Download Soil-Water-Plant Relationships Topics to be covered: Soil Definitions:

2/26/2015
Topics to be covered:
•Soils and sustainable soil
management
•Water availability and conservation
•Plant – water relationship
•Irrigation methods and systems
Soil-Water-Plant
Relationships
Jose F. De Soto
UCCE - Ventura
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Soil Definitions:
• “The top layer of the earth’s surface suitable for the growth
of plant life” American Heritage Dictionary
• “ The weathered and fragmented layer of the earth’s
terrestrial surface” Introduction to Soil Physics
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Main Soil Components:
Sand
Mineral Soil Particles
•Largest particle in the soil
•It feels gritty and rough
•It does not hold nutrients
•It rapidly loses water and dries out
•Plenty of aeration for good plant
growth
•Easy to till
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Silt
•Size is smaller than sand
•Feels smooth and powdery
•When wet it feels smooth but
not sticky
•Generally resemble sand particles
•Has some of the physico-chemical
attributes of clay
Clay
•Smallest of the particles
•Particles fit tightly together
•Does not let water and air go through
easily
•It’s smooth when dry and sticky when
wet
•Easily molds into a ribbon when wetted
•Holds a lot of nutrients
•Difficult to till
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Soil Texture
•Qualitatively, it represents the “feel” of
the soil material, whether coarse or fine
and smooth.
•Quantitatively, it denotes the measured
distribution or the proportions of the
various size ranges of particles that
occur in a given soil.
Texture Triangle
Soil Texture
•The percentage
units (0-100%)
of sand, silt, and
clay are listed
along the sides
of the triangle.
•It determines water intake rates, water
storage, the ease of tillage, and the
amount of aeration.
•Soil texture refers only to the mineral
fraction of the soil.
http://www.public.iastate.edu/~aros
si/texture%20triangle.jpg
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Soil Structure
•It is the arrangement and
organization of the particles in
the soil
•There are three broad categories:
single grained, massive and
aggregated
Soil Structure
•Soil structure affects retention and
transmission of fluids in the soil
•Affects germination, root growth,
tillage and erosion
•Preferred in a loose and highly
porous and permeable condition
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Sustainable Soil
Management
•Avoid compaction
•Aerate compacted
soils
•Prevent erosion
•Use:
-organic matter,
-compost and
-mulches
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Organic Matter
Compost
•Energy source for soil microbes
•Considered a soil amendment more
than a fertilizer
•Helps restore soil biology
•Well decomposed compost is best:
- reduces tie-up of Nitrogen
- reduces potential for soil borne
diseases
•Stores nutrients for plant use
•Humus = Organic portion of the soil
remaining after prolonged microbial
decomposition. It is the glue that binds
soil particles together to prevent soil
erosion
Amending soil with compost
•Helps form soil aggregates
•Improves soil structure and soil tilth
•Reduces surface crusting and soil
erosion
•Improves air and water movement
Mulches
•Prevent raindrops from splashing on the soil
surface
•↑ water penetration, ↓ erosion
•Reduce annual weeds
•Conserve soil moisture  ↑ root growth
•Insulate roots from temperature extremes
•Protect plants from mechanical injury
•Improve plant establishment
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Types of Mulch
Mulch reduces Evaporation from soil
but not transpiration
•Wood Clips
•Compost
•Ground bark
•Rice hulls
•Straw or hay
•Rocks
•Artificial – plastic, ground tires etc.,
The golden rule of
gardening:
•“If you treat your soil well, it
will treat your plants well.”
Questions?
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Supply Sources
2. Where is the
water?
Los Angeles
Aqueduct
Colorado River
Aqueduct
State Water
Project
Local
Water Sources for Ventura County
Water Limitations
•Ground water
•Santa Clara River (United Water)
•Lake Casitas (Casitas)
•State Water Project (Calleguas)
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Water Limitations
Other water limitations
Key Delta Risks
2000
• Population growth
1500
• Environmental issues
1000
Fishery Declines
Delta smelt
500
0
1967 1973 1979 1985 1991 1997 2003
Seismic Risk
Flooding Risk
Bay Area Faults
Jones Tract (2004)
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3. Plants and Water
Questions?
Why plants need water?
1 - Chemical reactions in cells
Why plants need water?
2. Photosynthesis
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Why plants need water?
6CO2 + 6H2O +
Energy ↔
C6H12O6 + 6O2
3. Transpiration:
A plant must lose water
in order to grow
Which is a process similar to
•Water lost
through
stomata is
called
TRANSPIRATION
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Evapotranspiration Values
Crop Evapotranspiration
Et crop = Eto x Kc
Where:
Et = Evapotranspiration
Eto = Reference Evapotranspiration, or potential
evapotranspiration referenced to grass, when grass Kc = 1.00
Kc = Crop Coefficient
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Crop Coefficients
Alfalfa
0.94
Avocados
0.80
Chiles
0.59
Grass
0.85 – 0.95
Lemons
0.56
Lettuce
0.63
Strawberries 0.87
How many gallons is an inch?
• One cubic foot contains 7.48
gallons
Then,
• 1 in/sqft =
7.48/12in = 0.62 gal
• 1 inch/acre =
0.62 gal x 43,560 sqft = 27,007
gal/acre-inch
What do I do with that?
•Total Eto for VC in July was 5.80 inches
•Total precipitation was 0.01 inches
•Avocado Kc is 0.80
How much do I need to irrigate in July?
(5.80 – 0.01) x 0.80 = 4.63 inches
Following with the example…
•4.63 acre-inch x 27,007 gal/acre-inch =
125,042 gallons
•125,042 gal/100 emitters/10 gal/hr =
125 hrs of irrigation needed to replace
the water lost and recharge the soil
profile to full capacity
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Landscape Evapotranspiration
Landscape Example
Et = Eto x KL
• Large mature planting of Star Jazmine in full sun and little
wind exposure:
Where:
Et = Evapotranspiration of Landscape
Eto = Reference Evapotranspiration
KL = Landscape Coefficient
Species Factor
Density Factor
Microclimate Factor
• Star jasmine is classified as moderate in the WUCOLS list
(0.4 to 0.60) then ks (species) = 0.5
• Is a mature plant with full canopy, average density, then kd
(density) = 1.0
• Microclimate is equal to Eto (full sun, open area, no winds)
and classified as average then kmc = 1.0
(0.1 – 0.9)
(0.5 – 1.3)
(0.5 – 1.4)
Then KL = 0.5 x 1.0 x 1.0 = 0.5
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Factors that determine ET
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VC Monthly Average Eto
•Soil moisture
•Plant type
•Stage of plant development
•Weather factors:
- Solar radiation
- Wind Speed
- Humidity
- Temperature
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5
4
3
Ten yr avg
2
1
0
Jan Mar May Jul Sep Nov
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Watering Index
Factors Affecting Frequency of Irrigation
• Water infiltration rate
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Dec.
Oct.
Nov.
Aug.
Sept.
July
May
June
April
March
Jan.
(inch/hr):
Feb.
Percent of July ET
Monthly Irrigation Index without Rain
Very slow
< 0.06
Slow
0.06 – 0.2
Moderate
0.6 – 2.0
Rapid
6.0 – 20.0
Very rapid
> 20.0
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Factors Affecting Frequency of Irrigation
• Soil water holding capacity:
- Saturation ( 0 kPa)
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Factors Affecting Frequency of Irrigation
•Plant water use
Gravitacional water
- Field capacity (-33 kPa)
Available for plant use
•Depth of rooting
- Wilting point (-1500 kPa)
Capillary water
- Oven dry
•Irrigation method and output
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Monitor Soil Moisture
Use the ‘Feel’ Test
Dry
Medium
Soil probe
Wet
Soil sampling tube
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General principles for watering
•Irrigate established plants deeply and
infrequently
•Avoid watering everyday
•Water below the current root system
during each watering to encourage
deep rooting
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General principles for watering
•Don’t apply water at a greater rate than
it can be infiltrated
•Water cycling may be necessary to
avoid run-off
•Divide the total amount of water
required per day into 2 - 4 cycles
•Apply water as close to initial event as
possible before soil dries out
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General principles for watering
•Irrigate crop plants for optimum
production
•Irrigate landscape plants for good
looks and maintenance
That’s all folks !!!
Any questions?
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