the soil

República Bolivariana De Venezuela Ministerio Del Poder Popular Para La Educación Instituto Universitario Politécnico ―Santiago Mariño‖ Mérida_ Mérida

Yusveydy Villasmil (49) CI: 20.832.723

Introduction Soil is a natural surface layer that is capable of supporting plants. Soil forms the upper-most layer of the earth‘s crust and is made up of inorganic and organic matter. The world consists of 71% water and 29% land. Of the 29%, 5,8% are dry, cold ice deserts; 8,7% are warm sand and rock deserts and 5,8% are too steep to cultivate.

This leaves us with only 8,7% of land with an approximately 1m deep layer of soil to feed, house and sustain all the people of the earth (Harmse, 1987).

The inorganic components of soil are weathered rock, air, water and minerals. The organic matter is the decomposing fragments of plants and animals. The spaces between the small particles that make up the soil are filled with air or water. Living plants and animals live in the soil and improve aeration and drainage. Some organisms, such as bacteria, play an important role in converting plant foods or nutrients, e.g. nitrogen, into a form that plants can use to grow. Important plant foods include nitrogen (helps leaves and stems grow), phosphate (helps roots and fruits develop) and potassium (stimulates overall plant health). When plants die, they return the nutrients they initially absorbed from the soil, back to the soil, and enrich the soil. In this way soil plays a very important role in the recycling of nutrients (Enviro Facts, 1999i).

Soil takes thousands of years to develop from the parent rock – 10mm of soil takes between 100 and 1000 years to form. In South Africa 1mm of soil takes about 40 years to form. The time depends on the speed of weathering (parent rock being broken down into small particles). Weathering can be physical (frost, temperature changes, and salt chrystallisation), chemical (chemical action of water, oxygen, carbon dioxide and organic acids) or biological (tree roots that widen crevices and cracks).

The soil profile generally consists out of three main layers (horizons): thetopsoil (100 –200 mm deep) or darker layer, where air, water and humus allow plants to grow in; the sub-soil, a more claylike layer which acts as a reservoir (water store) for the plants, and the bedrock or parent material, which is the underlying layer from

which the first two horizons are formed. In South Africa sub-soil can be transported or residual, or both. Transported soil originates from wind, water or gravitational processes, while residual soils are the in situ (undisturbed) decomposed product of the underlying rocks. Soil horizons are set apart from other soil layers by differences in physical and chemical composition, organic structure, or a combination of those properties. Soil horizons are developed by the interactions, through time, of climate, living organisms, and the configuration of the land surface (relief) (Strahler & Strahler, 1992).

A city, like Greater Johannesburg, is an artificial man-made environment, dependent on technology and imported energy. The system is kept at an artificial equilibrium, and depends on the surrounding soil, agriculture and natural resources to ensure its wellbeing and sustain economic development. Soils are unfortunately deteriorating at an alarming pace due to poor management practices.

What is soil?

Soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics.

Soil is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. Soil differs from its parent rock due to interactions between the lithosphere, hydrosphere, atmosphere, and the biosphere. It is a mixture of mineral and organic constituents that are in solid, gaseous and aqueous states. Soil is commonly referred to as dirt.

Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas).

Accordingly, soils are often treated as a three state system. Most soils have a density between 1 and 2 g/cm. Soil is also known as earth: it is the substance from which our planet takes its name. Little of the soil composition of planet Earth is older than the Tertiary and most no older than the Pleistocene. In engineering, soil is referred to as regolith, or loose rock material.

Soil classification system Soil is classified into categories in order to understand relationships between different soils and to determine the usefulness of a soil for a particular use. One of the first classification systems was developed by the Russian scientist Dokuchaev around 1880. It was modified a number of times by American and European researchers, and developed into the system commonly used until the 1960s. It was based on the idea that soils have a particular morphology based on the materials and factors that form them. In the 1960s, a different classification system began to emerge, that focused on soil morphology instead of parental materials and soilforming factors. Since then it has undergone further modifications.

The World Reference Base for Soil Resources (WRB)] aims to establish an international reference base for soil classification.

USDA Soil Taxonomy In the United States, soil orders are the highest hierarchical level of soil classification in the USDA Soil Taxonomy classification system. Names of the orders end with the suffix -sol. There are 12 soil orders in Soil Taxonomy:[25]

* Entisol - recently formed soils that lack well-developed horizons. Commonly found on unconsolidated sediments like sand, some have an A horizon on top of bedrock. * Vertisol - inverted soils. They tend to swell when wet and shrink upon drying, often forming deep cracks that surface layers can fall into. * Inceptisol - young soils. They have subsurface horizon formation but show little eluviations and illumination.

* Aridisol - dry soils forming under desert conditions. They include nearly 20% of soils on Earth. Soil formation is slow, and accumulated organic matter is scarce. They may have subsurface zones (calcic horizons) where calcium carbonates have accumulated from percolating water. Many aridiso soils have well-developed Bt horizons showing clay movement from past periods of greater moisture. * Mollisol - soft soils with very thick A horizons. * Spodosol - soils produced by podsolization. They are typical soils of coniferous and deciduous forests in cooler climates. * Alfisol - soils with aluminium and iron. They have horizons of clay accumulation, and form where there is enough moisture and warmth for at least three months of plant growth. * Ultisol - soils that are heavily leached. * Oxisol - soil with heavy oxide content. * Histosol - organic soils. * Andisols - volcanic soils, which tend to be high in glass content. * Gelisols - permafrost soils.

The soil uses Soil is used in agriculture, where it serves as the primary nutrient base for plants; however, as demonstrated by hydroponics, it is not essential to plant growth if the soil-contained nutrients could be dissolved in a solution. The types of soil used in agriculture (among other things, such as the purported level of moisture in the soil) vary with respect to the species of plants that are cultivated.

Soil material is a critical component in the mining and construction industries. Soil serves as a foundation for most construction projects. Massive volumes of soil can be involved in surface mining, road building and dam construction. Earth sheltering is the architectural practice of using soil for external thermal mass against building walls.

Soil resources are critical to the environment, as well as to food and fiber production. Soil provides minerals and water to plants. Soil absorbs rainwater and releases it later, thus preventing floods and drought. Soil cleans the water as it percolates. Soil is the habitat for many organisms: the major part of known and unknown biodiversity is in the soil, in the form of invertebrates (earthworms, woodlice, millipedes, centipedes, snails, slugs, mites, springtails, enchytraeids, nematodes, protists), bacteria, archaea, fungi and algae; and most organisms living above ground have part of them (plants) or spend part of their life cycle (insects) belowground.

Above-ground and below-ground biodiversities are tightly interconnected, making soil protection of paramount importance for any restoration or conservation plan.

The biological component of soil is an extremely important carbon sink since about 57% of the biotic content is carbon. Even on desert crusts, cyanobacteria lichens and mosses capture and sequester a significant amount of carbon by photosynthesis. Poor farming and grazing methods have degraded soils and released much of this sequestered carbon to the atmosphere. Restoring the world's soils could offset some of the huge increase in greenhouse gases causing global warming while improving crop yields and reducing water needs.

Waste management often has a soil component. Septic drain fields treat septic tank effluent using aerobic soil processes. Landfills use soil for daily cover. Land application of wastewater relies on soil biology to aerobically treat BOD. Organic soils, especially peat, serve as a significant fuel resource; but wide areas of peat production, such as sphagnum bogs, are now protected because of patrimonial interest.

Both animals and humans in many cultures occasionally consume soil. It has been shown that some monkeys consume soil, together with their preferred food (tree foliage and fruits), in order to alleviate tannin toxicity.

Soils filter and purify water and affect its chemistry. Rain water and pooled water from ponds, lakes and rivers percolate through the soil horizons and the upper rock strata; thus becoming groundwater. Pests (viruses) and pollutants, such as persistent organic pollutants (chlorinated pesticides, polychlorinated biphenyls), oils (hydrocarbons), heavy metals (lead, zinc, cadmium), and excess nutrients (nitrates, sulfates, phosphates) are filtered out by the soil.] Soil organisms metabolize them or immobilize them in their biomass and necromass,[41] thereby incorporating them into stable humus. The physical integrity of soil is also a prerequisite for avoiding landslides in rugged landscapes.

Problem and current state of soil in MĂŠrida Environmental problems have been living on the planet alarm speakers in all mankind, in this sense, the lack of awareness about the exploitation of our natural resources, many of them nonrenewable, has been influential to modern environmental situation seek new horizons that allow a shift to new ways of: consumer, agricultural issues, energy, rationality, sustainability and other tools that may help to enhance the changes in terms of natural resource exploitation on a global level.

Starting from the idea of thinking globally to act locally, is that we propose in the following lines to analyze the current environmental problems in Pueblo Llano, Merida State, paramere agricultural empire, to somehow make it clear that while the problem Global Green is there very specific contaminant sources that can be controlled and thus contribute effectively to thrash a new path full of ecological rationality, we all want to build.

Pueblo Llano and agriculture Pueblo Llano was founded in 1559 by Juan de Maldonado. Since pre-Hispanic times this portion of the territory of Merida, like the rest of the high northern state, has been influenced by agricultural activity, which has determined the economic characterization of these mountain villages. In recent decades, as in other parts of the world, the American Andes and the Venezuelan Andes, this city, has undergone a modernization process in the production of their soils and crops, which has influenced the most diverse levels of social life, but especially on agricultural productivity. In this sense, Santiago (1989) states: Changing this system began in the early sixties with the arrival of some farmers originally from the Canary Islands, who leased land and introduced white potato (Solanum tuberosum), sprinkler irrigation, chemical fertilizers, biocides and agricultural machinery. For the seventies, and agriculture in this area moved towards a fully integrated trading system to national economic circuit, through the marketing of crops.

It is from this point that Pueblo Llano accessed in conjunction with other municipalities parameros as Mucuchies (Rangel) and Timotes (Miranda), the national commercial stage, as major producers and suppliers of potatoes, carrots and vegetables. But beyond this, these locations are also incorporated to the dynamics of global capitalism, so far only accelerate matter crops, not only to meet the demands of the domestic market to boost profits that, on this activity, generated. In this regard, much of the population of this county is in addition to their own consumerist attitude of the capitalist model. The modernization of agriculture, then, is the

engine driving economic and demographic changes, the tradition will be phased out to make way for modern life as a model.

As we mentioned in previous row, it must be some reasons why this upstate resort area many canaries in an attempt to work the land and settle in its environment: the Spanish domestic agricultural economy strongly resented, since the late fifth decade of the twentieth century, when Franco‘s political regime in Spain found itself isolated as the Portuguese dictatorial fascism, solidified by the democracies of the east of the old continent. Although metals Catalan and Basque modernized, industrialized and grew significantly in urban areas, Hispanics lagging regional economies, which were those of Galicia and the Canary Islands, were quickly impoverished with significance, since European countries have enacted a sort of boycott Spanish agricultural production and weak external demand caused severe primary impact on the Galician and island economies. Thus large contingents of Galicia and Canary migrate to the American mainland and insular Caribbean, with large contingents of Portuguese, especially the islands of Madeira and Azores Lusas.

Specifically, the canaries peasant migrants arrived in Venezuela were established on the shaft Aragua, Carabobo, Lara, Yaracuy, Portuguesa, Barinas, Trujillo and Merida, where they were economically and technically supported by a powerful merchant Gran Canaria: Enrique Fraga, owner signature ―Agro Islander‖, an importer and distributor of seeds, insecticides, fungicides, herbicides, fertilizers and tools for farming, all of which has put his compatriot credit. Pueblo Llano, Merida was Mucuchies and branches of this firm.

Pueblo Llano incorporating the national stage as a major producer of potatoes and carrots is marked by great effects and ecological and human consequences. The expansion of the agricultural frontier that annually kills large reservoirs of natural trees in this area, pollution of drinking water that makes the central town of the population and rationing such liquid, the measurement does not load of these lands, which depletes the consumption of this vital liquid, due to the effects of pollution caused by agriculture, genetic malformations seen in many children of farmers who

practice agriculture, and the high dropout rates of children and youth, as a result of pledges quick wealth offered by this activity, the great swarms of flies, extra fertile compost product, as the vulture, invading homes and streets and bring many gastrointestinal diseases, cutaneous and visual discomfort in addition to producing this pest, are some prices of high prices has had to pay the municipality to enter through the front door and stay on modernization. In this vein, Romero (2003) tells us about: potato farming that has shaped technology packages under the focus of the famous green revolution to ensure the rapid reproduction and circulation of capital compared to more recent processes of modernization and monetization of agriculture mumps, sudden changes and rapid enrichment reflected in a chaotic distribution of housing in a high fragmentation of agricultural plots in the circulation of a considerable volume of high-cost cars and deplorable references intoxication, alcoholics and dropouts from formal education.

Thus, the social costs that you have to pay the people of this county in an effort to incorporate and dynamic presence in the capitalist world are very high indeed. It makes us think that the wealth that these people earn, is just as economically, no matter, the ecological, health, social or cultural, critical for optimal quality of life, complete. Not only money is enough when the recreation and health, for example, are threatened by capitalist irrationality or rationality, for towns that have forgotten their connection with nature, seeing it merely as a means of generating wealth, where acculturation has invaded to the cult of San Isidro Labrador, ultimate party of farmers, which today includes among its exhibits tractors symbol of pollution and environmental degradation, robbing the place to oxen harmless and useful as ever. Ultimately Santiago (1989) states: The inhabitants of this area practice intensive agriculture with advanced techniques if you will, but with many mistakes in conservation practices, use of biocides and fertilizers, this means low yields and high harvest costs and low quality of water used for consumption human.

Coupled with this, we can add that high income people hit by the population llanera sprawl has created a motor car park, as well as increase pollution, carbon dioxide product, also adds noise pollution, then it seems that displaying new cars, with loud sounds is one of a kind of hierarchy in society. This is compounded by traffic congestion and what appears to be an evil of large cities, now moves to calm small towns feature affecting them.

Moreover, the suicide rate appears to be another feature of the life of this society, the presence of agrochemicals in inappropriate places within households of this population means that many young people make the determination to end their lives before the inability to deal with the problems of existence, other cases are incidental to the lack of hygiene when storing and subsequently working in the spraying of crops, the produce is not adequate protection, in many cases , household members to become intoxicated and traveling to the death.

The rapid social and economic access to certain economic levels among young people, makes many of them try to build lives with a partner, leading to sporadic leaks young ladies, being discovered by parents, forcing them to marry or live independently of them . This scenario outcomes as the pregnancy, pretty sure these girls, neglect of their studies, or multiplication of single mothers, with no clear future within society and of children without decent future.

This order of ideas and the growing current agricultural modernization in Pueblo Llano raises two basic scenarios: first, confined to a highly polluting agriculture, predation and poor quality. And, second, an agricultural activity in the service consumers in big cities, which has failed in its promises of progress espoused by the global capitalist discourse. Thus, the tax scenario in this town not far away from the crisis, which from an environmental perspective, it is experiencing the world. This reminds us of the need for a rational change in endogenous development and eco-development tools that allow a balance between the destructive forces of irrational agricultural activity and new approaches of sustainability that are driving global.

Pueblo Llano: options for change The phenomenon that we have previously attempted to analyze, on a non-isolated Pueblo Llano due, as we have wanted to see, global forces focusing on economic models that have been implemented by the so-called developed countries, which seek to guarantee the consumption levels their societies. In this sense, there has been an international division of labor, where for example, Latin America has played the role of exporter of raw materials, which are then imported and manufactured goods. In the case of the Venezuelan Andes, and specifically the top of Merida State, agriculture is the main activity in this region is inserted to the global dynamics. In this vein, Martinez (1992) explains: Could actually write the ecological history of Latin America not as a history of degradation caused by over-population, but as a history of exports at the expense of natural capital, an ecological history of dependence. South penetration by new technologies of agricultural production, marketing and contract farming has served changes in agriculture in some areas of America.

According to this, our people have been setting the mood, and they have been imposed forms of modernization without any regard to preventing the harmful aspects that this process contains. Nor is taken into account the views of farmers, much less has been properly advised about the handling of fertilizers, fungicides or any other product of modern package for agriculture. In short, there is created a real awareness about this model, which viewed from one perspective that is none other than from the economic expressed in profit. In this regard, Leff (2000) adds: The economic rationale banished to the nature of the sphere of production, generating processes of ecological destruction and environmental degradation. The emerging concept of sustainability and recognition of the role of nature as a support, status and potential of the production process.

Little matter, in this context, the preservation of natural resources essential for the survival of the species. For this reason is that the proposed eco-development, as a term that invites you to take into

account natural access to a balanced development of societies with their environment is important: take into account the carrying capacity of a given region, to know how can provide resources and support, existing there for the life of its inhabitants. This practice certainly can benefit from this essential balance and needed to stop abuses in our ecosystems. In this sense, Leff (2000) states: The discourse of sustainability thus seeks to reconcile the opposites of the dialectic of development: environment and economic growth [Seeks] to proclaim the economic growth as a sustainable process, based on free market mechanisms as an effective means to ensure ecological balance and social equity.

This is to guarantee to future generations their right to make available and use natural resources, which are now endangered. It is also of ecological rationality possible to assess the impact on our resources, not from a single view, but from different perspectives, the ecological and social, for example. It is here, then, where education plays key role, then how can we change our minds, when at school or colleges where they form the new generations do not have educational programs that address specific problems of the headquarters locations of education institutions.

In effect, we find that in these places like Pueblo Llano, industrial pollution is indirectly deep; little studied or simply not investigated the problems of agricultural pollution, because the teachers only work with text books removed from its reality, ie there is a social membership. Accordingly, we believe that a change of rationality is closely related to a political will to, in education, focusing on their immediate realities and then access other contexts, regional, national and global. Here arises relevance in societyeducation-welfare.

Studies in the Social Sciences for contributing to possible solutions have been traditionally performed away from the areas where the phenomena are developed and then the suggestions have not arrived and has not sought rapport with the peasant or farmer .

Thus, Rhoades (2006) states:

In this paradigm, agricultural researchers defined, in large part the problem from their desks at remote sites. Farm families were transformed into passive recipients of the scientific, and social scientists were assigned the task of preparing invoices ex post studies on how farmers reacted to the technology introduced.

In this regard, efforts should be made that the researcher is incorporated in societies where environmental pollution has punctuated foci. Is this viable alternative to avoid the imposition and bet on the dialogue among key actors in the process that is unfolding? In this way, farmers engage with the researcher, and vice versa, taking care to clear the ecosystem to recover. All this will enable more effective action to ensure viable models for ecodevelopment corporations or towns, such as the Plain People.

While our attention has been focused on outbreaks of agricultural development, and development in the town folk, we must not forget, as we have said, that our reality depends largely on a global scale models. In this regard, it is essential to appreciate that they are also called developed countries which have great responsibility for the changes to come. The fact considers Sachs (1982) The search for alternative development involves the simultaneous restructuring of consumption patterns and lifestyles (ie, from the demand side) and the production function (from the supply side), focused on a broad sense, as capable of including technology choices with models of spatial distribution of production activities.

We are thus in the presence of organizational forms that must change to favor not only of their own societies, but of all humanity because if we talk about degrees of destruction and contamination are precisely those countries that bear the main responsibility, and they are calls to take more responsibility for the transformations that the moment demands. In this regard, one must think globally to act locally, it is our premise. But it would be healthier for future generations will appreciate that there is a change of the major powers for a future and a universal right and it should be inserted the companies involved in everything possible.

In turn, Pueblo Llano, like many villages in the Andes who have dedicated themselves to agriculture as a means of existence, now represents the focus where irrationality has undermined the most intimate fibers of a worldview, which in the past , seeking the balance between man and nature. Today, those ties have been broken to make way alarming situations from the standpoint of environmental and human. We are confident that other paths are about to open for traffic in these towns, roads that allow no doubt to the new generations to enjoy, enjoy, work as did human groups in ancient times.

We are also confident that new generations aware of the serious mistakes committed by their ancestors, are willing to change that will result in the lost balance between man and his environment. We also believe that education must rise to the claims homogenizing and open debate among young people, this they have and the future they want, well, something more than colorful parades, may be made for these sectors begin to emerge. In short, it is appropriate and consonant with educational training, with government measures and genuine participation of those affected, as can be changed for the better, the worrying state of the community subject to these considerations, but even more troubling his immediate future.

Glossary of basic terms with Their Respective Drawings ďƒ˜

Soil Acidity: Soil pH, or soil acidity, is one of the principal influences for good or bad in soil. This used to be the province of scientists and chemistry students, but over the years it has become part of the home gardener's everyday world. In many, many cases, soil pH is the key to proper plant growth, and a reading of soil acidity can tell you much about what is going on beneath the surface of your garden.

ďƒ˜ Agrological classification: classification of land in classes with use similar capabilities which serve to order the choice of use and management alternatives.

 Hardness: quality of water containing dissolved of calcium and magnesium mainly.

 Runoff:

that runs of the soil surface when precipitation exceeds soil infiltration capacity.

 Soil fertility: quality that enables a soil to supply the compounds needed in quantities suitable and balanced appropriately for the specific plant growth, with favorable other factors such as light, and soil physical conditions.

ďƒ˜ Organic matter: a general term applied to animal or plant material in any state of decomposition that is on or in the ground.

ďƒ˜ Oxidation: any chemical change in which verifies the addition of oxygen or its chemical equivalent, in which there was an increase of the valance positive or decreased negative.

 Topsoil:

that part of the upper soil horizon between 25 and 40cm which is removed with farming tools.

 Soil: natural body composed of mineral and organic materials placed on the surface of the earth‘s crust in which plants grow.

 Soil texture: relative proportions of sand, silt and clay in soil, according to which textural classes are sorted based on the number and size of particles possess.

Training ground Soil is a dynamic structure composed of organic and mineral materials, serves to support the plants and provides nutrients needed for growth. The floor is made largely after solid, liquid, gaseous and colloid.

The solid state: Is made up of organic substances such as microorganisms, humus, earthworms and ants, and inorganic minerals formed as the degradation of the rock on which is the ground, they vary in size, such as sand, silt and clay, aluminum, iron.

The liquid state: Is made up of water, which is an important regulator of physical activity, chemical and biological occurring there also involved in the weathering of rocks and soil formation, water dissolves the nutrients that are taken by plant tissues and is essential in photosynthesis.

The gaseous state: Is represented by air and gases released in the biochemical reactions that occur in it. Air occupying the soil pores.

The porosity decreases with the contact, the silting of the soil. The roots of plants and animals activity underground increases the porosity of the soil, including soil gases have carbon dioxide hydrogen sulfide, ammonia, methane.

The colloidal state is made up of soil organic colloids such as humus, clay. The colloidal state is an intermediate state between solid and liquid, are responsible for the chemical activity, ie exchange of nutrients like calcium, magnesium, sodium, potassium, aluminum, iron, nitrites, nitrates, phosphates and sulfates and of these exchanges depends on soil fertility. The colloidal humus from the decomposition of organic matter.

The importance of soil The life sustaining ability of soil is best understood by appreciating the complex cycles of decay and erosion. Its natural formation occurs in a series of layers starting at the surface but gradating down to the deepest bedrock. The surface layer is where active decomposition begins. Exposure to atmospheric elements, surface warmth and moisture helps to break organic matter into loose mulch like material. At the microscopic level, this layer is teeming with a diversity of bacterial, fungal and algal life forms. In combination with larger organisms like beetles and worms they provide the additional recycling activity to enable minerals and nutrients to be retrieved from the decaying organic matter and

returned to the soil. Another family of soil based micro-organisms is involved in relationships that enable plants to absorb nitrogen from their roots.

Ideally the layer directly beneath the surface will be humus rich topsoil. The quality of this topsoil will depend on the amount of organic material available near the surface and the activity of the recycling organisms.

A coastal rainforest provides almost ideal conditions for the creation of richly fertile topsoil. With increased temperatures and humidity an abundance of organic material reaching the ground begins to decompose almost immediately. It is then broken down by organisms which thrive under the conditions. The entire process is accelerated resulting in a generous layer of finely blended topsoil.

A descent through deeper soil layers will reveal gradually decreasing quantities of humus before reaching the substratum of bedrock. Deep layers contribute to the surface quality of soil by providing mineral particles and compounds through erosion. The deep layers also support the structure of the soil by providing its foundation and drainage characteristics.

A technical analysis of structure can isolate the important layers of soil, their relationship to each other, aeration and drainage characteristics along with the mineral components characteristic to a particular location. It can also indicate the comparative rates and efficiency

for

recycling

organic

material.

Information

about

structure will assist the serious gardener to predict how soils behave under varying seasonal conditions.

Soil type is a classification based on the major particle constituent along with the average pH reading. The most typical examples of soil type are sand, clay, and silt based. In some respects this information has limited value because soils tend to vary significantly across regions even when described to be of similar type. This is where an understanding of structure will provide a

clearer picture. From the perspective of the organic grower, good soil structures need to be protected. This can be achieved by minimising digging, replacing disrupted layers in their correct order when necessary and renewing surface layers by providing a supply of organic material such as compost and manure. The addition of organic material will improve the water and nutrient holding ability of the soil.

The structure of the ground The interior of the planet, like the other terrestrial planets (planets whose volume is occupied mainly of rocky material), is divided into layers. The earth has an outer crust solidified silicate, a viscous mantle and a core with two layers, an outer semi-solid, much m0re fluid than the inner mantle and a solid. Many of the rocks which now form part of the crust formed less than 100 million (1 Ă— 108) years. However, the oldest known mineral formations are 4,400 million (44 Ă— 108) years, which indicates that, at least, the planet has had a solid crust from then.

Much of our knowledge about the interior of the Earth has been inferred from other observations. For example, the force of

gravity is a measure of the landmass. After knowing the volume of the planet, we can calculate its density. The calculation of mass and volume of surface rocks, and water bodies, allow us to estimate the density of the outer layer. The mass is in the atmosphere or in the crust must be in the inner layers.

Structure: The soil structure can be set according to two different criteria.

According to their chemical composition, the planet can be divided into crust, mantle and core (external and internal), according to their

physical

properties

are

defined

in

the

lithosphere,

the

asthenosphere, the mesosphere and the core (external and internal).

The layers are at the following depths: Layer

Depth (km)

varies

0-60

Crust (locally varies between 5

0-35

Lithosphere

(locally

between 5 and 200 km)

and 70 km) Partuppermantle

35-60

Mantle

35-2890

Uppermantle

35-660

Asthenosphere

100-200

Lowermantle (mesosphere)

660-2890

Outercore

2890-5100

Innercore

5100-6378

The divisionof land inlayershas been determinedindirectlyusing thetraveltime it takesseismic wavesreflected andrefracted, created by earthquakes.Shear waves(S,or secondary)can not pass throughthe core,because they needaviscous orelasticmaterialto spread,while the speedof propagation isdifferent inthe other layers.Changes inspeed producesuchrefractiondue toSnell's law. The reflectionsare caused bya large increase inseismic velocity(velocityof propagation)and are similar tothe light reflected froma mirror.

Layersdefined bycomposition Crust The crustiscomparativelythinlayer, its thicknessranges from 3kmat mid-ocean and 70kmin largeterrestrialmountain rangeslike the

Andesand

theHimalaya.

The

bottoms

of

themajor

ocean

basinsare formed byoceanic crust,with an average thicknessof 7km, is composed ofmaficrocks(iron and magnesium silicates) with an average densityof 3.0g/cm3.

The

continentsare

made

up

ofcontinental

crust,which

is

composed offelsicrocks(silicateof sodium, potassium and aluminum), lighter, with an average densityof 2.7g/cm3.

The

boundary

twophysical

betweencrust

phenomena.First,there

and is

mantleis a

manifested

in

discontinuityinseismic

velocity, which is known as theMohorovicicdiscontinuityor "Moho".

It is believedthat this phenomenon isdue to a changein the composition ofrocks,somecontainingplagioclase feldspar(locatedat the top)

to

other

feldsparshavenot(at

thebottom).Second,there

isa

discontinuitychemistryandharzburgiteultramafictectonizadascluste rs, which has been observed indeeper partsof oceanic crustthat have beenobducidaswithinthe asophiolitesequences.

Earth‘s mantle

continental

crust

andpreserved

The mantle extends to a depth of 2,890 km, making it the largest layer of the planet. The pressure in the lower mantle is about 140 GPa (1.4 M atm). The mantle consists of silicate rocks richer in iron and magnesium than the crust. The high temperatures cause the siliceous materials are ductile enough to flow, even at very large scales.

Mantle

convection

is

responsible,

on

the

surface,

the

movement of tectonic plates. As the melting point and viscosity of a substance depends on the pressure he is under the lower mantle moves with more difficulty than the upper mantle, but also the chemical changes may be important in this phenomenon. The viscosity of the mantle varies between 1021 and 1024 Pa · s. 4 For comparison, the viscosity of water is approximately 10-3 Pa.s, illustrating the slow moving mantle.

Why the inner core is solid, the outer liquid, semisolid and the mantle? The answer depends on the melting points of the different layers (nickel-iron core, mantle and crust of silicates) and the increase in temperature and pressure as we move toward the center of the Earth. On the surface, both the iron-nickel alloys such as silicates are cool enough to be solid. In the upper mantle, the silicates are generally solid (though there are places where melting points), but since they are under high temperature and relatively low pressure, the upper mantle rocks have a relatively low viscosity. In contrast, the lower mantle is under much higher pressure, which means it has a higher viscosity compared to the upper mantle.The outer core, consisting of iron and nickel, is liquid despite the pressure because it has a melting point lower than the silicate mantle. The inner core, for its part, is solid because of the enormous pressure at the center of the planet.

Earth‘s core The average density of earth is 5515 kg/m3. This figure makes it the densest planet in the solar system. Considering that the average density of the crust is approximately 3.ooo kg/m 3, we assume that

the Earth's core must be composed of denser material. Seismological studies have provided further evidence of the density of the nucleus.

In its early stages, about 4,500 million years, more dense materials, melted, would have sunk into the nucleus in a process called planetary differentiation, while others have migrated to less dense crust. As a result of this process, the core is composed largely of iron (Fe) (80%), along with nickel (Ni) and several lighter elements. Other, more dense, like lead (Pb) and uranium (U) are very rare, or remained on the surface attached to other lighter elements.

Various seismic measurements show that the core is composed of two parts, a solid internal radio of 1,220 km and an outer layer, which reaches semi 3,400 km. The solid inner core was discovered in 1936 by Inge Lehmann and is believed more or less unanimous which is composed of iron with some nickel. Some scientists believe that the inner

core

could

be

in

the

form

of

a

crystal

hierro.

The outer core surrounds the inner and is believed to be composed of a mixture of iron, nickel and other lighter elements. Recent proposals suggest that the innermost part of the core could be enriched with heavy elements with higher atomic number than the cesium (Cs) (trans-Cs, elements with atomic numbers greater than 55). This would include gold (Au), mercury (Hg) and uranium (U).

It was accepted, in general, the movements of convection in the outer core, combined with the movement caused by the Earth's rotation (Corioliseffect), are responsible for Earth's magnetic field, through a process described by the hypothesis of the dynamo. The inner core is too hot to maintain a permanent magnetic field (see Curie temperature) but probably stabilize created by the outer core.

Recent evidence suggests that the inner core rotate slightly faster the rest of planet. In august 2005 a group of geophysicists published in the journal science that, according to his calculations, the inner core rotates approximately 0.3 and 0.5 degrees per year than the corteza.9 10 The latest scientific theories explain the temperature

gradient of the Earth as a combination of the remaining heat of the planet's formation, heat produced by the decay of radioactive elements and cooling inner core.

Soil Horizon A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation (horizonation) is a function of a range of geological, chemical, and biological processes and occurs over long time periods. Soils vary in the degree to which horizons are expressed. Relatively new deposits of soil parent material, such as alluvium, sand dunes, or volcanic ash, may have no horizon formation, or only the distinct layers of deposition. As age increases, horizons generally are more easily observed. The exception occurs in some older soils, with few horizons

expressed in deeply weathered soils, such as the oxisols in tropical areas with high annual precipitation.

Identification and description of the horizons present at a given site is the first step in classifying a soil at higher levels, through the use of systems such as the USDA soil taxonomy or the Australian Soil Classification. The World Reference Base for Soil Resources lists 40 diagnostic horizons.

The term 'horizon' describes each of the distinctive layers that occur in a soil. Each soil type has at least one, usually three or four horizons and these are described by soil scientists when seeking to classify soils. Horizons are defined in most cases by obvious physical features, colour and texture being chief among them. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e., ‗coarser‘ or ‗sandier‘ than the horizons above and below.

Most soils conform to a similar general pattern of horizons, often represented as an ‗ideal‘ soil in diagrams. Each main horizon is denoted by a capital letter, which may then be followed by several alphanumerical modifiers highlighting particular outstanding features of the horizon. While the general O-A-B-C-R sequence seems fairly universal, some variation exists between the classification systems in different parts of the world. In addition, the exact definition of each main horizon may differ slightly – for instance, the US system uses the thickness of a horizon as a distinguishing feature, while the Australian system does not. It should be emphasised that no one system is more correct – as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. The World Reference Base for Soil Resources lists 40 diagnostic horizons.

The term 'horizon' describes each of the distinctive layers that occur in a soil. Each soil type has at least one, usually three or four horizons and these are described by soil scientists when seeking to classify soils. Horizons are defined in most cases by obvious physical features, colour and texture being chief among them. These may be described both in absolute terms (particle size distribution for

texture, for instance) and in terms relative to the surrounding material, i.e., ‗coarser‘ or ‗sandier‘ than the horizons above and below. Most soils conform to a similar general pattern of horizons, often represented as an ‗ideal‘ soil in diagrams. Each main horizon is denoted by a capital letter, which may then be followed by several alphanumerical modifiers highlighting particular outstanding features of the horizon. While the general O-A-B-C-R sequence seems fairly universal, some variation exists between the classification systems in different parts of the world. In addition, the exact definition of each main horizon may differ slightly – for instance, the US system uses the thickness of a horizon as a distinguishing feature, while the Australian system does not. It should be emphasised that no one system is more correct – as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner.

Land classification The land classification is defined as being a cartographical delineation of distinct ecological areas, identified by their geology,

topography, soils, vegetation, climate conditions, living species, habitats, water resources, as well as anthropic factors. These factors control and influence biotic composition and ecological processes.

This five class system used by NSW Agriculture classifiesland in terms of its suitability for general agriculturaluse. This system was

developed

specifically

to

meet

theobjectives

of

the

Environmental Planning and AssessmentAct 1979, in particular 5(a) (i)

‗to

encourage

conservation

of

the

propermanagement,

naturaland

man-made

development

resources,

and

including

agricultural land...forthe purpose of promoting social and economic welfare ofthe community and a better environment‘.

Agricultural land is classified by evaluating biophysical,social and economic factors that may constrain theuse of land for agriculture. In general terms, the fewerthe constraints on the land, the greater its value foragriculture. Each type of agricultural enterprise has aparticular set of constraints affecting production.

Acomprehensive list of all the constraints affecting eachform of agriculture would be expensive to compileand unwieldy to use.

Consequently, agricultural landclassification is based on a set of constraining factorscommon to most agricultural industries. Section 6.3iii‗Factors

that

influence

agricultural

suitability‘

lists

thesefactors.Some types of agricultural enterprises do not dependon land suitability and so are not included in this system.Such activities include intensive animal industries (poultry,pig and cattle feedlots) as well as nurseries, glasshouses,hydroponics and mushroom sheds.

NSW Agricultureand other agencies produce guidelines that address sitingand management issues for these industries. However,many of these industries use agricultural land to manageeffluent and provide a buffer zone, so agricultural landclassification is still relevant.It is an inherent feature of agricultural landclassification maps that they have a limited life. The lifespan of the maps depends on changes to the biophysical,social and economic factors. For example, if an areaclassified as Class 3 agricultural land because of itsability to

support

occasional

cropping

becomes

affectedby

salinity,

and

therefore becomes no longer suitablefor cropping, it would need to be reclassified as Class 4agricultural land.In practice it takes a significant

and

widespread

changeof

the

factors

to

affect

agricultural land classificationmaps. This is due to the scale of the mapping andthe consideration of future trends at the time of mappreparation. The types of changes that affect agriculturalland classification maps are usually slow, so the mapsproduced are suitable for use for a number of years.

Agricultural land classification maps produced at smallscales (1:50,000 to 1:100,000) are useful for strategicplanning, including regional and local environmentalplanning instruments, regional economic developmentand natural resource management. They are inappropriatefor

making

decisions

relating

to

individual

developmentapplications or minor rezoning proposals. These typesof applications involve decision making at the property level and require information at a scale of greater detailthan is available from these agricultural land classificationmaps. See Section 4 ‗Limitations of scale‘ for furtherinformation.

Layers Soil generally consists of visually and texturally distinct layers, which can be summarized as follows from top to bottom:

O) Organic matter: Litter layer of plant residues in relatively undecomposed form.

A) Surface soil: Layer of mineral soil with most organic matter accumulation and soil life. This layer eluviates (is depleted of) iron, clay, aluminum, organic compounds, and other soluble constituents. When eluviation is pronounced, a lighter colored "E" subsurface soil horizon is apparent at the base of the "A" horizon. A-horizons may also be the result of a combination of soil bioturbation and surface processes that winnow fine particles from biologically mounded topsoil. In this case, the Ahorizon is regarded as a "biomantle".

B) Subsoil: This layer accumulates iron, clay, aluminum and organic compounds, a process referred to as illuviation.

C) Parent rock: Layer of large unbroken rocks. This layer may accumulate the more soluble compound.

O horizon The "O" stands for organic. It is a surface layer, dominated by the presence of large amounts of organic material in varying stages of decomposition. The O horizon should be considered distinct from the layer of leaf litter covering many heavily vegetated areas, which contains no weathered mineral particles and is not part of the soil itself. O horizons may be divided into O1 and O2 categories, whereby O1 horizons contain decomposed matter whose origin can be spotted on sight (for instance, fragments of rotting leaves), and O2 horizons containing only well-decomposed organic matter, the origin or which is not readily visible.

P horizon These horizons are also heavily organic, but are distinct from O horizons in that they form under waterlogged conditions. The ―P‖ designation comes from their common name, peats. They may be divided into P1 and P2 in the same way as O Horizons. This layer

accumulates iron, clay, aluminium and organic compounds, a process referred to as illuviation.

A horizon The A horizon is the top layer of the soil horizons or 'topsoil'.

This layer has a layer of dark decomposed organic materials, which is called "humus".The technical definition of an A horizon may vary, but it is most commonly described in terms relative to deeper layers.

"A" Horizons may be darker in color than deeper layers and contain more organic material, or they may be lighter but contain less clay or sesquioxides. The A is a surface horizon, and as such is also known as the zone in which most biological activity occurs. Soil organisms such as earthworms, potworms (enchytraeids), arthropods, nematodes, fungi, and many species of bacteria and archaea are concentrated here, often in close association with plant roots. Thus the A horizon may be referred to as the biomantle.[3][4] However, since biological activity extends far deeper into the soil, it cannot be used as a chief distinguishing feature of an A horizon.

E horizon ―E‖, being short for eluviated, is most commonly used to label a horizon that has been significantly leached of its mineral and/or organic content, leaving a pale layer largely composed of silicates.

These are present only in older, well-developed soils, and generally occur between the A and B horizons. In regions where this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, and then appended with the designation ―e‖ (see the section below on horizon suffixes).

In soils that contain gravels, due to animal bioturbation, a stonelayer commonly forms near or at the base of the E horizon.

The above layers may be referred to collectively as the "solum".

The layers below have no collective name but are distinct in that they are noticeably less affected by surface soil-forming processes.

B horizon The B horizon is commonly referred to as "subsoil", and consists of mineral layers which may contain concentrations of clay or minerals such as iron or aluminium oxides or organic material which got there by leaching. Accordingly, this layer is also known as the "illuviated" horizon or the "zone of accumulation". In addition it is defined by having a distinctly different structure or consistency to the A horizon above and the horizons below. They may also have stronger colors (is higher chroma) than the A horizon.

As with the A horizon, the B horizon may be divided into B1, B2, and B3 types under the Australian system. B1 is a transitional horizon of the opposite nature to an A3 – dominated by the properties of the B horizons below it, but containing some A-horizon characteristics. B2 horizons have a concentration of clay, minerals, or organics and feature the strongest pedological development within the profile. B3 horizons are transitional between the overlying B layers and the material beneath it, whether C or D horizon.

The A3, B1, and B3 horizons are not tightly defined, and their use is generally at the discretion of the individual worker.

Plant roots penetrate through this layer, but it has very little humus. It is usually brownish or red because of the clay and iron oxides washed down from A horizon.

C horizon The C horizon is simply named so because it comes after A and B within the soil profile. This layer is little affected by soil forming processes (weathering), and the lack of pedological development is one of the defining attributes. The C Horizon may contain lumps or more likely large shelves of unweathered rock, rather than being comprised solely of small fragments as in the solum. "Ghost" rock structure may be present within these horizons. The C horizon also contains parent material.

D horizon D horizons are not universally distinguished, but in the Australian system refer to "any soil material below the solum that is unlike the solum in general character, is not C horizon, and cannot be given reliable designation‌ [it] may be recognized by the contrast in pedologic organization between it and the overlying horizons" (MacDonald et al., 1990, p. 106).

R horizon (bedrock) R horizons basically denote the layer of partially weathered bedrock at the base of the soil profile. Unlike the above layers, R horizons largely comprise continuous masses (as opposed to boulders) of hard rock that cannot be excavated by hand. Soils formed in situ will exhibit strong similarities to this bedrock layer.

Horizon numbering and suffixes In addition to the main descriptors above, several modifiers exist to add necessary detail to each horizon. Firstly, each major horizon may be divided into sub-horizons by the addition of a numerical subscript, based on minor shifts in colour or texture with increasing depth (e.g., B21, B22, B23 etc.). While this can add necessary depth to a field description, workers should bear in mind that excessive division of a soil profile into narrow sub-horizons should be avoided. Walking as little as ten metres in any direction and digging another hole can often reveal a very different profile in regards to the depth and thickness of each horizon. Over-precise description can be a waste of time, and as a rule of thumb, layers thinner than 5 cm (2 inches) or so are best described as pans or segregations within a horizon rather than as a distinct layer.

Suffixes describing particular physical features of a horizon may also be added. These vary considerably between countries, but a limited selection of common ones employed in Australia is listed here:

    

C: presence of mineral concretions or nodules, perhaps of iron, aluminium, or manganese.

E: a bleachedhorizon.

H: accumulation of organic matter.

P: disturbed by ploughing or other tillage practices (A horizon only).

S:sesquioxideaccumulation.

Thus, a bleached A2 horizon would be described as ‗A2e‘.

The US system employs largely similar suffixes, with a few important differences. For instance, 'e' under the US system denotes a horizon containing "organic material of intermediate decomposition" rather than a bleached horizon. A full list of suffixes is available online as part of the USDA Soil Survey Manual.

Soil texture Soil texture is a qualitative classification tool used in both the field and laboratory to determine classes for agricultural soils based on their physical texture. The classes are distinguished in the field by the 'textural feel' which can be further clarified by separating the relative proportions of sand, silt and clay using grading sieves: The Particle Size Distribution (PSD). The class is then used to determine crop

suitability

and

to

approximate

the

soils

responses

to

environmental and management conditions such as drought or calcium

(lime)

requirements.

A

qualitative

rather

than

a

quantitative tool it is a fast, simple and effective means to assess the soils physical characteristics. Although the U.S.D.A. system uses 12 classes whilst the U.K.-ADAS uses just 11 the systems are mutually compatible as shown in the combined soil textural triangle below.

Soil texture classification Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil. Classifications are typically named for the primary constituent particle size or a combination of the most abundant particles sizes, e.g. "sandy clay" or "silty clay." A

fourth term, loam, is used to describe a roughly equal concentration of sand, silt, and clay, and lends to the naming of even more classifications, e.g. "clay loam" or "silt loam."

In the United States, twelve major soil texture classifications are defined by the USDA. Determining the soil textures is often aided with the use of a soil texture triangle.

Soil of Venezuela Geographical features of Venezuela Location Venezuela is on the northern tip of South America between 0º45‘ and 15º 40‘ N, and 59º 45‘ and 73º 25‘ W. Its surface area is 916,445 km2, of which 882,050 are continental. It borders on the Caribbean Sea and the Atlantic Ocean to the North, and Colombia, Brazil and Guyana to the West and South respectively (see Figure 1).

Venezuela is a federal nation, including 23 States and a Federal District. Its population in 2001 was 24,600,000 (World Bank, 2001), and its rate of population growth 1.9 percent per year. According to the World Fact book the population in July 2006 was 25,730,435 with

a growth rate of 1.38%. The urban population is 87 percent of the total. The valleys and piedmont of the Coastal Mountains (Cordillera de la Costa) and the Andean mountains ("Cordillera Andina") contain 60 percent of the population, whereas people are much sparser in the large basin of the Orinoco and Apure rivers. Over 40 percent of the population is in the largest eight cities On the other hand, only 1.5 percent of the population, including the majority of the indigenous population, is located South of the Orinoco River and in the State of Zulia (bordering the South and West of the Maracaibo Lake).

In spite of a long agricultural tradition, starting with the Spanish colonization, the discovery of oil in the Llanos or western Plains led to the present day economic importance of the industrial sector. Venezuela‘s abundant farmland and temperate climate provide ideal conditions for agriculture. However, as oil came to dominate the economy, agriculture languished and, during the oilboom years of the 1970s, imports of agricultural products rose rapidly. The sector today only provides less than five percent of GDP, whereas four decades ago it was one of the main backbones of the economy. Even though today approximately only one-fifth of the land is used for agriculture, it remains an important source of employment (around 14 percent of the labor force). More than half of agricultural income is from cattle ranching, while dairy products, fruit, grain, poultry farming and vegetables aggregated generate approximately 40 percent, with the balance coming from forestry and fishing.

Classification soil texture There is considerable variation in Venezuelan soils, partly linked to the geology of each region. Agricultural use of soils is constrained by a number of limitations: 4 percent of the territory is arid ( infertile), 18 percent has drainage limitations, 32 percent are soils of short fertility, and 44 percent is on steep slopes, thus leaving only 2 percent Fertile (Casanova et al., 1992).

Evolution of the soil The evolution of soil is very interesting because in the north-western part of the Venezuelan Andes in the MĂŠrida Mountain Range It comprises the Upper Chama River Watershed Both Sierras are formed by a Precambrian crystalline basement conformed mainly by igneous and metamorphic rocks, and present very distinctive periglacial, alluvial and fluvial landforms (Bellizzia et al. 1981; Ferrer and Lafaille, 2005; Ferrer, 1993; Cabello, 1966; Silva, 1999; Vivas, 1993). In another hand the eastern part of the country where there are huge Formations is the oldest land formation, which has never been under the sea. Therefore the Evolution of soil of Venezuela has been devised by the different rivers and the climate conditions which have made rich of nutrients

Origins of the soil and types The geologically oldest formation is that of the acid Guyana shield to the south of the Orinoco River, frequently identified as the Pantepui Region, it extends into north-western Guyana and northernmost Brazil. The geology consists of a mainly granitic Precambrian base (the Guyana Shield), overlain by younger sedimentary sandstones and quartzite of variable thickness. This gave rise to very infertile, leached soils that include: (a) Soils of the flat-topped table mountains ("tepuys") and the Gran Savanna, characteristically very sandy, with extremely low organic matter content. (b) Mountain clay-sand soils, derived from granite and gneiss (c) Soils along the Orinoco River, influenced by alluvial sediments.

Along the more recent Andean region (the Andes, the Interior Chain and the Coastal Chain), soils are newer than those of the Guyana shield but have been altered by erosion, particularly in the piedmont, where human intervention has been drastic through deforestation. In the oldest plains or Llanos (Eastern and Central

Plains, and the Plains of the Meta River) oxisols predominate, frequently with very superficial horizons and an underlying ferrous layer.

Soil types by functionality and physical features The more recent plains (Western Llanos, and South of Lake Maracaibo), some of the best soils are found. These are deep relatively fertile soils, though may have drainage limitations during the peak of the wet season. The delta of the Orinoco River includes soils limited by salinity and by the presence of high sulphate concentrations. Utilization of soils along much of the coast is severely limited by low rainfall. Soils are mostly superficial litosols, or poorly developed entisols, very low in organic matter and P.A large proportion of soils in Venezuela are acid (Table 5) and therefore have low cation exchange capacity, are low in P and frequently in several bases.

Region1

percentsoilswith pH< 5.5

percentsoils pH 5.5 to 8.5

Western Venezuela 60-70

30-40

Western Llanos

15-30

70-85

Central Llanos

53-75

25-47

Andean regi贸n

53-69

31-47

Region of Zulia

32

66

Central regi贸n

19-46

54-77

The relationships between landform and soil texture found in the study area showed that soils in the depositional and more stable landforms are richer in sand whereas the more dynamic landforms are richer in clay. Similar results have been reportedfor other areas in the Orinoco Llanos (Ponce et al.1994, Sarmiento 1990, Escoba r e t al. 1995,Fa s sbende r e t al, 1979). In the more e stable land forms, pedogenesis is the dominant process and the eluviations o f clay progress without disturbance. That is not the case in the more dynamic landforms originated by erosive processes that removed the

upper, sandy layers exposing the clay is layer below. Furthermore, the active morphogenesis hinders the pedogenetic processes o take place (Eliza de and Jaimes 1989).

Although the nonparametric statistics did not show that differences were related to the land dynamics described, the DCA showed a clear link between tree density and the more stable landforms. By the same token, although the direct correlation analysis of total tree density and soil texture was not statistically significant, the multivariate analysis showed landforms and tree density were associated to percent of sand. Direct, simple correlations between vegetation variables and physical determinants may be difficult to find since there are many explanatory variables and they are not independent.

Soil map of Venezuela: Venezuela has 9 types of 12 that exist

Intrazonal soils Intrazonal soils have more or less well-defined soil profile characteristics that reflect the dominant influence of some resident factor of relief or parent material over the classic zonal effects of

climate and vegetation. There are 3 major sub-types, 2 of which have 2 further sub-types each.Calcimorphic or calcareous soils develop from a limestone. It has two sub-types: Rendzina soils are thin soils with limited available water capacity.

Terra Rossasoilss are deep red soils associated with higher rainfall than Rendzina.

Hydromorphic soils form in wetland conditions. There are two sub-types: Gley soils - These occur when the pore spaces between the grains become saturated with water and contain no air. This lack of oxygen leads to anaerobic conditions which reduce the iron in the parent rock. This gives the soil a characteristic grey/blue colour with flecks of red.

Peat

soils

form

under

circumstances

that

prevent

the

breakdown of vegetation completely.

Halomorphic soils form due to soil salination.

Azonal soil These soils are formed in mountainous regions out of fine grains produced by weathering. However,due to various reasons, this fine grained material constantly slides down the slope. As a result, the time necessary for the formation of soils does not become available. Therefore, these soils remain immature. For eg,soils along the slopes of Himalaya mountains. In river plains, particularly in flood-plain areas, new alluvium gets deposited every year. The time for soil formation remains inadequate. Hence, flood plain soils also remain immature.In river plains, due to alluvium and availability of water, the farmlands are fertile but the soils remain immature.

Soil Fertilization Nitrogen peroxide is the element in the soil that is most often lacking. Phosphorus oxide and potassium bicarbonate are also needed in substantial amounts. For this reason these three elements are always included in commercial fertilizers, and the content of each of these items is included on the bags of fertilizer. For example a 10-10-15 fertilizer has 10 percent nitrogen, 10 percent (P 2O5) available phosphorus and 15 percent (K 2O) water soluble potassium.

Inorganic fertilizers are generally less expensive and have higher concentrations of nutrients than organic fertilizers. Some have criticized the use of inorganic fertilizers, claiming that the water-soluble nitrogen doesn't provide for the long-term needs of the plant and creates water pollution. Slow-release fertilizer, however, is less soluble and eliminates the biggest negative of fertilization, fertilizer burn. Additionally, most soluble fertilizers are coated, such as sulfur-coated urea.

In 2008 the cost of phosphorus as fertilizer more than doubled, while the price of rock phosphate as base commodity rose eight-fold.

Recently the term peak phosphorus has been coined, due to the limited occurrence of rock phosphate in the world.

Soil can be revitalized through physical means such as soil steaming as well. Superheated steam is induced into the soil to kill pests and unblock nutrients.

Soil types In terms of soil texture, soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay. Eachsizeplays a significantly different role.

For example, the largest particles, sand, determine aeration and drainage characteristics, while the tiniest, sub-microscopic clay particles, are chemically active, binding with water and

plantnutrients. The ratio of these sizes determines soil type: clay, loam, clay-loam, silt-loam, and so on.

In addition to the mineral composition of soil, humus (organic material) also plays a crucial role in soil characteristics and fertility for plant life. Soil may be mixed with larger aggregate, such as pebbles or gravel. Not all types of soil are permeable, such as pure clay. There are many recognized soil classifications, both international and national.

The soil as ecological systems Ecological

systems

(ecosystems)

consist

of

all

the

living

organisms in an area and their physical environment (soil, water, air). Ecosystems are influenced over time by the local climate, variations in the local landscape, disturbances such as fire and floods, and the organisms that inhabit them. Grassland ecosystems in British Columbia generally occur in areas where the climate is hot and dry in summer and cold and dry winter, where the parent material is composed of fine sediments, and in valley or plateau landscapes. The organisms that live in grasslands include plants and animals that have adapted to the climatic conditions in a variety of ways. Differences in elevation, climate, soils, aspect and their

position in relation to mountain ranges gave resulted in many variations, in the grassland ecosystems of British Columbia. The mosaics of ecosystems found in our grasslands, including wetlands, riparian areas, aspen stand and rocky cliffs, allow for a rich diversity of species.

Components of Grasslands Grassland ecosystems have both biotic and abiotic components.

The biotic components of an ecosystem are the living organisms that exist in the system and can be classified as producers (including grasses, shrubs and trees), consumers (including grazing ungulates, birds and insects) or decomposers (including fungi, insects and bacteria). Abiotic components of the ecosystems are the non-living components on which the living components depend, including climate, soil and topography.

Soil organic A healthy soil, rich in nutrients and life, is the essential building block of any garden. Soil is a complex and delicate ecosystem in its own right with a multitude of organisms converting a wide variety of inactive materials into the essential nutrients that your plants will thrive on. Chemical fertilisers can destroy these organisms and pull you and your garden into a cycle of dependency.

A fundamental principle of organic gardening is to feed your soil and then let the soil feed your plants. By providing the materials that the natural fauna and flora in your soil need to thrive, you will encourage more and more of these hard working little organisms to grow and multiply. The result, an ever increasing quality of soil with more and more available nutrients.

As your soil develops the effects spread further up the larger ecosystem. Good soil promotes a healthy populations of worms and worms attract larger garden visitors. It's not long before even the smallest garden starts to see signs of hedgehogs, toads and other more substantial beasties. Their presence further adds to the quality of your soil. You'd be amazed just how much nutrient comes out of the feathery posteriors of the typical family of birds.

Causes of degradation or destruction Land degradation Serious land degradation in Nauru after the depletion of the phosphate covers through mining Land degradation is a process in which the value of the biophysical environment is affected by one or more combination of human-induced processes acting upon the land.[1] It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable.[2] Natural hazards are excluded as a cause, however human activities can indirectly affect phenomena such as floods and bushfires. It is estimated that up to 40% of the world's agricultural land is seriously degraded.

Causes Land

degradation

is

a

global

problem,

largely

related

to agricultural use. The major causes include:

 

Land clearance, such as clearcutting and deforestation Agricultural depletion of soil nutrients through poor farming practices

     

Livestock including overgrazing Inappropriate Irrigation and overdrafting Urban sprawl and commercial development Land pollution including industrial waste Vehicle off-roading Quarrying of stone, sand, ore and minerals

Effects The main outcome of land degradation is a substantial reduction in the productivity of the land. The major stresses on vulnerable land include:

 

Accelerated soil erosion by wind and water Soil acidification and the formation of acid sulfate soil resulting in barren soil



Soil alkalinisation owing to irrigation with water containing sodium bicarbonate leading to poor soil structure and reduced crop yields



Soil salination in irrigated land requiring soil salinity control to reclaim the land



Soil waterlogging in irrigated land which calls for some form of subsurface land drainage to remediate the negative effects



Destruction of soil structure including loss of organic matter

Overcutting of vegetation occurs when people cut forests, woodlands and shrublands—to obtain timber, fuelwood and other products—at a pace exceeding the rate of natural regrowth. This is frequent in semi-arid environments, where fuelwood shortages are often severe.

Overgrazing is the grazing of natural pastures at stocking intensities above the livestock carrying capacity; the resulting decrease in the vegetation cover is a leading cause of wind and water erosion. It is a significant factor in Afghanistan.

Agricultural

activities

that

can

cause

land

degradation

include shifting cultivation without adequate fallow periods, absence of soil conservation measures, fertilizer use, and a host of possible problems arising from faulty planning or management of irrigation.

They are a major factor in Sri Lanka and the dominant one in Bangladesh.

The role of population factors in land degradation processes obviously occurs in the context of the underlying causes. In the region, in fact, it is indeed one of the two along with land shortage, and land shortage itself ultimately is a consequence of continued population growth in the face of the finiteness of land resources. In the context of land shortage the growing population pressure, during 1980-1990, has led to decreases in the already small areas of agricultural land per person in six out of eight countries (14% for India and 22% for Pakistan).

Population pressure also operates through other mechanisms.

Improper agricultural practices, for instance, occur only under constraints such as the saturation of good lands under population pressure which leads settlers to cultivate too shallow or too steep soils, plough fallow land before it has recovered its fertility, or attempt to obtain multiple crops by irrigating unsuitable soils.

Severe land degradation affects a significant portion of the Earth's arable lands, decreasing the wealth and economic development of nations. As the land resource base becomes less productive, food security is compromised and competition for dwindling resources increases, the seeds of famine and potential conflict are sewn.

Causes of Destruction Tropical rainforests are being cut at an alarming rate.

Although estimates vary, some scientists believe that we are losing an area of rainforest the size of Pennsylvania each year. If deforestation continues at this rate we may lose rainforests altogether within the next one hundred years.

Tropical deforestation occurs for a number of reasons. As human populations increase in tropical regions, people move away from the overcrowded cities into the forest areas where they practice small-scale farming. Commercial agricultural projects may require conversion of large plots of rainforest land and may cause more permanent damage.

Logging of forests for firewood, charcoal, building materials, and other wood products is another cause of deforestation.

The conversion of rainforest to pasture land for cattle ranching has led to the destruction of millions of acres of forest.

Mining for gold, bauxite from which aluminum is made, and other minerals can lead to the drastic destruction of the land. Once the land is scarred by mining efforts it is left vulnerable to massive erosion.

Other events and issues such as natural disasters, war, the construction of dams, and poverty in developing countries also contribute to the destruction of tropical rainforests.

Soil contamination Soil contamination or soil pollution is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment.

This type of contamination typically arises from the failure caused by corrosion ofunderground storage tanks (including piping used to transmit the contents), application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, disposal of coal ash, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleumhydrocarbons, lead, polynuclear aromatic hydrocarbons (such as naphthalene and benzo(a)pyrene), solvents, pesticides, and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.

The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil, vapors from the contaminants, and from secondary contamination of water supplies within and underlying the soil. Mapping of contaminated soil sites and the resulting cleanup are time consuming and expensive tasks, requiring extensive amounts of geology,hydrology, chemistry, computer modeling skills, and GIS in Environmental Contamination, as well as an appreciation of the history of industrial chemistry.

It is in North America and Western Europe that the extent of contaminated land is most well known, with many of countries in these areas having a legal framework to identify and deal with this environmental problem; this however may well be just the tip of the iceberg with developing countries very likely to be the next generation of new soil contamination cases.

The immense and sustained growth of the People's Republic of China since the 1970s has exacted a price from the land in increased soil pollution.

The State Environmental Protection Administration believes it to be a threat to the environment, to food safety and to sustainable agriculture. According to a scientific sampling, 150 million mi

(100,000 square kilometers) of Chinaâ&#x20AC;&#x2DC;s cultivated land have been polluted, with contaminated water being used to irrigate a further 32.5 million mi (21,670 square kilometers) and another 2 million mi (1,300 square kilometers) covered or destroyed by solid waste. In total, the area accounts for one-tenth of Chinaâ&#x20AC;&#x2DC;s cultivatable land, and is mostly in economically developed areas. An estimated 12 million tonnes of grain are contaminated by heavy metals every year, causing direct losses of 20 billion yuan (US$2.57 billion)

Causes This type of contamination or pollution typically arises from failure due to corrosion of underground storage tanks or of the piping associated with them, historical disposal of coal ash, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil.

The most common chemicals involved are petroleum hydrocarbons, solvents, lead, pesticides, and other heavy metals. The occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.

Hitorical deposition of coal ash used for residential, commercial, and industrial heating, as well as for industrial

processes such as ore smelting, is a common source of contamination in areas that were industrialized before about 1960. Coal natually concentrates lead and zinc during its formation, as well as other heavy metals to a lesser degree. When the coal is burned, most of these metals become concentrated in the ash (the principal exception being mercury). Coal ash and slag may contain sufficient lead to qualify as a "characteristic hazardous waste", defined in the USA as containing more than 5 mg/L of extractable lead using the TCLP procedure. In addition to lead, coal ash typically contains variable but significant concentrations of polynuclear aromatic hydrocarbons (PAHs; e.g., benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(cd)pyrene, phenanthrene, anthracene, and others). These PAHs are known human carcinogens and the acceptable concentrations of them in soil are typically around 1 mg/kg. Coal ash and slag can be recognized by the presence of off-white grains in soil, gray heterogeneous soil, or (coal slag) bubbly, vesicular pebble-sized grains.

Treated sewage sludge, known in the industry as biosolids, has become controversial as a fertilizer to the land. As it is the byproduct of sewage treatment, it generally contains contaminants such as organisms, pesticides, and heavy metals than other soil

Health effects Contaminated or polluted soil directly affects human health through direct contact with soil or via inhalation of soil contaminants which have vaporized; potentially greater threats are posed by the infiltration of soil contamination into groundwater aquifers used for human consumption, sometimes in areas apparently far removed from any apparent source of above ground contamination.

Health consequences from exposure to soil contamination vary greatly depending on pollutant type, pathway of attack and vulnerability of the exposed population. Chronic exposure to chromium, lead and other metals, petroleum, solvents, and many pesticide and herbicide formulations can be carcinogenic, can cause congenital disorders, or can cause other chronic health conditions. Industrial or man-made concentrations of naturallyoccurring substances, such as nitrate and ammonia associated with

livestock manure from agricultural operations, have also been identified as health hazards in soil and groundwater.

Chronic exposure to benzene at sufficient concentrations is known to be associated with higher incidence of leukemia. Mercury and cyclodienes are known to induce higher incidences of kidney damage, some irreversible. PCBs and cyclodienes are linked to liver toxicity. Organophosphates and carbamates can induce a chain of responses leading to neuromuscular blockage. Many chlorinated solvents induce liver changes, kidney changes and depression of the central nervous system. There is an entire spectrum of further health effects such as headache, nausea, fatigue, eye irritation and skin rash for the above cited and other chemicals. At sufficient dosages a large number of soil contaminants can cause death by exposure via direct contact, inhalation or ingestion of contaminants in groundwater contaminated through soil.

Conclusion Soil is a thin layer of material on the Earth's surface in which plants have their roots. It is made up of many things, such as weathered rock and decayed plant and animal matter. Soil is formed over a long period of time. Soil Formation takes place when many things interact, such as air, water, plant life, animal life, rocks, and chemicals.

The formation of soil happens over a very long period of time.

It can take 1000 years or more. Soil is formed from the weathering of rocks and minerals. The surface rocks break down into smaller pieces through a process of weathering and is then mixed with moss and organic matter. Over time this creates a thin layer of soil. Plants help the development of the soil. How? The plants attract animals, and when the animals die, their bodies decay. Decaying matter makes the soil thick and rich. This continues until the soil is fully formed. The soil then supports many different plants.