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Chapter 15 Soil Resources. Read dust storm in china and measures taken to control it (Page number 335) Millions of trees defend China against raging dust.

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Presentation on theme: "Chapter 15 Soil Resources. Read dust storm in china and measures taken to control it (Page number 335) Millions of trees defend China against raging dust."— Presentation transcript:

1 Chapter 15 Soil Resources

2 Read dust storm in china and measures taken to control it (Page number 335) Millions of trees defend China against raging dust storms from the Gobi desert. Shown are pines and poplars developed by Chinese scientists to grow rapidly in poor soil. The agricultural land is protected by the Great Green Wall.

3 Soil Definitions 1)The unconsolidated organic and mineral material on the earth’s surface that is capable of supporting plants. (MA Envirothon Team Resource Manual) 2)A dynamic natural body, in which plants grow, that is composed of mineral and organic materials and living organisms. (Brady & Weil, 11 th Ed.)

4 Soil-Forming Factors Parent material (rock that is slowly broken down by biological, chemical, and physical weathering processes in nature.) Climate (when temperatures are below freezing decomposition of organic matter and water movement are slow, soil dvelopment in the humid tropics is accelerated by the rapid weathering of rock and soil minerals, the leaching of nutrients, and the decompostion of organic detritus.)precipitation and temperature changes Topography (presence or absence of mountains and valleys, steep slopes have little or no soil on them because soil and rock are continually transported down the slopes by gravity; moderate slopes and valleys, may encourage the formation of deep soils) Organisms (plant roots, lichens produce acids, animals that burrow or tunnel, such as earthworms, voles, mix the soil, distributing organic and mineral matter Time Grasslands soil have rich organic matter How long climate has been altering parent material over geologic time

5 Soil Composition 45% Mineral particles (broken down pieces of rock) 5% Organic matter (humus - from dead organisms, worm castings, leaf litter) 25% Water (precipitation) 25% Air (More with sandy soil, less with clay soil) Soil organisms - Millions in one teaspoon of fertile agricultural soil! - bacteria, fungi, algae, microscopic worms. provide ecological services such as worm castings, decomposition to humus, breaking down of toxic materials, cleansing water, nutrient cycling from decomposers or upon death

6 Components of Soil Mineral materials = boulder, stone, cobble, gravel, sand, silt, and/or clay sized particles of gneiss, granite, schist, or slate. Organic materials = leaf litter, crop residue, decomposing animal bodies, and compost. Living organisms = plant roots, earthworms, nematodes, fungus, bacteria colonies

7 Soil Nutrients (NPK) Organic - animal manure, bone meal, compost (slow-acting, long-lasting) Delay in availability to plants, needs time for the organic material to decompose Delay causes low level of nutrient leaching Improves water holding capacity Inorganic - Manufactured from chemical compounds (fast-acting, short-lasting) Highly soluble so immediately available to plants High solubility also makes it leach quickly (pollutes water) Suppresses growth of microorganisms Source of nitrogen gases that increase air pollution Production requires much energy from fossil fuels, increasing CO 2 emissions.

8 Soil Horizons

9 Soil horizon O Horizon: Organic or litter layer, topmost layer A Horizon: Topsoil; mostly inorganic minerals with some organic material and humus mixed in; crucial for plant growth E Horizon: Eluviation horizon; loss of minerals by leaching, a process whereby solid materials are dissolved and transported away, only found in forested areas, light colored B Horizon: Subsoil; zone of accumulation or deposition of leached minerals and organic acids from above, clay and minerals, (iron, aluminum and calcium) C Horizon: Slightly altered parent material R Horizon: Bedrock

10 Soil Organisms

11 Fungi

12 Ecosystem services provided by soil organisms Maintaining soil fertility by decaying and cycling organic material Earthworms ingest soil and obtain energy and raw materials by digesting some of the compounds that make up of humus. Castings, bits of soil that have passed through the gut of an earthworm, are deposited on the soil surface. In this way, nutrient minerals from deeper layers in the soils are brought to upper layers. Earthworm tunnels serve to aerate the soil and the worms; waste products and corpses add organic material to the soil.

13 Soil organisms Ants live in the soil in enormous numbers, constructing tunnels and chambers that aerate it. Food brought in by the ants and the left Over is eventually decomposed and add to the organic matter in the soil. Ants also bury seeds in the soil and help in reproduction Symbiotic association between the roots of plants and fungi. When mycorrhizal fungi are absent from the soil, the reestablishment of certain tree species is retarded.

14 Nutrient Cycling Leaching causes some nutrient minerals to be lost from the soil ecosystem to groundwater, the weathering of the parent material replaces much or all of them. Dusts carried in the atmosphere help replace nutrient minerals in certain soils. Hawaiian rainforest soils, for example, receive dust inputs from central Asia, a distance more than 600km away.

15 Soil characterization Soil can be characterized by color and several other traits: Texture Structure pH

16 Soil Texture Determined by size of particles Three main categories: Clay = particles < mm diameter Silt = particles 0.002–0.05 mm diameter Sand = particles 0.05–2.0 mm diameter Best for plant growth is loam, an even mix of these three types.

17 Physical differences The size of sand and clay give a horizon different physical & chemical properties. Sand particles are much larger than clay particles and, sand is blocky shaped while clay is platy. A collection of sand particles create air spaces that are larger and more connected than those created by a collection of clay particles. Chemical differences Soil minerals are present in charged forms or ions. Sand particles have no charge on their surface. Clay particles have negative charge on their surface and adsorb elemental nutrients such as Ca, Mg, Fe, NO 3, PO 4.

18 Loam Is an ideal agricultural soil. Has an optimum combination of different soil particle sizes. It contains 40% each of sand and silt, and about 20% of clay. Generally larger particles provide structural support, aeration, and permeability to the soil, whereas smaller particles bind into aggregates, or clumps, and hold nutrients and water. Sandy soil is not desirable because they do not hold mineral or water and plants grown in such soils are more susceptible to mineral deficiencies and drought. Clayey soil provide poor drainage and often do not contain enough oxygen.

19 Soil Texture Chart It is possible find the type of soil by making use of the soil texture chart. We can determine the percentage of each component in a soil sample and then plot the results. ( make sure the sum of the sand plus silt plus clay will always be 100 percent.


21 Soil Characteristics Understand what soil is and how it forms. Compare and contrast the characteristics of different soils. What type do you have around your house? 1) clay = “layer silicates that are formed as products of chemical weathering of other silicate minerals at the earth's surface. They are found most often in shales, the most common type of sedimentary rock.” 2) silt = rock worn into tiny pieces (coarser than clay, but finer than sand). usually 1/20 millimeter or less in diameter 3) sand = quartz or silica worn down over time. grains with diameters between 0.06 mm to 2 mm 4) organic matter (humus) 5) Loam = soil containing a mixture of clay, sand, silt and humus. Good for growing most crops.


23 Soil pH Most soil ranges from 4 to 8 The soil of the Pygmy forest in Mendocino County, California, is acidic, with a pH of 2.8 to 3.9 Soils in Death Valley, California, have a pH of 10.5 At a low pH, the aluminum and manganese in soil water are more soluble, and the roots absorb them in toxic concentrations. Certain mineral salts essential for plant growth, such as calcium phosphate, become less soluble and less available to plant at a higher pH. An acidic soil has a relatively reduced ability to bind postiviely charged ions to it.

24 Soil Porosity and Permeability Porosity - volume of water that “fits between” the soil particles Permeability - rate of flow of water through soil % retention - how much water is “trapped” by soil Porosity and Permeability are directly related; when one is high, the other is high as well. % water retention is inversely related to both. ______________________________________________________________ Clay -  porosity  permeability,  retention 2) Silt -  porosity,  permeability,  retention 3) Sand -  porosity,  permeability,  retention 4) Organic matter -  porosity,  permeability,  retention

25 Major soil Groups Spodosol Regions with colder climate, ample precipitation, and good drainage Coniferous forest Do not make good farmland because they are too acidic and are nutrient-poor because of leaching. Refer Page number 343 in your text book for diagrams

26 Alfisol Brown to gray-brown A-horizon Moderately weathered forest soils Found: Moist temperate forest biomes Most organic material is found in living plants Adequate for agriculture if supplemented with fertilizer or organic material

27 Mollisols Primarily found in temperate, semiarid grasslands Fertile soils Dark brown to black A –horizon rich in humus Soluble minerals remain in the upper layers because precipitation is not great enough to leach them into lower layers. Best agricultural soil Most of the world’s grain crops are grown in mollisols.

28 Aridisols Thin light colored and contain a lot of sand. Found: Dry lands and deserts Susceptible to salinization Crops can be grown on aridisols, if water is supplied by irrigation

29 Oxisols Low in nutrient minerals Exist in tropical and subtropical areas with ample precipitation Little organic material accumulates on the forest floor (O- hroizon) because leaves and twigs are rapidly decomposed. A-horizon is rich with humus Most organic matter is found in living plants

30 Soil Problems Soil erosion Mineral depletion of the soil Soil salinization Desertification Sustainable soil use The wise use of soil resources, without a reduction in the amount of fertility of soil, so that it is productive for future generation

31 Soil Erosion Wind, water, ice, and other agents promote soil erosion Rainfall loosens soil particles, and then transported by moving water. Effects of soil erosion Reduces the amount of soil in an area and limits the growth of plants Causes a soil to lose its fertility because essential nutrient mineral and organic matter in the soil are removed. Leads to loss of productivity of crops and use of more fertilizers Sediments that gets into water bodies affect water quality and fish habitats. Sediments with pesticides add to pollution

32 Cause and prevention of soil erosion Poor soil management practices Poor agricultural practices Removal of natural plant communities Unsound logging practices Clearcutting large forested areas Sufficient plant cover limits the amount of soil erosion. Roots help to hold the soil in place.

33 The American Dust Bowl Read page number 346 in your text book

34 Nutrient mineral depletion As plant and animal detritus decomposes innatural ecosystems, nutrient minerals are cycled back to the soil for reuse. In agriculture, much of the plant material is harvested. Because the nutrient minerals in the harvested portions are unavailable to the soil, the nutrient cycle is broken, and fertilizer must be added periodically to the soil. Learn more about mineral depletion in Tropical Rainforest soils (page number 348)

35 Soil Salinization The gradual accumulation of salt in a soil, often as a result of improper irrigation methods. Irrigation water contains small amounts of dissolved salts. The continued application of such water, leads to the gradual accumulation of salt in the soil. When the water evaporates, the salts are left behind, particularly in the upper layers of the soil, which are the layers important for agriculture. The level can get high to an extent that plants can get poisoned or their roots get dehydrated. When soil is waterlogged, capillary movement may carry salts from groundwater to the soil surface, where they are deposited as a crust of salt.

36 Salinization & Waterlogging


38 Desertification

39 Asia and Africa the largest land areas with extensive soil damage, and rapid population growth is the main cause. Prolonged periods of drought (Sahel). During droughts the soil cannot support crop or grazing animals. The Sahelians must use the land to grow crops or they will starve. Overexploitation leds to desertification To reclaim the land would require restricting its use for many years so it could recover.

40 Soil conservation and Regeneration Conservation tillage Crop rotation Contour plowing Strip cropping Terracing Shelterbelts

41 Conservation Tillage Decaying residues from the previous year’s crop (rye) surround young soybean plants in a field in Iowa. Conservation tillage reduces soil erosion as much as 705 because plant residues from the previous season’s crops are left in the soil, partially covering it and helping it hold it in place until the newly planted seeds are established

42 Crop rotation The planting of a series of different crops in the same field o over a period of years

43 Contour plowing, Strip Cropping, and Terracing Plowing that matches the natural contour of the land. Furrows run around hills rather than in straight rows. Strip cropping, a special type of contour plowing, produces alternating strips of different crops along natural contours. For example, alternating a row crop such as corn with a closely sown crops such as wheat reduces soil erosion Terracing: nutrient minerals and soil are retained on the horizontal platforms instead of being washed away.


45 Preserving Soil Fertility pros and consfertilizers List and describe some of the pros and cons of using fertilizers. What different sorts of fertilizers are available? Experimental data comparing methods! Click on the picture!

46 Organic and Inorganic Fertilizers Organic fertilizers include natural materials as animal manure, crop residues, and compost. They are complex and their exact composition vary. The nutrient minerals in the organic fertilizers become available to plants only as the organic material decomposes. They are slow-acting and long- lasting Inorganic fertilizers are manufactured from chemical compounds and their exact composition are known. They are immediately available to plants. They also quickly leach away.

47 Use of Inorganic Fertilizers Highly soluble Mobile and often leach into groundwater or surface run-off, polluting the water. Do not improve the water holding capacity of soil as organic fertilizers do They are also a source of nitrogen containing gases that are air pollutants Production of commercial inorganic fertilizers requires a great deal of energy

48 Soil Nutrients (NPK) Organic - animal manure, bone meal, compost (slow-acting, long-lasting) Delay in availability to plants, needs time for the organic material to decompose Delay causes low level of nutrient leaching Improves water holding capacity Inorganic - Manufactured from chemical compounds (fast-acting, short-lasting) Highly soluble so immediately available to plants High solubility also makes it leach quickly (pollutes water) Suppresses growth of microorganisms Source of nitrogen gases that increase air pollution Production requires much energy from fossil fuels, increasing CO 2 emissions.

49 Soil Reclamation Stabilizing the land to prevent further erosion Restoring the soil to its former fertility To stabilize the land, the bare ground is seeded with plants that eventually grow to cover the soil, holding it in place. After the Dust Bowl, land in Oklahoma and Texas was seeded with drought- resistant native grasses. Plant shelterbelts to lessen the impact of wind ( a row of trees planted as a windbreak to reduce soil erosion of agricultural land. Restoration of soil fertility to its original level is a slow process. Use of the land must be restricted it cannot be farmed or grazed

50 Agroforestry Concurrent use of forestry and agricultural techniques on the same land area to improve degraded soil and offer economic benefits. For example nitrogen fixing acacias and other trees might be intercropped with traditional crops such as millet and sorghum. The trees reduce soil erosion, regulate the release of rainwater into groundwater and surface waters, provide habitat for the enemies of the crop pests, fix nitrogen and improve soil fertility, when the leaves fall they decompose, and add nutrients to the soil. Over time the degraded land improves. Higher crop yield, forest provides the farmer with food such as fruits and nut, wood, and other products.

51 Soil conservation Policies in the United States The Soil conservation Act of 1935 Conserve natural resources on private lands The Food Security Act (Farm Bill) of Requires farmers with highly erodible land to develop and adopt a five-year conservation plan for their farms that includes erosion-control measures. If they don’t comply, they lose federal agricultural subsidies such as price supports. The Conservation reserve Program (CRP) is a voluntary subsidy program that pays farmers to stop producing crops on highly erodible farmland

52 READ Practicing Environmental Principles Page 351. Go over the rock cycle, formation of rocks and minerals, types of rocks, weathering and erosion from the given handout. Environmental Science Friedland (Pagenumber )

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