Plastic mulches have been used commercially for the production of vegetables since the early 1960's, and their usage is still increasing throughout the world. Plastic mulches provide many positive advantages for the user, such as increased yields, earlier maturing crops, crops of higher quality, insect management, and weed control. They also allow other components, such as drip irrigation, to achieve maximum efficiency. Although a variety of vegetables can be successfully grown using plastic mulches, muskmelons, tomatoes, peppers, cucumbers, squash, eggplant, watermelons, and okra have shown the most significant responses.

The color of a mulch determines its energy-radiating behavior and its influence on the microclimate around the vegetable plant. Specifically, color determines the surface temperature of the mulch and the underlying soil temperatures. Soil temperatures under black plastic mulch during the daytime are generally 5OF higher at a 2-inch depth and 3OF higher at a 4-inch depth compared to bare soil. Black mulch is predominate in vegetable production systems in the United States.

By contrast, clear plastic mulch absorbs little solar radiation but transmits 85 % to 95 %, with the relative transmission depending on the thickness and degree of opacity of the polyethylene. The lower surface of clear plastic mulch usually is covered with condensed water droplets. This water is transparent to incoming short-wave radiation, but is opaque to outgoing long wave infrared radiation, so that much of the heat lost to the atmosphere from a bare soil by infrared radiation is retained by clear plastic mulch. Thus, daytime soil temperatures under clear plastic mulch are generally 8 to 14'F higher at a 2-inch depth and 6 to 9'F higher at a 4-inch depth compared to bare soil. Clear plastic mulches generally are used in the cooler regions of the United States to warm up the soil faster in the springtime. Clear plastic mulches require the use of a fumigant or herbicide to control weeds that will grow under them.

White, white-on-black, or silver reflective mulches may result in a slight decrease in soil temperature (-20F at a 1-inch depth to -0.7'F at a 4-inch depth compared to bare soil), because they reflect back into the plant canopy most of the incoming solar radiation. These mulches are used to establish crops like cauliflower or tomatoes in mid-summer, when soil temperatures are high and any reduction in soil temperatures is beneficial.

A new family of mulches includes wave-length-selective mulches, which selectively transmit radiation in some regions of the electromagnetic spectrum but not in others. These mulches absorb photosynthetically active radiation (PAR) and transmit solar infrared radiation, providing a compromise between black and clear mulches. The infrared-transmitting (IRT) mulches afford the weed control of black mulch, but are intermediate between black and clear mulches in terms of increasing soil temperature. The color of these mulches can be blue-green (IRT-76, AEP Industries Inc., Moonachie, NJ; or Climagro, Leco Industries, Inc., Quebec, Canada) or brown (Polyon-Barkai, Poly West, Encinitas, Calif.). These mulches warm up the soil like clear mulch but without the accompanying weed problem.

Red, blue, orange, or yellow mulches reflect different radiation patterns into the canopy of a crop such as tomato, thereby affecting photosynthesis and/or plant morphogenesis, and can increase early yields, as was the case with red mulch. The colors also can affect the behavior of certain insects. Yellow and, to a lesser degree, orange surfaces attract the green peach aphid. Mulches with an aluminum or silver surface color have been used to repel certain aphids and reduce incidence of aphid-borne viruses in summer squash plantings.

Once the mulch has been selected, ensuring that it is applied properly is important. in commercial production, the mulch is typically applied by machine. Three basic operations are involved in application:

Bedding and pressinig the soil. Several bedding machines are available to growers in single- and multiple-row models. With " super-bedders, " the soil is raised and then bedded in one operation. In other situations, the soil is first raised in one operation with hilling discs or double disc hillers on a tool bar. The bed is then compressed to a uniform height and density using a bed press pan. The bedded rows should be spaced on 5- and 6-foot centers, depending on the equipment. A bed 4-6 inches high and 30 inches wide, with a slope from the center to the edge of 1.25 inches, is commonly used for vegetable production. The slope will allow excess rainfall to run off the mulch.

Laying the mulch and drip tube. The soil must have adequate moisture (enough for seed germination) when plastic mulch is laid. Temperatures should be at least 50 F, and the soil should be well worked and free from undecomposed plant debris. Take time to adjust the machine so that the press wheels hold the plastic firmly against the bed and the covering discs place soil halfway up the side of the bed but not on top. Also, when starting applications, anchor the plastic and drip tube by covering the end with soil and having a person stand on the drip tube.

For single-row crops, such as tomatoes, cucumbers, muskmelons, honeydews, watermelons, and pumpkins, the drip irrigation tube should be placed 4-5 inches from the center of the bed and 2-3 inches deep, with the emitter holes facing upward. For double-row crops of summer squash, okra, eggplant, and peppers, the drip tube should be placed directly on the center of the bed and buried 2-3 inches deep. A roll contains approximately 7,500 feet of drip tube, depending on the manufacturer. On 5-foot row centers, there are 8,712 linear feet of row per acre, so a grower would require about 3.5 rolls (2,000 ft. rolls) of plastic mulch and 1 1/4 rolls of drip tube per acre. On 6-foot centers, the per acre requirements would be 3 rolls of plastic mulch and 1 roll of drip tube.

Disposal continues to be a problem with plastic mulches and drip irrigation tape or tubing that are not photodegradable. Unlike used greenhouse film which is relatively clean and does have a recycling market established, field mulch and drip irrigation tape/tubing are dirty making recycling not as attractive. In field incineration of plastic mulch is not recommended.