root zone through evaporation or wind drifts of spray droplets, leaks in the
pipe system, surface runoff, subsurface runoff, or deep percolation within
the irrigated area. Irrigation requirements (IR) are determined by dividing
the desired amount of water to provide to the plant (ETc), by the Ea as a
decimal fraction (Eq.1). For example, if it is desired to apply 0.5 in to the
pumped. Hence, when seasonal water needs are assessed, the amount
of water needed should be based on the irrigation requirement and all the
needs for water, and not only on the crop water requirement. For more
information, consult “Field Evaluation of Microirrigation Water Application
Uniformity” at <>. Catch cans can be used in
Eq. 1 Irrigation requirement =
IR = ETc/Ea
FERTIGATION/CHEMIGATION
Irrigation systems are often used for delivery of chemicals such as
fertilizers, soil fumigants, or insecticides. The crop may require nutrients
when irrigation is not required, e.g. after heavy rainfall. Fertilizer injection
schedules based on soil test results are provided in Chapter 2 of this
production guide. Fertigation should not begin until the system is pressurized.
It is recommended to always end a fertigation/chemigation event with
or chemical deposits in the irrigation system, and/or rinse crop foliage. The
the fertilizer from the irrigation point to the farthest point of the system.
SYSTEM MAINTENANCE
Irrigation systems require periodic maintenance throughout the growing
season. These activities may require system operation during rainy periods
to ensure that the system is ready when needed. In addition, drip irrigation
systems may require periodic maintenance to prevent clogging and system
failure. Typically, cleaning agents are injected weekly, but in some instances
more frequent injections are needed.
FROST PROTECTION
For some crops, irrigation is used for frost protection during winter
growing seasons. For strawberry production, sprinkler irrigation is primarily
used with application rates of about 0.25 in per hour during freeze events.
Water freezes at 32ºF, while most plant tissues freeze at lower tempera-
the relatively higher temperature of groundwater can be used for cold
protection. Growers may also irrigate to raise the water table throughout the
and duration of freeze events, the depth to the existing water table level,
-
letin HS931 “Microsprinkler Irrigation for Cold Protection of Florida Citrus”
and Irrigation Scheduling Tools Using Florida Automated Weather Network
OTHER USES
Other irrigation uses vary according to the type of crop, system charac-
-
gation for dust control; wetting of dry row middles to settle dust and prevent
sand from blowing during windy conditions; and, wetting of roadways and
drive aisles to provide traction for farm vehicles.
IRRIGATION SCHEDULING
Irrigation scheduling consists simply of applying water to crops at the
“right” time and in the “right” amount and it is considered an important BMP.
The characteristics of the irrigation system, crop needs, soil properties, and
atmospheric conditions must all be considered to properly schedule irriga-
and reduced yields from inappropriate amounts of available water and/or
nutrients. In sandy soils, excessive water applications may reduce yield and
quality, and increase the risk of nutrient leaching.
A wide range of irrigation scheduling methods is used in Florida, with
corresponding levels of water management (Table 2). The recommended
method (level 5) for scheduling irrigation (drip or overhead) for vegetable
crops is to use together: the crop water requirement method that takes into
account plant stage of growth associated with measurements of soil water
status, and guidelines for splitting irrigation (see below). A typical irrigation
schedule contains (1) a target crop water requirement adjusted to growth
stage and actual evaporative demand, (2) adjustment of irrigation application
based on soil moisture, (3) a rule for splitting irrigation, (4) a method to
account for rainfall, and (5) record keeping (Table 3). For seepage irrigation,
the water table should be maintained near the 18-inch depth (measured
from the top of the bed) at planting and near the 24-inch depth when plants
are fully grown. Water tables should be maintained at the proper level to
ensure optimum moisture in the bed without leading to oversaturation of the
root zone and potential losses of nutrients. Water tables can be monitored
of the water table. For more information on observation well construction
consult ‘Water Table Measurements and Monitoring for Flatwood Citrus’ at
SOIL WATER STATUS, SOIL WATER TENSION, AND SOIL VOLUMETRIC
WATER CONTENT
Generally, two types of sensors may be used for measurements of soil
water status, those that measure soil water potential (also called tension
or suction) and those that measure volumetric water content directly. Soil
Table 3.2. Levels of water management and corresponding irrigation scheduling method.
Water Mgt. Level Irrigation scheduling method
0 Guessing (irrigate whenever), not recommended
1 Using the ”feel and see” method, see ftp://ftp-fc.sc.egov.usda.gov/MT/www/technical/soilmoist.pdf
2 Using systematic irrigation (Example: ¾ in. every 4th day; or 2 hr every day)
3 Using a soil water tension measuring tool or soil moisture sensor to start irrigation
4 Schedule irrigation and apply amounts based on a budgeting procedure and checking actual soil water status
51 Adjusting irrigation to plant water use (ETo), and using a dynamic water balance based on a budgeting procedure and plant stage of growth,
together with using a soil water tension measuring tool or soil moisture sensor
1 Recommended method
12 2019 Vegetable Production Handbook of Florida
/soilmoist.pdf