the dirt on soil! an introduction to soil chemistry

Mrs. LongHorticulture I

Fall 2013

The Dirt on Soil!An Introduction to Soil Chemistry

What is soil?

Soil is the unconsolidated cover on the surface of the earth.

Soil is made up of mineral particles, organic particles, air and water.

Soil is capable of supporting plant growth.

Soil ComponentsThe 4 parts of soil

MineralMatter45%

SoilWater25%

SoilAir

25%

OrganicMatter

5%

About ½ of the soil volume is solid particles

About ½ of the soil volume is pore space

Anchor plant rootsSupply water to plant rootsProvide air for plant rootsFurnish nutrients for plant

growthRelease water with low levels

of nutrients

Functions of agricultural soils

Organic matter is the glue that holds the aggregates together

Large pores (spaces) between aggregates are filled with air in a moist soil.

Small pores are filled with water in a moist soil. Even smaller pores inside the aggregates (not shown) are also filled with water.

Soil StructureThe arrangement of sand, silt, and clay particles to form larger aggregates. How they fit together!

1/10 inch

SandLoose

SiltyGranular

ClayeyPlaty or

Blocky

Soil Structure

The mineral part of soil consists of sand, silt, and clay particles

Sand – Largest particles – low moisture holding capacity

Silt – Medium particles – good moisture holding Clay – Smallest particles – Hold a lot of water Loam – equal parts sand, silt, clay – ideal texture!

Soil Texture

Sand0.1 – 0.002 in2 – 0.05 mm

Silt0.002 – 0.0001 in0.05 - 0.002 mm

ClayLess than 0.0001 inLess than 0.002 mm

1/100 in

Parent MaterialMechanical weathering – breaks down rock

into smaller pieces without changing soil chemistry

Chemical weathering – breaks down rocks into smaller pieces by chemical reaction

Biological weathering – results from activities of living organisms

Where does soil come from?

Mechanical Weathering

Chemical Weathering

Biological Weathering

Bring a small soil sample from your yard at home.Make sure its clean.Bring in a full quart-sized ziploc bag full of soilYOUR NAME has to be on it!!

Homework for 04/

5.02 Discuss the soil profile and soil sampling for surface and subsurface layers.

10/31/12

Soil Sampling

Soil Particle Size Lab (Part I)Take your soil sample (1 per group)Place a cup full of soil into a jarFill the jar to the top with water and tighten

the lid.Shake for 3 minutes.Set to side (labeled) until tomorrow!

Before we start today:

Soil LayersSoil layers are called

horizons.Layers parallel to

earth’s surfaceDefined usually by

color, texture and physical features.

O horizonThe O horizon

contain Organic matter

Uppermost dark Colored

Most fertileMade of leaves,

twigs, waste, decaying matter

A horizonTopsoilPorous mix of humusJust below the OHome to earthworms

and microorganismsBrown in color

B horizonSubsoilClayey with high

mineral contentBrownish redReceives a lot of

leached material

C horizonParent materialClumps of

unweathered rocks

R horizonBedrockCannot be dug by

handVery few roots can

penetrate

PurposeDetermines levels of

fertility in soil Use this information

to make accurate fertilizer recommendations for growing plants

A soil test shows deficiencies, excesses and imbalances can be avoided.

The Soil Testing Laboratory Kits are available at

local garden centersSubmit samples to

NC Dept of Agriculture and Consumer Service Agronomic Division

https://www.youtube.com/watch?v=vb5wtgaKGUs

Lime & Fertilizer Recommendations

Information from a soil test will help you select the proper liming and fertilization program to obtain optimal growth of lawn, garden and ornamental plants.

Step 1Create a visual grid

of the area to be planted.5-10 subsamples

from the siteSample before the

growing season

Step 2Use a stainless steel

soil-sampling probeTake the surface

sample to tillage depth4 inches for lawns6-8 inches for crops

Step 3Mix soil samples

together.

Step 4 Remove any:

GrassRocksAny other material

SOIL ONLY!!

Step 5Place soil samples in

a boxGet one from County

ExtensionAlso need Soil

Sample Information Sheet

Step 6Send soil tests to

RaleighFree for residents

NCDA&CS Agronomic Services DivisionMailing Address: 1040 Mail Service Center, Raleigh NC 27699-1040Physical Address: 4300 Reedy Creek Road, Raleigh NC 27607-6465Phone: (919) 733-2655; FAX: (919) 733-2837

Perform the: Soil Testing Webquest (Activity 5.02.02)

Classwork

Making “Dirt”Bedrock at bottom - RParent material - CSubsoil - BTopsoil - AOrganic matter – O

Today’s Lineup

Types of Horticulture Soils

Peat MossOrganicPartially decomposed

material from Swamps

Holds moisture

Perlite

InorganicNatural volcanic

materialHelps with soil

aeration and water holding capacity

Organic MatterDead plant or animal

tissueContains Carbon!

Decayed organic matter

Used for soil conditioning

Fertilizer

OrganicCompost

BarkOrganicLarger matterPromotes drainageMainly for trees and

shrubs

Sphagnum MossOrganicDehydrated bog

plantsHolds moistureVery acidicHanging baskets

AdvantagesSterilepH is neutralDisease and weed

freeGood for starting

plantsEasy to mixImproves plant

uniformity

ExpensiveLight weight

Horticulture SoilsDisadvantages

HydroponicsThe process of

growing plants without soil.

No soil & problems associated with soil.Easy to control nutrient content of plants.

Advantage of Hydroponics

Plant support must be provided with strings, wires, or stakes.

Water quality must be high.Diseases spread through water.More moisture or humidity in air to cause

favorable environment for disease organisms.More expensive.

Disadvantages of Hydroponics

Hydroponic Lettuce

Background on Today’s Lab

Soil pH is a measure of the acidity or alkalinity of soils

pH ranges from 0-14, 7 being neutralIdeal pH is 5.5-7.5

pH

LimeRaises the soil pH Lowers the soil pH

pHCalcium/Sulfur

Soil Texture TriangleGive names to soils

combosClay

Sandy ClaySilty ClayClay LoamSandy Clay LoamSilty Clay Loam

LoamSandy LoamSilty Loam

SandLoamy Sand

Silt

PermabilityRate at which water moves through the soil

Physical Properties of Soil

Water Holding CapacityAbility of soil to hold water for plant use

Physical Properties of Soil

PorosityAmount of air space between particles

Physical Properties of Soil