Presentation on theme: "Definition of Soil The outermost solid layer of the Earth"— Presentation transcript:
1 Definition of Soil The outermost solid layer of the Earth A natural product formed from weathered rock by the action of climate & living organismsA collection of natural bodies of earth that is composed of mineral & organic matter, & is capable of supporting plant growth
2 Soil FormationVideo: Soil Formation Soil formation - Parent material is slowly broken down by biological, chemical and physical weathering. Biological - Respiration of plant roots and other organisms produce CO2, which reacts with soil water to produce carbonic acid (H2CO3). Chemical - Acids crack rocks water seeps in breaks down particles. Physical - Weathering introduces water that breaks down particles. Time scale - Formation of 2.5 cm of topsoil takes yrs.
4 Soil FormationComplex mixture of organic and inorganic components Parent material = starting material that affects the composition of the resulting soil Weathering = the processes that break down rocks and minerals (1st step in soil formation) Erosion = the movement of soil from one area to another38% of Earth’s surface has been converted for agriculturecultivating soil, producing crops, and raising livestock for human use and consumption
5 Soil Composition 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
8 Soil Texture determined by the proportion of particle size classes Video: Soil Texturedetermined by the proportion of particle size classestexture is partly inherited from parent material and partly a result of the soil forming processparticle classification:rock fragments (> 2.0mm diameter)sand ( mm)silt ( mm)clay (<0.002mm)texture is important for indicating pore spaceimportant in the movement of water and air, penetration by roots, and water storage capacityParticles equal 50% of the soil volume and the other 50% is pore space.45% mineral matter5% organic matter (humus*)25% air25% water
9 ClayClay is 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.Plants grown in clay soils are more susceptible to waterlogging, and oxygen depletion (think small pore size, low porosity).
10 SiltSilt is rock worn into tiny pieces (coarser than clay, but finer than sand).Silt is usually 1/20 millimeter or less in diameter.
11 SandSand is quartz or silica worn down over time.Sand grains have diameters between 0.06 mm to 2 mm.Plants grown in sandy soils are more susceptible to mineral deficiencies and drought.
12 Loam Loam is soil containing a mixture of clay, sand, silt and humus (organic matter). Loam is good for growing most crops - ideal agricultural soil. 40% sand (larger - structural support, aeration, permeability) 40% silt (smaller - holds nutrient minerals and water) 20% clay (even smaller - holds nutrient minerals and water)
13 Soil Porosity and Permeability Porosity - volume of water that “fits between” the soil particlesPermeability - rate of flow of water through soil% water retention - how much water is “trapped” by soil, the amount of water per unit volume a soil can hold is influenced by texture, clay minerals, organic content, particles, & soil structurePorosity and Permeability are directly related - when one is high, the other is high as well% water retention is inversely related to both
14 Soil ProfileSoil profile – distinctive layering of horizons in the soil.Soil horizon – developmental layers in the soil with its own characteristics of thickness, color, texture, structure, acidity, and nutrient concentration.
16 O = Organic or litter layer A = Topsoil; mostly inorganic minerals with some humus (organic materials); crucial for plant growthE = Eluviation horizon; leaching = a process whereby solid materials are dissolved and transported awayB = Subsoil; zone of accumulation of leached minerals and organic acids from aboveC = Slightly altered parent materialR = BedrockHumus = any organic matter that has reached a point of stability, will not break down any further, contributes to moisture and nutrient retention
19 Soil Acidity (pH) pH - concentration of H+ ions Scale - From 0 (very acidic) to 14 (very basic, or alkaline)pH of most healthy soilspH matters because it affects solubility of nutrient mineralsAluminum and Manganese are more soluble in low pH - roots sometimes absorb too much (toxic levels)Soil pH affects leaching - high pH increases leaching of important ions such as K+Causes of changes - acid rain, decomposition, leaf litter, mining (acid sulfate soils)Remediation- Too high pH, add acidic leaf litter- Too low pH, add lime
21 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 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 microorganismsSource of nitrogen gases that increase air pollutionProduction requires much energy from fossil fuels, increasing CO2 emissions.
22 Fertilizers Organic… manure adds N and soil bacteria & fungi green manurecompostmushroom sporesInorganic…1/4th of the world’s crops depend on this.N, K, PExperimental data comparing methods!Click on the picture!
26 Soil Degradation Natural Artificial Wind, weather, water Most of the world’s soil is not ideal for agricultureWe are losing 5–7 million hectares (12–17 million acres) of productive cropland per yearNaturalWind, weather, waterArtificialOver cultivating, poor planningOvergrazing rangelandDeforestation, especially on slopes
30 Soil Conservation Soil moves….due to water, wind, and people Loss of topsoil…the most fertileSoil ends up as sediment in water
31 Soil Conservation Drought and degraded farmland produced the 1930s DUST BOWL:Drought and degraded farmland produced the 1930sStorms brought dust from the U.S. Great Plains all the way to New York and Washington
32 Soil Conservation Legislation in recent years: As a result of the Dust Bowl, the U.S. Soil Conservation Act of 1935 and the Soil Conservation Service (SCS) were createdLocal agents in conservation districts work to educate farmers and help them conserve soilLegislation in recent years:Food Security Act of 1985Conservation Reserve Program, 1985Freedom to Farm Act, 1996Low-Input Sustainable Agriculture Program, 1998
33 Soil Testing Soil Texture Soil Porosity Soil Permeability Soil MoistureSoil Fertility – pH, NPKSoil Salinity – we will set this up next week as a separate lab