Prescription Fertilization of Woody Plants in Desert and Arid Soils
Robert Ll. MorrisEmeritus, University of NevadaEmail: [email protected]
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