Soils & irrigation for the high desert

1. Soils & Irrigation for the High Desert
Presenter: Louise Grabell,
Master Gardener,
Pinal Co. Cooperative Extension
University of Arizona
Rick Gibson, Pinal Co. Extension Agent
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2. • Understand the nature of soil.
• Understand the effects of pH, salts, and caliche on desert
soils and what can be done to modify their presence.
• List soil plant nutrients and their uses.
• Describe the roles of organic matter and microorganisms.
• Develop a plan to improve soil health.
• Understand the critical relationship between soil, water,
and plants.
• Determine the water needs of all the plants in my
landscape, and how best to provide it.
• Understand the basics of an irrigation system and proper
scheduling.
• Know the concept of “xeriscape” and its application.
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3. Basic Needs of Plants
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• Water
• Sunlight
• Nutrients
• Air

4. Soil Characteristics
 Color
 Texture
 Structure
 Drainage
 Depth
 pH
 Microorganisms
 Animals
 Water Holding Capacity
 Permeability
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5. Weathering & Erosion are Aided by:
• Rain
• Glaciers
• Vegetation
• Wind
• Chemical changes
• Alternate heating/cooling
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6. We Live in a Basin and Range Province
• Plate tectonics has caused the crust to be squeezed
together and pulled apart.
• As a result, high mountain ranges and deep valley
basins have been created.
• Southern deserts are in an area where collisions and
separations occurred in the past.
• Weathering has continually destroyed the rock
surface.
• Erosion carries away the debris, filling the valleys with
deep alluvial soils.
• If the soil does not have the same mineral content as
the mountains in the area, then it is a transported soil.
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7. 7
Soil Composition By %

8. What Does Soil Look Like?
 Mineral Particles
 sand
 silt
 clay
 Open Spaces
(pores)
 air
 water
 Organic Materials
 carbon-based
CARBON
-BASED
SILT
SAND
SAND
SAND
SILT
SAND
CLAY
WATER
WATER
WATER
AIR
AIR
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9. Soil Texture
 Texture refers only to the size of mineral
particles
 sand 2 to 0.05 mm
 silt 0.05 to 0.002 mm
 clay less than 0.002 mm
 Different textures are a result of
proportional mixtures of sand, silt, and clay.
 Excluded are:
 organic matter
 large particles (larger than 2 mm)
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10. Why Is Texture Important?
• Determines the amount of water and fertilizer
needed for good plant nutrition.
• Affects soil drainage.
• Impacts aeration…% of pore space.
• Affects leaching capacity and cation exchange
capacity.
• It is difficult to significantly change soil texture.
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11. Cation Exchange
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 Cations are positively charged mineral ions in the soil.
Ex: calcium [Ca+], magnesium [Mg+], potassium [K+], iron
[Fe+], etc.
 Certain soil particles can attract cations because they
have electrostatic forces…charges on their surfaces.
 Mainly clay particles and organic matter can do this.
 Thus, essential mineral ions are “captured” by soil
particles and held for uptake by plant roots.
 This process is called “cation exchange” [CE]
 CE occurs better in alkaline soils.
 CEC = cation exchange capacity.
 Poorly drained arid soils tend to absorb sodium ions
[salt].

12. Soil Structure
 Soil structure is the way the soil particles aggregate
based on the types of particles and pores.
 Soil aggregates are a factor of the parent material.
 Soil structure is destroyed by cultivation…and traffic.
 Cultivation enhances oxidation and the decay of
organic matter.
 Cultivation breaks up the aggregates and reduces
aeration and water flow.
 Soil structure can be improved by adding mineral,
organic, and inorganic amendments.
 Clay soils need cultivation and amendments for plant
growth…other than native types.
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13. Organic Matter Content
High
organic
matter
soils
Low
organic
matter
soils
slow plant growth in arid climate
rapid decomposition in warm soils
rapid decomposition in
well-drained soils
rapid decomposition in tilled soils
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14. Carbon-Nitrogen Ratio In Soil
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 The C-N ratio is a measure of the proportions of carbon to
nitrogen in organic amendments.
 Organics are decomposed by microbes in the soil,
releasing nitrogen for plant uptake.
 If the C-N ratio is higher for nitrogen, then the excess
nitrogen is released into the soil and used by plants.
 If the C-N ratio is higher for carbon, the microbes will
utilize soil nitrogen for further decomposition, immobilizing
soil nitrogen, and preventing plants from getting it.
 In general, as fresh organic material is decomposed,
microbes use 75% of the carbon for energy and 25% of
the nitrogen to grow their cells…the remaining nitrogen is
absorbed by plant roots.
 Organics with a C-N ratio greater than 10:1 will require
additional nitrogen.

15. Benefits of Organic Matter
 Improves tilth [suitability for growing
crops]
 Improves water-holding capacity
 Improves nutrient-holding capacity
 Adds nutrients
 Feeds microorganisms
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16. pH
 Measures the acidity or alkalinity of a solution…%
of hydrogen ions.
 Measured on a scale of 1 to 14; 7 is neutral
[water].
 More H+ ions = more acidic soil and the lower its
pH.
 Most plants do best in a pH range of 6.5 to 7.5.
 More minerals are soluble in acidic soils.
 The more alkaline the soil, the less iron will
dissolve.

17. Caliche
 Soil particles cemented together by
lime
[calcium carbonate - CaCO3 ]
 Caliche is a problem because it
 restricts water flow
 reduces root penetration
 has a high pH
 reduces the availability of iron
 is like cement!

18. Causes of Soil Salinity
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 Existing soluble salts in the soil…from parent material.
 Deposition of salts from the evaporation of ancient inland
seas.
 High rate of evaporation at the surface, concentrating
salts.
 Low annual rainfall.
 Salty irrigation water and poor drainage.
 In arid regions, most of the salts present in irrigation
water are chlorides, sulfates, carbonates, and
bicarbonates of calcium magnesium, sodium, and
potassium.
 Sodicity specifically refers to the amount of sodium in the
soil.

19. Problems Caused by Soil
Salinity19
 Growth of salt-tolerant weeds.
 Water becomes less available
for root uptake.
 Causes plant stress.
 Plants may be stunted.
 Dark green leaves will turn
yellow.
 White edge on leaves appears.

20. Resolving Salinity Problems
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 Lower the pH of the soil…add
aluminum sulfate or iron sulfate.
 Add organics to increase drainage.
 Treat the soil with gypsum…a
calcium source.
 Irrigate thoroughly to leach away the
salts…good drainage is necessary.
 Leaching is a catch 22…why?

21. Signs of Nutrient Deficiencies
• Nitrogen – older leaves
yellow first
• Iron – interveinal chlorosis
• Phosphorus – purplish
leaves, especially on
margins
• Zinc – stunted growth;
witches’ broom

22. Fertilizers Add Nutrients
• All-purpose fertilizer supplies 3 nutrients: nitrogen,
phosphorous, and potassium.
• The numbers on the bag tell you their percentages by
weight: a 20 lb bag of 5-10-5 contains 5% or 1 lb of N,
10% or 2 lb of P, and 5% or 1 lb of K.
• Nitrogen is the main nutrient lacking in SaddleBrooke
soil [few organics and microbes]
Ammonium sulfate (21-0-0)
Ammonium phosphate (16-20-0)
Urea (45-0-0)
N
sources
Incomplete
fertilizers

23. So, what is soil?
• A result of the interaction of the
atmosphere, hydrosphere, and lithosphere.
• Structurally, soil is composed of all three
states of matter: solid, liquid, and gas.
• The components of soil are both inorganic
[mainly] and organic.
• How we use it will affect its ability to
sustain plant/crop production.
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24. • Understand the soil-water relationships around my
home.
• Determine the water needs of all plants in my
landscape.
• Plan for proper irrigation.
• Understand the basics of an irrigation system and
proper scheduling.
• Understand the use of “xeriscapes” in the desert
environment.
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25. The amount you irrigate depends on:
• Evapotranspiration [ET].
• Amount of precipitation [amount vs. infiltration rate].
• Seasonal requirements.
• Wasted water from the irrigation system…efficiency.
[spray drift, over-watering, pooling, run-off]
• Timing of system valves…seasonal & time of day.
• Slope of the land…or that of your neighbors!
• Leaching.
• Condition of the soil…only about 65% of water delivered by
the irrigation system is available to plants!
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26. 26
The Hydrologic Cycle

27. Infiltration Rates
[soil water movement]
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28. Porosity & Permeability
Porosity does not guarantee permeability.
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29. Consolidation & Porosity
Clay soils are extremely compacted…difficult to wet and difficult to dry.
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30. Why consider a drip system?
• Drip irrigation uses a low volume of water.
• Drip irrigation maintains constant moisture around the
roots.
• Drip irrigation applies water accurately to where it is
needed.
• Drip irrigation avoids water loss to evaporation.
• Drip irrigation can be easily adjusted to accommodate
new plantings or reduce the watering of older plantings.
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31. Water needs can vary….
• Seasonal effects……monsoon.
• Wind and wind-channeling.
• Exposure…amount of solar
radiation.
• Microclimates around
your house.
• Types of plants.
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32. Createdor not, microclimatesexist around
your homebecauseof:
• Radiationfrom solid surfaces.
• Sheltered locations…wind.
• Wet spotsfrom irrigation.
• Slopingterrain.
• Shade from trees…or other structures.
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33. How deep must the water penetrate?
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 Annuals, perennials, ground covers… 1 foot
 Shrubs ………………………………………… ….2 feet
 Trees ………………………………………………. 3 feet

34. A soil probe is essential….
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Push a metal rod
into the soil to see
how far the water
has penetrated.
Soil probe

35. Trees are special:
• As trees grow, they require more irrigation.
• Drip emitters should be increased in number
as the diameter of the tree increases.
• Emitters must be moved to the edge of the
canopy where the water-absorbing roots are
located.
• Native trees such as mesquites and palo
verdes should not be on regular irrigation
after their first year. 35

36. You should know the components of your own
plan.
• First, decide how you want your landscape to
look. Get ideas from neighbors.
• Divide your plantings into groups: trees,
shrubs, citrus, and vegetable/flower bed and
free-standing planters.
• Make sure you have separate valves for each
group. Ex: all citrus on one valve.
• Learn how to use your timer before your
landscaper leaves!
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37. 37

38. Divide your estate into sections based
on plant types and water needs.
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Now you will know how many valves you will need.

39. 39
The system is simple!

40. The timer does the work!
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41. 41
Know your drip emitter; their output can vary
from .5 to 2 gallons per hour.
There are other designs…manufacturer’s preference.

42. Soil water penetration
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43. What Does Your Timer Do!
• The timer controls your entire system.
• The timer has a separate control for each
valve’s start/stop times and days of the week.
• The timer has a “set” mode for adjusting the
run times and days when each valve will run.
• The timer can be seasonally adjusted…once
you are not afraid to touch it!
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44. What you need to know:
• How many valves are in my system?
• Can I control each valve without calling my
landscaper?
• How many gallons per hour do my emitters release?
Standard is 1 gallon per hour.
• How deeply do I need to water?
• Are shrubs and trees and citrus on the same valve?
Oy!
• Other than flower and vegetable gardens, daily
watering is unnecessary.
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45. Let’s talk scheduling:
• Valves that irrigate shrubs should be set to water sufficiently to a
depth of 12 inches.
• For trees, a three-foot depth of wetness should be achieved.
• Once you know how long it takes to achieve the desired depth, set
your valves to run once every 5-7 days in hot weather, and every
10-14 days in cold weather.
• Observe your plants and shrubs to make sure this schedule is
keeping them healthy.
• If your plants are doing well, try to stretch your schedule…every
garden is different.
• Flowers/potted plants require daily watering.
• New plantings will need more frequent watering.
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46. Maintaining your system:
• It’s probably a good idea to open the endcaps
and let the water run for a minute or two to wash
out the pipes annually.
• Clean drippers, nozzles, etc.
• Replace broken sprayer heads, etc.
• Run your system and check all drippers to make
sure water is flowing.
• Run your system and check for leaks…you can fix
these yourself.
• Do this NOW while the weather is cool.
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47. Water conservation in your yard = xeriscape.
 A term first used by the Denver Water Dept.
in 1981.
 Using drought-resistant plants.
 Using less irrigation water…water less frequently, but
more deeply.
 Using creative landscaping to get the “green”.
 Lowering your water usage leaves more to the
community.
 If water restrictions are applied, xeriscape plants will
tend to survive.
 Xeriscaping saves time and money!
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48. Seven steps to using 50% less water:
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• Proper planning and design
• Proper soil analysis and improvement
• Appropriate plant selection
• Practical turf areas…or not!
• Efficient irrigation
• Use of mulch
• Appropriate maintenance
• Xeriscape wherever possible.

49. Identifying low water-usage plants:
Smaller size, e.g., mesquites vs. oaks.
Slower growing.
Modified leaves, ie, cactus spines.
Fewer stomates.
Waxy coating.
Lower fertilizer requirement.
Wide-spread, shallow root systems.
Note: drought-tolerant plants use lots of water
when actively growing, and then become
dormant in dry season. Ex: Ocotillo, mesquite.
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50. Xeriscaping in Clay….
• Be aware that clay soils can store water.
• Clay soil has poor drainage.
• Heavy clay soil may have to be amended with
organic matter.
• Select plants that adapt to clay soil: lantana;
sage, yucca etc.
• Dig a little deeper to prepare for planting.
• Don’t fight the dry spots [rocks, slopes].
• In the high desert….work with the natives!
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