soil and water kelly young ua cooperative extension

Soil and WaterKelly Young

UA Cooperative Extension

Objectives:• Discuss soil components, texture,

chemistry• Consider relationships between soil,

water, plants and air• Learn about the properties of water• Compare and contrast fertilizers• Suggest soil amendments

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Ideal Soil Composition

Desert soils have significantly less than 5% organic matter. Why?

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• Maricopa County soils:–Mineral–Alkaline–Arid–Probably some caliche–May be rocky and shallow,

particularly in foothills–May be saline–May be heavy 6

Soil Texture

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beachball

frisbee

dime

Soil texture affects water movement

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Determine your soil texture

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Soil Texture Triangle

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Soil Compaction

• Compaction reduces pore space:– Restricts H2O and O2

– Poor root development

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Capillary Action• Cohesion – “like sticking

to like”– Water molecules stick

together• Adhesion – “sticking to

unlike”– Water molecules stick to

certain surfaces• Capillary action – drawing

of water in a narrow tube

Soil-Plant-Air Continuum

Stomata Factors affecting opening and closing:• Light, especially blue light• Water• Temperature• CO2

Water moves down its concentration gradient•Concentration of water is–Highest in soil–High in plant–Low in air

When transpiration > water uptake by roots, wilting occurs.

Water loss• Evaporation – change of water phase

from liquid to gas• Transpiration – evaporation of water

from leaves• Evapotranspiration (Et) – combined loss

of water directly from soil evaporation and transpiration

Factors that affect Et

• Temperature• Relative humidity• Wind speed• Light intensity• Type of plant

Terry’s 1-2-3 RuleWatering depth1. 1 ft - Flowers, vegetables and other small

annuals2. 2 ft – Shrubs3. 3 ft – Trees

Root volume• V = ½( 4/3 π r3)Π ≈ 3.14r = ½ diameter

If a tree has a 12’ diameter:

r = 6’The root volume

would occupy approximately

452 cubic feet.

Root volume V = ½( 4/3 π r3)

Π ≈ 3.14r = ½ diameter

Assume 5 years later the tree has a 20’ canopy:r = 10’Now, the root volume would occupy

approximately 2093 cubic feet!

Soil Chemistry

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atom

• Cations:– NH4

+, K+, Fe++, Ca++

• Anions:– NO3

-, SO42-

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Cation Exchange Capacity

Clay particle

Organic matter and clay carry a negative charge

Plant Nutrients

Macronutrients• C• H• O• N• P

• K• Ca• Mg• S

Micronutrients• Fe• Zn• Mn• B• Mo• Cu 31

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Nitrogen deficiency

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Phosphorus deficiency

pH is a measure of acidity/alkalinity34

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Zn deficiency

Fe deficiency

• Add nutrients to the soil• Organic and inorganic forms• Usually salts• Can burn plants• Must be watered in

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Fertilizers

Fertilizer analysisN-P2O5-K2O

(nitrogen-phosphate-potash)

Complete fertilizerIncomplete fertilizerSlow release fertilizers

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“Organic” versus “Chemical” fertilizers

OrganicManure, compost, fish emulsion, etc.Sometimes recycles wasteMay be resource intensiveCan be bulky, heavyMicronutrientsPathogens, weedsSalt

ChemicalAmmonium nitrate, urea, superphosphate, etc.Can be energy intensive to makeLighter weightSaltMust be purchasedSalt

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Salinity• Na, Ca, K

and other salts accumulate in soils

How does soil become saline?

• Shallow watering• Fertilizers• Irrigation water quality• Application of other salty

substances to soil.

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Soil Amendments• Used to modify soil chemistry

–Gypsum (Calcium sulfate) – temporarily removes Na from soil

–Soil sulfur – may eventually reduce pH after many yearly applications

–Organic matter

What should be added to the native soil when planting trees and shrubs in the landscape?

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1. Organic matter2. Fertilizer3. Organic matter

and fertilizer4. Nothing, only

native soil should be backfilled into the planting hole.

Possible causes of “unthriftiness”

• High soil salinity

• Root diseases• Root parasitic

nematodes

Questions?

Contact me at kyoung@arizona.edu.

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