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