Southeastern U.S. Vegetable Crop Handbook - 2021 - 35

receive weekly nutrient applications through the drip system while
a sandy soil with low nutrient holding capacity will respond best
with a daily fertigation program. Fertigation rates are provided under
crop specific recommendations later in this handbook.
MULCHES AND ROW COVERS
Mulches
Plastic mulches
Plastic mulches have been used in vegetable production for many
years to control weeds, conserve moisture, improve yield and
quality, and acquire several other benefits. The most widely used
mulches for vegetable production are black, white-on-black, clear,
and metalized polyethylene mulches. Black mulch is most widely
used, especially for spring applications where both elevated soil
temperatures and weed control are desired. Clear plastic mulch is
used when maximum heat accumulation is desired and weed control
is not as critical, as weeds will grow well under clear plastic.
White-on-black plastic (with white-side of the plastic facing up)
is used for late spring and summer plantings where the benefits of
moisture retention and weed control are valued and heat accumulation
may be detrimental. Growers often apply diluted white latex
paint (1 part paint to 5 parts water) to black mulch when double
cropping. Metalized mulch, commonly referred to as reflective or
silver mulch, is used to combat aphids and thrips that vector viral
diseases. Metalized mulch should reflect a recognizable image
(that is, be mirror-like) to be most effective.
Degradable mulches
Biodegradable plastic mulches provide similar benefits of standard
polyethylene mulches. They are becoming more common, but usually
cost more than conventional polyethylene. This additional expense
may be offset by reduced labor and disposal costs at the end
of the season, as these do not need to be removed from the field for
disposal. Biodegradable plastic mulches are designed to degrade
in the soil by microorganisms when soil moisture and temperatures
are favorable for biological activity. Biodegradable film will
usually be retained on the surface of the soil rather than be blown
away from the application site. In addition, all of the biodegradable
film will eventually decompose, including the tucked edges buried
in the soil, into carbon dioxide, water, and microbial biomass. It
is recommended that biodegradable mulch be tilled into the soil
at the end of the harvest or growing season. Cover crops can be
planted the next day after biodegradable plastic mulch has been rototilled
into the soil.
Photodegradable and oxodegradable mulches are made with
conventional plastic, with additives that make the mulch break into
pieces when exposed to the UV radiation in sunlight, heat, and/or
oxygen, respectively. These fragments will not biodegrade in the
soil, but rather will accumulate in the soil and in bodies of water,
where they can enter the food chain.
For more information on biodegradable mulches, visit www.
biodegradablemulch.org.
Organic mulches
Organic mulches such as straw, pine straw, compost, and coarse
hay provide weed control and moisture retention, while keep2021
Vegetable Crop Handbook for Southeastern United States
ing soils cooler than bare ground. One benefit of using organic
mulches is that they add organic matter back to the soil when incorporated
after the growing season. Using hay often introduces
weed seeds into a field. Regardless of the organic mulch chosen,
a thick layer is required to adequately cover the soil and prevent
weed seed from germinating and breaking through the mulch layer,
which can make weed management even more difficult than if
no mulch were used. When using organic mulches, supplemental
nitrogen may be needed to compensate for the nitrogen that is lost
to soil microbes in the process of breaking down the organic mulch
(i.e., nitrogen immobilization).
Bed Formation and Drip Irrigation
Bed formation and moisture are critical to the success of growing
vegetables with plastic or biodegradable mulches. Beds should
be smooth, free of clods and sticks, and of uniform height. Black
mulches warm the soil by conduction, so mulches must fit tightly
over the soil. Tight contact between the mulch and soil will allow
better transmission of heat from the sun. Raised beds allow the soil
to drain and warm more quickly.
Drip tape is commonly laid under the plastic mulch in the same
field operation. The soil should be moist when the mulch is applied
since it is difficult to add enough water to thoroughly wet the width
of the bed when using drip irrigation. Steep slopes may limit row
length when using drip tape; normally row lengths should not exceed
300 to 600 feet depending on the specifications of drip tape.
Fumigants and Herbicides
Follow label directions for fumigants and herbicides used with
plastic mulches. Fumigants and herbicides often have a waiting
period before seeds or transplants can be planted. Transplanters
and seeders are available to plant through plastic or biodegradable
mulch. In fields with a history of nutsedge, appropriate measures
must be taken in order to reduce or eliminate infestations as plastic
mulches, whether conventional or biodegradable cannot control
nutsedge. Nutsedge will compromise plastic mulch by piercing it,
though it cannot penetrate paper mulch.
Fertilization and Fertigation
Prior to laying plastic mulch, soil pH should be adjusted with
lime as recommended by a soil test. Soil pH cannot practically be
changed once plastic mulch is established within a field. Vegetables
produced on plastic mulch, but without the ability to supply
nutrients through the drip irrigation system, should have all of their
required fertilizer incorporated into the beds prior to applying the
mulch. Broadcasting the fertilizer before bedding has been shown
to be an effective method of application since the bedding process
moves most of the fertilizer into the bed. Growers not able to fertilize
with their irrigation system need to be careful not to overwater
beds, as excessive irrigation can push soluble nutrients (i.e. nitrate,
sulfate) below the plants' effective root zone. Growers using fertigation
should follow the recommendations for each specific crop.
Fertigation schedules are listed for cantaloupe, cucumber, eggplant,
okra, pepper, summer squash, tomato, and watermelon later
in this handbook. Also, refer to the previous section for further information
on fertilization.
35
http://www.biodegradablemulch.org
Southeastern U.S. Vegetable Crop Handbook - 2021

Table of Contents for the Digital Edition of Southeastern U.S. Vegetable Crop Handbook - 2021
