Envirothon

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Soil Science Basics For Evirothon John Sloan Texas Agricultural Experiment Station Dallas

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Soils/Land Use Envirothon Key Points 1S Recognize soil as an important and dynamic resource. 2S Recognize and understand the features of a soil profile. 3S Describe basic soil properties and soil formation factors. 4S Understand the origin of soil parent materials. 5S Identify soil constituents (clay, organic matter, sand and silt). 6S Identify and list soil characteristics (e.g., texture, structure, etc.) and their relation properties. 7S Determine basic soil properties and limitations (e.g., mottling and permeability) by observing a soil pit or a soil profile. 8S Understand the nature of plant nutrients, and how they are held by soil. 9S Recognize the characteristics of wetland (hydric) soils. 10S Understand soil drainage classes and know how wetlands are defined. 11S Understand soil water, its movement, storage, and uptake by plants. 12S Understand the effects of land use on soils. 13S In land use planning discussions, discuss how soil is a factor in or is impacted by non-point source pollution. 14S Identify types of soil erosion and discuss methods for reducing erosion. 15S Utilize soil information, including a soil survey.

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1S Recognize soil as an important and dynamic resource.

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Chemical Physical Biological

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Five Crucial Ecological Roles of Soils Medium for plant growth Recycling system for nutrients and organic wastes Habitat for soil organisms Engineering medium System for water supply and purification

Slide6: 

A healthy soil has abundant biological activity. Biological activity contributes to beneficial chemical and physical soil properties.

Living Organisms: Microorganisms: 

Living Organisms: Microorganisms

Living Organisms: Soil Animals: 

Living Organisms: Soil Animals Nematodes Earthworms Springtails Mites Ants and termites Millipedes, centipedes

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2S Recognize and understand the features of a soil profile.

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O A B C E

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Vegetation has an effect on the formation of the soil profile O A E Bt C1 C2 A1 A2 Bt C1 C3 C2k

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3S Describe basic soil properties and soil formation factors.

Soil Forming Factors: 

Soil Forming Factors Parent material – (unconsolidated material in which soil development occurs) Climate – (temperature and precipitation) Biota – (living organisms and organic residues) Topography – (slope, aspect, elevation) Time

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4S Understand the origin of soil parent materials.

Slide15: 

Parent Materials Formation, Transportation and Deposition

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5S Identify soil constituents (clay, organic matter, sand and silt). 6S Identify and list soil characteristics (e.g., texture, structure, etc.) and their relation properties.

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What’s in soil? *

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Soil Color

Soil Color: 

Soil Color A good indicator of organic matter content Light color=low OM; dark color=high OM Also influenced by parent material Compare the red soils of East Texas to the Blackland soils of Central Texas

Soil Texture: 

Soil Texture Sand Silt Clay

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Medium Sand Course Sand 0 mm 1 mm 2 mm Relative Sizes of Soil Particles Fine Sand Very Fine Sand Silt Clay

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Number of particles per soil volume

Texture: 

Texture Texture can be estimated by the ribbon and feel method long ribbon = high clay no ribbon = sandy soil Major influence on water holding capacity Sand = low water holding capacity Clay = high water holding capacity Silt = high “available water” capacity

Soil Structure: 

Soil Structure

Soil structure: 

Single grained **Aggregated** Massive (Sand) (Silt loam) (brick) Soil structure Refers to the binding of soil particles into aggregates due to the presence of organic matter, clays, and oxides Good structure allows movement of water and air through the soil and into the rooting zone. Range of soil structures

How to improve soil structure: 

How to improve soil structure Increase soil organic matter with: Compost Manures Mulches Cover crops (green manures)

Slide29: 

11S Understand soil water, its movement, storage, and uptake by plants.

Soil Water: 

Soil Water Mostly affected by soil texture Soil water terms Gravitational water Capillary water Hygroscopic water

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Saturation -all pores are completely filled with water Field Capacity -most pores are filled with water except for the largest Wilting Point -only small pores contain water

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0% Water-filled pore volume 100% Oven Air Wilting Field Saturated Dry Dry Point Capacity

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Field Capacity Available water Unavailable water 0 30 20 10 Percent Soil Water Sand Sandy Loam Loam Silt Loam Clay Loam Clay Wilting Point

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Three-dimensional plot of infiltration rates for sandy soils

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Three-dimensional plot of infiltration rates for clay soils

Sandy textured soils: 

Sandy textured soils Water infiltrates and drains quickly, even when wet. Soil does not have a large reservoir of plant available water. Soils dry out quickly, leaving plants water-stressed.

Clay textured soils: 

Clay textured soils Water infiltrates and drains slowly, especially when the soil is already wet. The surface can become saturated fairly quickly, making the soil susceptible to erosion. The surface can become crusted and seal off water infiltration.

Slide39: 

8S Understand the nature of plant nutrients, and how they are held by soil.

Cation Exchange Capacity(CEC): 

Cation Exchange Capacity (CEC) Negative charged sites in soils that attract and “hold” positive ions (cations) K+, Na+, Mg2+, Ca2+, NH4+, Al3+, H+ Two types: Permanent (isomorphous substitution in clay minerals; Al3+ → Si4+ or Mg2+ → Al3+) pH dependent (functional groups on organic matter or broken clay edges; -O-H+, -COO-H+)

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Sources of Cation Exchange Sites Organic matter (pH dependent) Clay minerals (permanent)

Soil pH-A master variable: 

Soil pH -A master variable

Soil pH: 

Soil pH A master variable because it affects a wide range of soil properties, including: Chemical Biological Physical (indirectly)

Slide44: 

Normal pH range in soils

Slide46: 

Micronutrients

Soil Acidity: 

Soil Acidity Soils tend to become more acidic with time and weathering. What causes soil acidity?

Slide48: 

GENERAL SOIL MAP OF TEXAS Increasing soil pH Decreasing Rainfall

Alkaline SoilspH > 7: 

Alkaline Soils pH > 7 Calcareous soils High in calcium; freqently contain calcite pH is controlled by calcium carbonate chemistry pH range of 7 to 8.4 Saline and sodic soils High in sodium pH is controlled by sodium carbonate chemistry pH range of 8.4 to 10

Slide50: 

Houston Black Official State Soil of Texas Major soil in the Blackland Prairie region of Texas.

Nutrient Deficiencies in Alkaline Soils: 

Nutrient Deficiencies in Alkaline Soils Phosphorus Forms insoluble calcium and magnesium phosphate minerals at high pH

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7S Determine basic soil properties and limitations (e.g., mottling and permeability) by observing a soil pit or a soil profile.

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9S Recognize the characteristics of wetland (hydric) soils.

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Wetland Soils Organic matter accumulation

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Wetland Soils Oxydation-Reduction characteristics

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10S Understand soil drainage classes and know how wetlands are defined.

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Well Drained Moderately Well Drained Somewhat Poorly Drained Poorly Drained Relationship between landscape position and drainage class

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12S Understand the effects of land use on soils. 14S Identify types of soil erosion and discuss methods for reducing erosion.

Slide66: 

13S In land use planning discussions, discuss how soil is a factor in or is impacted by non-point source pollution.

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15S Utilize soil information, including a soil survey.