Soil PDF

Soil Soil may be defined as a thin surface covering that overlies the bedrock of most of the land area of the Earth. It is a resource that, along with water and air, provides the basis of human existence. Why is it important? Soil has the ability to perform a multitude of vital functions, includin...

Soil Soil may be defined as a thin surface covering that overlies the bedrock of most of the land area of the Earth. It is a resource that, along with water and air, provides the basis of human existence. Why is it important? Soil has the ability to perform a multitude of vital functions, including food production, storage and filtering of water, and supporting human activity and biological diversity. How does soil form? Soil develops when rock is broken down by weathering and material is exchanged through interaction with the environment. Organic matter becomes incorporated into the soil as the result of the activity of living organisms. Soil also contains water, minerals, and gases. The soil system is dynamic and it develops a distinct structure often with recognisable layers or soil horizons arranged vertically through the soil profile. Soil is essential for the development of most plants, providing physical support and nutrients. Plants are anchored in the soil by their roots. Nutrients, dissolved in soil water are necessary for the plants’ growth. Soil contains various organic matter, including dead material from plants and animals as well as animals that choose to live in the soil. Soils vary from place to place due to various conditions such as: the type of climate present in the area, rock type, land topography and other local soil-forming processes. The process of soil formation begins with the breaking down of bedrock which produces a layer of loose material called regolith. A section through that structure is known as a profile (as shown in Figure 1). O-Horizon – the organic material overlying the soil A-Horizon – the top layer of the soil B-Horizon – the middle layer C-horizon – the lowest layer R or D-horizon – unweathered parent rock Soil and Soil Conservation – Saviour Said SOIL SYSTEM Materials and energy are gained and lost, and so the system can be seen as a series of inputs, outputs, stores processes and recycling. Inputs to the system include: Water from precipitation or from further up the slope, gases from the atmosphere, respiration of soil organisms, nutrients from decaying and weathered rock and organic matter from decaying plants and animals. Outputs include: Nutrients taken up by plants, nutrients taken away by water, water lost at the surface of the soil by the evaporation and the soil particles lost by soil movement down-slope and erosion. Materials to be stored and recycled comprise: Dead organic matter deposited in the soil by plants and animals and the nutrients taken up and stored by plants SOIL COMPONENTS The main components of soils are water, air, organic matter, organisms and mineral particles. In a good agricultural soil mineral particles and organic matter from plants and animals take up about half the volume of the soil; air and water occupy the remainder. FACTORS THAT INFLUENCE SOIL FORMATION Soil and Soil Conservation – Saviour Said These include: The parent material (rock type) from which the soils form; The climatic conditions that prevail at the site during soil formation The type and amount of living organisms (especially vegetation cover) The human influence The topography of the land The length of time that the soil has been forming SOIL OF THE MALTESE ISLANDS Maltese soils can be significantly fertile and productive despite limiting natural geographical and climatic factors such as shallow depth and low levels of organic matter. Society underestimates the value of Maltese soil resources, in particular their ability to perform a multitude of vital functions, including food production, storage and filtering of water, and supporting human activity and biological diversity. Malta’s principal soil contamination sources include point sources such as quarries, industrial facilities, and waste dumps, and diffuse pollution from aerial deposition of dust or combustion products, exhaust emissions, lead shot, agricultural chemicals and application of manure and compost. Different soils form on different types of landscapes. Malta’s semi-natural landscapes include bare sea cliffs, garrigue, marshland, woodland, Blue Clay slopes, Blue Clay spring line, and blown sand. In rural landscapes of greater human influence there is widespread terracing of sloping land and more ‘made ground’. Maltese soils range from slightly to moderately alkaline. Due to their clay content of higher than 48 percent, two thirds of Maltese soils may be considered difficult to work. However these soils have higher nutrient retention and water filtration capacities. In general, the soils are non-saline, however, irrigation with poor quality water, especially saline treated sewage effluent, is increasing soil salinity. During the past 30 years, 4,500 ha of agricultural land has been lost to development, although the average annual rate of loss of land has decreased from approximately 200 ha per annum for the period 1971-1986, to approximately 80 ha per annum for 1986-2001. Soil is under increasing threat from a range of human activities, particularly urbanisation and development, and intensification of agricultural systems, which undermine its long-term availability and viability. Land degradation factors in the Maltese islands are summarised in the table below. Soil and Soil Conservation – Saviour Said Rural Recreational Industrial Urban Expanding Summer residencies Municipal By-pass development urbanisation accelerates urban dumps/landfills expansion (ex. Marsascala, Bugibba, Marsalfon, Xlendi) Fragmentation of Tourist holiday Derelict factories and Vacant plots land holdings apartments barracks (ex. White (inheritance law) accelerate urban Rocks) growth New job Seaside squatter Derelict and active Development of golf opportunities in ‘shanty’ towns quarries courses industry and services occupy agricultural instead of agriculture land (St. Thomas Bay, Armier) Field abandonment Parking areas take up Scrap yards abandoned/fallow agriculture land (Ramla l-Hamra, Ghajn Tuffieha) Part-time rather than Picnic areas and Firework factories full-time farming degraded barbeque sites Collapsed rubble Bird trappers walls, soil erosion ‘mansab’ and and pollution shooters clear field of fire Valley clearing – Off-road activities. heavy rain will lead to collapsed walls and therefore soil being lost. Soil and Soil Conservation – Saviour Said SOIL EROSION People depend on the soil for agriculture, and as such it is a valuable natural resource. Soils from continuously as the result of natural processes, and can therefore be regarded as a renewable resource. However the soil-forming process operate very slowly and the misuse or mismanagement of the soil may lead to damage or erosion or can disrupt the processes by which the soil forms. Soil is eroded naturally by weather elements such as wind and water but also by human activities such as land development, quarrying, waste disposal, overexploitation of freshwater resources, deforestation, Soil erosion – (the loss of soil by wind and water) and desertification (the loss of soil fertility) are two serious problems affecting our world. DESERTIFICATION Desertification – is a term applied to land degradation in drylands resulting mainly from adverse human impacts. Desertification was arguably the first environmental issue to be recognised as taking place on a global scale – UNCCD (United Nations Convention to Combat Desertification) in Nairobi 1977. Desertification is mostly the result of human activities rather than the type of climate present. Factors that could lead to desertification include: overgrazing, overcultivation, excessive plant/tree cover clearance, salinization and the use of bad agricultural practices. Overgrazing So called over-grazing is a result of too much livestock being kept on a given area of pasture. If excessive grazing pressure continues, the loss of vegetation cover can result in soil erosion. Excessive grazing is another major contributor to soil damage, in part because cattle compact the soil, making it less able to retain water. Overcultivation Overcultivation - in which soil is exhausted by nutrient loss and erosion. Short sighted agricultural practices are practices that allow a farmer to profit over a short period of time but loose over the long term. Overcultivation due to the shortening of periods when the land is left free from cultivation (fallow) or from the use of mechanical over-cultivation leads to large-scale wind erosion of soils. One classic example is the DUST BOWL which occurred in the 1930’s in North America and lead to a recession. Not allowing fields to lie fallow and ploughing too frequently, contribute heavily to soil loss. Soil and Soil Conservation – Saviour Said Soil scientists estimate that the USA alone looses up to 3 billion metric tons of soil each year because of such practices. Excessive clearance – Deforestation Excessive clearance of vegetation and trees often occurs because of the demand for fuelwood and development. Forest and woodland is cleared for a variety of motives – but mostly to create agricultural land (what is known as the slash and burn method), pastoral land , fuelwood Salinisation Excessive concentrations of salts in irrigated soils adversely affect crop yields and can ultimately kill plants. Chemical pesticides Chemical pesticides help avert crop losses, but they can also cause long-term soil damage by destroying beneficial insects and the micro-organisms necessary to replenish soil nutrients. Most soil erosion is caused by moving water (gullying) classified under sheet erosion, rill erosion and gully erosion Sheet erosion occurs when surface water moves down a slope or across a field and peels off layers of soil. Rill erosion – the surface water forms fast-flowing little rivulets that cut small channels in soil Gully erosion- rivulets of fast-flowing water join and cut the channels wider and deeper. Soil and Soil Conservation – Saviour Said SUSTAINABLE AGRICULTURE AND SOIL CONSERVATION Sustainable agriculture takes many forms, but at its core is a rejection of the industrial approach to food production developed during the 20th century. This system, with its reliance on monoculture, mechanization, chemical pesticides and fertilizers, biotechnology (GM foods), and government subsidies, has made food abundant and affordable. However, the ecological and social price has been steep: erosion; depleted and contaminated soil and water resources; loss of biodiversity; deforestation; labour abuses; and the decline of the family farm. The concept of sustainable agriculture embraces a wide range of techniques, including organic, free-range, low-input, holistic, and biodynamic. The common line among these methods is an embrace of farming practices that imitate natural ecological processes. Farmers minimize tilling and water use; encourage healthy soil by planting fields with different crops year after year and integrating croplands with livestock grazing; and avoid pesticide use by nurturing the presence of organisms that control crop-destroying pests. Beyond growing food, the philosophy of sustainability also promotes broader principles that support the just treatment of farm workers and food pricing that provides the farmer with a liveable income. Critics of sustainable agriculture claim, among other things, that its methods result in lower crop yields and higher land use. They add that a wholesale commitment to its practices will mean inevitable food shortages for a world population expected to exceed 8 billion by the year 2030. There's recent evidence, though, suggesting that over time, sustainably farmed lands can be as productive as conventional industrial farms. Soil conservation involves reducing soil erosion and preventing and restoring soil fertility. There are different methods of soil conservation techniques. We are going to have a look at some of them. Conservation Tillage practices The principle is to leave the soil surface in a rough condition, and, where practical, protected with crop residues. This type of tillage facilitates easier infiltration of water by slowing surface water runoff, and minimizes soil erosion. Employed separately or in combination with crop rotations reduce soil erosion when compared to conventional ploughing. (A mulch tiller can reduce soil loss by up to 40%. Water-related soil losses can be reduced by up to 80%.) Conservation tillage farming include minimum tillage or no till-farming. The idea is to disturb the soil as little as possible. Soil and Soil Conservation – Saviour Said Contour ploughing Contour ploughing means ploughing across a slope following its contour lines. The ruts made run perpendicular to slopes, generally resulting in furrows that slow water run-off during rainstorms allowing the water time to settle into the soil. Ploughing and planting crops in row across, rather than up and down, the sloped contour of the land also helps reducing soil erosion. Crop and Residue Cover The benefits of growing the appropriate crops on specific soils are important as they reduce the erosive forces of water and wind by means of their canopy intercepting rain, and acting as a windbreak. Root systems stabilize the soil and reduce losses. Crop residues perform similar functions and, in addition, form small dams that help retain runoff water, thereby reducing erosion. Terracing Terracing can be used to reduce erosion on steep slopes, each of which is converted into a series of broad, nearly level terraces that run across the land contour. Terracing means building of earthen embankments across a slope (on the contour) to intercept runoff water and reduce soil erosion. Terraces are usually built in a series parallel to one another, with each terrace collecting excess water from the area above. Wind erosion control In areas prone to gusty winds, plant wind breakers in the form of trees, hedges and bushes or even wooden/plastic fences can be used to reduce the impact of the wind on the soil. Wind erosion can be reduced by wind breakers or shelter belts – long rows of trees planted so that they partially block wind. Strip cropping Strip cropping includes a row of crop such as corn is alternated in strips with a crop that completely covers the soil. Crop rotation Soil and Soil Conservation – Saviour Said Crop rotation is the planned order (spanning 2 or 3 years or longer) of specific crops planted on the same field. It also means that the succeeding crop belongs to a different plant family than the previous one. Besides reducing soil erosion, crop rotation maintains soil fertility by preventing the depletion of the ‘same’ soil nutrients by the ‘same’ crops. It controls the build-up and spreading of diseases and pests. All this reduces reliance on synthetic chemicals (pesticides and fertlisers). Soil and Soil Conservation – Saviour Said