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) 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

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 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 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

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 Weather Soil Type 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) 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

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

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 536 gal of water 2,145 x 0.25 = 536 Soil Texture Field Capacity1 25 Percent Depletion2 Sandy loam 5 - 10 10 - 15 Loams 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 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 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 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

Mulches and Drip Irrigation: Review