Transcript Slide 1
Study the diagram below. Describe the influence of the various soil forming factors on the formation of a Podzol soil. Climate Relief Vegetation SOIL FORMATION Drainage Parent Material Soil Biota • Cold, wet climates • Coniferous Forests • Thin: Weathering is slow • Northern Latitudes • Thin layer of humus: Humification is slow • Moorlands • A lot of Leaching and Podsolisation • Iron and Aluminium pushed down •West of Ireland • Needles don’t decompose easily little humification • Produce an acid humus Relief Vegetation Climate SOIL FORMATION Drainage • A Horizon often waterlogged because of impermeable iron pan that forms inbetween A and B horizon. Parent Material • Weathered Slowly producing a shallow soil Soil Biota • Few Biota because cold climate • Therefore, little humification Brown Earths 2010 Question 18 Describe and explain the characteristics of any ONE soil type studied by you Mature soils have 3 distinct horizons (layers) A Horizon – Contains topsoil, humus, vegetation not decayed, Organic Content The most fertile part of the soil Suffers the most leaching B Horizon - Contains subsoil Contains leached mineral from A horizon C Horizon - The Regolith (recently formed soil) Sits ontop of bedrock Contains large particles. Brown Earths • Where they are found • Key words • 40-60 Degrees in Northern Hemisphere • Zonal Soil • Cool Temperate Climates • Burrowers and Mixers • Ireland-Russia in East • Loamy • Scotland-Portugal in South • Peds – space for water • Most common soil in Ireland • Crumb Texture mostly • Humification • Boulder Clay from Ice age deposits • Freeze Thaw and Chemical weathering • Hydrolysis Brown Earths • Crumb Structure • Micro-organism activity – Bacteria • Slightly acidic to slightly alkaline – it varies 5-7 • What impact do the following process have on Brown Earths ? • Weathering – Mechanical/Chemical • Erosion • Leaching • Calcification • Humification • Salinisation??? Brown Earth Soil (10,000 years) They form in warm climates, with mild winters and summers. South East Ireland Found in areas that have rainfall all year. 1,600-1,800 mm per year Found in areas of deciduous forest – Oak/Ash – Ireland's natural vegetation Weathering is quite slow due to cool climate – What types of weathering? Some Humification because deciduous trees shed leaves every year. Mild climate assist decomposition Lots of humus in these soils due to climate. Some Leaching – because precipitation exceeds evaporation. What does it look like? •Quite shallow • Quite thick Humus • Mild Acid Humus • Light Brown A Horizon – because calcium, magnese are leached out by rain • Dark Brown B Horizon – because minerals have been washed down to here (Eluviation) • Horizons often Merge •These are the main characteristics of the Brown Earth Soil.Explain why these soils have these characteristics eg. Quite shallow because of slow weathering. Which is due to the cool climate etc. What does it look like? • Quite shallow - weathering is slow • Quite thick Humus – because there is some humification • Mild Acid Humus – because humification is slow • Light Brown A Horizon – because calcium, magnese are leached out by rain • Dark Brown B Horizon – because minerals have been illuviated here. • Horizons often Merge - biota mix the soil Brown earth soils are widespread in Ireland, except in highland areas. Soil organisms, like earthworms, mix the materials together, merging the boundaries between the horizons. These soils are leached, but not heavily, so the aluminium and iron oxides are dispersed through the soil to give the overall brown colour. The original vegetation was deciduous forest, resulting in a layer of decaying leaves giving a rich humus. The deep roots of these trees reached down to the 'B' horizon (unlike coniferous trees) tapping the nutrient supply and allowing good drainage. Climate -Precipitation greater than evaporation during summer months, resulting in only moderate leaching. Warm summers Natural vegetations and soil organisms - mixed broad leaf, much plant litter through this is more easily broken down by more active soil biota. A moderate or moder type of humus would develop from the plant litter Relief and drainage - downward movement of water, moderate leaching likely Parent material - strong influence on soil development They generally have three horizons: the A, B and C horizon. Horizon A is usually a brownish colour, and over 20 cm in depth. It is composed of mull humus (well decomposed alkaline organic matter) and mineral matter. It is biologically active with many soil organisms and plant roots mixing the mull humus with mineral particles. As a result, the boundary between the A and B horizons can be ill defined in unploughed examples. Horizon B is mostly composed of mineral matter which has been weathered from the parent material, but it often contains inclusions of more organic material carried in by organisms, especially earthworms. It is lighter in colour than the A horizon, and is often weakly illuviated (leached). Due to limited leaching only the more soluble bases are moved down through the profile. Horizon C is made up of the parent material, which is generally permeable and non- or slightly acidic, for example clay loam. Brown Earths - Characteristics Colour Texture Structure Humus Content Water Content PH Value Brown Earths - Colour • Brown due to soil formation processes • Humification is main process – Dark Brown • What is humification? • What Plant Litter creates the humus? • How does humus make its way down through the soil? • No Distinct Horizons • Burrowers/Mixers – impact of climate Brown Earths - Texture • How fine or coarse the soil is • Equal amts of Sand and Silt and Clay = Loamy • Loamy means space for air and water to pass through • Well Drained • Crumby structure due to rich organic content of soil and living organisms • Mild temperatures – Cool Temperate Oceanic • This helps – Burrowers and Mixers Brown Earths – Humus Content • Rich due to Deciduous Vegetation • Process = Humification • Moderate rainfall – eg. 1600-1800 mm in South East of Ireland • Relief also affects the humus content – too high = less. The humus content in South East is affected by low-lying,undulating land • Mild Winters/Warm Summers – Decomposition is highest in these conditions BROWN EARTHS – PH Value • Refers to how acidic or alkaline the soil is • Acidic soils = low ph value • Alkaline soils = high ph value • Parent Rock generally influences the ph value • Acidic Brown Earths form on Sandstone and Alkaline Brown Earths form on Limestone • PH Values of Brown Earths encourage the activity of earthworms and Bacteria