Southeastern U.S. Vegetable Crop Handbook - 2022 - 40

FOR A 10% STOCK SOLUTION:
Injection rate of chlorine, gph = [(Desired available chlorination
level, ppm) x (Irrigation flow rate, gpm)] divided by
1,667.
FOR A 15% STOCK SOLUTION:
Injection rate of chlorine, gph = [(Desired available chlorination
level, ppm) x (Irrigation flow rate, gpm)] divided by
2,500.
It is important to note that chlorine will cause water pH to rise.
This is critical because chlorine is most effective in acidic water.
If your water pH is above 7.5 before injection, it must be acidified
for chlorine injection to be effective.
* Approved backflow control valves, low pressure drains,
and interlocks must be used in the injection system to prevent
contamination of the water source.
* Chlorine concentrations above 30 ppm may kill plants.
IMPORTANT NOTES:
Fertilization. Before considering a fertilization program for
mulched-drip irrigated crops, be sure to have the soil pH
checked. If a liming material is needed to increase the soil pH,
the material should be applied and incorporated into the soil as
far ahead of mulching as practical. For most vegetables, adjust
the soil pH to around 6.5. When using drip irrigation in combination
with mulch, apply the recommended amount of preplant fertilizer
and incorporate it 5 to 6 inches into the soil before laying
the mulch. If equipment is available, apply the preplant fertilizer
to the soil area that will be covered by the mulch. This is more efficient
than a broad- cast application to the entire field.
The most efficient method of fertilizing an established
mulched crop is through a drip irrigation system, which is installed
during the mulching operation. Due to the very small
holes or orifices in the drip tape, high quality liquid fertilizers,
or water-soluble fertilizers must be used. Since phosphorous is
a stable non-mobile soil nutrient and can cause clogging of the
drip tape emitters, it is best to apply 100% of the crop's phosphorous
needs pre-plant. Additionally, apply 20 to 40% of the crop's
nitrogen and potassium needs pre-plant. The remainder of the
crop's nutrient needs can be applied through the drip system with
a high-quality liquid fertilizer such as 8-0-8, 7-0-7, or 10-0-10.
Generally, it is not necessary to add micronutrients through the
drip system. Micronutrients can be best and most economically
applied pre-plant or as foliar application if needed.
The amount of nutrients to apply through the drip system
depends upon the plant's growth stage. In general, smaller
amounts of nutrients are needed early in the plant's growth with
peak demand occurring during fruit maturation. The frequency
of nutrient application is most influenced by the soil's nutrient
holding capabilities. Clay soils with a high nutrient holding capacity
could 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 keeping
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,
40
2022 Vegetable Crop Handbook for Southeastern United States
http://www.biodegradablemulch.org
Southeastern U.S. Vegetable Crop Handbook - 2022

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