Prescription Fertilization of Woody Plants in Desert and Arid Soils

Robert Ll. MorrisEmeritus, University of NevadaEmail: MorrisR@unce.unr.edu

Blog Xtremehorticulture of the DesertYahoo discussion group: desert_horticulture

Characteristics of desert soils

Structureless High pH (alkaline) High salts Low organic matter

Plant Nutrients

Needed in Large AmountsCarbon

Hydrogen OxygenNitrogen

PhosphorusPotassiumCalcium

MagnesiumSulfur

Needed in Much Smaller Amounts

IronManganese

ZincBoron

ChlorineCobalt

Molybdenum

Nutrients Needed in Large Amounts

Nitrogen PhosphorusPotassiumCalciumMagnesiumSulfur

Nitrogen

Increases leaf and stem growth Darkens green leaf color Increases stored food Can make plants less tolerant of freezing weather Boosts spring recovery and recovery from damage Nitrogen fertilizers typically dissolve easily in water and move

with water through the soil profile

Shortage of Nitrogen Slow growth Light green leaf

color Thin canopy

Shortage of Nitrogen

On pines candles are smaller

Canopy is not dense Needles at the ends

of branches

Nitrogen

Too Much?Rapid growthDense canopy

Dark green leavesLeaf scorch and possible damage

Wastes moneyEnvironmental pollution

Phosphorus Root production Stem strength Flower and seed production Deficient in cold, wet soils

Phosphorus

Too Much?Moves slowly in the soil

TroublemakerToxicity

Wastes moneyEnvironmental pollution

Not Enough?Poor growth or performance

Disease susceptibilityReduced flowering

Poor root development

Phosphorus deficiencyPurple coloration in severe deficiency

Potassium Landscape plant needs are usually underestimated Stress resistance

Potassium

Too Much? Nothing visual Wastes money

Not the environmental problem that nitrogen and

phosphorus can be

Not Enough? Poor tolerance to stress

Disease susceptibility Poor heat tolerance Poor cold tolerance

Nutrients Needed in Smaller Amounts

IronManganeseZincBoronChlorineCobaltMolybdenum

Desert Soils and Available Nutrients

The Benefits of Decomposing Organics to the Soil

Lowers soil pH Adds nutrients Improves soil

chemistry Provides natural

chelates Preserves soil

moisture Increases soil “good

guys”

Micronutrients

IronManganese

Zinc

Micronutrients - Iron

Found on newest leaves

Early stages, leaf yellow with green veins

Advanced stages leaf is pure yellow combined with scorch

Micronutrients - Iron

Micronutrients - Iron

Iron

Causes: High soil pH Soils kept too wet Rock mulches High phosphorus Damage to trunk or stems

Iron Fertilizers and Strategies Add more iron

Iron sulfate Lower the pH

Iron with sulfur Keep iron available to

plants Chelates

Organic amendments Lower soil pH and

natural chelates

Soil applied Foliar applied Injection

What is a Chelate? Chelates help make minor elements available to plants Examples are EDTA, DTPA and EDDHA Some chelates perform better in desert soils than others

Desert Soils and the Best Chelate

Micronutrients - Manganese Confused with iron Difficult to identify Leaf veination green

like “magic marker” Soil applications,

foliar and injection

Micronutrients - Zinc Rosette of leaves on ends of

branches Smaller leaves than normal Leaf discoloration Soil applications, foliar and

injection.

What Is the Perfect Fertilizer?

The perfect fertilizer: Builds a reservoir of nutrients needed by the plant Replaces nutrients taken from the soil by the tree Maintains the plant in good health

Are soil tests necessary?

Liebig’s Law of the Minimum

Plant growth is limitedby the nutrient in leastsupply.

What is the Perfect Ratio? Ratio (NPK) is determined by type of plant, previous

fertilizer applications, soil condition and soil tests if done Generally nitrogen is highest amount followed by

potassium and phosphorus lowest Typical ratios: 3-1-2, 3-1-3, 4-1-2, 4-1-3, 4-1-4

What is the Perfect Timing? Single applications late winter/early spring Split applications; ½ late winter, ½ after flowering/fruiting Avoid applications of nitrogen to winter tender plants

after August 1 Late fall application

What is the Perfect Amount? Adjust rates according to growth in previous years and

general health of the tree Rates typically 1 - 2 lbs of N per 1000 sq ft under the

tree canopy

How to Apply Fertilizers Soil applied

Place 6 inches deep near sources of water Foliar applied

Spray to runoff Use wetting agent to improve foliar uptake

Trunk injection Use only when no other option is available Inject in root flares of older trees or as low on trunk as possible Inject with the smallest hole possible

Late Fall Fertilization Apply late enough so that new growth is not encouraged

but before leaf drop Builds nitrogen in storage tissue Contributes to early spring greenup/leaf emergence and

may eliminate the need for a spring application

Resources Blog: Xtremehorticulture of the Desert Yahoo Discussion Group: desert_horticulture