation, some removal of clay • E horizon o zone of maximum removal (loss of OC, Fe, Mn, Al, clay…) • B horizon o forms below O, A, and E horizons o zone of maximum accumulation (clay, Fe, Al, CaC03, salts…) o most developed part of subsoil (structure, texture, color) o < 50% rock structure or thin bedding from water deposition Master Horizons • C horizon o little or no pedogenic alteration o unconsolidated parent material or soft bedrock o < 50% soil structure • R horizon o hard, continuous bedrock A vs.
    [Show full text]
  • Soil Acidification the Unseen Threat to Soil Health and Productivity
    Soil Acidification The unseen threat to soil health and productivity www.ces.vic.gov.au February 2009 Fact Sheet No. 7 This fact sheet is one of a series, developed from material presented in Victoria’s first comprehensive State of the Environment Report. The Report is a major undertaking of the Commissioner for Environmental Sustainability and covers a broad range of environmental issues affecting the State. Its purpose is to improve community understanding of Victoria’s environment, and through the use of recommendations, to ensure its protection for present and future generations. The report was released in December 2008 and is available at www.ces.vic.gov.au Key findings Acidification is also linked to erosion, salinity, and loss of soil biodiversity. Bacteria, earthworms and other soil organisms are • The cost of lost productivity to Victoria due to soil generally sensitive to soil pH and tend to decline as soils become acidification is estimated at $470 million per year. more acidic. • Soil acidification is accelerated by some land management practices and the area of acid soil is increasing. Victoria has up to 8.6 million ha of acidic soils including • Naturally acidic soils can’t be distinguished from soils 4–5 million ha of strongly acidic soils, which mostly occur acidified by agriculture. naturally and are indistinguishable from those with accelerated • The use of acidifying fertiliser, to support more intensive acidification. agriculture, is increasing in Victoria. • Only 5.5% of the area requiring treatment with lime to restore Coastal acid sulfate soils are a different category of acid soils and critical soil pH levels is sufficiently treated.
    [Show full text]
  • Port Silt Loam Oklahoma State Soil
    PORT SILT LOAM Oklahoma State Soil SOIL SCIENCE SOCIETY OF AMERICA Introduction Many states have a designated state bird, flower, fish, tree, rock, etc. And, many states also have a state soil – one that has significance or is important to the state. The Port Silt Loam is the official state soil of Oklahoma. Let’s explore how the Port Silt Loam is important to Oklahoma. History Soils are often named after an early pioneer, town, county, community or stream in the vicinity where they are first found. The name “Port” comes from the small com- munity of Port located in Washita County, Oklahoma. The name “silt loam” is the texture of the topsoil. This texture consists mostly of silt size particles (.05 to .002 mm), and when the moist soil is rubbed between the thumb and forefinger, it is loamy to the feel, thus the term silt loam. In 1987, recognizing the importance of soil as a resource, the Governor and Oklahoma Legislature selected Port Silt Loam as the of- ficial State Soil of Oklahoma. What is Port Silt Loam Soil? Every soil can be separated into three separate size fractions called sand, silt, and clay, which makes up the soil texture. They are present in all soils in different propor- tions and say a lot about the character of the soil. Port Silt Loam has a silt loam tex- ture and is usually reddish in color, varying from dark brown to dark reddish brown. The color is derived from upland soil materials weathered from reddish sandstones, siltstones, and shales of the Permian Geologic Era.
    [Show full text]
  • Soil As a Huge Laboratory for Microorganisms
    Research Article Agri Res & Tech: Open Access J Volume 22 Issue 4 - September 2019 Copyright © All rights are reserved by Mishra BB DOI: 10.19080/ARTOAJ.2019.22.556205 Soil as a Huge Laboratory for Microorganisms Sachidanand B1, Mitra NG1, Vinod Kumar1, Richa Roy2 and Mishra BB3* 1Department of Soil Science and Agricultural Chemistry, Jawaharlal Nehru Krishi Vishwa Vidyalaya, India 2Department of Biotechnology, TNB College, India 3Haramaya University, Ethiopia Submission: June 24, 2019; Published: September 17, 2019 *Corresponding author: Mishra BB, Haramaya University, Ethiopia Abstract Biodiversity consisting of living organisms both plants and animals, constitute an important component of soil. Soil organisms are important elements for preserved ecosystem biodiversity and services thus assess functional and structural biodiversity in arable soils is interest. One of the main threats to soil biodiversity occurred by soil environmental impacts and agricultural management. This review focuses on interactions relating how soil ecology (soil physical, chemical and biological properties) and soil management regime affect the microbial diversity in soil. We propose that the fact that in some situations the soil is the key factor determining soil microbial diversity is related to the complexity of the microbial interactions in soil, including interactions between microorganisms (MOs) and soil. A conceptual framework, based on the relative strengths of the shaping forces exerted by soil versus the ecological behavior of MOs, is proposed. Plant-bacterial interactions in the rhizosphere are the determinants of plant health and soil fertility. Symbiotic nitrogen (N2)-fixing bacteria include the cyanobacteria of the genera Rhizobium, Free-livingBradyrhizobium, soil bacteria Azorhizobium, play a vital Allorhizobium, role in plant Sinorhizobium growth, usually and referred Mesorhizobium.
    [Show full text]
  • Advanced Crop and Soil Science. a Blacksburg. Agricultural
    DOCUMENT RESUME ED 098 289 CB 002 33$ AUTHOR Miller, Larry E. TITLE What Is Soil? Advanced Crop and Soil Science. A Course of Study. INSTITUTION Virginia Polytechnic Inst. and State Univ., Blacksburg. Agricultural Education Program.; Virginia State Dept. of Education, Richmond. Agricultural Education Service. PUB DATE 74 NOTE 42p.; For related courses of study, see CE 002 333-337 and CE 003 222 EDRS PRICE MF-$0.75 HC-$1.85 PLUS POSTAGE DESCRIPTORS *Agricultural Education; *Agronomy; Behavioral Objectives; Conservation (Environment); Course Content; Course Descriptions; *Curriculum Guides; Ecological Factors; Environmental Education; *Instructional Materials; Lesson Plans; Natural Resources; Post Sc-tondary Education; Secondary Education; *Soil Science IDENTIFIERS Virginia ABSTRACT The course of study represents the first of six modules in advanced crop and soil science and introduces the griculture student to the topic of soil management. Upon completing the two day lesson, the student vill be able to define "soil", list the soil forming agencies, define and use soil terminology, and discuss soil formation and what makes up the soil complex. Information and directions necessary to make soil profiles are included for the instructor's use. The course outline suggests teaching procedures, behavioral objectives, teaching aids and references, problems, a summary, and evaluation. Following the lesson plans, pages are coded for use as handouts and overhead transparencies. A materials source list for the complete soil module is included. (MW) Agdex 506 BEST COPY AVAILABLE LJ US DEPARTMENT OFmrAITM E nufAT ION t WE 1. F ARE MAT IONAI. ItiST ifuf I OF EDuCATiCiN :),t; tnArh, t 1.t PI-1, t+ h 4t t wt 44t F.,.."11 4.
    [Show full text]
  • Drummer Illinois State Soil
    Drummer Illinois State Soil Soil Science Society of America Introduction Many states have designated state symbols such as bird, flower, fish, tree, rock, and more. Many states also have a state soil – one that has significance or is important to the state. As there are many types of birds, flowers, and trees, there are hundreds of soil types in our state but Drummer is the official state soil of Illinois. How important is the Drummer soil to Illinois? History Drummer was first established as a type of soil in Ford County in 1929. It was named after Drummer Creek in Drummer Township. 1n 1987, Drummer was selected as the state soil by the Illinois Soil Classifiers Association over other soils such as Cisne, Flanagan, Hoyleton, Ipava, Sable, and Saybrook. Since then, Drummer has been repeatedly chosen by other as- sociations who work with soil. In 1992, the Illinois Association of Vocational Agriculture Teachers sponsored a state soil election in their classrooms and Drummer won by a margin of 2 to 1. In 1993, the statewide 4H Youth Conference also selected Drummer out of 6 nomi- nees. Also in 1993 at the FFA state convention, Drummer and Ipava were tied in the contest. Finally, in 2001, after many attempts, it was finally passed by the Illinois Legislature and signed into law by Governor George Ryan. What is Drummer Soil? It is the most common among the dark colored soils or “black dirt” of Illinois. The dark color is due to the high amount of organic matter inherited from the decomposition of the prairie vegetation that is growing on the soil.
    [Show full text]
  • Dynamics of Carbon 14 in Soils: a Review C
    Radioprotection, Suppl. 1, vol. 40 (2005) S465-S470 © EDP Sciences, 2005 DOI: 10.1051/radiopro:2005s1-068 Dynamics of Carbon 14 in soils: A review C. Tamponnet Institute of Radioprotection and Nuclear Safety, DEI/SECRE, CADARACHE, BP. 1, 13108 Saint-Paul-lez-Durance Cedex, France, e-mail: [email protected] Abstract. In terrestrial ecosystems, soil is the main interface between atmosphere, hydrosphere, lithosphere and biosphere. Its interactions with carbon cycle are primordial. Information about carbon 14 dynamics in soils is quite dispersed and an up-to-date status is therefore presented in this paper. Carbon 14 dynamics in soils are governed by physical processes (soil structure, soil aggregation, soil erosion) chemical processes (sequestration by soil components either mineral or organic), and soil biological processes (soil microbes, soil fauna, soil biochemistry). The relative importance of such processes varied remarkably among the various biomes (tropical forest, temperate forest, boreal forest, tropical savannah, temperate pastures, deserts, tundra, marshlands, agro ecosystems) encountered in the terrestrial ecosphere. Moreover, application for a simplified modelling of carbon 14 dynamics in soils is proposed. 1. INTRODUCTION The importance of carbon 14 of anthropic origin in the environment has been quite early a matter of concern for the authorities [1]. When the behaviour of carbon 14 in the environment is to be modelled, it is an absolute necessity to understand the biogeochemical cycles of carbon. One can distinguish indeed, a global cycle of carbon from different local cycles. As far as the biosphere is concerned, pedosphere is considered as a primordial exchange zone. Pedosphere, which will be named from now on as soils, is mainly located at the interface between atmosphere and lithosphere.
    [Show full text]
  • Agricultural Soil Carbon Credits: Making Sense of Protocols for Carbon Sequestration and Net Greenhouse Gas Removals
    Agricultural Soil Carbon Credits: Making sense of protocols for carbon sequestration and net greenhouse gas removals NATURAL CLIMATE SOLUTIONS About this report This synthesis is for federal and state We contacted each carbon registry and policymakers looking to shape public marketplace to ensure that details investments in climate mitigation presented in this report and through agricultural soil carbon credits, accompanying appendix are accurate. protocol developers, project developers This report does not address carbon and aggregators, buyers of credits and accounting outside of published others interested in learning about the protocols meant to generate verified landscape of soil carbon and net carbon credits. greenhouse gas measurement, reporting While not a focus of the report, we and verification protocols. We use the remain concerned that any end-use of term MRV broadly to encompass the carbon credits as an offset, without range of quantification activities, robust local pollution regulations, will structural considerations and perpetuate the historic and ongoing requirements intended to ensure the negative impacts of carbon trading on integrity of quantified credits. disadvantaged communities and Black, This report is based on careful review Indigenous and other communities of and synthesis of publicly available soil color. Carbon markets have enormous organic carbon MRV protocols published potential to incentivize and reward by nonprofit carbon registries and by climate progress, but markets must be private carbon crediting marketplaces. paired with a strong regulatory backing. Acknowledgements This report was supported through a gift Conservation Cropping Protocol; Miguel to Environmental Defense Fund from the Taboada who provided feedback on the High Meadows Foundation for post- FAO GSOC protocol; Radhika Moolgavkar doctoral fellowships and through the at Nori; Robin Rather, Jim Blackburn, Bezos Earth Fund.
    [Show full text]
  • Pore Pressure Response During Failure in Soils
    Pore pressure response during failure in soils EDWIN L. HARP U.S. Geological Survey, 345 Middlefield Road, M.S. 998, Menlo Park, California 94025 WADE G. WELLS II U.S. Forest Service, Forest Fire Laboratory, 4955 Canyon Crest Drive, Riverside, California 92507 JOHN G. SARMIENTO Wahler Associates, P.O. Box 10023, Palo Alto, California 94303 111 45' ABSTRACT Three experiments were performed on natural slopes to investi- gate variations of soil pore-water pressure during induced slope fail- ure. Two sites in the Wasatch Range, Utah, and one site in the San Dimas Experimental Forest of southern California were forced to fail by artificial subsurface irrigation. The sites were instrumented with electronic piezometers and displacement meters to record induced pore pressures and movements of the slopes during failure. Piezome- ter records show a consistent trend of increasing pressure during the early stages of infiltration and abrupt decreases in pressure from 5 to 50 minutes before failure. Displacement meters failed to register the amount of movement, due to location and ineffectual coupling of meter pins to soil. Observations during the experiments indicate that fractures and macropores controlled the flow of water through the slope and that both water-flow paths and permeability within the slopes were not constant in space or time but changed continually during the course of the experiments. INTRODUCTION The mechanism most generally ascribed (for example, Campbell, 1975, p. 18-20) to account for rainfall-induced failure in soils indicates that an increase in the pore-water pressure within the soil mantle results in a reduction of the normal effective stresses within the material.
    [Show full text]
  • The Soil Food Web
    THE SOIL FOOD WEB HEALTHY SOIL HEALTHY ENVIRONMENT The Soil Food Web Alan Sundermeier Extension Educator and Program Leader, Wood County Extension, The Ohio State University. Vinayak Shedekar Postdoctural Researcher, The Ohio State University. A healthy soil depends on the interaction of many organisms that make up the soil food web. These organisms live all or part of their life cycle in the soil and are respon- sible for converting energy as one organism consumes another. Source: Soil Biology Primer The phospholipid fatty acid (PLFA) test can be used to measure the activity of the soil food web. The following chart shows that mi-crobial activity peaks in early summer when soil is warm and moisture is adequate. Soil sampling for detecting soil microbes should follow this timetable to better capture soil microbe activity. The soil food web begins with the ener- gy from the sun, which triggers photo- synthesis in plants. Photosynthesis re- sults in plants using the sun’s energy to fix carbon dioxide from the atmosphere. This process creates the carbon and organic compounds contained in plant material. This is the first trophic level. Then begins building of soil organic matter, which contains both long-last- ing humus, and active organic matter. Active organic matter contains readily available energy, which can be used by simple soil organisms in the second trophic level of the soil food web. Source: Soil Biology Primer SOILHEALTH.OSU.EDU THE SOIL FOOD WEB - PAGE 2 The second trophic level contains simple soil organisms, which Agriculture can enhance the soil food web to create more decompose plant material.
    [Show full text]
  • Lnt. Agrophysics,1993, 7,133-140 MEASUREMENT TIME AND
    lnt. Agrophysics,1993, 7,133-140 MEASUREMENT TIME AND SPATIAL VARIABILITY OF FIELD INFIL1RATION M. Kutilek, V. Kuraz, M. Krejca Department of Irrigation and Drainage, Czech Technical University in Prague Thaikurova 7, 166 29 Prague 6, Czech Republic A b s t r a c t. Infiltration studies were performed on For the estimation of some soil hydraulic arenic chemozems of quartemality fluvial terrace of Labe functions the inverse solution of inftltration is (Elbe). We studied the applicability of infiltration equations of Philip (2-pararnetric ), and 3-pararnetric, of Brutsaert and applicable as an expedient and fast method. Hy­ Swartzendruber, using 70 inflitration tests performed on a draulic functions and parameters of inftltration regular grid on a plot covered for 4 years by grass. The best are then used for the quantitative discussion on applicability was found for the 3-pararneter equations, but the dynamics of soil structure. Our studies there is no unique recommendation. The probability density function (PDF) of estimates of soil hydraulic characteristics were, therefore, aimed at the evaluation of the is defonned by errors of estimates due to the approximate field inftltration tests. The main problems were: character of equations used. The log-normal distribution is a 1. Field testing of quasi-analytical and ap­ well-acceptable approximation for sorptivity S, saturated proximative equations of infiltration. hydraulic conductivity Ks and rates of inflitration. Only for 2. Application of the tested equations to the some estimates of hydraulic functions a weak spatial va­ riability was found for the distance of 7.5 m. Long time va­ study on the long time alteration of the soil fabric riability of infiltration and its parameters after ploughing and porous system after ploughing.
    [Show full text]
  • Soil Erosion
    Soil erosion Soil erosion in sloping agricultural land in Tunisia. Photolibrary on soil erosion processes. The most serious form of soil degradation is from accelerated erosion. Erosion is the washing or blowing away of surface soil, sometimes down to the bedrock. While some erosion takes place without the influence of man, the soil is lost so slowly that it is usually replaced through natural processes of decay and regeneration so soil loss and creation of new soil are balanced. What keeps soil in a natural state from eroding is vegetation. Undisturbed by man, soil is usually covered by a canopy of shrubs and trees, by dead and decaying leaves or by a thick mat of grass. Whatever the vegetation, it protects the soil when the rain falls or the wind blows. The leaves and branches of trees and the cushion of grass absorb the force of raindrops, and root systems of plants hold the soil together. Even in drought, the roots of native grasses, which extend several metres into the ground, help tie down the soil and keep it from blowing away. With its covering of vegetation stripped away, however, soil is as vulnerable to damage as a tortoise without its shell. Whether the plant cover is disturbed by cultivation, grazing, burning, or bulldozing, once the soil is laid bare to the erosive action of wind and water, the slow rate of natural erosion is greatly accelerated. Losses of soil take place much faster than new soil can be created, and a kind of deficit spending begins with the topsoil.
    [Show full text]