DOCSLIB.ORG

Soil Organic Matter Fact Sheet

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Soil Organic Matter Fact Sheet Agronomy Fact Sheet Series Fact Sheet 41 Soil Organic Matter Soil organic matter is the fraction of the soil Benefits of Stable Soil Organic Matter that consists of plant or animal tissue in There are numerous benefits to having a various stages of breakdown (decomposition). relatively high stable organic matter level in an Most of our productive agricultural soils have agricultural soil. These benefits can be grouped between 3 and 6% organic matter. into three categories: Soil organic matter contributes to soil productivity in many different ways. In this Physical Benefits fact sheet, we describe the various Enhances aggregate stability, improving components of organic matter and the water infiltration and soil aeration, different roles organic matter plays in soil reducing runoff. productivity. We also discuss field Improves water holding capacity. management practices that will help preserve Reduces the stickiness of clay soils or increase soil organic matter levels over making them easier to till. time. Reduces surface crusting, facilitating seedbed preparation. What is Soil Organic Matter? Organic matter is made up of different Chemical Benefits components that can be grouped into three major types: Increases the soil’s CEC or its ability to hold onto and supply over time essential 1. Plant residues and living microbial nutrients such as calcium, magnesium biomass. and potassium. 2. Active soil organic matter also referred Improves the ability of a soil to resist pH to as detritus. change; this is also known as buffering 3. Stable soil organic matter, often capacity (see Agronomy Fact Sheet #5). referred to as humus. Accelerates decomposition of soil The living microbial biomass includes the minerals over time, making the nutrients microorganisms responsible for decomposition in the minerals available for plant (breakdown) of both plant residues and active uptake. soil organic matter or detritus. Humus is the stable fraction of the soil organic matter that is Biological Benefits formed from decomposed plant and animal Provides food for the living organisms in tissue. It is the final product of decomposition. the soil. The first two types of organic matter Enhances soil microbial biodiversity and contribute to soil fertility because the activity which can help in the breakdown of these fractions results in the suppression of diseases and pests. release of plant nutrients such as nitrogen, Enhances pore space through the actions phosphorus, potassium, etc. of soil microorganisms. This helps to The humus fraction has less influence on increase infiltration and reduce runoff. soil fertility because it is the final product of decomposition (hence the term “stable organic Organic Materials matter”). However, it is still important for soil Over time, the application and incorporation of fertility management because it contributes to organic materials can result in an increase in soil structure, soil tilth, and cation exchange stable soil organic matter levels. Sources of capacity (CEC, see Agronomy Fact Sheet #22). organic materials include: This is also the fraction that darkens the soil’s Crop residues. color. Animal manure. Department of Crop and Soil Sciences 1 College of Agriculture and Life Sciences Compost (Figure 1). material added, and tillage and rotation Cover crops (green manure) practices, also depend on: Perennial grasses and legumes. Soil temperature. The quickest increases are obtained with Precipitation and soil moisture holding sources that are high in carbon such as capacity. compost or semi-solid manure. Soil type and drainage class. Existing microbial community. Soil fertility status and soil pH. Monitoring Soil Organic Matter To get an idea of the effect of farm management practices on soil organic matter buildup or decrease, soil samples should be taken over time. Consistency in sampling time is important to build records for fields over time (see Agronomy Fact Sheet #1). Although other tests are available, most laboratories will do a loss-on-ignition (LOI) test to estimate the organic matter content of the soil. At Cornell University, soil is exposed to 105oC (221oF) for 1.5 hours to remove soil moisture and then to Figure 1: Compost application can increase soil 500oC (932oF) for 2 hours to determine LOI. organic matter levels over time. Not all laboratories us the same method so for accurate records over time, it is important to Organic Matter Management consistently use the same laboratory service. Farm practices that help to maintain or increase soil organic matter levels: In Summary Use of conservation tillage practices (for With careful management the preservation and example zone tillage or no-till). Tillage accumulation of soil organic matter can help to exposes the organic matter to air and improve soil productivity resulting in greater will result in the lowering of stable farm profitability. organic matter due to increased mineralization rates and erosion losses. Additional Resources o Cornell University Agronomy Fact Sheet series: Rotation of annual row crops with nmsp.css.cornell.edu/publications/factsheets.asp. perennial grass or legume sods will reduce erosion and build up organic Disclaimer matter as a result of the decomposition This fact sheet reflects the current (and past) authors’ best of the rootmass. effort to interpret a complex body of scientific research, Establishment of legume cover crops and to translate this into practical management options. Following the guidance provided in this fact sheet does not will enhance organic matter assure compliance with any applicable law, rule, regulation accumulation by providing the nitrogen or standard, or the achievement of particular discharge (N) needed for decomposition of freshly levels from agricultural land. added organic materials, especially For more information those with a high C to N ratio (corn stover, cereal straw, heavily bedded manure, etc.). Avoiding soil compaction which increases waterlogging, and maintaining proper pH to enhance microbial activity and decomposition of Nutrient Management Spear Program freshly added materials. http://nmsp.css.cornell.edu Actual buildup of stable organic matter will, in Megan Fenton, Carl Albers, Quirine Ketterings addition to the amount and source of organic 2008 Department of Crop and Soil Sciences 2 College of Agriculture and Life Sciences .
Load more

Recommended publications
  • The Effects of Detritus Input on Soil Organic Matter Content and Carbon Dioxide Emission in a Central European Deciduous Forest
    Acta Silv. Lign. Hung., Vol. 7 (2011) 87–96 The Effects of Detritus Input on Soil Organic Matter Content and Carbon Dioxide Emission in a Central European Deciduous Forest a* b c István FEKETE – Zsolt KOTROCZÓ – Csaba VARGA – b b Zsuzsa VERES – János Attila TÓTH a Institute of Environmental Science, College of Nyíregyháza, Nyíregyháza, Hungary b Department of Ecology, University of Debrecen, Debrecen, Hungary c Department of Land and Environmental Management, College of Nyíregyháza, Nyíregyháza, Hungary Abstract – A major objective of our research was to survey soil biological activity and organic matter content reduction in a Central European oak forest during treatments of various detritus inputs within the Síkf őkút DIRT ( Detritus Input and Removal Treatments ) Project. Beside the control, three detritus removal and two detritus duplication treatments were applied. Our examinations have proven that soil organic matter content declined relatively fast in detritus removal treatments. The reduction was especially remarkable in root detritus removal treatments, where – due to the lack of transpiration – soils were moister during the whole year than in the other treatments. The higher moisture content, despite of the reduction of detritus input, produced an intense soil respiration. This can be explained by the fact that decomposing organisms have increased the use of soil organic matter. Detritus input reduction had a significantly greater effect on soil respiration and organic matter content than detritus input duplication of the same extent. The latter did not cause any significant change compared to the control. litter manipulation / soil respiration / DIRT Project / humus content / climate change Kivonat – Az avarinput hatása a talaj szerves anyag tartalmára és szén-dioxid kibocsátására egy Közép-európai lombhullató erd őben.
    [Show full text]
  • Fact Sheet 3: Organic Matter Decline
    Sustainable agriculture and soil conservation Soil degradation processes Fact sheet no. 3 Organic matter decline What is organic matter decline? Soil organic matter includes all living soil organisms together with the remains of dead organisms in their various degrees of decomposition. The organic carbon content of a soil is made up of heterogeneous mixtures of both simple and complex substances containing carbon. The sources for organic matter are crop residues, animal and green manures, compost and other organic materials. A decline in organic matter is caused by the reduced presence of decaying organisms, or an increased rate of decay as a result of changes in natural or anthropogenic factors. Organic matter is regarded as a vital component of a healthy soil; its decline results in a soil that is degraded. A soil that is rich in organic matter (Source: Soil Atlas of Europe) Why is soil organic matter/carbon important? Soil organic matter is a source of food for soil fauna, and contributes to soil biodiversity by acting as a reservoir of soil nutrients such as nitrogen, phosphorus and sulphur; it is the main contributor to soil fertility. Soil organic carbon supports the soil’s structure, improving the physical environment for roots to penetrate through the soil. Organic matter absorbs water – it is able to hold about six times its weight in water – making it a lifeline for vegetation in naturally dry and sandy soils. Soils containing organic matter have a better structure that improves water infiltration, and reduces the soil’s susceptibility to compaction, erosion, desertification and landslides. On a global scale, soils contain around twice the amount of carbon held in the atmosphere and three times the amount found in vegetation.
    [Show full text]
  • 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]
  • Soils and Fertilizers for Master Gardeners: Soil Organic Matter and Organic Amendments1 Gurpal S
    SL273 Soils and Fertilizers for Master Gardeners: Soil Organic Matter and Organic Amendments1 Gurpal S. Toor, Amy L. Shober, and Alexander J. Reisinger2 This article is part of a series entitled Soils and Fertilizers for Master Gardeners. The rest of the series can be found at http://edis.ifas.ufl.edu/topic_series_soils_and_fertil- izers_for_master_gardeners. A glossary can also be found at http://edis.ifas.ufl.edu/MG457. Introduction and Purpose Organic matter normally occupies the smallest portion of the soil physical makeup (approximately 5% of total soil volume on average, and usually 1 to 3% for Florida’s sandy soils) but is the most dynamic soil component (Figure Figure 1. Typical components of soil. 1). The primary sources of soil organic matter are plant Credits: Gurpal Toor and animal residues. Soil organic matter is important for maintaining good soil structure, which enhances the What is the composition of soil movement of air and water in soil. Organic matter also organic matter? plays an important role in nutrient cycling. This publication is designed to educate homeowners about the importance Soil organic matter contains (i) living biomass: plant, of soil organic matter and provide suggestions about how to animal tissues, and microorganisms; (ii) dead tissues: partly build the organic matter in garden and landscape soils. decomposed materials; and (iii) non-living materials: stable portion formed from decomposed materials, also known as humus. Soil organic matter typically contains about 50% carbon. The remainder of soil organic matter consists of about 40% oxygen, 5% hydrogen, 4% nitrogen, and 1% sulfur. The amount of organic matter in soils varies widely, from 1 to 10% (total dry weight) in most soils to more than 90% in organic (muck) soils.
    [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]
  • Fractionation and Characterization of Natural Organic Matter from Certain Rivers and Soils by Free-Flow Electrophoresis
    Fractionation and Characterization of Natural Organic Matter from Certain Rivers and Soils by Free-Flow Electrophoresis GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1817-E Fractionation and Characterzation of Natural Organic Matter from Certain Rivers and Soils by Free-Flow Electrophoresis By J. A. LEENHEER and R. L. MALCOLM ORGANIC SUBSTANCES IN WATER GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1817-E UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 73-600209 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington, D. C. 20402 - Price 35 cents (paper cov«?r) Stock No. 2401-02400 CONTENTS Page Abstract ___________________________________________ El Introduction __________________________________ __ 1 Methods and materials __________________________________ 3 Sample preparation ______ _______ _ __ 3 Sample description _________________________________ 3 Separation procedure _______ ___________ __ 4 Assay of fractions ___________________________________ 4 Results and discussion _ _______________ 5 Conclusions ________________________________________ 12 References _____________________________________ __ 14 ILLUSTRATIONS Page FIGURES 1-3. Graphs showing: 1. Organic-carbon and optical-density electrophoretic fraction- ation curves for organic materials from soil and from river water ___________________________ E6 2. Organic-carbon and polysaccharide electrophoretic
    [Show full text]
  • Determining the Fraction of Organic Carbon RISC Nondefault Option
    Indiana Department of Environmental Management Office of Land Quality 100 N. Senate Indianapolis, IN 46204-2251 GUIDANCE OLQ PH: (317) 232-8941 Indiana Department of Environmental Management Office of Land Quality Determining the Fraction of Organic Carbon RISC Nondefault Option Background Soil can be a complex mixture of mineral-derived compounds and organic matter. The ratios of each component can vary widely depending on the type of soil being investigated. Soil organic matter is a term used by agronomists for the total organic portion of the soil and is derived from decomposed plant matter, microorganisms, and animal residues. The decomposition process can create complex high molecular weight biopolymers (e.g., humic acid) as well as simpler organic compounds (decomposed lignin or cellulose). Only the simpler organic compounds contribute to the fraction of organic carbon. There is not a rigorous definition of the fraction of organic carbon (Foc). However, it can be thought of as the portion of the organic matter that is available to adsorb the organic contaminants of concern. The higher the organic carbon content, the more organic chemicals may be adsorbed to the soil and the less of those chemicals will be available to leach to the ground water. A nondefault option in the Risk Integrated System of Closure (RISC) is to use Foc in the Soil to Ground Water Partitioning Model to calculate a site specific migration to ground water closure level. In the Soil to Ground Water Partition Model, the coefficient, Kd, for organic compounds is the Foc multiplied by the chemical-specific soil organic carbon water partition coefficient, Koc.
    [Show full text]
  • Progress and Challenges in Using Stable Isotopes to Trace Plant Carbon and Water Relations Across Scales
    Biogeosciences, 9, 3083–3111, 2012 www.biogeosciences.net/9/3083/2012/ Biogeosciences doi:10.5194/bg-9-3083-2012 © Author(s) 2012. CC Attribution 3.0 License. Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales C. Werner1,19, H. Schnyder2, M. Cuntz3, C. Keitel4, M. J. Zeeman5, T. E. Dawson6, F.-W. Badeck7, E. Brugnoli8, J. Ghashghaie9, T. E. E. Grams10, Z. E. Kayler11, M. Lakatos12, X. Lee13, C. Maguas´ 14, J. Ogee´ 15, K. G. Rascher1, R. T. W. Siegwolf16, S. Unger1, J. Welker17, L. Wingate18, and A. Gessler11 1Experimental and Systems Ecology, University Bielefeld, 33615 Bielefeld, Germany 2Lehrstuhl fur¨ Grunlandlehre,¨ Technische Universitat¨ Munchen,¨ 85350 Freising-Weihenstephan, Germany 3UFZ – Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig, Germany 4University of Sydney, Faculty of Agriculture, Food and Natural Resources, 1 Central Avenue, Eveleigh, NSW 2015, Australia 5College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin Bldg, Corvallis (OR), USA 6Center for Isotope Biogeochemistry, Department of Integrative Biology, University of California, Berkeley, CA 94720, USA 7Potsdam Institute for Climate Impact Research (PIK) PF 60 12 03, 14412 Potsdam, Germany 8CNR – National Research Council of Italy – Institute of Agro-environmental and Forest Biology, via Marconi 2, 05010 Porano (TR), Italy 9Laboratoire d’Ecologie, Systematique´ et Evolution (ESE), CNRS AgroParisTech – UMR8079, Batimentˆ 362, Universite´ de Paris-Sud (XI), 91405 Orsay Cedex, France 10Ecophysiology of Plants, Department of Ecology and Ecosystem Management, Technische Universitat¨ Munchen,¨ Von-Carlowitz-Platz 2, 85354 Freising, Germany 11Institute for Landscape Biogeochemistry Leibniz-Zentrum fur¨ Agrarlandschaftsforschung (ZALF) e.V., Eberswalderstr.
    [Show full text]
  • Agricultural Soil Compaction: Causes and Management
    October 2010 Agdex 510-1 Agricultural Soil Compaction: Causes and Management oil compaction can be a serious and unnecessary soil aggregates, which has a negative affect on soil S form of soil degradation that can result in increased aggregate structure. soil erosion and decreased crop production. Soil compaction can have a number of negative effects on Compaction of soil is the compression of soil particles into soil quality and crop production including the following: a smaller volume, which reduces the size of pore space available for air and water. Most soils are composed of • causes soil pore spaces to become smaller about 50 per cent solids (sand, silt, clay and organic • reduces water infiltration rate into soil matter) and about 50 per cent pore spaces. • decreases the rate that water will penetrate into the soil root zone and subsoil • increases the potential for surface Compaction concerns water ponding, water runoff, surface soil waterlogging and soil erosion Soil compaction can impair water Soil compaction infiltration into soil, crop emergence, • reduces the ability of a soil to hold root penetration and crop nutrient and can be a serious water and air, which are necessary for water uptake, all of which result in form of soil plant root growth and function depressed crop yield. • reduces crop emergence as a result of soil crusting Human-induced compaction of degradation. • impedes root growth and limits the agricultural soil can be the result of using volume of soil explored by roots tillage equipment during soil cultivation or result from the heavy weight of field equipment. • limits soil exploration by roots and Compacted soils can also be the result of natural soil- decreases the ability of crops to take up nutrients and forming processes.
    [Show full text]
  • Humus-Producing Materials and the Making and Use of Compost
    174 August, 1926 No seed of the Carolina clover is available commercially; but where it is abundant, seedheads can readily be gathered and scattered where wanted. Seed of the low hop clover is not to be had in quan- tity, but that of the least hop clover can be bought in England under the name suckling clover or Trifolium minus. It can also be had from certain seed dealers in Oregon, who clean it out of alsike clover seed; but the Oregon seed is usually quite foul with weed seeds and there is at present no information as to how these weeds will behave in the East. Seeding of all of these clovers should be done in early fall or late summer. Much of the seed of the Carolina clover is hard, so that if a quick stand is wanted a rather heavy seeding must be made. No experiments have been made with these plants, but in view of the small size of the seed it seems as though five pounds per acre of the hop clovers and eight pounds of Carolina clover should be enough. To insure even distribution it is well to mix the seed with sifted loam or sand. Humus-Producing Materials and the Making and Use of Compost By R. A. Oakley and H. L. 'Vest oyer Organic matter, or humus, as a constituent of soil, bears a very important relation to the growth of plants. This is a fact that was discovered by man early in his agricultural efforts. Just as he had a knowledge of the plants that were worth his while to grow, it is reasonable to suppose he early learned the difference between poor and productive soils, and what common substances he could add to them to increase their productivity.
    [Show full text]
  • Is Extraterrestrial Organic Matter Relevant to the Origin of Life on Earth?
    IS EXTRATERRESTRIAL ORGANIC MATTER RELEVANT TO THE ORIGIN OF LIFE ON EARTH? D. C. B. WHITTET Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. (Received 19 August 1996) Abstract. I review the relative importance of internal and external sources of prebiotic molecules on Earth at the time of life's origin 3.7 Gyr ago. The ef®ciency of synthesis in the Earth's atmosphere was critically dependent on its oxidation state. If the early atmosphere was non-reducing and CO2- dominated, external delivery might have been the dominant source. Interplanetary dust grains and micrometeorites currently deliver carbonaceous matter to the Earth's surface at a rate of 3 5 7 10 kg/yr (equivalent to a biomass in 2 Gyr), but this may have been as high as 5 10 kg/yr (a biomass in only 10 Myr) during the epoch of late bombardment. Much of the incoming material is in the form of chemically inactive kerogens and amorphous carbon; but if the Earth once had a dense (10-bar) atmosphere, small comets rich in a variety of prebiotic molecules may have been suf®ciently air-braked to land non-destructively. Lingering uncertainties regarding the impact history of the Earth and the density and composition of its early atmosphere limit our ability to draw ®rm conclusions. 1. Introduction In at least one sense, a connection between the Universe at large and life in our small corner of it is inevitable. The hydrogen, carbon, nitrogen, oxygen, and other elements that make up our bodies and other living things were created billions of years ago in the interiors of stars and, in the case of hydrogen, in the the Big Bang itself (see Trimble, 1997, in this volume for an eloquent review).
    [Show full text]