  Forms Framework for soil and gives stability when mixed with finer particles.  Does not stick together  Spherical structure  Contributes little to plant nutrition  Quartz Sand

  Spherical like sand but smaller  Feels smooth without being sticky  Fine enough to suspend in flowing water  “silted in”  Loess – wind deposited material Silt

  Secondary minerals formed by drastic alteration of parent material.  Plate- like shape  So small they can only be seen with high powered electron microscope. Clay

  % Sand, Silt, Clay  Sand –> 2mm-0.05mm  Silt -> mm  Clay -> less than 0.002mm Texture

6 / 25 Soil Texture  Relative proportions means that once you know 2 can determine the third  See text for copy of texture triangle

7 / 25 Evaluating Soil Texture  Measure only mineral particles < 2mm diameter  Several ways to obtain this number!  30% silt  40% sand  25% clay

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  Rubbing moist soil between thumb and forefinger.  Gritty - sand  Slippery but not sticky – silty  Very sticky and can form ribbon - clayey  Mixture of sand, silt, clay = Loam  Simple loam – 20%Clay, 40%silt, 40%sand Texture field tests

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 11 / 25 What is Soil Structure?  Arrangement of soil particles  clustered units of soils or Peds  Resulting from  biological,  physical,  And chemical forces  Aggregates are the soil granules  particles that are held together or “bonded,” by organic matter (clay and humus)  Granular aggregates are most desirable!

  Granular – A Horizon, dark surface soil w/organic matter. Drains quickly  Platy – occurs between A&B horizon, humid climate necessary, “hard pan”, poor drainage  Blocky – B horizon, subsoil, moderate drainage, humid regions with forests. (encourages root development)  Prismatic – B horizon in arid environment (desert and prairie) Fibrous root systems common.  Columnar – In sodium-affected soils of grassland regions  Massive – Highly compacted soil  Loose – No structure present (beach sand) Soil Structure Shape

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 Good and Bad

  Well-Aggregated = High-quality soil  Destructive forces  Raindrop impact, wetting rapidly, rapid freezing, intensive tillage, compaction  Takes several years for soil to recover  Soil without humus becomes cloddy when repeatedly tilled.  Good management  Organic matter addition, closely spaced vegetation with fibrous roots, protect bare soil from rain. Benefits of Aggregation

17 / 25 Deterioration of Soil Structure  Compaction  Increased by influx of Na+  Causes small particle dispersion  Restricts water percolation  Affects chemistry  Another reason road salt is bad!

 18 / 25 Pore Size and Permeability  Pore spaces = voids  Macropores & Micropores  Relation to the environment:  Gravitational Water  Relation to plant roots:  To plants: pore sizes are more important than total pore space  A balance of large and small pores is the result of soil texture

  Macropores and Micropores  Good structured soils have 50% porosity  Amount and size important  Density – bulk density  Solid particles and the pore size between them  Compaction increases density  Water 1g/cm 3  The greater the Bulk density the less the pore space. Porosity

  Can indicate soil hydrology and mineral composition  Measured 3 ways  Hue – spectral color  Value – lightness /darkness  Chroma – purity of color  Hue  Brown: decomposed organic matter  Red-yellow: oxidized minerals (Iron oxides)  Black: Rich organic matter (muck)  White: Sandy soils (quartz)  Gray: Limestones or clay (iron reduced)  Many soils mottled Soil Color

21 / 25 Munsell Soil Color Chart  Hue: dominant color from spectrum  Value: amount of reflected light (blackness or whiteness)  Chroma: color purity

  Temp: Most variable at upper levels  All Equipment must be below the frost line  Moisture  Determines consistency  Water must be available to plants - transpiration  Solvent for nutrients  Testing:lysimiter, neutron probe, conductivity block  Moisture retention forces  Adhesion: water to soil (clay/humus)  Cohesion: water to water Soil Temp. and Moisture

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  1.The degree to which water clings to the soil is the most important soil water characteristic to a growing plant. This concept is often expressed as soil moisture tension. Soil moisture tension is negative pressure and commonly expressed in units of bars. During this discussion, when soil moisture tension becomes more negative it will be referred to as "increasing" in value. Thus, as soil moisture tension increases (the soil water pressure becomes more negative), the amount of energy exerted by a plant to remove the water from the soil must also increase. One bar of soil moisture tension is nearly equivalent to -1 atmosphere of pressure (1 atmosphere of pressure is equal to 14.7 pounds per square inch at sea level).  2. A soil that is saturated has a soil moisture tension of about bars, or less, which requires little energy for a plant to pull water away from the soil. At field capacity most soils have a soil moisture tension between 0.05 and 0.33 bars. Soils classified as sandy may have field capacity tensions around 0.10 bars, while clayey soil will have field capacity at a tension around 0.33 bars. At field capacity it is relatively easy for a plant to remove water from the soil.  3.The wilting point is reached when the maximum energy exerted by a plant is equal to the tension with which the soil holds the water. For most agronomic crops this is about 15 bars of soil moisture tension. To put this in perspective, the wilting point of some desert plants has been measured between 50 and 60 bars of soil moisture tension. Handout – Moisture Tension

  Unit: ATM (Atmosphere Moisture Tension)  Moisture Categories  1.Gravitational Water - 0ATM  2.Field Capacity Water – 1/3 ATM  3.Wilting Point Water – 15 ATM  4.Hydroscopic Water - 31 ATM  Categories change depending on seasons  Salt will affect soil moisture tension  As soil moisture tension increases the amount of energy exerted by a plant to remove the water from the soil must also increase. Soil Moisture Tension

  Environmental Conditions  Temp.  Humidity  Wind  Site Exposure  Soil Properties  Moisture Content  Location of soil Moisture  Resistance to moisture flow  Plant Factors  Extent of root system  Type of plant (physiological Makeup)  Age/ Growth Rate  Health  Fungi Water Absorption by Plants

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 “Illinois Bus Ride”

 Lupines, lespedezas, Basptisians

 Parvenu quack-grass

 Puccoons

 Dogfennel Horsethistle

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