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SCIENCE OF SOIL Soil A collection of natural bodies developed in the unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants and has properties due to the effects of climate and living matter acting upon parent material, as conditioned by topography, over a period of time GENESIS OF SOIL Rocks are chief sources for the parent material over which soils are developed Types of rocks Igneous  Sedimentary  Metamorphic Genesis includes –weathering of rocks & formation of soil Primary and Secondary Minerals  Primary Minerals: Minerals that have persisted with little change in composition since they were extruded in molten lava(eg quartz, mica and feldspars).They are most prominent in sand and silt fractions  Secondary Minerals: Minerals such as the silicate clays and iron oxides, have been formed by the breakdown and weathering of less resistant minerals as soil formation progressed Weathering of rocks It is physical and chemical disintegration and decomposition of rocks Weathering creates the parent material over which the soil formation takes place Later weathering, soil formation and development proceeds simultaneously Physical weathering  Temperature  Water  Wind  Plants & animals Chemical weathering  Solution  Hydration  Hydrolysis  Acidification  Oxidation  Reduction Soil formation The mineral weathering combines with the associated physical and chemical phenomena constitute the process of soil formation It includes1 The addition of organic & mineral materials The loss of these materials from the soil Translocation of materials from one point to Another within the soil column Transformation of minerals & organic substances within the soil Two Approaches:  Pedological  Edaphological The origin of the soil ,its classification, and its description are examined in pedology (pedon-soil or earth in greek) Pedology is the study of the soil as a natural body and does not focus primarily on the soli’s immediate practical use A pedologist studies, examines, and classifies soils as they occur in their natural environment 10 Soil Conservation Definition Soil conservation is using and managing land based on the capabilities of the land itself 40 Soil Conservation Measures Agronomic Measures  Contour Cultivation – By ploughing and sowing across the slope, each ridge of plough furrow and each row of the crop act as an obstruction to runoff, providing more opportune time for water to enter into the soil and reduce soil loss  Tillage – Tillage alters soil physical characters like porosity, bulk density, surface roughness and hardness of pans Conventional tillage includes ploughing twice or thrice followed by some secondary operations like harrowing and planking that smoothen and pack the soil in seed-bed and/or control weeds  Mulching – Mulches are any material such as straw, plant residues, leaves, loose soil or plastic film placed on the soil surface to reduce evaporation, erosion or to protect plant roots from extremely low or high temperature 41 Cropping Systems: It represents cropping patterns used on a farm and their interaction with farm resources, other farm enterprises and available technology Cropping pattern indicates yearly sequence and spatial arrangements of crops and fallow in an area Practically, it implies different crops grown either in combination or sequentially in farm over the years Therefore, growing a crop which produces the maximum cover, in addition to principle crops like rice or wheat, reduces runoff and soil loss For example, cow pea and green gram are important cover crops for the rainy season Tobacco, being a clean cultivated crop, allows higher runoff and soil loss These losses can be reduced by growing cowpea or green gram during early monsoon before tobacco is planted Strip-cropping: long and narrow strips of erosion resisting crops (e.g groundnut, beans) are alternated with strips of erosion permitting crops (e.g maize) The strips are laid across the slope Use of chemicals: Soil stability can be increased by spraying chemicals like polyvinyl alcohol at 480 kg/ha 42 Mechanical Measures  Contour Bunding – Runoff from any given surface is along the line of greatest slope and the velocity of runoff increases with the vertical distance through which it is moved The contour bund being on the same elevation, assures that the depth of water against the bund is uniform throughout its length It ensures uniform distribution of water above the bunds and therefore, better cultivation possibilities than any other type of bund As the bunds are at regular intervals, they intercept the runoff from attaining erosive velocity and causing erosion The velocity of flowing water is slowed down and water thus held on the field for a longer time, soaks into the soils  Broad Base Terrace - A terrace is a combination of ridge and channel built across the slope These terraces have wide base and low height of ridge and usually formed with machinery BBTs are constructed in soils with high clay content which develop deep cracks in summer (e.g Black soil) 43 Bench Terracing - Bench terracing consists of transforming relatively steep land into a series of level strips or platforms across the slope of the land It reduces the slope length and consequently erosion The field is made into a series of benches by excavating the soil from upper part of the terrace and filling in the lower part On steeply sloping and undulated land, farming practices is possible only with bench terracing It is usually practiced on slopes ranging from 16 to 33% Trenching –Contour trenches are made in non-agricultural land for providing adequate moisture conditions in order to raise trees or grass species The trenches are usually 60 cm × 48 cm in size The spacing varies from 10 to 30 m Vegetative Barriers – these are closely spaced plantations-usually a few rows of grasses or shrubs - grown along contours They act as barrier to check the velocity of overland flow and entrapment of silt load behind them Khus (Vettiveria zelanica) is the most suitable plant for this purpose 44 Grassed Waterways – These are drainage channel either developed by shaping the existing drainage ways or constructed separately Suitable perennial grasses that are not edible by cattle, deep rooted and spreading type are established subsequently for the stability of the waterway (e.g Panicum repens, Brachiara mutica, Cynodon dactylon, Paspalum notatum) The objectives are- to provide drainage, to convert gullies or unstable channels into stable channels by providing grass cover, and for leading water at non-erosive velocity into a water body Gully Control – The basic approach to gully control involves reduction of peak flow rates through the gully and provision of stable channel for the flow that has to be handled Temporary and permanent structures such as check dams, drop-spill ways are constructed 45 Agrostological Measures  Grasses prevent soil erosion by intercepting rainfall, by binding the soil particles and by improving soil structure A grass-legume association is ideal for soil conservation E.g Pennisetum pupureum, Cenchrus ciliaris, Setaria sphacelata Forestry Measure  Afforestation and re-forestation in wastelands 46 AA 47 48 Semi-circular & triangular contour bunds 49 50 51 52 53 Check dam 54 [...]...Composition of soil 11 Soil Profile and its Layers(Horizons)  Examination of a vertical section of a soil as seen in a roadside cut or in the walls of a pit dug in the field, reveals the presence of more or less distinct horizontal layers Such a section is called a profile, and the individual layers are known as horizons 12 13 Topsoil and Subsoil  When a soil is ploughed and cultivated, the natural state of. .. manipulated part of the soil is referred to as the surface soil or the topsoil  The subsoil is comprised of those soils layers underneath the top soil 14 Mineral (inorganic) and organic soils  Mineral soils: Mineral or inorganic in composition, low in organic matter ranges from 1 -6%  Organic soils: 50% organic matter by volume (at least 20% by weight) 15 Soil Texture and Soil Structure  Soil Texture:... acres of productive lands are oversalted because of improper water management 32 Soil Erosion  Soil erosion is the process of detachment of soil particles from the parent body and transportation of the detached soil particles by wind or water Mechanism of Water Erosion: a Detachment b Transportation Causes: a Natural b Anthropogenic 33 Forms of Water Erosion  Sheet Erosion: uniform removal of top soil. .. Cobalt(Co) 25 Soil Air Soil air differs from the atmospheric air in several respectsFirst ,the composition of soil air is quite dynamic and varies greatly from place to place within a given soil Second, soil air generally has a higher moisture content than the atmosphere; the relative humidity of soil air approaches 100% when the soil moisture is optimum Third, carbon dioxide in soil air is often several... normal atmosphere 26 Composition of soil air Particulars Percentage by volume Nitrogen Oxygen Carbon dioxide Atmospheric air 79.00 20.95 0.03 Soil air 79.20 20.60 0.25 Sandy soil air 79.20 19.95 0.30 Loamy soil air 79.20 19.20 0.62 Clay soil air 79.20 19.69 0.66 Manured soil air 79.20 18.23 1.85 27 Soil Degradation  Soil degradation is a concept in which the value of the biophysical environment is... important liquid Although some of the soil moisture is removed by the growing plants, some remains in the tiny pores and in thin films around soil particles The soil solids strongly attract the soil water and consequently compete for it with plant roots 20 Soil Solution  The soil solution contains small but significant quantities of soluble inorganic and organic compounds, some of which contain elements... 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 salinization in irrigated land requiring soil salinity control to reclaim the land Waterlogging... Proportions of different sized particles present in soil  Soil Structure: The arrangement of the sand silt and clay particles within the soil 16 Table:General properties of three major inorganic soil particles Property Sand (0.052mm) Silt (0.002-0.05mm) Clay(
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