LESSON SIX: MULCHES AND DRIP

IRRIGATION

High TunnelFruit and Vegetable Production

ObjectivesEvaluate 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 productionMain 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

efficiencyDisadvantages 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 onset of flowering and reducing early yield Should 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 cropThicker film is easier to be removed by hand, but

costs moreCommon 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 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

Polyethylene MulchesWhite 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 cucumberbeetle, leafhoppers

Can be used as a trap crop Blue has been showed to increase muskmelon,

cucumber, and summer squash yields

Polyethylene MulchesRed, 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 tunnelsWets only a portion of the root zoneUsually associated with plastic mulchHigh management, compared with overheadHigher quality and possibly higher yieldsInstallation 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

Shallow6-12 in.

BroccoliGreensOnion

Snap BeansPeppers

Moderate18-24 in.

CabbageCucumber

MuskmelonEggplant

Potato Tomato

DeepMore than

36 in.

AsparagusLima 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 turningon irrigation system

Soil Texture Inches/FootSands 0.5 – 1.0

Sandy loam 1.0 – 1.5Loams 2.0 – 2.5

Silt loams 2.5Clay 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

fieldDetermine 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 ExamplePepper Crop in Central Missouri SoilsSoil Type = Loam

Holds 2.4in available water per foot per acre Rooting Depth = 1.0 feet for pepperBed 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

longWetted 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 bed2.67 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

536 gal of water 2,145 x 0.25 = 536

SoilTexture

FieldCapacity

1

25 PercentDepletion2

Sandy loam 5 - 10 10 - 15 Loams 10 - 15 20 - 30 Silt loams 15 - 20 25 - 35 Clay loams 25 - 40 40 - 50

Scheduling Irrigation Example

Apply Water Shallow tensiometer reading 25 cbar, apply 540

galsCalculating 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