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High Tunnel
Fruit and Vegetable Production
LESSON SIX:
MULCHES AND DRIP
IRRIGATION
Objectives
Evaluate high tunnel cropping situations where
either organic or plastic mulches would be
optimum.
List the six types of plastic films and the
advantages of each.
Summarize how to schedule irrigation and how
much irrigation water to apply.
Plasticulture System
Revolutionized vegetable production
Main Components
Plastic
Mulches (Polyethylene)
Drip or Trickle Irrigation
Other Components for Outdoor Production
Windbreaks
Raised
Beds
Transplants
Row Covers
Plasticulture System
Main Advantages of Plasticulture System
Season
extension
Higher yields per unit area
Cleaner and higher quality produce
More efficient use of water
Reduced leaching of fertilizer
Reduced soil erosion
Fewer weed problems
Plasticulture System
Additional advantages
Reduced
soil compaction
Elimination of root pruning
Potential decrease in incidence of disease
Better management of certain insect pests
Opportunity to double crop with maximum
efficiency
Disadvantages of Plasticulture System
Plastic
disposal problems
Cost of material, application and disposal
Mulches
Polyethylene Mulches
Modifies
microclimate
Increases
soil temperature and reflectivity
Decreases soil water and nutrient loss
Increased
soil temperature most important factor
Favorable
for continued root growth
Dependent on coolness of spring weather
Mulches
Polyethylene Mulches (Continued)
Certain
vegetables are best suited for use with
plastic mulches in high tunnels
Tomatoes,
Peppers, Eggplants, Cucumbers and
Summer Squash
Organic Mulches
Tend
to keep soil temperatures cool
Delays
Should
onset of flowering and reducing early yield
not be applied to spring crops
Mulches
Polyethylene
Linear
Low
and High Density
Thickness – 0.5 to 1.25 mil.
Various colors
Film thickness determines time it may stay on crop
Thicker film is easier to be removed by hand, but
costs more
Common plastic mulch sizes
48
to 60 inches wide
Rolls of 2,000 to 4,000 feet
Polyethylene Mulches
Black Plastic
Opaque,
body absorber that radiates energy
Absorbs most ultraviolet, visible and infrared
wavelengths of incoming radiation
Becomes an energy sink during the day, causing
possible plant stem damage
Much of absorbed energy can be transferred to
soil by conduction if good contact exists
Daytime temperature approx. 5 degrees F higher
at the 2in. Depth and 3 degrees higher at 3in
depth compared to bare soil
Polyethylene Mulches
Clear Plastic
Absorbs
very little solar radiation
Transmits 85-95% to the soil
Depending
Retains
on thickness and degree of opacity
most of heat lost to night sky by bare soil
Daytime high temperatures are 8-14°F higher at
2in depth and 6-9°F higher at 4in depth
Used for vine crops most responsive to soil temps
Must use a herbicide to control weeds
Polyethylene Mulches
White and Silver
Southern
states: establish a crop when soil
temperature is high (late Summer)
Silver reflects incoming radiation
Causes
disorientation of insect flight
Yellow, Blue
Attracts
insects such as green peach
aphid, striped and spotted cucumber
beetle, leafhoppers
Can be used as a trap crop
Blue has been showed to increase muskmelon,
cucumber, and summer squash yields
Polyethylene Mulches
Red, Brown, Green
Selectively
transmits or reflects radiation
Transmits solar infrared radiation
Soil
temperature response
between black and clear plastic
Prevents most weed growth
Also
called infrared transmitting
(IRT) mulches
Known to affect flower development, fruit set and
increased maturation of tomato fruits
Mulch is translucent, resulting in soil-warming effect
Cost is about 1.5 times that of black plastic
Disposal
Current use in North America estimated at
600,000 acres per year
Plastic film must be retrieved from field and
discarded after growing season
Some can be recycled, most is discarded by
placement in private landfills
Biodegradable Film
Potential of tilling film into soil after harvest
Results in savings from no pick-up or disposal
If plastic biodegrades before crop matures,
weed competition may increase
May
significantly reduce yield or quality of crop
Costs almost 50% more than current
nondegradable plastic mulch
Mulch Application
Growers should be conservative in setting out
early plantings
High
tunnels do not give much
protection against freezing
temperatures
Transplant stress from cold
temperatures can significantly
impact vegetable yield and quality
“Buttoning”
– Broccoli & Cauliflower
“Catfacing” - Tomatoes
Mulch Application
Modified plastic mulch layers have been
designed for use in high tunnels
36in-wide
plastic
Makes a 3 to 4in. high bed, 18in. Wide
17 foot wide high tunnel can accommodate 4 beds
21 foot wide high tunnel can accommodate 5 beds
Drip tape generally placed 2in. deep
Placed
in center or to one side of bed, depending
Depending
on crop
Trickle Irrigation
Almost used exclusively in high tunnels
Wets only a portion of the root zone
Usually associated with plastic mulch
High management, compared with overhead
Higher quality and possibly higher yields
Installation costs lower than overhead on
acreages smaller than 5 acres
Trickle Irrigation
Advantages
Low
flow rate
Smaller pump (less energy)
Less capital expenditures for a small acreage
Spaces between rows not wetted
Automation possible
Apply during windy conditions
Decreased damage may be realized
Fertilizer can be applied, if needed
Trickle Irrigation
Disadvantages
Increased
management skill needed
Higher daily maintenance
Clean water essential; emitters may clog
Frost protection not provided
Moisture distribution limited on sandy soils
Lateral line damage
From
rodents, insects and labor
Soil Water Loss
Affected By:
Crop
Species
Rooting
Depth, Planting
Density, Shading of ground,
Mulching
Weather
Temperature,
Light intensity,
Wind speed, Relative humidity
Soil
Type
Texture,
Water-holding
capacity, Infiltration rate
Rooting
Depth
Crops
Shallow
6-12 in.
Broccoli
Greens
Onion
Snap Beans
Peppers
Moderate
18-24 in.
Cabbage
Cucumber
Muskmelon
Eggplant
Potato
Tomato
Deep
More than
36 in.
Asparagus
Lima Bean
Watermelon
(Seeded)
Soil Water Loss
Soil Water-Holding Capacity (WHC) = the amount of
water a soil type can hold
Important to know the soil type when calculating
amount of water to apply
Trickle system wets only a portion of root zone
Only
allow 25-30%
depletion of soil
water before turning
on irrigation system
Soil Texture
Inches/Foot
Sands
0.5 – 1.0
Sandy loam
1.0 – 1.5
Loams
2.0 – 2.5
Silt loams
2.5
Clay loams
2.0 – 2.5
Soil Water Loss
Available water for plant growth and development
Product
of soil type and effective root growth
Ex: Mature tomato grown on plastic mulch in loam soil
Has
an available water amount of 3.75 in.
How Fast is Crop Using Water?
Plant
appearance = poor (wilting)
Soil appearance = better
Soil moisture meters – best
Tensiometers
and watermarks
Scheduling Irrigation
First, determine how much root zone water has
been lost
Apply water when there is no more than a 25-30%
depletion in the limited wetted zone
High
tunnel is more like a desert than a typical field
Determine how many gallons of water to replace
“Bathtub”
approach
What is the crop-wetted volume of soil in terms of
gallons at 25% depletion?
Scheduling Irrigation Example
Pepper Crop in Central Missouri Soils
Soil Type = Loam
Holds
2.4in available water per foot per acre
Rooting Depth = 1.0 feet for pepper
Bed or Row Spacing = 4.5 ft. between rows
Twin
rows, 18in. Apart, 4ft. wide plastic
In-row spacing at 15 inches
30 x 96 foot tunnel – allows 6 rows wide by 90 ft long
Wetted Radius of Bed = 16 inches
Varies
according to soil type
Scheduling Irrigation Example
Crop Wetted Volume = Use the given formula
that 1 acre-inch of water = 27,000 gallons
6 rows by 90 feet = 540 linear feet of bed
2.67 feet of wetted diameter x 540 linear feet =
1,442 square feet or 0.033 acres under plastic or
the trickle system
Rooting depth is 1.0 feet x 2.4 inches of water
per foot = 2.4 inches of water/foot/acre at field
capacity
Scheduling Irrigation Example
2.4 x 0.033 = 0.794in. x 27,000 gallons per inch
= 2,145 gallons available at field capacity
Allowing 25% depletion before turning on pump
Tensiometer
should read 25 cbar
Would have lost
Soil
536 gal of water
Texture
2,145
x 0.25 = 536
Field
25 Percent
Capacity
Depletion2
1
Sandy loam
Loams
Silt loams
5 - 10
10 - 15
15 - 20
10 - 15
20 - 30
25 - 35
Clay loams
25 - 40
40 - 50
Scheduling Irrigation Example
Apply Water
Shallow
tensiometer reading 25 cbar, apply 540 gals
Calculating Pump Run Time
Need
to know the trickle emitter delivery rate
Typical system for vegetables might deliver 0.53
gallons/hour/emitter
Our 540 linear feet of row = 540 emitters, 0.53
gal/hour/emitter = 286 gal/hour for the system
Replacing 536 gal: 536/286 = 1.87 or 2 hours to run
the pump
Trickle Irrigation In Review
1) Soil Water Volume Available to the Crop
Soil type to determine AWC at field capacity
Wetting radius (or diameter) of trickle
application and length of lateral run
Linear feet of crop system to calculate acres
under plastic
Effective rooting depth of the crop
Calculate available gallons at field capacity for
the crop acreage
Trickle Irrigation in Review
2) How Fast is the Crop Losing Water
Allow only 25-30% depletion of AWC
Tensiometer trigger point for soil type
3) How Long to Run the System
Emitter output in gallons/hour/100 linear feet
How many 100-foot units for the crop acreage?
Calculate system delivery in gallons per hour
per crop acreage
Divide gallons needed by the delivery rate to see
how long to run the pump
Mulches and Drip Irrigation: Review