Plant Nutrition Indicators & Soil Assessment

Lab 7: Plant Nutrition Indicators & Soil Assessment

Objectives

By the end of this lab, you'll understand:

• How to assess soil texture, drainage, and fertility using simple field tests

• How to diagnose nutrient deficiencies by observing plant symptoms

• How soil properties influence which plants can grow in different locations

• The relationship between soil characteristics and plant diversity

• Why desert soils are unique and how they affect plant growth

Background

Soil is more than dirt! It's a complex mixture of minerals, organic matter, water, air, and living organisms. Understanding soil helps you predict what plants will thrive in different locations.

Key Concepts:

Soil Texture: The proportion of sand, silt, and clay particles

• Sand (largest, 0.05-2 mm): Feels gritty, drains fast, low nutrients

• Silt (medium, 0.002-0.05 mm): Feels smooth like flour, moderate drainage

• Clay (smallest, <0.002 mm): Feels sticky when wet, drains slowly, holds nutrients

Soil Structure: How particles clump together

• Good structure = pore spaces for roots, water, and air

• Poor structure = compacted, roots struggle

Organic Matter: Decomposed plant/animal material

• Improves fertility, water retention, and structure

• Dark color indicates high organic content

Plant Nutrients: Essential elements for growth

• Macronutrients (needed in large amounts): N, P, K, Ca, Mg, S

• Micronutrients (needed in tiny amounts): Fe, Mn, Zn, Cu, B, Mo

ARIZONA-SPECIFIC SOIL CHARACTERISTICS

Unique Features of Mohave County Soils:

1. Alkaline pH (7.5-8.5+)

• Cause: Low rainfall leaves calcium carbonate (caliche) in soil

• Effect: Reduces availability of iron, zinc, manganese

• Result: Iron chlorosis common (yellow leaves with green veins)

2. Low Organic Matter (<1%)

• Cause: Low plant productivity + rapid decomposition in heat

• Effect: Poor water retention, low nitrogen

• Result: Sandy, light-colored soils

3. Caliche Layers (Calcrete)

• What: Concrete-hard layer of calcium carbonate

• Where: 1-3 feet below surface

• Effect: Blocks root penetration and drainage

• Recognition: White, chalky material; fizzes vigorously with vinegar

4. High Salinity in Some Areas

• Cause: Evaporation concentrates salts

• Where: Low-lying areas, poorly drained sites

• Effect: Toxic to many plants

• Recognition: White crusty surface

5. Minimal Topsoil

• Desert soils often lack the rich, dark A-horizon of forest soils

• Biological soil crusts (cryptobiotic crusts) replace traditional topsoil in undisturbed areas

Materials

Required:

• Trowel or small shovel

• 5 clear glass jars with lids (quart-size mason jars work great)

• Bottled water (at least 1 gallon)

• Measuring tape or ruler

• White vinegar (small bottle, 8 oz)

• Hydrogen peroxide (3%, small bottle)

• Camera (smartphone is fine)

• Field notebook and pencils

• 5 ziplock bags or small containers for soil samples

• Permanent marker for labeling

Part 1: Analyze Soil Physical Properties

Goal: Use simple field tests to characterize soil texture, drainage, structure, and chemistry. These properties determine what plants can grow where.

Step 1: Collect Soil Samples

For each of your 5 sites:

Collection Procedure:

1. Choose your sampling spot:

   • Find a typical area (avoid ant mounds, animal burrows, rock piles)

   • Avoid edges (sample center of habitat)

   • Clear away surface litter (leaves, rocks)

2. Dig to proper depth:

   • Dig down 6 inches (15 cm) with trowel

   • This is the root zone for most plants

   • Arizona note: You may hit caliche! If so, note depth and describe it

3. Collect sample:

   • Gather about 1 cup of soil from the bottom of hole

   • Mix soil from multiple scoops within the hole

   • Place in labeled ziplock bag or jar

4. Label clearly:

   • Site name/number

   • Date and time

   • GPS coordinates or description

   • Any observations (smell, color, moisture)

5. Clean sample:

   • Remove large rocks (>5 mm)

   • Remove roots and plant material

   • Remove any obvious trash or debris
     
     
     
     
     
     

6. Document the site:

   • Take photos of:

     • Overall landscape

     • Soil profile in your hole

     • Plants growing there

     • Any caliche or unusual layers

Your 5 samples:

• Site 1: Natural desert _____

• Site 2: Wash/arroyo _____

• Site 3: Irrigated garden _____

• Site 4: Disturbed soil _____

• Site 5: Riparian/north slope _____

Site 1: Natural Desert Soil

• Undisturbed desert scrubland

• Native vegetation (creosote, brittlebush)

• Represents baseline desert conditions

Site 2: Wash/Arroyo Soil

• Sandy, well-drained

• Enriched by periodic flooding

• Often has deeper soil, more organic matter

Site 3: Irrigated Garden/Landscape

• Amended with compost

• Regular watering

• Represents improved desert soil

Site 4: Disturbed/Construction Soil

• Compacted, possibly mixed with fill

• Poor structure

• May have buried debris
  
  
  
  

Site 5: Riparian/Wetland Area (if accessible)

• Near water source

• Higher organic matter

• Different plant community

• Alternative if no wetland: North-facing slope (cooler, more moisture retention)

Arizona safety note: Watch for scorpions and spiders when digging!

Step 2: Test A - The Ribbon Test (Quick Texture)

Why this test? Texture determines water retention, drainage, and nutrient availability. It's the foundation of soil classification.

What you're testing: How well soil particles stick together when wet.

Procedure:

For each soil sample:

1. Prepare the soil:

   • Place about 2 tablespoons of soil in your palm

   • Break up any clumps

   • Remove any remaining rocks

2. Add water gradually:

   • Add drops of water while kneading

   • Goal: Consistency like Play-Doh

   • Not dripping wet, not crumbly dry

   • Should feel moldable
     
     
     
     

3. Form a ball:

   • Squeeze and roll soil in your palm

   • Ball should hold together when you open your hand

   • If it falls apart: Too dry, add more water

   • If it's sloppy: Too wet, add more soil

4. Make a ribbon:

   • Place ball between thumb and forefinger

   • Press soil upward to form a ribbon

   • Let ribbon extend out as far as it will go

   • Stop when ribbon breaks from its own weight

   • Measure the ribbon length before it breaks

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

5. Interpret results:

Ribbon length:

• Less than 2 cm (<1 inch): SANDY SOIL

  • Feels gritty, like sandpaper

  • Won't hold together well

  • Water drains quickly

• 2-5 cm (1-2 inches): LOAM

  • Feels smooth but slightly gritty

  • Forms medium ribbon

• More than 5 cm (>2 inches): CLAY

  • Feels sticky, slippery when wet

  • Forms long ribbon

  • Drains slowly, can be hard when dry

6. Note the feel:

   • Gritty = sand particles (large)

   • Smooth/silky = silt particles (medium)

   • Sticky/slippery = clay particles (tiny)

Recording:

Arizona expectation: Most desert soils are sandy to sandy loam (short ribbons). Wash soils may be very sandy. Garden soils may be amended with clay.

Step 3: Test B - The Jar Settling Test (Precise Texture)

Why this test? Gives you exact percentages of sand, silt, and clay. More precise than ribbon test. Takes 24 hours but minimal effort.

The principle: Different particle sizes settle at different rates. Sand settles in seconds, silt in hours, clay in days.

Procedure:

For each soil sample (do all 5 at once):

1. Fill jar 1/3 full with soil:

   • Use dried, crumbled soil

   • Break up all clumps thoroughly

   • Remove rocks and roots

   • About 1 cup of soil

2. Add water to 2/3 full:

   • Leave air space at top (for shaking)

   • Use room-temperature water

3. Add settling agent:

   • Add 1/4 teaspoon salt

   • This helps particles separate more clearly

   • Or use 1 tablespoon of dish soap (same effect)

4. Shake vigorously for 1-2 minutes:

   • Shake HARD—really mix it up!

   • All soil particles must be suspended

   • Soil-water mixture should look like chocolate milk

5. Set on level surface:

   • Place on table/counter where it won't be disturbed

   • Mark start time on jar with marker

   • DO NOT MOVE for 24 hours

6. Observe settling:

   • After 1 minute: Sand settles (bottom layer)

   • After 1 hour: Silt settles (middle layer)

   • After 24 hours: Clay settles (top layer)

   • Water on top may still be slightly cloudy (tiniest clay particles)

After 24 hours, measure layers:

Use ruler to measure from bottom of jar:

• Mark bottom of sand layer: _____ mm

• Mark bottom of silt layer: _____ mm

• Mark bottom of clay layer: _____ mm

• Mark water line: _____ mm

Calculate layer thicknesses:

• Sand layer = (silt bottom) - (sand bottom) = _____ mm

• Silt layer = (clay bottom) - (silt bottom) = _____ mm

• Clay layer = (water line) - (clay bottom) = _____ mm

• Total soil height = sand + silt + clay = _____ mm

Calculate percentages:

• % Sand = (sand layer ÷ total soil height) × 100 = _____%

• % Silt = (silt layer ÷ total soil height) × 100 = _____%

• % Clay = (clay layer ÷ total soil height) × 100 = _____%

(Percentages should add up to 100%!)

8. Take photos:

   • Photo of all 5 jars side-by-side

   • Clear view of layers

   • Include ruler for scale

   • Label each jar in photo

Use Soil Texture Triangle:

Plot your percentages on the soil texture triangle to determine exact soil class:

Example:

• 60% sand, 30% silt, 10% clay = Sandy Loam

• 20% sand, 40% silt, 40% clay = Clay Loam

• 80% sand, 10% silt, 10% clay = Loamy Sand

Recording:

Arizona patterns to expect:

• Natural desert: 60-85% sand (Sandy/Sandy Loam)

• Wash: 70-90% sand (Very sandy)

• Garden: Variable (depends on amendments)

• Disturbed: Variable, possibly compacted clay

Step 4: Test C - Drainage Test

Why this test? Drainage determines whether roots get enough oxygen. Too fast = plants dry out. Too slow = roots drown, rot.

Do this test in the field at each site.

Procedure:

At each of your 5 sites:

1. Dig test hole:

   • About 6 inches (15 cm) deep

   • About 4 inches (10 cm) wide

   • Straight sides (not cone-shaped)

   • Clear out any loose soil

2. Fill hole completely with water:

   • Use water bottle

   • Fill to the very top

   • Note if water drains immediately or pools

3. Start timer:

   • Use phone stopwatch

   • Start the moment water is poured

4. Measure drainage time:

   • How long until water is completely absorbed?

   • Check every 1-2 minutes initially

   • Record time in minutes
     
     
     
     

5. Interpret results:

Drainage time:

• Less than 5 minutes: FAST drainage

  • Sandy soil

  • May dry out quickly

  • Good for drought-tolerant plants

• 5-15 minutes: MODERATE drainage

  • Loam soil

  • Ideal for most plants

  • Good balance of retention and drainage

• 15-30 minutes: SLOW drainage

  • Clay soil

  • May stay wet too long

  • Risk of root rot

• 30+ minutes or standing water: VERY SLOW/POOR drainage

  • Heavy clay or compacted soil

  • Suitable only for wetland plants

  • May need amendment or drainage system

Arizona note: If water drains in <1 minute, soil is extremely sandy (common in washes). If you hit caliche, water may pool on top indefinitely!

6. Observe soil structure while digging:

Structure types:

• Single grain: Particles don't stick together at all

  • Looks like: Beach sand

  • Common in: Pure sand, desert dunes

• Granular: Small crumbs, like cookie crumbs

  • Looks like: Good garden soil

  • Common in: Amended soils, forest soils

• Blocky: Forms chunks or blocks when broken

  • Looks like: Building blocks

  • Common in: Clay soils

• Platy: Forms flat plates or layers

  • Looks like: Stacked pancakes

  • Common in: Compacted soils, problem soils

• Massive: No structure, solid mass

  • Looks like: Concrete

  • Common in: Severely compacted, caliche

7. Check for barriers:

   • Dig a bit deeper (to 12 inches if possible)

   • Feel for hardpan or caliche layer

   • If you hit hard layer:

     • Measure depth to layer: _____ inches

     • Describe: Color, texture, hardness

     • Test with vinegar (caliche will fizz!)

Step 5: Test D - Organic Matter Content

Why this test? Organic matter improves everything: fertility, water retention, structure. Desert soils are typically very low (<1%), while garden soils may be 5-10%.

What is organic matter? Decomposed plant and animal material (humus). Provides nutrients, feeds soil organisms, improves structure.

Four Simple Tests:

For each soil sample:

1. Color Test

The rule: Darker = more organic matter

Procedure:

1. Examine dry soil color

2. Rate on 1-10 scale:

Scale:

• 1-3: Light grey, tan, or beige → LOW organic matter (0-1%)

  • Common in: Desert soils, subsoil, sandy soils

• 4-6: Brown or reddish-brown → MODERATE organic matter (1-3%)

  • Common in: Agricultural soils, disturbed soils

• 7-10: Dark brown to black → HIGH organic matter (3-10%+)

  • Common in: Forest soils, wetlands, heavily amended gardens

Recording:

• Color rating (1-10): _____

• Estimated organic matter:   Low  /  Moderate  /  High

Arizona note: Most desert soils rate 1-3 (very light colored). If you find dark soil, it's usually from amendments or riparian area.

2. Smell Test

The rule: "Good earth" smell = organic matter decomposition

Procedure:

1. Wet soil slightly (add few drops of water)

2. Crush between fingers

3. Smell carefully

Interpretations:

• Rich, earthy "forest floor" smell: HIGH organic matter

  • Pleasant, musty aroma

  • Smells like woods after rain

• Mild or no smell: MODERATE organic matter

• No smell or chemical/dusty smell: LOW organic matter

  • Just smells like dust or minerals

Recording:

• Smell:  Rich/earthy  /  Mild  /  None/dusty

• Indicates:  High OM  /  Moderate OM  /  Low OM

3. Float Test

The rule: Organic matter is lighter than mineral soil—it floats!

Procedure:

1. Fill clear jar or glass with water

2. Add 1 tablespoon of soil

3. Stir gently for 10 seconds

4. Let settle for 1 minute

5. Observe what's floating on top

Interpretations:

• Lots of floating bits (brown, fibrous): HIGH organic matter

• Some floating specks: MODERATE organic matter

• Nothing floating (all sinks immediately): LOW organic matter

Recording:

• Floating material:  Abundant  /  Some  /  None

• Indicates:  High OM  /  Moderate OM  /  Low OM

4. Texture/Aggregation Observation

The rule: Organic matter acts like glue, binding particles into crumbs (aggregates)

Procedure:

1. Take slightly moist soil

2. Gently rub between fingers

3. Observe how it behaves

Interpretations:

• Forms soft crumbs/aggregates: HIGH organic matter

  • Crumbles like good potting soil

  • Holds shape but breaks apart easily

• Forms some clumps but dusty: MODERATE organic matter

• Feels like powder or paste: LOW organic matter

  • Sandy: Falls apart completely

  • Clay: Smears like paste, no structure

Recording:

• Aggregation:  Good crumb structure  /  Some clumps  /  No structure

• Indicates:  High OM  /  Moderate OM  /  Low OM

Summary Rating:

For each site, combine all 4 tests:

Step 6: Test E - Chemical Indicators

Why these tests? pH and carbonates dramatically affect nutrient availability. Arizona's alkaline soils create specific challenges.

Test 1: Fizz Test (Alkalinity/Carbonates)

What it detects: Calcium carbonate (lime) in soil—the cause of high pH in desert soils

The chemistry: Vinegar (acid) + calcium carbonate → carbon dioxide gas (bubbles!)

Procedure:

1. Place 1 tablespoon of soil in small container or jar lid

2. Add 5-10 drops of white vinegar

3. Watch and listen closely for 30 seconds

Interpretations:

• Vigorous fizzing/bubbling: HIGH carbonates

  • pH likely 8.0-8.5+

  • Very alkaline soil

  • May have visible white deposits (caliche)

  • Very common in Mohave County!

• Slight fizzing: MODERATE carbonates

  • pH likely 7.5-8.0

  • Mildly alkaline

• No reaction: LOW/NO carbonates

  • pH likely <7.5 (neutral or acidic)

  • Unusual in Arizona (except heavily amended soils)

Recording:

• Fizz test result:  Vigorous  /  Slight  /  None

• Estimated pH:  >8.0  /  7.5-8.0  /  <7.5

Arizona note: Most natural desert soils will fizz vigorously! This is why iron chlorosis (yellowing) is so common—high pH locks up iron.

Test 2: pH Test Strips (If Available)

What it measures: Exact pH (acidity/alkalinity) on 0-14 scale

The pH scale:

• 0-6.5: Acidic (rare in Arizona)

• 6.5-7.5: Neutral (ideal for most plants)

• 7.5-14: Alkaline (common in Arizona)

Procedure:

1. Make soil solution:

   • Mix 1 part soil with 2 parts distilled water

   • Stir thoroughly

   • Let settle for 5 minutes

2. Test the liquid:

   • Dip pH strip into clear liquid (not soil sediment)

   • Wait 10-30 seconds

   • Remove and compare to color chart

3. Read result:

   • Match strip color to chart

   • Record pH value

Interpretations:

• pH 4-6: ACIDIC

  • Rare in Arizona

  • May be heavily amended soil

  • Good for: Blueberries, azaleas, rhododendrons

• pH 6.5-7.5: NEUTRAL

  • Ideal for most plants

  • Best nutrient availability

  • Good for: Vegetables, most flowers

• pH 7.5-9: ALKALINE

  • Common in Arizona!

  • Reduces Fe, Mn, Zn availability

  • Good for: Native desert plants, Mediterranean herbs

Recording:

• pH measurement: _____

• Classification:  Acidic  /  Neutral  /  Alkaline

Test 3: Peroxide Test (Organic Matter)

What it detects: Organic matter (alternative method to float test)

The chemistry: Hydrogen peroxide reacts with organic matter, releasing oxygen gas (fizzing)

Procedure:

1. Place 1 tablespoon of soil in small container

2. Pour 2-3 tablespoons of hydrogen peroxide (3%) over soil

3. Observe reaction for 1-2 minutes

Interpretations:

• Vigorous fizzing/foaming: HIGH organic matter (3-10%+)

  • Lots of bubbles, may overflow container

  • Reaction lasts several minutes

• Moderate fizzing: MODERATE organic matter (1-3%)

  • Some bubbles, brief reaction

• No or very slight fizzing: LOW organic matter (<1%)

  • Few or no bubbles

  • Common in Arizona desert soils

Recording:

• Peroxide reaction:  Vigorous  /  Moderate  /  Slight/None

• Confirms OM rating:  High  /  Moderate  /  Low

Step 7: Record All Soil Data

Create comprehensive soil profile for each site:

Part 2: Assess Plant Nutritional Status

Goal: Learn to diagnose nutrient deficiencies by "reading" plant symptoms. Each deficiency creates a specific, recognizable pattern.

Why this matters: Knowing which nutrient is deficient helps you fix the problem. Adding the wrong fertilizer wastes money and can harm plants.

Step 1: Learn the Symptoms

Understanding nutrient mobility:

• Mobile nutrients (N, P, K, Mg): Plant moves them from old leaves to new growth

  • Deficiency shows in older/lower leaves first

• Immobile nutrients (Fe, Ca, Mn, Zn): Plant can't move them

  • Deficiency shows in younger/newest leaves first

NITROGEN (N) - Most Common Deficiency

What nitrogen does: Building block of proteins, DNA, chlorophyll—needed for ALL growth

Deficiency symptoms:

• Overall pale green or yellow color (chlorosis)

• Affects older/lower leaves FIRST (N moves to new growth)

• Stunted growth, plants stay small

• Small leaves, thin stems

• Poor flowering/fruiting

• Leaves may drop early

Why it happens:

• Low organic matter (main N source)

• Sandy soil (N leaches out)

• Heavy rain (washes N away)

Mnemonic: "Pale and puny"

Arizona context: Common in sandy desert soils with <1% organic matter. Desert plants adapted to low N.

PHOSPHORUS (P)

What phosphorus does: Energy transfer, root development, flowering/fruiting

Deficiency symptoms:

• Dark blue-green or purple/reddish tints on leaves

• Affects older leaves first

• Stunted growth, especially roots

• Poor flowering and fruit set

• Leaves may look dull, not glossy

• Leaf tips may die

Why it happens:

• Locked up by high pH (common in Arizona!)

• Cold soil (slows P uptake)

• Compacted soil (poor root growth)

Mnemonic: "Purple problem"

Arizona context: P often present but unavailable due to alkaline pH (8.0+). Add sulfur to lower pH or use acidic fertilizers.

POTASSIUM (K)

What potassium does: Water regulation, disease resistance, overall plant vigor

Deficiency symptoms:

• Brown, scorched leaf edges and tips (necrosis)

• Affects older leaves first

• Leaf edges curl downward

• Yellow areas between brown edges and green center

• Weak stems, plant wilts easily

• Poor drought tolerance

Why it happens:

• Sandy soil (K leaches)

• High sodium (competes with K)

• Imbalanced fertilizer (too much N, not enough K)

Mnemonic: "Burnt borders"

 

IRON (Fe) - VERY Common in Arizona!

What iron does: Essential for chlorophyll production

Deficiency symptoms:

• Yellow between leaf veins, veins stay green (interveinal chlorosis)

• Affects NEWEST/YOUNGEST leaves FIRST (Fe doesn't move in plant)

• Severe cases: entire leaf turns white or cream

• Growth continues but leaves stay yellow

• Reduced vigor

Why it happens in Arizona:

• High pH (7.5-8.5+) locks up iron in soil

• Iron present but unavailable to plants

• Especially bad in calcareous (high lime) soils

• Overwatering makes it worse

Mnemonic: "Yellow young leaves"

How to tell Fe from Mg deficiency:

• Iron: Youngest leaves affected

• Magnesium: Oldest leaves affected

• Both show interveinal chlorosis (yellow between veins)

Arizona fix:

• Apply iron chelate (chelated iron stays available at high pH)

• Lower pH with sulfur

• Improve drainage

• Choose iron-efficient varieties

MAGNESIUM (Mg)

What magnesium does: Center of chlorophyll molecule, enzyme activation

Deficiency symptoms:

• Yellow between veins, veins stay green (interveinal chlorosis)

• Affects OLDER leaves FIRST (Mg moves to new growth)

• May have reddish or purple tints along with yellowing

• Advanced: brown dead spots develop

• Leaf edges may curl upward

Why it happens:

• Sandy, acidic soils (rare in Arizona)

• High potassium or calcium (competes with Mg)

• Leaching in irrigated sandy soils

Mnemonic: "Like iron, but old leaves"

Arizona note: Less common than Fe deficiency, but possible in heavily amended acidic soils or with imbalanced fertilizer.

CALCIUM (Ca)

What calcium does: Cell wall structure, root tip growth

Deficiency symptoms:

• Distorted, curled, or dead growing tips

• Affects newest growth (Ca doesn't move in plant)

• New leaves twisted, deformed, or dead

• Blossom end rot on tomatoes, peppers, squash (classic symptom!)

• Root tips die back

• Sticky or slimy feel to new growth

Why it happens:

• Inconsistent watering (even if Ca present in soil)

• Rapid growth period (demand exceeds supply)

• High nitrogen (promotes growth faster than Ca can move)

Mnemonic: "Crippled tips"

Arizona note: Rare in alkaline soils (plenty of Ca). If you see it, problem is usually water uptake, not soil Ca levels.

Quick Reference Chart:

Step 2: Survey Plants Across Your Sites

Visit each of your 5 soil sites and examine at least 20 plants total (4+ per site).

Why multiple plants? One sick plant might have disease, not nutrient deficiency. Patterns across many plants indicate soil problems.

For Each Plant, Record:

A. Basic Information:

• Plant species: _____ (or "Unknown forb," "Grass species," etc.)

• Location: Which soil site? _____

• Take photo: Especially if showing symptoms

B. Leaf Color (Rate 1-10):

Scale:

• 1-3: Pale yellow-green → Likely N deficient

• 4-6: Medium green → Possibly deficient or stressed

• 7-10: Dark, healthy green → Well-nourished

Recording: Leaf color: _____ (1-10)

C. Growth Vigor:

Compare to what you'd expect for this species:

• Stunted - Much smaller than expected (50% or less of normal)

• Below average - Somewhat small (50-75% of normal)

• Normal - Typical size for species

• Above average - Larger than typical

• Robust - Exceptionally large and vigorous

Recording: Growth vigor: _____

D. Leaf Size:

Compare to typical leaf size for this species:

• Much smaller than normal

• Slightly smaller

• Normal size

• Larger than normal

Recording: Leaf size: _____

Tip: If you don't know what's "normal," compare plants of same species in different locations.

E. Discoloration Patterns:

• Overall yellowing (entire leaf pale) → Suggests N deficiency

• Yellow between veins, veins green (interveinal chlorosis) → Suggests Fe or Mg

• Purple or dark blue tints → Suggests P deficiency

• Brown/scorched leaf edges → Suggests K deficiency

• Brown spots (scattered) → Could be disease or K

• White or bleached areas → Severe Fe deficiency

• No discoloration (healthy green) → Well-nourished

F. Location of Symptoms:

Critical for diagnosis!

• Oldest/lowest leaves show symptoms first → Mobile nutrient (N, P, K, Mg)

• Youngest/newest leaves show symptoms first → Immobile nutrient (Fe, Ca, Mn)

• Whole plant affected equally → Environmental stress or severe deficiency

Recording: Where symptoms appear: _____

G. Flowering/Fruiting:

Assess reproductive effort:

• Abundant - Lots of flowers/fruits

• Moderate - Some flowers/fruits

• Few or none - Poor reproduction

Recording: Flowering/fruiting: _____

Why it matters: Poor flowering suggests P or K deficiency.

H. Your Diagnosis:

Based on symptoms, what nutrient might be deficient?

Decision tree:

1. Are symptoms on old or new leaves?

   • Old leaves → N, P, K, or Mg

   • New leaves → Fe or Ca

2. What's the specific pattern?

   • Pale all over + old → N

   • Purple tint + old → P

   • Scorched edges + old → K

   • Yellow with green veins + old → Mg

   • Yellow with green veins + new → Fe (most common in AZ!)

   • Deformed tips → Ca

3. Check soil data:

   • High pH + young yellow leaves → Almost certainly Fe

   • Sandy + pale → Likely N

   • Low OM + stunted → Likely N

Recording: Suspected deficiency: _____ (or "None - appears healthy")

Step 3: Organize Your Plant Data

Create comprehensive plant assessment table:

Analysis Questions:

1. Which deficiency was most common? _____

• Why do you think this is? _____

2. Did deficiencies correlate with soil type?

• Sandy soils showed more _____ deficiency

• Alkaline soils showed more _____ deficiency

• Low OM soils showed more _____ deficiency

3. Were native desert plants healthier than non-natives?  /  Yes  /  No

• Why? (Native plants adapted to low-nutrient desert soils)

4. Arizona-specific observation:

• How many plants showed iron chlorosis? _____ out of 20

• What was the average pH where Fe chlorosis occurred? _____

• Pattern: Fe chlorosis correlates with pH > _____

Part 3: Explore Vegetation-Soil Relationships

Goal: Discover which plants grow where and why. Some plants indicate specific soil conditions—they're "soil detectives"!

The principle: Plant distribution isn't random. Soil properties (texture, pH, moisture, nutrients) determine which species can survive.

Step 1: Survey Plant Diversity at Each Site

At each of your 5 soil sites, conduct vegetation survey:

A. Identify Dominant Species

Dominant = most abundant or covering most area

How to determine:

1. Stand in middle of site

2. Look around—what do you see most of?

3. Which species covers the most ground?

List the 2-3 most dominant species:

• Dominant #1: _____ (covers ____% of area)

• Dominant #2: _____ (covers ____% of area)

• Dominant #3: _____ (covers ____% of area)

Recording: Dominant species: _____, _____, _____

B. Count Species Richness

Species richness = total number of different species in an area

Procedure:

1. Mark out 10m × 10m area (use pacing: ~30 ft × 30 ft)

2. Walk systematically through area

3. Count each different plant type

4. Don't worry about exact IDs—just distinguish different species

Tips:

• Count grasses as separate types if clearly different

• Count "forb species 1," "forb species 2," etc. if unknown

• Seedlings count if you can identify them

Recording: Total species count: _____

Expected patterns:

• Desert: 5-15 species (low diversity)

• Wash: 10-20 species (moderate diversity)

• Garden: Variable (depends on management)

• Disturbed: 3-10 species (often weedy species)

• Riparian: 15-30+ species (high diversity)

C. Look for Indicator Species

Indicator species = plants that reveal specific soil conditions

They're like "soil reporters"—if you see them, you know something about the soil!

Arizona-Adapted Indicator Species:

ALKALINE SOIL INDICATORS (pH > 7.5):

• Saltbush (Atriplex spp.) - Tolerates high pH and salinity

• Shadscale - Very alkaline, salty soils

• Greasewood (Sarcobatus) - High pH, saline areas

• Russian thistle (tumbleweed) - Disturbed alkaline sites

• Kochia - Alkaline, poor soils

HIGH NITROGEN/FERTILE SOIL:

• Clover (Trifolium) - Also ADDS nitrogen (legume)

• Nettles - Rich, moist, fertile soil

• Lambsquarters - Nitrogen-rich soil

• Pigweed (Amaranthus) - Fertile, disturbed soil

POOR/LOW NUTRIENT SOIL:

• Plantain - Compacted, poor soil

• Dandelion - Tolerates anything (not specific!)

• Moss - Very low nutrients, acidic (rare in AZ)

• Annual grasses - Poor, disturbed soil

WET SOIL/HIGH MOISTURE:

• Cattails (Typha) - Standing water

• Sedges (Carex) - Wet or boggy soil

• Rushes (Juncus) - Moist to wet soil

• Willows (Salix) - Seasonally wet

• Cottonwood (Populus) - High water table

DRY/WELL-DRAINED SOIL:

• Creosote bush - Excellent drainage, dry

• Brittlebush - Well-drained, rocky slopes

• Prickly pear - Dry, well-drained

• Yucca - Very dry, fast drainage

DISTURBED/COMPACTED SOIL:

• Bermuda grass - Compacted, disturbed

• Puncture vine (goathead) - Compacted paths

• Cheat grass - Disturbed desert

• Bindweed - Disturbed, compacted

Recording for each site:

Indicator species found: _____, _____, _____

What they indicate:

• Soil pH: Acidic  /  Neutral  /  Alkaline

• Moisture: Dry  /  Moderate  /  Wet

• Fertility: Low  /  Moderate  /  High

• Disturbance: Undisturbed  /  Moderate  /  Highly disturbed

D. Estimate Plant Density and Coverage

Two different metrics:

1. Density = How many individual plants per unit area

Procedure:

1. Mark 1 square meter (about 3 ft × 3 ft)

2. Count individual plants inside

3. Record number

Recording: Density: _____ plants per m²

Expected ranges:

• Sparse: <10 plants/m²

• Moderate: 10-50 plants/m²

• Dense: >50 plants/m²

2. Coverage = Percentage of ground covered by vegetation

Procedure:

1. Look straight down at 1 m² plot

2. Estimate what % of ground is hidden by plants (leaves, stems)

3. Ignore rocks and bare soil

Scale:

• 0-25%: SPARSE coverage

  • Lots of bare ground visible

  • Common in harsh desert

• 25-75%: MODERATE coverage

  • Mix of plants and bare ground

  • Typical of most desert sites

• 75-100%: DENSE coverage

  • Little bare ground visible

  • Common in irrigated areas, riparian zones

Recording: Coverage: _____%

Step 2: Record Vegetation Data

Comprehensive vegetation-soil relationship table:

Analysis Questions:

1. Which site had the highest species richness? _____

• Why do you think this is? _____

• What soil properties support diversity? _____

2. Which site had the lowest species richness? _____

• What limits diversity here? _____

3. Did indicator species accurately predict soil conditions?

• Example: You found saltbush and soil pH was _____ (alkaline/neutral/acidic)

• Match?  /  Yes  /  No

4. Patterns you observed:

• Sandy soils → _____ type of plants (deep-rooted? shallow?)

• High pH soils → _____ type of plants (native? introduced?)

• Wet soils → _____ diversity (high? low?)

• Disturbed soils → _____ type of plants (native? weedy?)

5. Arizona-specific observations:

• Most common soil challenge: High pH  /  Low OM  /  Poor drainage  /  Salinity

• Most common plant adaptation: Deep roots  /  Small leaves  /  Water storage  /  Deciduous

Final Integration: Soil-Plant Connections

Create a Site Summary for Each Location:

For each of your 5 sites, write a comprehensive description:

Site 1: Natural Desert

Soil characteristics:

• Texture: Sandy loam (65% sand, 25% silt, 10% clay)

• Drainage: Fast (3 minutes)

• Organic matter: Very low (<1%), color rating 2/10

• pH: Highly alkaline (8.3), vigorous fizz test

• Structure: Single grain, no aggregation

Vegetation characteristics:

• Dominant species: Creosote bush, brittlebush, bursage

• Species richness: 8 species in 100 m²

• Density: Low (12 plants/m²)

• Coverage: Sparse (30%)

• Indicator species: Creosote, brittlebush → dry, alkaline, low nutrients

Plant health observations:

• 60% of plants showed iron chlorosis (yellow young leaves)

• Confirms high pH locks up Fe

• Native plants generally healthy despite low nutrients

Adapted to harsh conditions