Plastic Mulch Culture for Vegetables

Steven P. Kovach, Extension Horticulturist

Larry M. Curtis, Extension Agricultural Engineer

David G. Himelrick, Extension Horticulturist

Growing vegetables on raised beds with plastic mulch has become the standard method in many parts of the country, especially for high-value crops. Alabama crops well suited to this method are tomatoes, strawberries, peppers, surnmer squash, eggplant, cucumbers, melons and cole crops. Irrigation is needed to make plastic mulch successful. Since micro-irrigation lines can go under the mulch, delivering water to beds only, micro- is ideally suited for plastic mulch culture. Micro-irrigation also uses much less energy and water than do methods such as furrow irrigation or overhead sprinklers.

Advantages

The combination of plastic mulch and micro-irrigation has demonstrated potential for high yields and profits. Other advantages include:

Soil warming, resulting in earlier planting and harvest, and potential for double cropping
No soil splash on plants-a cleaner, healthier crop
Minimum cultivation-less root pruning, fewer weed problems
Less soil compaction
More efficient fertilizer use, with less leaching; also, water quality is protected
More efficient use of irrigation water
Less crop flooding in wet weather

Cautions

Per-acre costs for plastic mulch culture, including both operating and capital outlays, are high. Although returns usually provide correspondingly high profits, there is little room for error and a high level of management attention is needed. For example, since plants will receive water only from the irrigation system, reliable equipment and frequent and careful monitoring are essential. For most applications, soil fumigation is also a requirement.

In addition to costs of the irrigation system and of the plastic mulch itself, equipment and labor costs can be significant. Specialized machinery is available to prepare beds, fertilize, fumigate and lay mulch either in separate operations or in combination. Since most plastic mulch is not bio- or sunlight-degradable, additional labor costs usually include end-of-season removal and proper disposal of the mulch.

Scheduling

Irrigation for plastic mulch culture production is usually done on a daily basis, but may be done every other day, twice daily, or on some other schedule, depending primarily on the soil type. Since sandy soils hold much less water than clay or loam type soils, they must be irrigated in smaller but more frequent applications. For more information, see the publication on irrigation scheduling and publications on particular crops in this handbook.

Fertigation

Another advantage of micro-irrigation. is that fertilizer can be applied through the system. This method, called fertigation, provides plants with nutrients (usually nitrogen and potassium) as needed, so that the plants make the most efficient use of fertilizers. Soil type must be taken into account for fertilization as well as water management, since movement of dissolved fertilizers in the bed is also influenced by soil type. For more iriformation, refer to publications on fertigation and on particular crops in this handbook.

System Design and Operation

The drawing illustrates cross sections of plastic-mulched beds and shows how soil type affects water distribution. Since roots will develop only in the wetted zone, bed width should match the wetted width. If the bed is wider than the wetted width, bed space will be wasted, and any pre-plant fertilizer in the. unwetted zone will not be used by plants.

Drip tape, an inexpensive, disposable plastic tubing with uniformly spaced outlets formed-in as part of the tape, is commonly used in plastic mulch culture. Drip tape typically comes in 4- to 15-mil wall thicknesses. Heavier-gauge multiseason drip tubing with factory-installed "in-line" emitters is also used. The irrigation fine may be laid on the bed surface or buried 1 to 2 inches deep, with outlets facing upward. For single row crops such as tomatoes, cucumbers and watermelons, the line should be offset 4 or 5 inches from the bed center. For double row crops such as summer squash, okra, and beans, the line should be placed at the center of the bed.

Drip line used with plastic mulch is usually rated in terms of gallons per minute per 100 feet when operated at the recommended pressure. The actual flow will depend on the flow at each outlet and the spacing of the outlets. A typical flow would be one half gallon per minute per 100 feet. The designer should select a fine with outlets spaced so that a continuous band is wetted under the plastic mulch. The length of row and field elevation changes must also be considered by the designer to insure uniform water application over the field.

Line plugging is the most common problem encountered in micro-irrigation, especially with tape products. Publications in this handbook describe techniques for dealing with this problem. Another problem sometimes encountered is damage to drip lines by insects or animals, especially rodents. Pest control measures may be necessary.

References

Boswell, M.J. 1985. Micro-irrigation Design Manual. James Hardie Irrigation Co., El Cajon CA.

Clark, G.A. and D.Z. Haman. 1988. Micro-irrigation in Mulched Bed Production Systems: Irrigation Depths. Circular AE-72, Florida Cooperative Extension Service, University of Florida.

Clark, G.A. and D.N. Maynard. 1989. Response of micro-irrigated vegetable crops on various bed widths. Soil and Crop Science Society of Florida, Proceedings 49 (9/26-28):88-90.

Hochmuth, G. 1988. Polyethylene Mulching for Early Vegetable Production in North Florida. Circular 805, Florida Cooperative Extension Service, University of Florida.

Lamont, W.J., Jr. 1991. Drip irrigation: Part of a complete vegetable production package. Irrigation Journal (April 1991), 10-15.

Sanders, D.C. 1988. Using Plastic Mulches and Drip Irrigation for Vegetable Production. Leaflet 33, Agricultural Extension Service, North Carolina State University.

Sanders, D.C. 1988. An Introduction to Drip Irrigation for Vegetables. Leaflet 33-C, Agricultural Extension Service, North Carolina State University.

Publication No.

Micro-Irrigation Handbook ANR-654

Jan. 1999

Steven P. Kovac, Extension Horticulturist,

Larry M. Curtis, Extension Agricultural Engineer, Professor, Biosystems and Agriculture Engineering, and

David G. Hemelrick, Extension Horticulturist.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

This document is author-produced (unedited).