The Role of the Landscape Architect in Soils Management


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Soil Structure and the role of the Landscape Architect

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The Role of the Landscape Architect in Soils Management

  1. 1. 1. IntroductionThe basis and purpose of this report is to gain an understanding of soil formation,development, structure, properties, plant growth in soils and the role of the landscapearchitect. The justification for this report is to understand that soil is a living medium host to alarge number of living organisms. Landscape architects use the soil as a growing medium,for creating shapes within the landform, directing views and traffic and for stabilityunderfoot. These elements require (most of the time) the completion of earthworks. Withoutan adequate understanding of soil and its properties, soil damage will become inevitable.Such problems can create a domino effect, limiting the success of the design scheme. Other reasons for this report include the fact that there is little legislation regardingthe use and management of soil in Ireland. The legislation that is in place is regarded asinsufficient. With soil classed as a finite resource, its management and successfulmaintenance is paramount. This report will look at methods of classification and soil remediation. Both subjectsare important for a landscape architect to fully understand soil and its role in the landscape.These methods will be explored through scientific papers and case studies. A n interviewwill also be carried out with a landscape architect to gain views on soil management fromthose working in the profession. The outcome of this report will conclude with present soil issues and their impact onthe landscape architecture profession. 2. What is Soil? 1
  2. 2. “Soil is the collection of natural bodies on the Earth’s surface, in places modified, or evenmade by man of earthly materials, containing living matter and supporting or capable ofsupporting plants outdoors.” – Soil Conservation Service, Keys to Soil Taxonomy, 1975Soil is a loose mass of fragmented and chemically weathered rock with an admixture ofhumus. It is formed over time through various processes of physical, chemical and biologicalweathering (White, R, 2006). Its composition, structure and properties are dependent uponthe soil’s relevant location, climate, topography, parent material, present living organismsand other, external, abiotic/biotic factors. Soil is formed over (hundreds of) thousands ofyears, through a process known as the rock cycle (Bennet, Sauer, Hampstead, 2001). Topsoil is the most productive layer of the soil profile. One hectare of topsoil cancontain nearly 5 tonnes of living organisms. It can take 500 years to form just a twocentimetre thickness of top soil. In this sense, soil can be described as being finite, non-renewable (Mirsal, I, 2008). Topsoil is the layer most plants and crops are grown in. It is theonly layer that has sufficient amounts of the macro and micro nutrients needed for successfulplant growth (Gobat, J, Aragno, M, Matthey, W, 2004). A number of different types of soil exist, each with its own advantages and drawbacksin the landscape architects mind. There is no such thing as a bad soil. Soils can bemanipulated, some more easily than others, to meet growing requirements. Appropriatelevels of pH (nutrients), structure (drainage) and cation exchange capacity are vital to a plantshealth in a soil system (Pitty, A, 1979). Healthy soil systems are important because of their worldwide use as a growingmedium for crops and also for grazing livestock. Increasing problems with soil erosion anddesertification are present on the African continent, parts of inland China and coastlinesworldwide (Mirsal, I, 2008). With increasing world populations and a need for more food,this has led to intensive agricultural practices that have not allowed enough times for soils tofallow between crops/grazing rotations. This in turn has lead to a loss of nutrients anddamage to soil structure, which results in death and loss of vegetation along with the soilbinding properties of root systems. Excessive applications of fertiliser have also had thesame effect, in conjunction with salinization (White, R, 2006). It is up to the landscape architect to understand an adequate level of soil knowledge tomaximize the potential of a site, identify appropriate plants, remedy problems and improvesoil conditions, without damaging surrounding sites. This report will aim to identify theinformation needed by the landscape architect in the field. The report will do this bydescribing the present problems, formation of soil, its effects on the surrounding environment(built, plants, etc) and how to remediate soil. This report will also state the role of thelandscape architect in each case. 3. Formation of Soil 2
  3. 3. Soil Formation is predominantly caused by physical weathering. The minerals present in theparent material can also cause chemical reactions speeding up the process. The formation anddevelopment process determines a soils structure and properties (Pitty, A, 1979).There are five key processes by which soil is formed. They are; leaching, eluviation,illuviation, podsolisation, gleying (Wesley, 2010). Leaching is a removal of solublecomponents in the soil column. Eluviation is soil particles held in suspension, for e.g. clay, isremoved. Illuviation is where the soil particles are held in suspension, for e.g. clay, isaccumulated. Podsolisation happens when a strongly acidic soil solution causes thebreakdown of the clay minerals. Gleying happens in waterlogged or anaerobic conditionswhen the iron compounds are considerably reduced or removed from the soil completely(Gobat, J, Aragno, M, Matthey, W, 2004). Fig. 3.1.1 Soil Formation The formation and development of soil could take up to one hundred years or even upto a thousand years. Soil is formed through the minerals and the weathering of rocks. Therock surface breaks down into smaller pieces of rocks through the process of weathering andthen it’s mixed with organic matter that decays and becomes broken down. Over time theprocess creates a thin layer of soil (White, R, 2006).Plants contribute to the development of soil. When the Plants attract animals, they stayaround the area and when the animals die or are killed, the animal’s bodies decay. TheDecaying matter makes the soil rich. This will continue until the soil is formed to its fullstage. Then the soil is capable of supporting many different plant species (Bennet, Sauer,Hampstead, 2001). Decomposition of plant matter happens in many stages. It begins with leaching bywater; the most easily lost and soluble carbon compounds are liberated in this process.Another early process is physical breakup or fragmentation of the plant material into smallerbits which have greater surface area for microbial colonization and attack. Smaller dead 3
  4. 4. plants, this process is largely carried out by the soil invertebrate fauna, while in the largerplants, mainly parasitic life-forms such as insects and fungi play a major breakdown role andare not aided by numerous detritivore species. Following this, the plant deritus (consistingof cellulose, hemicellulose, microbial products, and lignin) undergoes chemical changes bymicrobes (Pitty, A, 1979). Different types of compounds decompose at different rates. This isdependent on their chemical structure. For example, lignin is a component of wood, which issomewhat resistant to decomposition and can in only be decomposed by certain fungi, forexample the black-rot fungi. Said Fungi are thought to be seeking the nitrogen content oflignin rather than its carbon content. The remaining product of decomposing plants is ligninwith a very complex chemical structure causing the rate of microbial breakdown to slow. Warmth determines the speed of plant decay, with the rate of decay increasing as heatincreases, for example a plant in a warm environment will decay over a shorter period oftime. In most grassland ecosystems, natural damage from fire, insects that feed on decayingmatter, termites, grazing mammals, and the physical movement of animals through the grassare the primary agents of breakdown and nutrient cycling, while bacteria and fungi play themain roles in further decomposition. The chemical aspects of plant decomposition alwaysinvolve the release of carbon dioxide (Gobat, J, Aragno, M, Matthey, W, 2004). These processes show the importance of living organisms in the soil and landscape. Italso highlights the point, that, landscape architects should encourage a diverse amount of lifein the soil to continue these processes. Fig. 3.1.2 Decaying plant material.3.1 Weathering ProcessesOne of the major important influences on the formation of soils is weathering. Theweathering process is the breaking down of rocks (Wesley, 2010). There are two types ofweathering that have different effects, physical and chemical. Soil Formation begins after thefirst stages of rock weathering takes place. The fragments of the rock become known asregolith. The name regolith is given to all the loose soil material of the earth. Over time, dueto physical processes, this becomes soil (Pitty, A, 1979). 3.1.1 Physical Weathering 4
  5. 5. Physical weathering (disintegration) is the process of breaking down rocks intoconsecutively smaller pieces, with no alterations made to the fragments chemicalproperties. Examples of physical weathering include wind, freezing water in cracks,hydraulic action and Glaciations (abrasion) (Pitty, A, 1979). Fig. Physical Weathering3.1.2 Chemical WeatheringChemical (biogeochemical) weathering is a process that occurs after chemicalreactions, causing alterations in the molecular arrangement of minerals. Chemicalweathering progresses much slower than physical weathering (White, R, 2006).Fig. Process of chemical weathering 4. Factors and Development 5
  6. 6. 4.1. Parent MaterialSoil parent material contains data on genesis and the grain-size of distribution in the parentmaterials of soil formation. Soil minerals were either deposited as unsorted material, till, orwhen it was sorted it got transported by water or else by wind before it got deposited assediment. It is made from a mixture of grain sizes that comes from boulders to clay. Thestones are normally angular, but where as those that are sorted materials are rounded throughabrasion (Pitty, A, 1979).4.2 ClimateDepending on the climate, soils can vary. The temperature and the moisture amounts causedifferent kinds of patterns of weathering and leaching (Wesley, 2010). The wind redistributessand and lots of other particles especially in the arid regions. The amount, timing, intensity,and a kind of precipitation in a influence of soil formation. The seasonal and daily changes intemperature affect the moisture effectiveness of, the rates of chemical reactions, biologicalactivity, and kinds of vegetation (Gobat, J, Aragno, M, Matthey, W, 2004).4.3 TopographyThe slope and aspect affect the moisture and temperature of soil. Steep slopes facing the sunare considerably warmer. Steep soils may erode away and lose their topsoil as it forms. Theymay be thinner than the more nearly level soils that receive deposits from areas upslope.Deeper and darker coloured soils can be expected on the bottom of the land (Pitty, A, 1979).4.4 Biological factorsMicro-organisms, animals, plants and human’s species affect soil formation. Micro-organisms and animals mix up soils and form pores and burrow (Dunne, Buchanan, 2009)s.The plant roots open up channels in the soils. The different roots types have different effectson soils. Grass roots are fibrous, near the surface of the soil and easily are decomposed,adding organic matter. The taproots open up pathways through the dense layers. Micro-organisms affect chemical change between the roots and the soil. Also, Humans can mix thesoil to a large extent that the material in the soil is again considered parent material (White,R, 2006).4.5 TimeThe time for all the factors to interact with the soil also is a factor (Bennet, Sauer,Hampstead, 2001). Over a period of time, the soil features reflect on the other formingfactors. The soil formation process is continuous. Deposited materials, like e.g. depositionfrom floods, show no features from the soil development in activities (White, R, 2006). Allprevious surface and soil underlying horizons become buried. The biological time clockresets back to the start for all these soils. all the terraces exceeding the active mudflats, while 6
  7. 7. genetically similar to the floodplain, that are older land surfaces show more in thedevelopment features (Dunne, Buchanan, 2009).These soil the forming factors of the soil still affect the soils even on “firm” landscapes. Thematerials are deposited on the surface, and then are blown or washed away from the surface.Additions, subtractions, and alterations are sluggish or rapid, depending on the climate orlandscape position and biological activity (Gobat, J, Aragno, M, Matthey, W, 2004).When a soil scientist is mapping soil he or she looks for similar areas with soil-formationfactors to find similar soils. The properties that are described are colours, structure, andtexture. Taxonomic names are given to the soils with the same kind of properties. A commonsoil in Midwest North America reflects on the moderate and the humid climate and the nativeprairie vegetation with a thick and nearly black surface layer. This is caused by the layerbeing rich in organic matter from the decomposing grass. It’s called a “mollic epipedon”. It’sone of the several types of surface horizons that we call “epipedons.” The soils in the desertgenerally have an “ochric” epipedon that is light coloured and is low in organic matter.Subsurface horizons also are normally used in the soil classification. Loads of forested areashave a subsurface horizon through an accumulation of clay that is called an “argillic” horizon(Pitty, A, 1979). It is important for the landscape architect to be aware of the factors involved in soildevelopment. Understanding will allow for appreciation of soils value and how fragile it is toexternal environmental factors. This understanding should influence the landscape architectin the decisions he/she makes, regarding earthworks. 5. Soil Properties and StructureA soils structure takes shape over time and its particles and properties are in a constant stateof change due to various factors, i.e. weathering, translocation, leaching of nutrients and pHimbalance cycle (Bennet, Sauer, Hampstead, 2001). A soils structure and properties isimportant information to understand while deciding the soils purpose in a design. Soilsphysical and chemical properties will decide what planting will be successful, what weightand amount of traffic can be taken and the information can also be used to mediate a solutionto improve or repair the soil to meet desired needs (Mirsal, I, 2008).5.1 TextureTexture is used to describe the consisting particles of soil in their measured proportions toone another (Fig 4.1.1). Unlike, soil structure, soil texture is only altered after long termdevelopment or significant changes to the environment cycle (Bennet, Sauer, Hampstead,2001). Texture can be defined into two groups, mineral texture, which covers the percentageof clay, sand and silt present; and organic texture, which covers the proportions of organicfibres present. Texture identification can give a landscape architect a quick on-site analysis 7
  8. 8. of the properties of that areas existing soil structure. By defining whether a soil is sandy,loam or heavy clay, a landscape architect can quickly identify/anticipate any possibleproblems with water logging, leaching or hardpan development (White, R, 2006). This willalso allow for remediation of the soil to avoid these problems. Fig. 5.1.1 Soil Texture Triangle5.2 StructureStructure is a variable attribute of soil changing with weather, season and traffic levels. Itspresent state is dependent on soil texture, water table, drainage and formation ofcolloids(Gobat, J, Aragno, M, Matthey, W, 2004). Soil structure is important for soil health.In the following sub-sections, the properties of soil structure (chemical and physical) will bediscussed. 5.2.1Macro pores, Meso pores and Micro pores Pores in soil structure are important for holding and circulating oxygen, nitrogen and carbon dioxide and for making water available to plants and allowing excess to drain away. Destruction of pores by compaction, for example, can lead to water logging in wet weather, cracking in dry and death of aerobic bacteria and other living organisms important for soil health (Board, 2004). The proportions of each respective type of pore determines a soils water holding capacity, level of organic matter content and nutrient capacity (White, R, 2006). 8
  9. 9. Fig. Micro Pores and Macro Pores Micro pores are important for retaining excess water and to stop plant rootsfrom drowning/rotting. They are mostly prevalent in clay soils. A high percentage ofmicro pores can lead to water-logging.Meso pores are used for retaining water and making it available to plant root systems.The proportion of meso pores is entirely dependent on soil texture. Meso poresusually exist in a soil that has an ideal ratio of micro to macro pores (Pitty, A, 1979). Macro pores are vital for plant root growth. They allow for excellent air(oxygen, nitrogen, carbon dioxide) circulation in the soil which is important for plantroots, bacteria (nitrogen fixing) and other living beneficial soil organisms. They arealso important for quick drainage of excess water from the soil. Excess macro porescan lead to leaching in soil and poor water retention cycle (Bennet, Sauer, Hampstead,2001). These pores and the soils proportions are entirely dependent on what particles/minerals make up the soil. These properties, however, can be amended through soilimprovers and selective planting (soil binders, fibrous root systems, etc).5.2.2AggregatesAggregates are bonded units of soil consisting of sand, silt and clay in variousproportions and ratios. They are essentially textural particles that have bondedtogether, through physical or chemical means (White, R, 2006). Soil aggregates areformed over two stages; aggregate formation and stabilization. Aggregate formation takes place over time when soil clods are broken up byvarious actions such as soil freezing, expansion, sudden wetting and root penetration.Soil aggregates become stabilized, when the aggregates can finally resist these forceswithout being broken down any further cycle (Bennet, Sauer, Hampstead, 2001).Clay mineral attraction and accumulation of organic matter help stabilize aggregates.Aggregates can then be divided into two sub-groups; Micro and Macro aggregates.The amount present in each soil is dependent on that soils texture. These aggregatesinfluence and share a direct relationship with soil porosity (Pitty, A, 1979) . Clayparticles are important in the formation of both of these aggregates. Micro aggregates 9
  10. 10. are formed when clay particles are defluoccated. However, they can become macro aggregates in the presence of certain minerals (Gobat, J, Aragno, M, Matthey, W, 2004).5.3 Physical PropertiesPhysical properties of soil determines to a large extent a soils use and purpose. It is importantto know the physical properties of soil so designs and their implications can be assured,justified. The physical properties are determined by the textural properties of soil (White, R,2006). 5.3.1Soil Porosity Soil porosity is used to describe/measure the amount of voids in a soil structure. These voids are important for adequate atmospheric exchanges, water drainage, available water and organic matter content capacity. Soil porosity also reveals whether or not a soil can be easily penetrated by a specific plants root system (Clay soil/hardpan/crusting) (Gobat, J, Aragno, M, Matthey, W, 2004). 5.3.2 Water Holding Capacity (WHC) A soils water holding capacity determines the amount of water a soil can retain after soaking. Results of water holding capacity test will indicate issues of water logging, lack of retention etc. WHC is dependent on the mineral content of a soil. Water holding capacity can also be directly influenced (and vice versa) by the infiltration rate of soil. Water retention can allow a landscape architect calculate the amount of water available to a plant and other properties such as field capacity, gravitational water and water retention capabilities of soil (White, R, 2006).5.4 Chemical PropertiesChemical properties of soil are influenced by soil texture and the surrounding environment(Gobat, J, Aragno, M, Matthey, W, 2004). Planting can have an adverse effect on soilchemical properties. These effects include pH change and introduction of nutrients notusually found in the soil i.e. nitrogen induction in peat lands. With a proper understanding ofa site’s soil (chemical) properties, the landscape architect can make plans to remediate thesoil if needed and anticipate any problems arising in the future. 5.4.1 pH 10
  11. 11. Soil pH is a measure of how acidic or alkaline a soil is. The pH scale runs from zero(acidic) to fourteen (alkaline), while seven is neutral. It is Important to know the pHlevels of soil for several reasons; • pH extremes affect the availability of certain nutrients • Certain pests and diseases can only exist within specific pH parameters • Plants and organisms have optimum and preferred pH ranges essential to their survivalSoil pH can change and be altered naturally and artificially. The most commoncauses are chemical weathering and dissolution of alkaline materials (limestone),decomposition of conifer needles and other acidic plants (Mirsal, I, 2008).Soil pH can be raised or lowered (alkaline/acidic) by the addition of fertilisers,composts, manures and appropriate selection of plant species. . Intentional change ofsoil pH can be caused by addition of fertilisers, lime and the introduction of certainconifer species which will change the soil pH. Soil pH is determined mostly by soiltexture. But other factors such as rainfall and parent material are also important(Pitty, A, 1979). Soil pH is an important factor to control for a planting scheme to besuccessful. Care must be taken when altering a soil’s pH, as it could have an adverseeffect on the surrounding ecosystems through process of run-off and leaching ofacidic chemicals from the soil to adjoining systems (White, R, 2006). In order tofurther understand soil pH, its effects and how it works (hence how it can becontrolled), the following sections will be looked at:5.4.2 Cation Exchange CapacityCation Exchange Capacity (C.E.C) measures a soil type’s capacity for exchange ofpositively and negatively charged particles between a soil and soil solution. CECdetermines soil fertility and the soils capabilities for nutrient retention. Low levels ofCEC in a soil would indicate a problem of leaching arising in the future. While, highlevels of CEC would indicate a clay soil and a possibility of limited nutrientavailability. Soils with low CEC are more prone to soil acidification, due to soilleaching and mineral replacement. However, if a site with a high CEC becomesacidified, it will take longer to be neutralised due to this same attribute (Gobat, J,Aragno, M, Matthey, W, 2004). 6. Soil Classification 11
  12. 12. Soil classification is where Soil scientists use a sophisticated naming systems, theclassification of soil is to describe and identify different types of soils. Over a extendedperiod of time different countries around the world have developed their own and differentkinds of the system (White, R, 2006).6.1 Soil mappingSoil mapping is a map that shows the distribution of different soil types and different types ofsoil properties e.g. texture, organic matter, soil pH, depths of horizons, that is in the space ofinterest (Wesley, 2010). It’s typically the finished result of the inventory in a soil survey, thesoil maps are most consistently used for land evaluation, agriculturalextension, environmental protection, spatial planning and projects alike (EnvironmentalProtection Agency Ireland, 2008). The traditional soil maps usually show only the generaldistribution of soils, accompanied by a soil assessment report. Many of the new soil diagramsare derived using a digital soil mapping technique. These maps are normally richer in contextand show a higher spatial detail than the original soil maps. The Soil maps are produced byusing (geo) statistical techniques and also contain an estimate of the model doubt. Fig. 6.1 Soil Map In the digital time the soil diagrams are being inputted in a digital structure and thenthey are used for a number of applications in environmental sciences and geosciences. In thiscontext, the soil diagrams are only the visualizations of the soil resource supplies that arenormally stockpiled in a Soil data System (SIS), in which the main part of it is a SoilGeographical Database. A Soil database System in most cases is, a mixture of polygon andpoint maps that are linked with attribute tables for profile observations, in the soil mappingunits and the soil classes. the different elements of an SIS could be influenced and thenvisualized against the spatial reference (polygons or grids) (Wesley, 2010). E.g. the soilprofiles could be used to make a spatial prediction from the different chemical and physicalsoil properties. It is important for the landscape architect to understand the soil classification system.It allows for a quick analysis of the relevant site and anticipation of any possible problems.Currently, according to the Environmental Protection Agency Ireland in 2008, soil mappingin Ireland is inadequate and needs to be updated and more concise in terms of structure andcontent. 12
  13. 13. 6.2 Environmental Protection Agency, IrelandThe three key environmental compartments are water, air and soil which are very importantto life on earth. Measuring soil quality can be more complex than it sounds. There are a widerange of natural soil types and characteristics and there can be many possible functions anduses which can make it very difficult to have a set objective standard (Mirsal, I, 2008). 6.2.1 Discussion document The group Environmental Protection Agency has made up a discussion document named ‘The Soil Protection Strategy for Ireland’. This uses existing knowledge on soil resources and highlights the pressures and environmental impacts can have on our soil (Environmental Protection Agency Ireland, 2008). The report states that we need to develop some sort of soil protection scheme for Ireland, which would include a national soil quality tracking programme. Fig. The most important influence on a farm is the type of soil that it uses. Plants grow in many different soil types. The most commonly known soil in Ireland would be the Brown soils. Brown soils are used most in Ireland because they are rich and fertile. These soils are commonly found in the Midlands and in the east counties in Ireland. Another type if soil found in Ireland is called peaty soil. You are able to spot this by searching through a thin layer of turf or peat on the surface. The Peaty soils can be quite wet and are very acidic. The plants Bog cotton, heather and coniferous trees are able to grow in these soils quite well but most plants cannot manage the harsh soil condition. Peaty soils are mainly found in and around most areas of the midlands and also in most parts of the west, north and south of Ireland. These are especially common in areas where there is a very high percentage of rainfall. Peaty soils are one of the low fertile soils and because of this the soil would not do well in crop farming. 13
  14. 14. Soils that are waterlogged are called gley soil. They consist of mostly clay and are usually a light grey colour. You can often tell where this type of soil is being used if you can see rushes growing. Land found with this type of soil in it is usually used by farmers for their animals to graze. If you wanted Gley soil could be drained and its quality greatly improved but to do this it can be expensive, and also you would have to dig drains for the water and add lime to reduce the acid. The majority of farmers prefer to use the land to let their livestock rough graze (Environmental Protection Agency Ireland, 2008).6.3 Soil HorizonsSoil horizon is a specific layer in the land area that is opposite to the soil surface and hasphysical characteristics which are different from the layers above and beneath. The horizonformation (horizonation) is a function of a range of geological, chemical, and biologicalprocesses and occurs over long time periods (Pitty, A, 1979). Soils can vary in the degree towhich horizons are expressed. Relatively new deposits of soil parent material, suchas alluvium, sand dunes, or volcanic ash, may have no horizon formation only the distinctlayers of deposition. As the age increases, horizons generally are more easily observed. Theexception occurs in some older soils, with few horizons expressed in deeply weathered soils,such as the oxisols in tropical areas with high annual precipitation. It is important for the landscape architect to be familiar with the soil horizons. On siteexcavations can reveal the soil profile and horizons; along with this, so can valuableinformation on the soils structures and possible problems. Soil horizons can indicate thepresence of hardpans, which will hinder root growth, or reveal evidence of leaching. The soilprofile can inform the landscape architect whether or not soil remediation/intervention will benecessary (Gobat, J, Aragno, M, Matthey, W, 2004). 6.3.1 O Horizon: The "O" stands for Organic. This organic layer of horizons is also called humus. It’s a surface layer that is dominated by large quantities of organic material in different stages of the decomposition (White, R, 2006). The O Horizon is distinctive from the layer of plant matter that litters and covers a lot of heavily vegetated areas, that has no mineral particles that are not weathered and it’s not a part of the topsoil itself. O horizons could be split into categories that are O1 and O2, whereby in the O1 horizons contain decayed matter where it’s origin can be identified on sight e.g. fragments decaying, and the O2 horizons that contain well-decomposed organic matter, where the origin isn’t readily visible (Pitty, A, 1979). 14
  15. 15. Fig. Soil Horizons6.3.2 A Horizon:A layer of mineral soil with the highest accumulation of organic matter and soil life,in the soil profile. This layer is lacking of iron, clay, aluminium, organic compounds,and other soluble materials. When eluviation is noticeable, a lighter coloured Esubsurface soil horizon is obvious at the base of the A horizon. A-horizons can be alsobe the result of a mixture of soil bioturbation and surface actions that winnow smallparticles from biologically mounded topsoil. In this type of case, the A-horizon isreferred to as a "bio mantle" (Gobat, J, Aragno, M, Matthey, W, 2004). A Horizon is the top layering of soil or under the O horizons. That is normallyknown as topsoil. The specialist definition of an A- Horizon may change but it’smore commonly explained in terms that are relative to deeper layers. The "A"Horizons will be more than likely be a darker colour than the deeper layers of the soiland will contain more organic material, but it could be a lighter colour but it willcontain less sesquioxides or clay. The A is a surface horizon, and is also known as thezone where most of the biological activity happens (Bennet, Sauer, Hampstead,2001). The organisms in the soil such as pot worms (enchytraeids), earthworms,nematodes, arthropods, fungi, and lots of species of archaebacteria and bacteria arefocused here, regularly in close proximity and contacted with plant roots. Thereforethe A-horizon may be concerned as the bio mantle. However, since the biologicalactivity extends very deep into the soil, that it cannot be used as a main distinctivefeature of an A Horizon. 15
  16. 16. Fig. B HorizonThis layer collects iron, clay, aluminium and organic compounds, an action knownas illuviation. The B Horizon is immediately below the a horizon layer and iscommonly known as ‘subsoil’, it consists of mineral layers and sometimes containconcentrations of clay or minerals like aluminium or iron, or can be organic materialthat gets there by leaching. This layer is also known as the "accumulation" horizon orthe "zone of illuviation". This can be defined by having a very different structure orconsistence to the A horizon above and the horizons underneath. They can also havestronger colours sometimes, than the A horizon (Pitty, A, 1979). Plant roots are able to penetrate through the B horizon layer, but it usually hasvery little humus. It is normally brownish or red because the clay and iron oxides canrust and are washed down from the A Horizon (Gobat, J, Aragno, M, Matthey, W,2004).Fig. C HorizonThis is a layer that contains large unbroken rocks. This layer can acquire the moresoluble compounds (Bennet, Sauer, Hampstead, 2001). The C Horizon is called thisas it comes after A and B within the soil group. This layer is rarely affected by the soil 16
  17. 17. forming processes such as weathering, the absence of pedological development is the major defining quality. The C Horizon can contain lumps or would more likely be large ridges of unweathered rock, instead of being comprised of small fragments as in the solum. Ghost rock structure can be seen within these certain horizons. The C Horizon can also contain types of parent material (White, R, 2006). Fig. The Great Soil GroupsThe great soil group is made up off 10 soil types these all have the same fundamentalarrangement of the soil horizon. The great soils group are the main unit of measure that areused to differentiate between Irish soils in the general soil map. Each one of the great soilgroups can be broke down into many different types (Environmental Protection AgencyIreland, 2008). These groups are further sub-divided and broken down, yet they represent themain soils in Ireland. Fig. 6.4.1 Soil Map of Ireland 1. Brown Podzolics 17
  18. 18. Brown podzolic soils are a subdivision of soil classification. They are classed with podzols because they are iron-rich. They are between podzols and brown earths. They are mostly found on hilly land in west Europe, and where the summers are relatively cool.2. Brown Earth Brown earth is a type of soil. It is commonly found in western and central Europe. They can be also common in lowland areas. The vegetation types that are most common are deciduous woodland and grassland. This is because of the natural fertility of brown earths. They are normally located in regions with a humid temperate climate.3. Podzols The Podsol (also spelled podzol, or known as spodosol) are the most used soils of coniferous, or boreal forests. Most podzols are not great soils for agriculture because they can be sandy and excessively drained. They can also have shallow rooting areas and poor drainage due to subsoil cementation.4. Grey Brown Podzols These are freely draining soils. That has clay that enriches the B horizon. These soils develop under temperate woodlands and that have a moderate rainfall, they can also be found in lowland areas.5. Gleys These soils consist of grey and yellow patches. This can be caused by the soil becoming waterlogged. This happens because the soils become waterlogged and the air is excluded and the supply of oxygen is greatly reduced.6. Rendzinas Rendzina soil is a dark, grayish-brown, humus-rich, intrazonal soil. This soil is most closely linked to the bedrock type and is an example of the initial stage of soil development. It’s most commonly formed by weathering of soft rock types. 18
  19. 19. 7. Regosols Regosols is a very weak mineral soil, regosols are found mostly in eroding lands the most common begin mountainous regions. The land usage may vary depending on the drainage quality.8. Lithosols This thin soil consists of rock fragments. It’s a soil with poorly defined horizon layers that consists mainly of partially weathered rock fragments.9. Blanket Peat Peat is brownish/black in colour and is made up of 90% water. It also contains partially decomposed remains of dead plant material for example: mosses, grasses and heathers. There are a limited amount of nutrients, low oxygen levels and high acidity this means that there are only certain types of plants that can sustain the harsh environment.10. Basin peat Basin peat is formed in low area and in rivers. These started to form around 7000 years ago and have been known to reach depths of up to 8 meters. They are not very useful for land usage but can respond well to drainage. Fig. 6.4.2 The Textural Triangle Soil Classification System 19
  20. 20. 7. Plant Growth and SoilsSoil structure, texture, and its properties (chemical and physical) will determine what plantlife can grow and survive with remediation. Plants can develop a mutual beneficialrelationship with soil by adding organic matter to the A horizon (fallen leaves, etc) (Dunne,Buchanan, 2009).7.1 Essential NutrientsFor successful plant growth to take place in soils there must be sufficient nutrients present.The nutrients required and their amounts differ, but there are nutrients which are absolutelyessential. It is important to know which nutrients are present in the soil and in whatquantities (White, R, 2006). This can help plan remediation practices in soils with eithertoxicities or deficiencies. Nutrient deficiencies/toxicities, can be confused with diseases andthey will always present physical symptoms in plants cycle (Bennet, Sauer, Hampstead,2001). When investigating a site, the present planting and its state of health will help indicatenutrient problems. Non-mineral nutrients are just as essential to a plants growth and success.These nutrients are oxygen, carbon and hydrogen and are absorbed into the plant from the airvia the stomata. Mineral nutrients are divided into two groups: 7.1.1 Macro Nutrients Macro nutrients are called so, not because of their mineral size, but because of the amounts used by plants. The macro nutrients are: • Nitrogen • Phosphorous • Potassium • Calcium • Magnesium • and Sulpher The first 3 nutrients, nitrogen (N), phosphorous (P) and potassium (K) are generally thought of as the major macro nutrients. This is because most plants exhaust the soil of these nutrients and without them successful plant growth cannot take place (Dunne, Buchanan, 2009). N, P and K are the primary components of any fertiliser application, as these macro nutrients are usually depleted or missing from the soil. Macro nutrients are the first minerals to be leached out of the soil (Pitty, A, 1979). 7.1.2 Micro Nutrients 20
  21. 21. The micro Nutrients are: • Boron • Copper • Iron • Chlorine • Manganese • Molybdenum • ZincThese nutrients are used in smaller amounts than macro nutrients (Dunne, Buchanan,2009). However, they are just as essential, specifically in the process ofphotosynthesis. The addition of chemical and organic fertilisers can be used toincrease the amount of these micro nutrients available to the plant (Pitty, A, 1979).This is done to combat deficiencies (chlorosis) and to prolong or encourage flowering.7.1.3 Factors Affecting AvailabilityNutrient availability to plants can be affected by several factors; amount of nutrients,light, temperature, water and pH.High concentrations of specific nutrients in soil can inhibit the availability of othernutrients to plants in the soil. This is due cation exchange capacity and the valency ofions. Soil texture will also determine how problematic this issue can be (Pitty, A,1979). Light and temperature will also affect nutrient availability to planting systems.This is due to the rate at which plants complete photosynthesis, which determines theamount of nutrients needed. If there is poor light, plants may not create the energyneeded to absorb essential nutrients deep in the soil. Temperature again affects therate at which plants absorb nutrients and loose excess water through evapo-transpiration (White, R, 2006). Water and its levels within the soil will determine nutrient availability. Ifthere inadequate water, the nutrients in the soil cannot become soluble and thuscannot be absorbed. Low levels of water, with excessive additions of fertiliser, maylead to high soil salinity, which will exacerbate the problems of nutrient availabilitycycle (Bennet, Sauer, Hampstead, 2001). Excess water in a soil with low cationexchange capacity will lead to leaching of nutrients from the soil, causing plantdisorders due to nutrient deficiencies. 21
  22. 22. pH, as discussed before, is an important soil property to control. Fluctuating levels of pH can lead to toxicities and deficiencies of soil nutrients. This is a result of certain nutrients being available to plants at specific levels of pH (Gobat, J, Aragno, M, Matthey, W, 2004). The landscape architect must understand the problems affecting nutrient availability and how to overcome them. Understanding the problem will help the landscape architect avoid or anticipate and remediate the problem.7.2 Root Growth and DeathSuccessful and vigorous root growth in soil relies on a number of factors. Soil texture andstructure will determine to what degree a plants root system can penetrate the macro andmicro pores (Gobat, J, Aragno, M, Matthey, W, 2004). Root death is possible in soils with poor drainage. This can lead to water logging(drowning of roots) and colonization of soil borne diseases which thrive in soils that are wetfor prolonged periods of time (i.e. phytophora). Dead roots and decomposition can lead tothe addition of organic matter to a soil, improving structure (Raviv, M, Lieth, J, 2008). Root growth through the soil profile improves soil stability and structure. It does thisby binding the soil together and resisting soil erosion. It also makes slope failure less likely.Penetrative root growth also breaks down soil clods and is instrumental in the soildevelopment process until a soil becomes “stable” (White, R, 2006). Root growth can be hindered by several occurrences in the soil profile. Thedevelopment of a hardpan can stop downward root growth leading to lateral growth. This canlead to unforeseen problems with root systems growing outside their proposed/predicted areacycle (Bennet, Sauer, Hampstead, 2001). This can lead to damage of hardscape, lawns, etc.Soil salinization, leading to high levels of salts in the soil profile, can burn the roots of plants,leading to plant death.7.3 Disease and PestsLiving organisms are vital to a healthy soil. These organisms include invertebrates, bacteriaand viruses. They are essential for producing nitrogen (bacteria), carbon dioxide (carboncycle) and for nutrient recycling upon their death and decomposition cycle (Bennet, Sauer,Hampstead, 2001). However, diseases and pests are also included within this group. As withall living soil organisms, the number of problem pests and diseases is dependent upon the soilcondition. Poor drainage and damp conditions will drown many pests, while diseases likephytophora. pH is also another factor in the amount of damage caused. pH may makenutrients unavailable to a plant, further weakening it against the pest/disease (Mirsal, I,2008). 22
  23. 23. Ways to tackle soil pests and diseases (especially considering the ban on use of soilborne insecticides/fungicides) include soil rotovation, aeration, drainage and ensuringadequate pH levels. Various other techniques and systems can also be employed, butgenerally a healthy, stable soil structure, will ensure protection (White, R, 2006).7.4 Soil Binding PlantsSoil binding plants are important in soil remediation and for the maintenance of soil structure.Soil binding plants are used in soils with low CEC, poor structure and have a high percentageof macropores and little or no organic matter. Soil binding plants help improve/maintain soilstability and prevent soil erosion. They do this in four ways. 1. The root system (i.e. fibrous, taproot) penetrates into the soil surface and through the pores of the soil. It surrounds and holds in place soil particles susceptible to soil erosion. 2. The plant growth above soil level reduces run off speed of rainfall. 3. The root system reduces the infiltration rate of water, making leaching of minerals from the soil less likely. 4. The root system and top growth of the plant(s) add organic matter to the soil through natural death and decomposition of roots and leaves, etc. This improves drainage, moisture retention and overall soil structure. Soil binding plants have been used to a large extent in areas suffering from soilerosion and desertification. In some instances, soil binders, in conjunction with other systemshave been able to stop desertification and reclaim land that was deemed useless due to soilerosion. However, care must be taken when selecting plants to use as a soil binder. Forinstance, on the west coast of Scotland Japanese Knotweed was used to a large extent to stopcoastal soil erosion. The plant soon became invasive and now its use is banned. Soil bindersare an attractive option for areas of high rainfall with sites in danger of slope failure(collapse). Soil binders can help counter the damage of landslides and may even preventthem (Mirsal, I, 2008). The use and understanding of soil binders can be used by the landscape architect toremediate and stabilize sites. With a number of positive attributes (soil binding, addition oforganic matter and reduction in run-off speed), the application of soil binders is broad. Withsoil erosion, desertification and indeed slope failures (specifically in Ireland) (EnvironmentalProtection Agency Ireland, 2008), becoming more problematic in future years, the use of soilbinders will be more relevant in a landscape architect’s plan to remediate affected areas.7.5 Nitrogen Fixing Bacteria, Mycorrhiza, Green Manures and Nutrient Recycling 23
  24. 24. Certain species of plants develop a symbiotic relationship with bacteria/fungi in the soil.These bacteria/fungi fix nitrogen from the air within the soils structural pores (Kolay, 2007).Green manures have deep taproots that penetrate deep into the soil taking advantage ofnutrients unavailable to other plants (Dunne, Buchanan, 2009). These two types of plantsthen re-introduce the nitrogen they absorb back into the slow after they die and decompose(Lamb, 2008). This significantly adds to the nutrient value of the organic matter of the soil.This then encourages healthier, stronger plant root and shoot growth, which in turn leads toimproved soil structural stability. Nitrogen fixing plants and green manures can be used inrelatively nutrient poor soils to improve their chemical properties and inevitably, theirphysical properties (Pitty, A, 1979).7.6 Living OrganismsLiving organisms in the soil are important for healthy plant growth in soils. Micro organismsin the soil break down the organic matter and mineral content of the soil to make nutrientsavailable to plants, while others fix nitrogen in the air (Board, 2004). Other micro organismscontrol and keep in check, pests and diseases. In a soil with a humus rich content, there aretwelve to fifteen species of micro organisms for each harmful pest/disease, doing this. Othermacro organisms such as earthworms, increase the number of micro organisms, increasenutrient content and improve soil structure (aeration) (Gobat, J, Aragno, M, Matthey, W,2004). As an ecosystems health can be measured by bio-diversity, it is never more relevantthan in soils.7.7 DrainageDrainage is important to soil health for many reasons. For one, adequate drainage allows forthe removal (dissolution) of accumulative, possible toxic, substances. Good drainage willstop rainfall exceeding evapo-transpiration, which leads to leaching of nutrients from the soil.Where drainage is not appropriate to the soils needs, damage to the soil structure will occur.Most common is compaction of the soil (Bennet, Sauer, Hampstead, 2001). This happenswith heavy traffic on a waterlogged soil. This leads to the removal (destruction) of airpockets in the soil. This then leads to the death of vital soil organisms and plant rootsthrough lack of oxygen. Following compaction, if the soil dries out too fast, crusting on thesoil surface can occur. This effectively seals the soil surface, blocking the carbon cycle fromtaking place. This leads to a build up of carbon dioxide and a lack of oxygen leading to soilmicro organism death. Crusting will lead to poor infiltration rates leading to pooling of wateron the soil surface. 24
  25. 25. Soil drainage is paramount to a soils usefulness and potential. Drainage is determinedby a soils structure. Soils with a large number of macropores have excellent drainage, butpoor retention, and the opposite is true with micropores and clay soils. Ways to provide andencourage good soil structure is by using deep rooting, soil binding plant species and by alsothe addition of decomposed organic matter. Drainage can also be maintained by soil aerationtechniques in the Autumn and early Spring (White, R, 2006).7.8 Heavy Metals and Toxicities in SoilsFormer industrial sites tend to have soils with high levels of heavy metals present. The mosttroublesome of these heavy metals are arsenic and aluminium. In the case of landreclamation, it is vital that these substances are removed, due to the danger they present to thepublic. Planting can be used as a method of removing these impurities from the soil.However, the planting palette that can be used is severely limited (White, R, 2006). The most ideal plants would be those with long taproots that can reach deep into thesoil, bringing the metals to the surface and absorbing them. The plants must also have atolerance for poor soil. One of the most successful plants that can be used in this situation isspecies of fern. The plants must then be destroyed afterwards, because they themselves posea health risk. There structure contains a large amount of the metals they absorbed (Mirsal, I,2008).7.9 Soil SalinitySoil salinity is the salt content of soil. Soil salinization is the accumulation of excess salt(s)in the soil profile. This is caused primarily by high salt levels, salt mobility, excessiveapplication of fertilisers, high levels of CEC, low levels of precipitation and excess evapo-transpiration. A low water table in the soil structure can also cause soil salinization. This iscaused by capillary action transport mobile salt minerals to the soil surface (Gobat, J, Aragno,M, Matthey, W, 2004). High salt levels in soil can lead to toxicities in plants and eventually their death.High levels of certain minerals can cause a change in pH. Soils that become heavily salinizedtend to have a poor structure and hence water infiltration is hampered. This can causeproblems when trying to leach the excess salts from the soil through remedial action. Soilsalinization is a key factor in soil erosion and desertification. High levels of salt lead to plantdeath, loss of organic matter, lack of soil binding action by roots and damage to soil structure(White, R, 2006). Soil salinization is now occurring more and more within in urban areas.This due to irrigation with water containing salts. All water contains some level of saltspresent within it and these build up in soil, slowly, over time. The solution most applied tothis problem is flushing or leaching the excess salts out of the soil with excess water. This is 25
  26. 26. costly and unsustainable. It is up to the landscape architect to develop sustainable use ofwater and adopt appropriate methods for dealing with excess soil salinity (Lawton, 2003). The easiest solution to soil salinization is by leaching or “washing out” the excess saltsfrom the soil. However, this can be expensive and is unsustainable as it wastes huge amountsof water. Furthermore, areas where salinization is most problematic, water is a scarceresource that is mainly used human use. By using appropriate planting and manipulating thelandscape, the excess salts can be removed by natural processes (Mirsal, I, 2008). The mostimportant elements to de-salinizing a soil are: 1. Xeriscaping: Xeriscaping uses water as efficiently as possible. With salinized soil, there comes a poor infiltration rate. Also salinization of soils tends to be most common in areas with low rainfall. Xeriscaping uses xeric planting which can tolerate droughts. 2. Bio-Swales: Bio- swales are man-made reservoirs which maximise amount of time water spends in the swale. This stops run-off and counter-acts the factor of a poor infiltration rate being present. This also concentrates water into leaching excess salts from the soil in a specific area. This allows the amount of water being used to achieve its maximum potential. 3. Mulching: Mulching the surface of heavily salinized soils allows for moisture retention and stops excess run off. If organic mulch is used, its decomposition will improve the soil structure, hence improving drainage and in turn aid in the leaching of excess salts from the soil. Mulching also stops excess evapo-transpiration from the soil and makes sure the water moves its way down through the soil. Inorganic mulches can also be used for the same effect, however, they must be used in conjunction with shade. Otherwise they will conduct heat, raising the soil surface temperature and increasing evapo-transpiration (Lawton, 2003). These actions were taken in a by Geoff Lawton a team of agriculturists, soil scientists andpermaculturists on a site in Jordan. This example will be investigated in greater detailthrough means of a case study, which is located in the appendix. 8. Artificial Creation and Manipulation of Soils8.1 CompostingComposting is the biological reduction and breakdown of organic wastes into nutrient richhumus. Composting is a natural process that occurs throughout the world (Brickell, C, 2002).The rate at which composting takes place is dependent upon: temperature, content, density,organism population (Micro and Macro) and degree of intervention. It is utilised by thelandscape architect to reduce waste, minimise energy input and reduce loss of energy (Lamb,2008). Composting is also used to improve soil structure and encourage plant growth. 26
  27. 27. The inclusion, creation and specification of composting facilities in residentialschemes by the landscape architect can be of great benefit to the community and indeed, theenvironment (Tracey, 2007). The following sub-sections will go through the types, methodsand effects of various composting practices. 8.1.1 Hot and Cold Composting Hot and cold composting are the two commonest ways of composting. The differences between the two are labour, degree of intervention and time. Cold composting is the simplest form of composting. It functions much as natural decomposition occurs in nature. The composition of cold composting materials predominantly green (lawn cuttings, etc). Cold composting is low maintenance. The process works by mounding the material to be composted on top of other composting material. This mound or pile is then colonized by micro organisms that help speed up the breakdown of the soil. The build up of heat in the pile also increase the breakdown rate of the organic material (Dunne, Buchanan, 2009). However, the constant addition of fresh material to be composted can lower the core temperature of the pile through conduction. This will interrupt the breakdown process and inevitably slow down decomposition. The pile may also need to be occasionally turned to keep the process moving at a steady pace. Another drawback of cold composting is that it can take between six months and two years to produce composted material suitable for use (Kolay, 2007). Hot composting is a more efficient, productive method of composting. Hot composting can be described as an accelerated form of composting. It can produce compost suitable for use in three to six weeks. This is considerably faster than cold composting; however, this rate does drop in winter (Hanson, 2000). Hot composting requires constant management to maintain optimum temperatures for aerobic micro-organisms. These are fundamental to the success of hot composting. If the pile is not turned enough, oxygen will be depleted, leading to colonization of anerobic bacteria. These will lead to the decomposition rate slowing down (Dunne, Buchanan, 2009). While Heavy maintenance is needed, the benefits are numerous. Hot composting kills weed seeds and pathogens, it doesn’t attract rodents, unlike cold composting and it has a high production rate (Hanson, 2000). Hot compost piles also denature and degrade traces of herbicides that may be present in material added to the pile. The management of the hot compost pile can be intense. The ratios of nitrogen (green organic material) to carbon (brown organic material) need to be strictly controlled, as does the temperature of the pile (Kolay, 2007). 27
  28. 28. In terms of landscape architecture and residential schemes, hot compostingwould be the more appropriate method. This is due to the piles not attracting rodentsand the destruction of weed seeds and pathogens. The speed at which hot compostpiles breakdown organic material would also significantly reduce domestic waste ifproperly managed.8.1.2 Simple Composting“Simple” composting can be regarded as any form of composting not done on anindustrial scale. Examples include vermicomposting and Layering. These methodswill be discussed later in this section. Layering is perhaps the most common method of composting. It is alsoreferred to as the “lasagne” method of composting. Its breakdown rate is entirelydependent on temperature and content. The process works by simply laying one layerof organic waste on top of another and allow for natural decomposition to take place(Lamb, 2008). This process can be done in either a container or by simply dumpingthe layers on a piece of land to be used in future. The container method results inhigher temperatures and a greater breakdown rate. It is argued that the optionaltemperature for composting, when using the layering method, is sixty degrees Celsius. The problems associated with this method are time and health issues. It cantake up to a year for the compost to be ready for use. The constant addition of organicwaste to the pile disrupts and slows down the process. This is because the fresh wasteis conducting heat from the pile. If the pile becomes too large, it will take muchlonger to break down. Also the process, depending on the content, can causedisturbing odours. The compost pile also needs to breathe (aeration). This can beachieved by placing the compost pile on top of a healthy soil. Otherwise the pileneeds to be turned with a pitchfork to introduce air (oxygen, carbon, nitrogen) into thesoil. Without aeration, micro organisms breaking down the soil will die and thedecomposition process will stop (Kolay, 2007). Layering is a simple process with little or no management needed. Theinduction of accelerators to the market has also made the process more attractive.Accelerators are chemicals that act as catalysts in the composting process speeding updecomposition. Although many feel the point of composting is defeated byintroducing chemicals into the mix (Hanson, 2000). Vermicomposting is the use of earthworms to breakdown organic matter in thecomposting process to produce high quality humus. The process is usually carried outin bins with sufficient earthworms added to breakdown the appropriate amount ofwaste (Brickell, C, 2002). Vermicomposting can reduce a households garbage outputby a third.Vermicomposting’s main advantage over traditional composting methods is that thebreakdown rate is not as dependent on temperature. The continuous addition of 28
  29. 29. organic waste to compost piles can disrupt the process by lowering temperaturethrough heat conduction. Vermicompost consists of worm casts and decomposedorganic matter. These worm casts contain five times the amount of nitrogen, seventimes the amount of phosphorous and up to eleven times more potassium then what isfound in “average” soil. The casts also condition soil to within a favourable pHrange, ideal for the majority of plant growth. As the worms breakdown the organicmatter they “eat” or “filter” it with their bodies. They intake beneficial micro-organisms from the organic matter and excrete eight times the amount of micro-organisms they ate. Another benefit of vermicomposting is that the majority ofpathogenic bacteria are killed in an earthworm’s gut (Board, 2004). The drawbacks of vermicomposting are few, but the main issues are smell andlabour. If vermicomposting bins begin to smell, its due to overloading of the system;simply put, there aren’t enough earthworms to keep up with demand. The solution tothis is more earthworms/bins. Another issue is the spreading of the vermicompost.To be sustainable it is favourable to separate the worms so they can be re-used in thecomposting bins. However, this can be labour intensive, messy and wasteful in termsof time. Vermicompost also loses much of its nutrient value if it dries out. It can alsobecome structurally unstable and very hard to re-wet (Board, 2004). Verimicompost is a very attractive method of composting. It uses organicmeans to recycle nutrients back into a system. It is faster than standard methods ofcomposting. The use of earthworms increases the nutrient value of the organic matterby increasing the amount of nutrients and micro-organisms in comparison to standardcomposting. Vermicompost can also be stored for over a year, giving great flexibilityin terms of its use and applications. Simple composting requires little or no skills, allowing communities tomanage their own composting programmes. With a little education provided by thelandscape architect through means of a development plan, simple composting can beused as a way for encouraging people to interact with their local spaces, thus creatinga sense of ownership and enriching the experience of the space (Tracey, 2007).8.1.2 Mechanized CompostingMechanical composting is the large scale manufacture of compost through theprocessing of raw organic materials. The process consists of several phases and cantake up to six weeks for a finished product. Environment conditions of the materialsbeing composted are monitored and controlled throughout (Kolay, 2007). The process begins by pulverizing the organic materials. Most practices crushthe materials in particles no larger than 5cm. This material is then mixed with sewageand other materials in a rotating chamber. Here, pH, moisture, temperature, nitrogen/carbon ratios and oxygen levels are controlled and monitored. This machine turns the 29
  30. 30. compost when needed and incubates the material providing optimum conditions for an adequate decomposition rate. Mechanical composting produces compost at a faster rate. The compost produced is also free of pathogens and weed seeds. Due to the rotation of the incubation chamber, aeration and drying occur, producing compost that is structurally more stable than compost produced by simple means (Kolay, 2007). There is some controversy however on the use of sewage in the mechanical composting process. The presence of heavy metals, such as cadmium and arsenic can cause serious pollution in soils if the compost used is not screened properly (Environmental Protection Agency Ireland, 2008). Mechanical processes also tend to be very expensive, labour intensive and dependant on the control of environmental conditions. To the landscape architect, procurement of compost from this method may be efficient and beneficial, but the threat of heavy metals being present could cause controversy with local communities and damage to the wider ecosystem, with the use of mechanically composted materials.8.2 FertilisersFertilisers are used in soil management to improve growth of plants by introducing orincreasing the presence of a specific nutrient(s). Fertilisers can also be used to raise soil pH. Fertilisers can help remediate the effects of a nutrient deficiency, extreme cationexchange capacity, leaching of soil or a pH imbalance (Brickell, C, 2002). There are anumber of organic and chemical fertilisers on the market, each with their own advantages,disadvantages. These include cost, environmental damage and degree of success (Dunne,Buchanan, 2009). The use of fertilisers is heavily debated. Many argue that fertilisers merely mask aproblem and that continued applications are needlessly applied and only cause damage.Intensive use of fertilisers can lead to soil salinization, which in turn can lead to toxicities andsoil erosion. Fertiliser applications also raise soil pH. Run off from fertilisers can also causedamage to the surrounding environments, such as eutrophication (White, R, 2006). It comes down to the fact that fertilisers are expensive to purchase, manage and applyand are wasteful in terms of external output, labour and money (Lamb, 2008).8.3 pHSoil pH can be adjusted through a number of practices. pH change can be achieved viaplanting, fertiliser application and/or addition of specific minerals (White, R, 2006). The 30
  31. 31. reasons for altering the pH of a soil are mainly due to making adequate levels of requirednutrients available to specific plant species i.e. ericaceous (acid loving) plants. Soil pH can be altered by planting of specific ericaceous species, i.e. conifers, whichslowly change the soil pH over time. An example of this is an alkaline fen bog beingcolonised by conifers and eventually turning into an acidic peat bog. Certain fertilisers (lime)can raise the pH of soil through the introduction of a range of ions (minerals). Unintentional soil pH changes can lead to the failure of a planting system. This isdone by the pH being too extreme for soil organisms to survive and/or nutrients becomingunavailable or available in toxic amounts cycle (Bennet, Sauer, Hampstead, 2001). Thesesymptoms can lead to the destruction of the soils structure. Soil pH can also alter thesurrounding environment (rivers, lakes) through run off of positively/negatively charged ions.Problems with unforeseen pH change are done to inadequate anticipation of problems andpoor site analysis. However, the source of the change may be external of the site and out ofthe control of the landscape architect. This is where preventative or remedial practices takehold. Altering a soils pH can be difficult depending on the soils texture and chemicalproperties. Soils with a clay texture and a high cation exchange capacity have a very highbuffering capacity. This means it takes longer for their pH to change, in comparison to a soilwith low buffering and cation exchange capacities. Once the pH of the soil with a highbuffering capacity is changed, it can be extremely difficult to remediate it. On the otherhand, soils with a low buffering capacity can become locked in a state of flux in anunpredictable environment (urban). Soils with a high buffering (good infiltration rate andwater retention) can help stop pH changes to the surrounding ecosystems by absorbing runoff that contains substances/minerals that would raise or lower pH (Pitty, A, 1979). 9. LegislationCurrently in Ireland, there is little legislation that is enforced in terms of soil management andprotection. In 2006 a European convention was held, to implement a E.U. wide induction ofeffective, adequate legislation regarding soil. The European Commission published the“Thematic Strategy for Soil Protection”. The aims of this publication was to ensure thesustainable use of soil, the preservation of soil and the regeneration of degraded soils to alevel of sustainable functionality (Environmental Protection Agency Ireland, 2008). The commission hopes to achieve this by completing and encompassing the entire soildata of Ireland that is currently insufficient. This will be followed by a critical assessment ofevidence of the current condition of Irish soils and the issues/problems putting theses said soilsystems under pressures. This stage will look at the source of these pressures and possiblesolutions. The report then highlights the need for a national soil monitoring system thatmaintains healthy soil conditions and establishes uses and importance of different soils andtheir relevant locations (O Regan, 2009). The corresponding section of the document also 31
  32. 32. states the importance of anticipating and identifying future problems/uses associated with thesoil in question. The report goes on to outline the need for a specific national framework planto cement a policy of soil remediation. In comparison to Ireland’s E.U. counterparts, it is farbehind in terms of these policies. The report also states a need for a policy on soilcontamination in Ireland. The commission goes on to state, in the report, a structure forregulating the application of sewage sludge to soil for agricultural and mechanicalcomposting purposes. This part of the report aim to counter the possible presence ofpoisonous heavy metals in the sewage being applied to the soil and the danger of spreading tothe wider ecosystem. This report, written in conjunction with the Irish environmentalprotection agency, was presented to the European commission and is part of a wider plan toprovide a framework for effective soil management in the E.U. (Environmental ProtectionAgency Ireland, 2008). These views of the E.U. commission are echoed by landscape architect, Terry O’Regan. Terry O’ Regan is the founder and head landscape architect of Terry O’ Regan andAssociates (formerly known as BHL Landscapes). Terry O’ Regan helped form the NationalLandscape Forum, which has been pushing for definitive, effective soil management policyand legislation in Ireland since 1994. While some progress has been made, (i.e. 2004legislation brought in on soil management and the inclusion of developing a national soilmanagement strategy in the national development plan) the time taken to do so can beregarded as inefficient (O Regan, 2009). To further investigate the goals of the national landscape forum and to gain an insighton soil management from the perspective of a landscape architect, I conducted a telephoneinterview with Terry O’ Regan. This interview was conducted on 7th December 2010.9.1 Telephone Interview with Terry O’ ReganTerry O’ Regan is a landscape architect and founded his own practice, BHL Landscapes (nowknown as Terry O’ Regan and Associates), in 1975. His practice has won numerous awardsthroughout the period of its operation. In 1994, worried about current practices regarding soilmanagement in Ireland and indeed Europe, Mr. O’ Regan founded Landscape AllianceIreland. Landscape Alliance Ireland is a non-governmental organisation pushing for suitablelegislation for policies regarding soil management in Ireland. Prior to this interview I e-mailed Mr. O’ Regan several questions and asked him forhis thoughts and views on these matters.Q.1.What is your view on soil legislation in Ireland? Mr. O’ Regan said that he felt that current legislation was not adequate and up to speed withour E.U. counterparts. He also stated that any government legislation on soil managementwas only relevant, in that it is enforced, with works regarding the national roads association 32
  33. 33. (NRA). In terms of landscape architecture, he stated that legislation was not enforced norfollowed by many in the profession or those in charge of regulation.Q.2.What problems have you encountered with soil management during your career as alandscape architect?Mr. O’ Regan replied to the question stating that the most common and problematic issue heencounters in his career is the occurrence of soil compaction. He stated it is mostly down to alack of understanding by those in many professions involved in earthworks on site. He statedthat this was most true with engineers who don’t view soil as a living medium. On sitestorage of soil was another problem Mr. O’ Regan brought up. He stated inadequate methodsof on-site soil storage lead to mixing of sub and topsoil. All of these problems combined,stated Mr. O’ Regan, lead to issues with drainage and water gathering in hollows on the soilsurface.Q.3. What should a landscape architect understand about soil?Mr. O’ Regan stated that a landscape architect must understand the soil profile and horizons.He said on site excavation can reveal sufficient information to the landscape architect on thesoil properties of that site. Mr. O’ Regan went on to say that the soil profile can reveal howvigorous root growth and penetration will be and if there will be any factors affecting rootdevelopment. Mr. O’ Regan made that the point that it was important for the landscape architect tounderstand the relationship between the sub and topsoil and the procedure for their properstorage. He stated that proper management of soil, including its storage will avoid mostoccurrences of compaction (due to traffic and piling topsoil higher than one metre).Q.4. What is your own approach to soil management?Mr. O’ Regan stated that for his own approach to soil management, he follows a number ofprocedures. For soil storage, he stores the first 200-300mm of topsoil of the site in their ownpiles. The next 300mm down of sub-soil is stored in its own piles as is the immediate600-750mm of remaining sub-grade. Mr. O’ Regan then went on to say that it is paramountto seed the piles with grass seed as soon as possible. This is done to counter act colonizationof weeds and the dispersal of their seeds in the soil. Mr. O’ Regan stated that this practice isvital to the long term value of the project at hand as it simplifies the weed problem and helpswith maintenance issues.Q.5. What practices do you use for soil improvement/remediation? 33
  34. 34. Mr. O’ Regan replied to the question stating that aeration of soil is the method he mostcommonly uses in his profession. He states this due to the high occurrence of compaction onsites. He said aeration is often needed to a depth of 450mm. He stated that compaction is themost problematic issue in Ireland currently and is the main reason for tree failures as it causesroot disruption. As the conversation progressed, Mr. O’ Regan brought up the topic of the nationallandscape alliance Ireland. He stated how the organisation is working for soil to be declareda national resource by the government of Ireland. The organisation aims for thegovernmental induction of adequate, effective soil management in Ireland. Mr. O’ Reganstated however that he has sought new legislation regarding soil management since 1994.While some changes have been made, Mr. O’ Regan feels it does not go far enough. Mr. O’Regan said the proposed new legislation had been taken seriously by minister for theenvironment, John Gormely. But, Mr. O’ Regan fears that moves to ratifying the legislationwill be delayed with the inevitable election of a different government. 10. On-Site Soil ManagementMost of the major impacts on soil properties happen as a result from activities that areassociated with construction (Pitty, A, 1979). Construction activity movement can haveadverse effects on soil in a number of different ways by, covering soil with resistantmaterials, effectively sealing it and resulting in important damaging impacts on the soils’these consist of physical, chemical and biological properties, and including the drainagecharacteristics, this contaminates the soil as a result of unintentional spillage when usingchemicals, or over-compacting soil whit the uses of heavy machinery and also the storage ofconstruction equipment, this reduces and worsening the soil quality in such ways as e.g. bymixing topsoil and subsoil together, wasting the soils when mixing it with eithercontaminated materials or construction waste, which has to be treated before the reuse oreven the disposal of it to a landfill if there is no other alternative (Mirsal, I, 2008).Fig. 10.1 Construction waste and heavy machinery 34
  35. 35. Even though the planning approval is always pre-requisite to all developmentproposals, considering the impact can have on the soil is very important in the environmentalassessment process as there is not a specific plan in place on the control and sustainability ofuse and management of soils on constructions sites (Environmental Protection AgencyIreland, 2008). Careful management is needed for topsoil and subsoil it is an important part ofsustaining the use of materials to be stripped, whether they are for sale off-site or for keepingon-site for using in later landscaping. If there is not a proper Soil Resource Plan then you arerunning the risk of losing, damaging or contaminating expensive soil resources (Defra, 2009). Topsoil is an essential resource and is an important component of most landscape jobswithin construction sites. It supplies an anchorage and oxygen for all plant roots; it releasesnutrients slowly, and, together with the underlying subsoil, keeps moisture to sustain ahealthy plant growth during long dry periods (Gobat, J, Aragno, M, Matthey, W, 2004). If re-usable soil resources are found on site they are stripped carefully to be reused on or off site.If topsoil’s are not stripped from areas that have potential for future construction sites, it cancause the project cost to increase. Subsoil is an important component of all soil. It provides moisture and storage, andlets rainfall into deeper horizon layers enabling trees, shrubs and grass to deep root. It alsohas a very important role in reducing surface water run-off and erosion, this is because waterlogging is controlled on the surface layers and that helps the vegetation and crops towithstand the dry summers, and provides a good planting base for tree (Defra, 2009)s. On most sites subsoil will not need to be stripped, but rather protected from damage,if found in areas that are designed for landscape plantings. On other constructions sites itmight have to be moved, reused or recycled if there are roads needed to haul and transportmaterials. It is vital for the landscape architect to clarify guidelines for onsite soil managementduring projects requiring earthworks. A set programme for best practice regarding soilmanagement would also be necessary if heavy machinery were involved on site. This is doneto avoid soil compaction and possible damage to tree roots. The landscape architect mustensure soil is stored in piles no higher than one metre (this height varies with practitioner).This is to keep the soil alive, otherwise compaction would occur under the soils own weight.This would lead to a loss of aerobic life and would detrimental to soil health. The landscapearchitect must also ensure, with regular on site inspections, that the topsoil and sub-soil arenot being mixed or stored together. This is done to maintain soil health (Defra, 2009). It isalso desirable for the landscape architect to seed the piles with grass seed. This is done tostop weed colonization on the soil storage piles. According to landscape architect Terry O’Regan, this is effective in the long run, in terms of maintenance (O Regan, 2009). 35
  36. 36. 11. SummarySoil is a finite resource that is used as a growing medium for plants and in the construction oflandforms cycle (Bennet, Sauer, Hampstead, 2001). Soil is essentially an ecosystem by itself,hosting large amounts of living organisms. For example, it is said that there are more livingorganisms in a teaspoon of soil, then all the humans who have ever lived. Soil is formed overhundreds, even thousands of years. Its properties and structures vary due to geographiclocation and the factors affecting its development (Pitty, A, 1979). A landscape architect must understand soil structure and properties to be able toimplement a successful planting system and indeed ensure any completed earthworks arestable and in no danger of slope failure, etc. Certain properties will influence the effects ofsoil on the surrounding environment and possible problems occurring in the future. Forexample, soil texture determines soil structure, from knowing the soil structure; a landscapearchitect can anticipate problems of leaching and high cation exchange capacity. Soil texturewill also indicate a soil’s buffering capacity and hence identify issues with soil pH.Properties of soil will invariably affect and influence other soil properties. For instance, howsoil pH affects the amount of nutrients available to plants (Gobat, J, Aragno, M, Matthey, W,2004). Soil remediation is a subject with increasing importance in the field of landscapearchitecture. This is due to a rise in the number of abandoned urban spaces being reclaimedand greened. These sites usually have poor soil structures with little nutrient content. Theuse of soil manipulation and strategic planting have redeveloped these areas through soilbinding, water retention and the addition of organic matter through natural decomposition ofplants (Mirsal, I, 2008). This shows the importance of successful plant growth in soils. Plantgrowth can also be used to stabilize, or bind soils, especially on slopes and in areas of highrainfall. Plant growth reduces run off, slows down the infiltration rate, increase aeration insoil and adds organic matter, hence improving soil structure (White, R, 2006). Manipulation and creation of soils through means of fertiliser, pH change andcomposting are effective methods, used by the landscape architect, to manage and improvesoils. The addition of fertilisers can improve plant growth and be a quick fix solution tonutrient deficiencies (Tracey, 2007). Fertiliser applications can also change pH. pH can bedesirable to manipulate when nutrients become unavailable due to pH extremes or when thesoil pH is not suitable for an intended planting system. pH can be manipulated by eitherorganic or chemical means. 36
  37. 37. Composting allows for the processing of raw organic material into a growing mediumthat improves structure and adds nutritional value to the soil. Composting can be effective inresidential schemes by reducing domestic organic waste output by up to a third (Tracey,2007). Current legislation in Ireland, regarding soil management and soil as a resource itself,is considered ineffective and inadequate (O Regan, 2009). 12. ConclusionSoil is a living medium that supports a variety of life by means of its applications as agrowing medium and through the natural process carried out within its biosphere by microorganisms to sustain themselves and the soils structure. Mismanagement of soil can lead tosoil damage which takes time, money, energy and knowledge to remediate (White, R, 2006). Successful soil management is the key to a sustainable, stable design. Understandingof soil and its needs will allow for a landscape architect to create earthworks and plantingsystems that are safe and appropriate. Only with understanding of the various soils and theireffects, can a successful design scheme be created by a landscape architect (Defra, 2009). Soil Remediation will come to the forefront of soil management practices in the nearfuture (Mirsal, I, 2008). With increasing land values in urban areas and lack of space, landreclamation, especially of industrial sites, will become an attractive option with the practiceof soil remediation. A larger number of cases involving soil erosion, salinization anddesertification will arise due to global warming, increasing urbanisation and the continuingintensification of agricultural practices in undeveloped countries (Pitty, A, 1979). Thepractice of soil remediation and its many methods provide effective results, for example, lookat the case study included in the appendix of this report. Concise, adequate legislation is needed in Ireland to ensure better soil managementpractices are not only encouraged, but enforced. This will result in healthier soil systems andsave time, money and energy in remediating problems such as compaction and replacing deadtrees/plants. New legislation will also allow for efficient use and storage of topsoil and avoidmixing and contamination of topsoil with sub-soils. The legislation must declare the soil ofIreland as a national resource and hence, must be protected as such. However, as stated in theinterview with Terry O’ Regan, it will be some years yet until the legislation needed isintroduced (O Regan, 2009). Soil is a complex, in depth subject that requires study and understanding. Alandscape architect can never call themselves an expert in the field of soil science. However,a landscape architect must be aware of the consequences of their actions concerningearthworks and the effect of planting systems on soil. Understanding of soil, its formation, function and limits will help the landscapearchitect develop sustainable designs involving earthworks and plantings. In the long term,adequate and appropriate soil management will save much energy and time in terms of 37
  38. 38. damaged soils (compaction) needing remediation. With increasing urbanisation, growingpopulations and a need for a larger food supply, the pressure on the earth’s soil is onlyincreasing. This makes the sustainable management of soil a necessity. Landscape architectsare paramount in the solution to soils problems. 13. References • Bennet, Sauer, Hampstead (2001). Soil Science Simplified. Iowa: Blackwell Publishing Professional. p9-95, p109-145. • Board, N (2004). The Complete Technology Book on Vermiculture and Vermicompost . Delhi: National Institute of Industrial Research. p1-14, p76-81, p254-260. • Brickell, C (2002). The Royal Horticultural Society Encyclopedia of Gardening. 2nd ed. London: Dorling Kindersley. p639-657. • Defra. (2009). Construction Code of Practice for the Sustainable Use of Soils on Construction Sites. Available: built-environ/documents/code-of-practice.pdf. Last accessed 12th December 2010. • Dunne, N, Buchanan, S (2009). Healthy Soils for Sustainable Gardens. Brooklyn: Brooklyn Botanic Garden. p6-25, p42-56, p58-67. • Environmental Protection Agency Ireland. (2008). Irelands Environment. Available: %20chap%2012.pdf. Last accessed 12th December 2010. • Gobat, J, Aragno, M, Matthey, W (2004). The living soil: fundamentals of soil science and soil biology. New Hampshire: Science Publishers Inc. p1-7, p13-31, p45-53, p70-72. • Hanson, B (2000). Easy Compost. 2nd ed. Brooklyn: Brooklyn Botanic Garden. p6-8, p21-50. • Kolay, A (2007). Manures and Fertilisers. Delhi: Atlantic Publishers and Distributors. p1-13. • Lamb, R. (2008). How Permaculture Works. Available: methods/permaculture.htm. Last accessed 4th • Lawton, G. (2003). Greening the Desert. Available: Last accessed 12th December 2010. 38
  39. 39. • Mirsal, I (2008). Soil pollution: origin, monitoring & remediation. 2nd ed. Germany: Springer-Verlag Berlin Heidelberg. p3-5, p10-11, p23-42, p47-54, p100-115, p117-122, p147-154, p273-280. • O Regan, T. (2009). National Landscape Forum. Available: http://landscape-forum- Last accessed 12th December 2010. • Pitty, A (1979). Geography and soil properties, . Cambridge: University Press. p1-35, p42-67, p69-77, p101-165, p174-195, p216-218. • Raviv, M, Lieth, J (2008). Soilless Culture: Theory and Practice. Amsterdam : Elsevier. p13-18, p253-256. • Tracey, D (2007). Guerrilla Gardening: A Manualfesto. Canada: New Society Publishers. p19-35, p186-193. • Wesley, L (2010). Fundamentals of Soil Mechanics for Sedimentary and Residual Soils . New Jersey: John Wiley and Sons Inc. p1-3, p37-40. • White, R (2006). Principles and practice of soil science: the soil as a natural resource. 4th ed. Oxford: Blackwell Publishing. p3-98, p112-128, p141-146, p 195-196, p200-202, p221-224, p233-258, p291-305, .13.1 Images • Fig. 3.1.1 Soil Formation. Available at: mation.jpg • Fig. 3.1.2 Decaying plant material. Available at: • Fig. Physical Weathering. Available at: Biologie/Botanik/tier_pfl_interak/meyer/Fragmentation3.jpg • Fig. Process of chemical weathering. Available at: http://www.icsu- • Fig. 5.1.1 Soil Texture Triangle. Available at: • Fig. Micro Pores and Macro Pores. Available at: • Fig. 6.1 Soil Map. Hengl T., 2003. Pedometric mapping: bridging the gaps between conventional and pedometric approaches. PhD thesis, University of Wageningen, Enschede, 214 pp. 39
  40. 40. • Fig. Available at: _Food_Web_Relocalization_files/soil%20in%20hand.jpg• Fig. Soil Horizons. Available at:• Fig. 6.4.1 Soil Map of Ireland. Available at: gxml! 0/2ocqn930ubywvi8z0wl9dhefnm6z926$sxq1ptbkcytdxx2q831o5m5a9mfccmm• Fig. 6.4.2 The Textural Triangle Soil Classification System. Available at:• Fig. 10.1 Construction waste and heavy machinery. Available at: of-practice.pdf. Last accessed 12th December 2010. 14. Appendix 40