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Chapter 15 Soil Resources. Overview of Soil Unit The Rock Cycle Igneous, sedimentary and metamorphic rock types What is soil? Soil Properties Major Soil.

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Presentation on theme: "Chapter 15 Soil Resources. Overview of Soil Unit The Rock Cycle Igneous, sedimentary and metamorphic rock types What is soil? Soil Properties Major Soil."— Presentation transcript:

1 Chapter 15 Soil Resources

2 Overview of Soil Unit The Rock Cycle Igneous, sedimentary and metamorphic rock types What is soil? Soil Properties Major Soil Orders Soil Problems Soil Conservation Soil Reclamation

3 The Rock Cycle The rock cycle is the natural process in which rocks transform from one rock type into another rock type over time, a type of natural recycling. Igneous rocks, which are formed from magma cooling underground, or lava above ground are formed from previous igneous, metamorphic, or sedimentary rocks which have become melted Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution. The processes that form sedimentary rock occur at the surface of the Earth and within bodies of water Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form".rockmetamorphism

4 Rock Cycle: Igneous

5 Sedimentary Rocks

6 Metamorphic Rock

7 The Rock Cycle

8 Soil Uppermost layer of earth’s crust that supports plants, animals and microbes Soil Forming Factors – Parent Material – Time – Climate – Organisms – Topography – Types: clay, sand, silt, and gravel (including a mixture of one or more or all

9 What is Soil? Produced very slowly – almost nonrenewable Production by… – Weathering of rock (parent material) – chemical & mechanical  this adds inorganic components – Deposit of sediments by erosion – Introduction of living organisms – succession  the biotic component – Decomposition of organic materials and dead organisms Development is slow years to produce 1 inch of topsoil Soil is different in different areas

10 Soil Composition Mineral Particles (45%) – Weathered rock – Provides essential nutrients for plants Organic Material (5%) – Litter, animal dung, dead remains of plants and animals, humus (picture) Water (25%) Air (25%)

11 Soil Composition Pore space – 50% of soil – Soil air- good for aeration – Soil water- provides water to roots

12 Soil Horizons O-horizon – Rich in organic material A-horizon – Topsoil B-horizon – Lighter colored subsoil C-horizon – Weathered parent material

13 Soil Organisms There are millions of microorganisms in 1 tsp of fertile agricultural soil

14 Soil Organisms Soil organisms provide ecosystem services – Def: Important environmental benefits that ecosystems provide Examples – Decaying and cycling organic material – Breaking down toxic materials – Cleansing water – Soil aeration (especially done by earthworms)

15 Nutrient Cycling Nutrients are cycled between plants, organisms and soil Example – Bacteria and fungi decompose plant and animal wastes – They are transformed into CO 2, soil nutrients and water

16 Soil Properties Soil Texture – Relative proportion of sand, silt and clay – Sand: 2mm-0.05mm – Silt: 0.05mm-0.002mm – Clay: >0.002mm

17 Soil Properties Soil texture affects soil properties Coarse textured soil (sandy) – Will not hold water well- flows through easily Fine textured soil (high in clay) – Poor drainage – Low oxygen levels in soil – Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+, NO 2 - )

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19 Soil Properties

20 Soil Acidity – Measured using pH scale 0-7 = acidic 7 = neutral 7-14 = basic – pH of most soils range from 4-8 – Affects solubility of certain plant nutrients – Optimum soil pH is 6-7 This is the pH where plant nutrients are most available to plants Soil amendments (ex: lime) can be used to achieve this pH

21 Major Soil Groups Variations in soil forming factors cause variation in soils around globe Soil Taxonomy – Separates soils into 12 orders – Subdivided into more than 19,000 soil series that vary by locality Five common soil orders – Spodosols, alfisols, mollisols, aridosols, oxisols

22 Major Soil Groups Spodosols – Form under coniferous forests – O-horizon composed of needles – E-horizon is ash-gray under A-horizon – Not good farmland- too acidic

23 Major Soil Groups Alfisols – Brown to gray-brown A- horizon – Precipitation high enough to leach most organics and nutrients out of O-, A- and B- horizons – Soil fertility maintained by leaf litter

24 Major Soil Groups Mollisols – Found in temperate, semi-arid grassland – Very fertile soil – Thick, dark brown/ black A-horizon – Soluble nutrients stay in A-horizon due to low leaching

25 Major Soil Groups Aridosols – Found in arid regions of all continents – Low precipitation preclude leaching and growth of lush vegetation – Development of salic horizon possible

26 Major Soil Groups Oxisols – Found in tropical and subtropical areas with high precipitation – Very little organic material accumulation due to fast decay rate – B-horizon is highly leached and nutrient poor

27 Soil Problems Soil Erosion – Def: wearing away or removal of soil from the land – Caused primarily by water and wind Why a problem? – Causes a loss in soil fertility as organic material and nutrients are eroded – More fertilizers must be used to replace nutrients lost to erosion Accelerated by poor soil management practices

28 Case in Point: American Dust Bowl Great Plains have low precipitation and subject to drought – severe drought – No natural vegetation roots to hold soil in place Replaced by annual crops – Winds blew soil as far east as NYC and DC. – Farmers went bankrupt

29 Soil Problems Nutrient Mineral Depletion

30 Soil Problems Soil Salinization – Def: gradual accumulation of salt in the soil, usually due to improper irrigation techniques Often in arid and semi-arid areas – The little precipitation that falls is quickly evaporated – Leaves behind salts Salt concentrations get to levels toxic to plants

31 Soil Problems Desertification – Def: degradation of once-fertile rangeland, agricultural land, or tropical dry forest into nonproductive desert Typically a human-induced condition Change in vegetation changes climate, further decreasing precipitation levels

32 Soil Conservation Conservation Tillage – Residues from previous year’s crops are left in place to prevent soil erosion – Includes no tillage o Crop Rotation Planting a series of different crops in the same field over a period of years Planting a series of different crops in the same field over a period of years Lessens pest and insect disease Lessens pest and insect disease

33 Soil Conservation Contour Plowing – Plowing around hill instead of up-down – Decreases soil erosion Strip Cropping – Alternating strips of different crops along natural contours Terracing – Creating terraces on steep slopes to prevent erosion Strip Cropping Terracing

34 Preserving Soil Fertility Organic fertilizers – Animal manure, crop residue, bone meal and compost – Nutrient available to plants only as material decomposes Slow acting and long lasting Inorganic fertilizers – Manufactured from chemical compounds – Soluble Fast acting, short lasting – Environmentally sound to limit use Mobile- easily leach and pollute groundwater

35 Soil Reclamation Two steps 1.Stabilize land to prevent further erosion 2.Restoring soil to former fertility Best way to do this is shelterbelts – Row of trees planted to reduce wind erosion of soil

36 Soil Conservation Policies in US Soil Conservation Act 1935 – Authorized formation of Soil Conservation Service, now called Natural Resource Conservation Service (NRCS) – Assess soil damage and develop policies to improve soil Food Security Act (Farm Bill) 1985 – Required farmers with highly erodible soil had to change their farming practices – Instituted Conservation Reserve Program Pays farmers to stop farming highly erodible land


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