1. High Tunnel Fruit and Vegetable Production
Lesson Six: Mulches and Drip Irrigation

2. 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.

3. 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

4. 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

5. 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

6. 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

7. Mulches Polyethylene Mulches (Continued) Organic Mulches
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 onset of flowering and reducing early yield
Should not be applied to spring crops

8. 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

9. 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

10. Polyethylene Mulches Clear Plastic Absorbs very little solar radiation
Transmits 85-95% to the soil
Depending on thickness and degree of opacity
Retains 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

11. Polyethylene Mulches White and Silver Yellow, Blue
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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. Soil Water Loss Affected By: Crop Species Weather Soil Type
Rooting Depth
Crops
Shallow 6-12 in.
Broccoli
Greens
Onion
Snap Beans
Peppers
Moderate in.
Cabbage
Cucumber
Muskmelon
Eggplant
Potato
Tomato
Deep More than 36 in.
Asparagus
Lima Bean
Watermelon
(Seeded)
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

21. 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

22. 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

23. 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?

24. 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

25. 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 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

26. Scheduling Irrigation Example
2.4 x = 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 536 gal of water
2,145 x 0.25 = 536
Soil
Texture
Field
Capacity1
25 Percent
Depletion2
Sandy loam
5 - 10
Loams
Silt loams
Clay loams

27. 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

28. Trickle Irrigation In Review
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

29. Trickle Irrigation in Review
How Fast is the Crop Losing Water
Allow only 25-30% depletion of AWC
Tensiometer trigger point for soil type
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

30. Mulches and Drip Irrigation: Review