Soil-and-Its-Uses土壤及其利用课件

Soil and Its UsesSoil and Its Uses1Outline:Soil FormationSoil PropertiesErosionSoil ConservationOutline:Soil Formation2Land-Portion of the world not covered by water.Soil-Mixture of minerals,organic material,living organisms,air,and water.Land-Portion of the world no3Soil FormationSoil formation begins with fragmentation of parent material.母岩母岩-Ancient rock layers with recent deposits from lava or glacial flows.熔岩或冰河流动熔岩或冰河流动Weathering 风化风化-Factors bringing about fragmentation 破碎破碎 or chemical change of parent material.Soil FormationSoil formation b4Mechanical Weathering 物理风化物理风化,原生矿物原生矿物 Results from physical forces reducing size of rock particles without changing the chemical nature of the rock.Freezing and Thawing CyclesErosion from Wind and Moving WaterMechanical Weathering 物理风化,原生5Chemical Weathering 化学风化，化学风化，次生矿物次生矿物-Involves the chemical alteration of rock in such a manner that it is more likely to fragment or be dissolved.Rock fragments exposed to atmosphere may oxidize,or otherwise chemically change.Chemical Weathering 化学风化，次生矿物 6Humus-Decaying organic material.mixed with the top layers of rock particles,and supplies some of the needed nutrients to plants.Increase the water-holding capacity and inorganic nutrient solubility(acid cond.)creates crumbly soil which allows adequate water absorption and drainage.Humus-Decaying organic mater7Other factors influencing soil formation:Burrowing animals bring nutrients up from deeper soil layers,improving soil fertility.Plant rootsBacteria and Fungi(decomposers)1 cm soil formation:15 years(warm,humid climate)to hundreds of yearsOther factors influencing soil8Soil PropertiesTexture 质地，矿物质机械组成质地，矿物质机械组成：Various particles are mixed in many different combination,resulting in soil classification.Determined by the size of soil particles.Gravel 石砾石砾,d2mm Sand 砂粒砂粒,0.05-2.0mmSilt 粉砂粒粉砂粒,0.002-0.05mmClay 粘粒粘粒,0.002mmSoil PropertiesTexture 质地，矿物质机9Too many large particles leads to extreme leaching.Too many small particles leads to poor drainage.Too many large particles leads10Soil classification:Clay 粘土粘土Silt 淤泥淤泥Sand砂土砂土 Loam壤土壤土Ideal for agricultureSoil classification:Clay 粘土11Structure-Refers to the way various soil particles clump together.土壤结构：土壤结构：土壤颗粒的空间排列方式及稳定土壤颗粒的空间排列方式及稳定程度，孔隙的分布及结合状况。程度，孔隙的分布及结合状况。How to change?Measured by?Friability-Soils ability to crumble.vs 粘结粘结性，结持性性，结持性Structure-Refers to the way 12In good soils 2/3 of the intra-soil spaces contain air after the excess water has drained.Oxygen for root cells and soil organism.In good soils 2/3 of the intra13Protozoa,nematodes,earthworms,insects,algae,bacteria,and fungi are typical inhabitants of soil.Protozoa,nematodes,earthworm14Soil ProfileSoil Profile 土壤质地剖面形态土壤质地剖面形态-A series of horizontal layers of different chemical composition,particle size,and amount of organic matter.Horizon 发生层发生层-Each recognizable layer of the profile.Soil ProfileSoil Profile 土壤质地剖15Soil-and-Its-Uses土壤及其利用课件16O Horizon-Litter-Un-decomposed or partially decomposed organic material.A Horizon-(Topsoil)Uppermost layer-contains most of the soil nutrients and organic matter.B Horizon-(Subsoil)Underneath topsoil.Contains less organic matter and fewer organisms,but accumulates nutrients leached from topsoil.-Poorly developed in dry areas.C Horizon-Weathered parent material-very little organic material.R Horizon-BedrockO Horizon-Litter-Un-decom17Most cultivated land can be classified as either grassland or forest soil.Grassland Soils-Usually have a deep A Horizon-low rainfall limits topsoil leaching.A horizon supports most root growth.Forest Soils-Topsoil layer is relatively thin,but topsoil leachate forms a subsoil that supports substantial root growth.(High rainfall areas)Most cultivated land can be cl18Soil-and-Its-Uses土壤及其利用课件19Soil Erosion 土壤侵蚀土壤侵蚀Erosion Wearing away and transportation of soil/topsoil by wind and water.Floodplain,delta,muddy water after stormEffect:leave a degraded area and bury vegetation where it settles.Soil Erosion 土壤侵蚀Erosion We20Natural process accelerated by agricultural practice.Worldwide 25.4,China 5 Billion tons/yrMade worse by deforestation and desertification.High-tech agricultural practices on poor land increase erosion and lead to the transport of associated fertilizers and pesticides.Natural process accelerated by21Most current agricultural areas lose topsoil faster than it can be replenished.Most current agricultural area22Wind erosion Most common in dry,treeless areas.After desertification.Wind erosion 23Soil ConservationWhen topsoil is lost,fertility is reduced or destroyed,thus fertilizers must be used to restore fertility.Raises food costs,and increases sediment loads in waterways.Soil ConservationWhen topsoil 24Soil-and-Its-Uses土壤及其利用课件25Water erosion control runoffWater erosion control runoff26Conservation PracticesContour Farming-Tilling at right angles to the slope of the land.Each ridge acts as a small dam.Strip Farming-Alternating strips of closely sown crops to slow water flow.Terracing-Level areas constructed at right angles to the slope to retain water-good for very steep land.Conservation PracticesContour 27Soil-and-Its-Uses土壤及其利用课件28Wind erosionWindbreaks-Planting of trees or other plants that protect bare soil from the full force of the wind.Wind erosion29TillagePlowing has multiple desirable effects:Weeds and weed seeds are buried/destroyed.Crop residue is turned under-decays faster and helps build soil structure.Leached nutrients brought closer to surface.Cooler,darker soil is brought to top and warmed.TillagePlowing has multiple de30ProblemEach trip over the field is an added expense to the farmer,and at the same time increases the amount of time the soil is open to erosion via wind or water.ProblemEach trip over the fiel31