Soil Composition & Ferterlizers

Northridge Garden GuildJune 29, 2010

Materials are a condensed version of information provided by the USU extension

service

Soil Composition

Jerry L. GoodspeedUtah State University Extension

USDA NRCS

Soil – what’s in it?

Why is soil important?

Like humans, plants thrive in a healthy environment

Good soil provides nutrients, oxygen and water to plants without stressWeak plants are more susceptible to disease and insects

Components of Soil (by volume)

Water25%

Air25%

Organic Matter

5%

Minerals45%

(Oxygen to roots)

(Transpirationand nutrient transport)

(Soil structure andnutrients for plants)

(Primary soil particlesand nutrients for plants)

Different soil profiles

What does your soil look like?

Topsoil-subsoil Characteristics

-high organic matter-low salts-high nutrients

-low organic matter-high clay and/ or lime-high salts-high pH

“Topsoil”

“Subsoil”

Individual Soil Properties

Soil Texture

The Percentage of sand, silt and clay in the soil

The mineral particles:sand, silt,and clay

The Effect of Particle Size

Sand particles Clay particles

Water flow

Air flow

Determining Soil Texture

By feelSoil testjar method

Fill a 1-quart jar ¼ full of soil

Fill the jar ¾ full of waterShake very well to suspend soilPlace on a flat surface and allow soil to settle

Sand

ClaySilt

Texture Effects on Soil’s Physical Properties

Texture available water Aeration Drainage Compaction

Sand

Loam

Silt loam

Clay loam

Clay

Treating Soil Texture “Problems”

Too much sand?You are luckyAdjust irrigation accordinglySelect drought tolerant plants

Too much clay?Good luck!Select plants tolerant of poor drainage, lack of oxygen

Either case: induce soil structure

Introduction of Organic Matter

The combination of sand, silt and clay combined with organic matter creates secondary particles called aggregates

Compaction

Destroys soil structureSeals off soil surface

Water runs off instead of into soil – drought resultsAir can’t enter or escape soil -

suffocationRoots can’t penetrate the soil

Stress – plants die

Soil Compaction

Preventing Compaction

Grates, bricks, sidewalks in high-use areas

Treating compaction

Eliminate the cause:Fence, hedge, signs

Add organic matter to soilAerate or till the soil

Aeration

Hollow Tine Aerator

“Instant air spaces” for water and oxygen movement into the plant root zone

Soil Drainage

Poor Drainage Problem

Prevent compaction?Add organic matterInstall subsurface drainage system Provide drainage ditchesDevelop raised bedsUse precise water management

Excessive Drainage Problem

Very sandy soilConsider sunken bedsAdd extra organic matterPrecise water management

Amending Soil with Organic Matter

Benefits:Improves drainageImproves water-holding capacityReduces compactionProvides nutrients to plantsImproves soil “tilth” (ease of tillage, working with a soil)Lowers soil pH

How much organic matter should I add?

How much is already there?Native Utah soils ~ 0.25 to 2.0%Ideal soils 5-10%

Are you satisfied with the current condition of your soil?Add some organic matter to maintain soil conditions

Should I add sand to my clay soil?

Adding/Preserving Organic Matter

Grow plants

Mulch around perennials

Add extra organic matter to gardens and other annual planting areas

Sources of Organic Matter

Wood ResiduesChips/sawdust/bark materials Add 1 to 2 lbs of nitrogen per 100 lbs of material

Grass clippings or green residuesCan’t go wrong with theseAllow to dry

Composts and animal manure• Watch for salts and weed seeds

How much Organic Matter Should I add?

Single applicationOne inch per year for normal applications in annual areas(new site needs significant improvement)

1 inch of material = 3 cubic yards spread over a 1,000 square foot area

Summary

Understand what you haveFigure out what you need

TextureCompactionDrainage

Fertilizers

Basic Master Gardener Training

Jerry L. GoodspeedUtah State University

Extension

16 Essential nutrientsMacronutrients (large quantities):

oxygen nitrogen phosphorushydrogen potassium sulfurcarbon calcium magnesium

Micronutrients (small quantities):zinc ironcopper manganesechlorine molybdenumboron

nitrogen Phosphorus Potassium

Sources of nutrients

Inorganic/Synthetic fertilizers

Organic Fertilizers

Manures composts, and other organic materials

Green manures (legumes and others)

Fertilizer label

Three numbers always appear on the label

1. % Nitrogen (N)2. % Phosphorus (P)3. % Potassium (K)

Just A few N-P-K labels out there

34-0-021-0-029-3-426-3-328-4-425-3-520-2-426-3-325-3-532-3-5

24-6-1216-4-816-16-1612-12-1222-4-1122-4-1420-27-518-5-95-10-109-17-9

Selecting a fertilizer

What nutrients are needed?Soil test

What ratio of nutrients are needed?Nitrogen alone or a “complete” fertilizer?Established landscapes need nitrogen annually; few landscapes need other nutrients

Are extras needed?cost factor: extras increase cost

Soil testing

Soil testing……prior to planting: ensures good success – especially in new landscapes

…diagnose problems

…every 2 to 3 years to monitor soil environment

Soil sampling

Sample areas with different soils

6-inch depth in turf

12-inch depth around woody vegetation and in gardens

Combine 4 to 6 sub-samples from the area for each sample submitted

Soil Test Report

Methods of application

Broadcast – evenly distributed on surface

Banding – applied in a narrow band on surface or in furrow opened adjacent to plant row

Foliar – applied in liquid form

Spreaders

Organic nutrient sources

Much lower concentration of nutrientsExample: 2-2-2 for composts

Good sources of organic matter

May need to supplement with inorganic nitrogen fertilizer

Green manures

Plants grown for the sole purpose of “storing” nutrients or producing nutrients (nitrogen) and organic matter for later use in the garden

Examples:Legumes (peas, beans, vetch, alfalfa)Small grains (rye, oats, barley, wheat)

Other considerations

Combine inorganic and organic nutrients

Practice crop rotation in garden

Return as much organic matter as possible to annual planting areas

Soil pH and Iron Chlorosis

Soil pH

Soil pH: the degree of acidity or alkalinity of soil

The pH scale: 2 4 6 8 10

12

Neutral (7.0)

acidic alkaline

Causes of iron chlorosis

High lime soils Buffer pH in 7.8-8.0+ rangePlanting acid-loving plants in Utah“Aggravating factors”

Cold soilsOver-irrigationSoil compactionOver-fertilizationOther stresses

Major pH problem:iron chlorosis

Solutions to iron chlorosis problem

Select iron efficient plantsTreat with ironChange soil pH?

pH tolerant = iron efficient plants

Avoid Watch

Blueberry Raspberries

Rhododendron Strawberries

Azalea Red maples

Silver Maple Red Oak

Pin Oak Catalpa

Aspen Jap. Maples

Amur maple Dogwoods

Willows Smoke tree

Hydrangea Grapes

Soil salinity

Soil salinity = soluble salts in soil

Salts inhibit plant growthSalts cause “chemical drought” Visual diagnosis: salt crusting/salt burnSoil test diagnosis:

Electrical conductivity (EC) EC > 2 deciSiemens/meter is a saline soil for horticulture uses

Examples

Sources of salts

Residual salts in new development areasIrrigation water

natural sourceswater softeners

Deicing salts (road throw and sidewalks)Over-application of fertilizers and/or manures and composts

Solutions to salt problems

Control the source:water, fertilizer, manure runoff, other?

Clean up the problem:Remove salts by leaching with water