Chapter 4: Soil Architecture and Physical Properties Introduction to Soils Chapter 4: Soil Architecture and Physical Properties

Physical Properties Physical Properties of the soil will deal with the particle aggregation as well as texture, colloidal properties, surface area, pore spaces, water in the soil and other physical properties.

SOIL COLOR Color plays an important role in differentiating different conditions of the soil.

Color Classification System Munsell color charts 1) Hue – red to yellow color of the soil 2) Chroma – brightness of the color –0 neutral gray 3) Value – lightness or darkness of the soil –0 being black

Color can give a clue to: OM content Water content Oxidation states of iron and possibly manganese oxides.

Dark Soils Usually high in organic matter Rich soils if there is not too much water

Light Soils Sandy High salts, gypsum or lime

Light Brown to Red Aging soils iron – oxidizing Drainage is fair

Bluish - Gray They have poor drainage Indicates no 02 in soil and could smell rotten called - Gleying soils

Mottled Colors Indicates a period of water logged and then drying out

The Soil Separates (USDA) SOIL TEXTURE the amount of sand silt and clay in the soil The Soil Separates (USDA) Sand - .05 – 2 mm Silt .05 - .002 mm Clay less then .002mm

Soil Texture triangle allows the classification of the soil texture into 12 classes.

Determining soil texture Ribbon test No ribbon – sandy loam Shorter then 1” – loam, silt, silt loam 1-2” – Sandy clay loam, silty clay loam, clay loam 2-3” – Sandy clay, silty clay clay

Measuring the soil separates in a jar Can one change soil texture?

Surface area considerations: It is the surface area of the soil that has the ability to hold water and be a site for chemical activity. The greater the surface area the greater the chemical activity and possible nutrient holding ability.  

Surface area of the soils and its affect Water holding capacity, fertility and total pore space. Sand Silt Clay

Total pore space of the soil Soil Porosity Total pore space of the soil Sand has less than clay Determining porosity %: Wet weight (grams) – dry weight (grams) Soil volume (cm3) X 100 = %

Permeability How the water moves through the soil Sand is rapid and clay is slow Textural types and their characteristics ie Soil Porosity, Permeability a) Clayey b) Silty c) Sandy

Soil Structure Soil Structure is how the soil separates combine to form larger aggregates

Types of structure peds natural formation clods caused by tillage a. Granular- ideal agronomic structure accomplished through correct cultural practices: in the A horizon Minimum tillage, done at the correct time incorporating organic matter and encouraging microbial action b. Platy- Usually in the lower depths of the A horizon or compacted soils c. Blocky- in the B horizon large aggregates that slows water penetration e. Single grain- Structure less – the absence of soil structure. f. Massive- Structure less - concrete

Structure Formation Soil adhesives released by fungi and organisms Good soil structure can be encourage through proper cultivation Organic matter Gypsum Culture practices done when soil is at proper water retention Avoid compaction 1) Equipment 2) Reduction of traffic through the field 3) Keep vegetation on the soil a.    

Soil Consistence Refers to soils ability to resist crushing and its ability to be molded. Such as for most soil Loose, Very Friable, Friable, Firm, Very Firm and extremely firm.

Soil Tilth Physical condition of the soil after tillage usually the granular form Compaction is detrimental to good soil tilth- Compaction causes Reduced porosity and permeability Reduced gas exchange Slow percolation rate and slow drying rate. Restricted root growth

Soil Particle Density As to the specific weight of the soil particles. This is a direct correlation to the parent material and should be between 2.6 to 2.75 g/cm3

Bulk Density Is the weight over volume. This will determine the amount of pore space in the soil. Clay – 1.15 Silt – 1.35 Sand – 1.8

Soil Temperature Corn needs 65-70F Germination is dependant on proper soil temperature. Corn needs 65-70F Most warm season crops need warm soil Root growth is more abundant when soil temperatures Soil Characteristics that affect temperature Dark soils warm fast Rocky soils warm fast Sandy soils warm fast Grandular loose soils warm quicker then compacted soils

Formation and Stabilization of Soil Aggregates:

Formation and Stabilization of Soil Aggregates: Both biological and physical processes are responsible for soil aggregates Physical Chemical Processes: Flocculation of Clays Clays will be the first to join together as they are attracted to each others negative and positive sides. Together with humic acid binds together the individual particles acting like glue to bind them together.

Biological Processes: Soil organisms – help bind particles together Earth worms Root exudates Fungal products ie glomalin Bacteria

Is the principle method of soil aggregate stabilization. OM Is the principle method of soil aggregate stabilization.