Introduction to Soils for the Introduction to Soils for the Master GardenerMaster Gardener

Dick WolkowskiExtension Soil Scientist

Department of Soil ScienceUniversity of Wisconsin - Madison

700different soils in Wis.

Productive soil must be fertile

• physical fertility– texture, structure, drainage, tilth

• chemical fertility– nutrient supply

• soil testing• nutrient additions

• biologically fertile– microorganisms– organic materials– soil environment

Soil formation-’weathering’

• physical – freezing, thawing,

wetting, drying, organisms

• chemical – dissolved minerals

moved in water– soil horizons formed

• 1 inch - 100 years

DeciduousDeciduous ConiferousConiferous PrairiePrairie

Soil = f (Climate, Parent material, Living organisms, Topography, Time )

Soil texture

• classes - sand, silt, clay

• names based on proportions

–loam, silty clay, loamy sand

–changing proportions not recommended

• clay also group of minerals

• montmorillinite, kaolinite.…

• nutrient storehouse

Textural classes

Soil organic matter

• plants, animals, microorganisms

– living, dead, decay products

– humus

• complex, dark-colored, reactive

• soil acidity reservoir

• nutrient storehouse

• difficult to significantly increase

Soil structure

• particles ‘glued’ into aggregates

– organic matter, clay, bacterial secretions, Fe/Al oxide coatings

• granular, platy, blocky

– finer aggregates in ‘topsoil’, massive in subsoil

• improve by adding organic residues– decay: 90% CO2 + H2O

Problem: ‘heavy’ soil

• aggregates tightly packed

– small pores

• poor drainage, roots suffocate

–‘cloddy’ if tilled wet

–compact easily

• improve with organic residues

– better crumb stability

– larger pores

• sand + clay = cement

Problem: ‘light’ soil

• aggregates too big to pack tightly

– large pore spaces

– droughty

• improve with organic residues

– ‘sponge’

– better water holding capacity

Organic residues

• compost, grass clippings, crop residues– annual gardens - 1 bu / 20 sq ft– perennial gardens - 1 bu / 10 ft

• do not add to tree/shrub planting hole

• green manure, fall cover crops– green topgrowth tilled under

• extra N needed for high C residues– microorganisms ‘tie-up’ N

• wood chips, sawdust, oat straw

Organic residues

• provides ‘food’ for microorganisms

– for every 100 lb. added, 90 lb. converted to water, carbon dioxide

• 10 lb. stable 1st year

• 1 lb. stable 2nd year

• microbial decay process

– more ‘glue’ for better crumb stability

– nutrients released

– fresh surfaces for nutrient holding

How to remember the 17 essential elements

C HOPKINS CaFe is Mighty Nice, But Many More Prefer Clara’s Zany Cup

Required for the plant to complete life cycle Directly involved in metabolism Can not be substituted by another nutrient Essential for a wide range of plants

Food for plants?

• plant, animal nutrition very different– plants manufacture basics

• protein, carbohydrate, sugar….–framework with C, H, O

• 14 essential soil elements–N, P, K - primary–Ca, Mg, S - secondary–B, Cl, Ni, Cu, Fe, Mn, Mo, Zn – trace

or micro

– animals (we) eat basics

Nutrient supply

• clay main ‘nutrient storehouse’ – negative charge– attracts, holds positive ions

–Ca ++, Mg ++, K +, NH4 +

• easily displaced, exchanged– plant uptake– some leaching on sandy soils

• negative ions remain in soil solution–NO3

-, Cl-, SO4=

Nutrients must be soluble

pore space

soil solution

plantroot

Nutrient exchange between clay and soil solution

Would Calvin be a good master gardener?

WHAT SOIL TESTING TELLS US

• Crop N need• Plant available P and K• Crop P and K need• Soil organic matter• Soil pH and lime

requirement• Other tests if requested

Soil testing is the onlypreplant method of knowingnutrient need!

A shovel is OK too, mix a smallamount in a clean bucket

Soil test

• rapid chemical analysis

• index of potential nutrient supply

– deficiency

– excess

• sample to show ‘true’ variation

– Composite

• UWEX lab in Madison

Sampling soils

• sample depth

– established turf - 4 inches

– new turf, gardens - 6 inches or tillage depth

– raised beds - depth of bed

– probe best, spade OK

• combine 5 subsamples – composite

Avoid unusual areas: backfill, wet spots, etc.

Sampling soils

• when– annual gardens, new turf

• fall, spring before tillage– perennials, problems, established turf

• anytime– suspected salt damage

• very early spring• sample each area separately

– repeat every 2-3 yrs

Useful laboratory tests

• routine

– soil pH, ‘buffer’ pH– organic matter %– available P and K

• other– Ca, Mg, S, Zn, B, Mn

• no good test/need– N, Fe, Cu, Cl, Mo, Ni

• ‘problem solving’– texture, soluble salts – Cl, Pb, As,...

UW Soil and Plant Analysis Lab8452 Mineral Point Rd, Verona

53593(West Madison Ag. Research

Station)

Soil test report

• potential for deficiency

• which nutrient needed

• how much to apply

– fertilizer for nutrient need

– lime, sulfur amendments for pH change

• when to apply

• when to STOP!

Soil test results

• excessively high– common for residential areas

– not detrimental– adding more not beneficial– avoid balanced blends, most organics

• low– build to optimum

• turf fertilizer blends

Soil test results - pH

• measure of acidity, alkalinity

– scale 1 - 14, optimum 6 - 7+

• add lime only if recommended

– incorporate 6 - 8 inches

• add aluminum sulfate to acidify

– new turf

• if strongly alkaline

– blueberry, rhododendron

Effect of soil pH on nutrient availability

Optimum pH for turf and gardens

• depends on species** pH range

– kentucky bluegrass 6.0 - 7.6

– creeping red fescue 5.3 - 7.5

– sweet corn 6.0

– potato 5.4 – 6.0

– green bean 6.8

– tomato 6.0

Soil test results - organic matter

• 2 - 4% most soils

– impractical and difficult to change

• nutrient reservoir

• used for calculating N and lime recommendations

Soil test results - N

• no direct measures on report

– N rec from crop need, organic matter

• promotes leaf growth

• excess N

– delays maturity

– moves below root zone and may contaminate ground water

Soil test results - P

• stimulates root growth and flowering– shallow rooted greater need

• optimum soil test P for turf and gardens- established turf 11 - 15 ppm

- sweet corn 16 - 25 ppm - green bean 16 - 25 ppm - tomato 31 - 45 ppm - potato 161- 200 ppm

Soil test results - K

• promotes disease resistance, winter hardiness– root crops require most– optimum soil test K for turf

- established turf 41 - 60 ppm- sweet corn 101 - 120 ppm

- green bean 101 - 120 ppm - tomato 121 - 180 ppm - potato 121- 160 ppm

Inorganic fertilizer

• sold on a percent by weight basis– N + P2O5 + K2O

• chemically simple– N in air plus natural gas– rock phosphate, potash mined, sized

and cleanedvery soluble saltseasily blendedmust be careful with rates

Inorganic fertilizer Nutrient

Type N P2O5 K2O--------------% ---------------

urea 46 0 0ammonium nitrate 33 0 0triple super P 0 46 0ordinary super P 0 20 0muriate of potash 0 0 60potassium sulfate 0 0 50di-ammonium phos. 18 46 0

Recommended fertilizer

Gardens

• avoid high N fertilizers for most crops

– sweet corn, potato are exceptions • uniform, low grade (e. g.10-10-10)

– does not match plant need

– over supply P and K

• micronutrients generally not needed

• adjust pH as necessary

Organic fertilizer

• chemically complex, contains C

– naturally occurring

– byproducts

• microorganisms must degrade

– slow release, rate ???

• improve structure with long-term use

Organic fertilizer Nutrient

Type N P2O5 K2O---------------%----------------

blood meal 13.0 1.5 0.6bone meal 2.2 27.0 0seaweed 1.5 1.0 4.9tree leaves 0.7 0.1 0.8greensand 0 1.4 6.3activated biosolid 6.0 3.0 0.2

Organic fertilizer

• may contain

– unnecessary nutrients, compounds

– nonessential elements

• does not add nutrition, improve flavor, enhance food safety and quality

• often more expensive per pound of nutrient

Foliar sprays: fruits, sensitive ornamentals

• trace, secondary elements

• soil Fe, Mn ‘fixed’ at high soil pH

• supply by spraying leaves

• temporary ‘fix’, requires repeating

• emergencies

– no substitute for soil applied nutrients

• leaf burn, expensive, extra work

• most spray falls on soil

Recommended fertilizer

Turf blends

• regular or maintenance - ‘high N’– soil test P, K optimum, above

• starter - ‘high P2O5’– soil test P below optimum

• winterizer - ‘high K2O’– soil test K below optimum

• use a “Holiday” schedule– sweep off driveways and sidewalks

Other turf management considerations• Mowing

– no shorter than 2.5 in.– cut no more than 1/3 at any time– normal height in fall

• Thatch– natural buildup – verti-cut, power-rake, core

• Water– 1 in. per week in summer, less in spring and fall– soak rather than sprinkle

• Shade– seed fescue– prune trees– mow higher– less water and fertilizer

Compost

What is Compost ?

• Material left after the aerobic decomposition of organic material(s)

OrganicMaterial + “bugs” + O2 Compost + CO2 + H2O

General Characteristics

• N availability much lower than fresh materials like manures, biosolids, food processing wastes (<10% of TN)

• Diverse array of “feedstocks” used to make compost

• Variability in quality of finished compost• Comes with lots of “things” besides

macro-nutrients

Assessment of maturity

• High concentrations of ammonium-N indicate immature compost- should be less than 40 ppm

• Measure microbial respiration under optimal

moisture, temperature conditions- High respiration= high activity= unstable- Low respiration=low activity= stable

• Test compost or compost blend BEFORE using

Fresh Vs. Composted Organic Matter

Fresh Wastes• High biological activity• Some have high nutrient

availability• Can immobilize nutrients

during early stages of decomposition

• Highly variable in physical traits

• Instability can increase Pythium damping off of certain crops

Compost• Already gone through

decomposition, stable• Mature compost should

provide some nutrients• Improves drainage and

other physical properties

• Provides for biological control of Phytophthora root rot

Making Your Own Compost

• Build a “bin” 5 x 5 x 5 ft.• Add organic materials and adjust to 40-60 %

water content– Use bulking agent for wet materials, add water to

dry materials– High C:N materials take longer

• Maintain aeration by frequent turning• Compost is finished when pile doesn’t re-heat

and it is difficult to distinguish initial materials