Soil Resources

Chapter 15

Soil ResourcesRead 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.

Soil DefinitionsThe unconsolidated organic and mineral material on the earths surface that is capable of supporting plants. (MA Envirothon Team Resource Manual)

A dynamic natural body, in which plants grow, that is composed of mineral and organic materials and living organisms. (Brady & Weil, 11th Ed.)3Note the difference in the dynamic aspect of the definitions.Soil-Forming FactorsParent 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 changesTopography (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 matterTime Grasslands soil have rich organic matterHow long climate has been altering parent material over geologic time

Soil Composition Soil Composition45% 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

5Components 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 coloniesSoil Nutrients (NPK)

Organic - animal manure, bone meal, compost (slow-acting, long-lasting)Delay in availability to plants, needs time for the organic material to decomposeDelay causes low level of nutrient leachingImproves water holding capacityInorganic - Manufactured from chemical compounds (fast-acting, short-lasting)Highly soluble so immediately available to plantsHigh solubility also makes it leach quickly (pollutes water)Suppresses growth of microorganisms Source of nitrogen gases that increase air pollutionProduction requires much energy from fossil fuels, increasing CO2 emissions.

7Soil Horizons

Soil horizonO Horizon: Organic or litter layer, topmost layerA Horizon: Topsoil; mostly inorganic minerals with some organic material and humus mixed in; crucial for plant growthE Horizon: Eluviation horizon; loss of minerals by leaching, a process whereby solid materials are dissolved and transported away, only found in forested areas, light coloredB 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 materialR Horizon: Bedrock

Soil Organisms 10Food web in soil courtesy of Jim Turenne.

Fungi Ecosystem services provided by soil organisms Maintaining soil fertility by decaying and cycling organic materialEarthworms 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.

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 leftOver 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.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. Soil characterizationSoil can be characterized by color and several other traits:TextureStructurepH

Soil TextureDetermined by size of particles

Three main categories:

Clay = particles < 0.002 mm diameter

Silt = particles 0.0020.05 mm diameter

Sand = particles 0.052.0 mm diameterBest for plant growth is loam, an even mix of these three types.

Physical differencesThe 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 differencesSoil 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, NO3, PO4.17Physical and chemical differences between sand & clay sized particles.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. Soil Texture ChartIt 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.

20Textural triangle showing the 12 main textural classes.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 diameter3) 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.21

22Flow chart for the feel method.Soil pHMost soil ranges from 4 to 8The soil of the Pygmy forest in Mendocino County, California, is acidic, with a pH of 2.8 to 3.9Soils in Death Valley, California, have a pH of 10.5At 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.Soil Porosity and PermeabilityPorosity - volume of water that fits between the soil particlesPermeability - rate of flow of water through soil% retention - how much water is trapped by soilPorosity 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

Major soil GroupsSpodosol Regions with colder climate, ample precipitation, and good drainageConiferous forestDo 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 Alfisol Brown to gray-brown A-horizonModerately weathered forest soilsFound: Moist temperate forest biomesMost organic material is found in living plantsAdequate for agriculture if supplemented with fertilizer or organic material

Mollisols Primarily found in temperate, semiarid grasslandsFertile soilsDark brown to black A horizon rich in humusSoluble minerals remain in the upper layers because precipitation is not great enough to leach them into lower layers.Best agricultural soilMost of the worlds grain crops are grown in mollisols.Aridisols Thin light colored and contain a lot of sand.Found: Dry lands and desertsSusceptible to salinizationCrops can be grown on aridisols, if water is supplied by irrigation

Oxisols Low in nutrient mineralsExist in tropical and subtropical areas with ample precipitationLittle organic material accumulates on the forest floor (O-hroizon) because leaves and twigs are rapidly decomposed.A-horizon is rich with humusMost organic matter is found in living plantsSoil ProblemsSoil erosionMineral depletion of the soilSoil salinizationDesertificationSustainable soil useThe wise use of soil resources, without a reduction in the amount of fertility of soil, so that it is productive for future generationSoil ErosionWind, water, ice, and other agents promote soil erosionRainfall 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 plantsCauses 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 fertilizersSediments that gets into water bodies affect water quality and fish habitats.Sediments with pesticides add to pollution

Cause and prevention of soil erosionPoor soil management practicesPoor agricultural practicesRemoval of natural plant communitiesUnsound logging practicesClearcutting large forested areasSufficient plant cover limits the amount of soil erosion. Roots help to hold the soil in place.The American Dust BowlRead page number 346 in your text bookhttp://www.youtube.com/watch?v=x2CiDaUYr90

Nutrient mineral depletionAs 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)Soil SalinizationThe 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.Salinization & Waterlogging

36Salinization & Waterlogging

37Desertification

Desertification 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 desertificationTo reclaim the land would require restricting its use for many years so it could recover. Soil conservation and RegenerationConservation tillageCrop rotationContour plowingStrip croppingTerracingShelterbelts

Conservation TillageDecaying residues from the previous years 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 seasons crops are left in the soil, partially covering it and helping it hold it in place until the newly planted seeds are established

Crop rotation The planting of a series of different crops in the same field oover a period of years

Contour plowing, Strip Cropping, and TerracingPlowing 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 erosionTerracing: nutrient minerals and soil are retained on the horizontal platforms instead of being washed away.

Preserving Soil Fertility 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!45Organic and Inorganic FertilizersOrganic 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-lastingInorganic fertilizers are manufactured from chemical compounds and their exact composition are known. They are immediately available to plants . They also quickly leach away.Use of Inorganic FertilizersHighly solubleMobile and often leach into groundwater or surface run-off, polluting the water.Do not improve the water holding capacity of soil as organic fertilizers doThey are also a source of nitrogen containing gases that are air pollutantsProduction of commercial inorganic fertilizers requires a great deal of energySoil Nutrients (NPK)

Organic - animal manure, bone meal, compost (slow-acting, long-lasting)Delay in availability to plants, needs time for the organic material to decomposeDelay causes low level of nutrient leachingImproves water holding capacityInorganic - Manufactured from chemical compounds (fast-acting, short-lasting)Highly soluble so immediately available to plantsHigh solubility also makes it leach quickly (pollutes water)Suppresses growth of microorganisms Source of nitrogen gases that increase air pollutionProduction requires much energy from fossil fuels, increasing CO2 emissions.

48Soil Reclamation Stabilizing the land to prevent further erosionRestoring the soil to its former fertilityTo 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 grazedAgroforestry 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.Soil conservation Policies in the United StatesThe Soil conservation Act of 1935Conserve natural resources on private landsThe Food Security Act (Farm Bill) of 1985.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 dont 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 farmlandREADPracticing Environmental PrinciplesPage 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 217-220)