Chapter 3. Principles and Practices of Irrigation Management for
Vegetables
L. Zotarelli, M.D. Dukes, G.D. Liu, E.H. Simonne, and S. Agehara
This section contains basic information on vegetable water use and
irrigation management, along with some references on irrigation systems.
Proper water management planning must consider all uses of water,
from the source of irrigation water to plant water use. Therefore, it is very
important to differentiate between crop water requirements and irrigation or
production-system water requirements. Crop water requirements refer to
the actual water needs for evapotranspiration (ET) and plant growth, and
primarily depend on crop development and climatic factors which are closely
related to climatic demands. Irrigation requirements are primarily determined
by crop water requirements, but also depend on the characteristics
of the irrigation system, management practices, and the soil characteristics
in the irrigated area.
BEST MANAGEMENT PRACTICES (BMP)
FOR IRRIGATION
BMPs have historically been focused on nutrient management and
fertilizer rates. However, as rainfall or irrigation water is the vector of off-site
nutrient movement of nitrate in solution and phosphate in sediments as well
as other soluble chemicals, proper irrigation management directly affects
Quantity Best Management Practices for Florida Vegetable and Agronomic
Crops” (accessible at ) manual cover all
major aspects of irrigation such as irrigation system design, system maintenance,
erosion control, and irrigation scheduling.
USES OF IRRIGATION WATER
Irrigation systems have several uses in addition to water delivery for
crop ET. Water is required for a preseason operational test of the irrigation
system to check for leaks and to ensure proper performance of the pump
crop establishment, crop growth and development, within-season system
maintenance, delivery of chemicals, frost protection, and other uses such
as dust control.
FIELD PREPARATION
to the natural water table, and the type of irrigation system. Drip-irrigated
preparation because drip tubes are not installed until after the beds have
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tion and may apply one or more inches of water for this purpose. Subirrigat-
crop establishment, plant growth needs, and frost protection. Subirrigation
water management requirements depend on the soil characteristics within
to raise the water table level as high as 18 to 24 in below the soil surface.
subsurface runoff requirements. As a rough guide, 1.0 to 2.5 in of water are
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rigation water table 30 in deep may need about 2 in of water to raise the
water table to 18 in, while a pre-irrigation water table at 48 in may require 5
in of water for the same result.
CROP ESTABLISHMENT
Vegetables that are set as transplants, rather than direct seeded, require
irrigation for crop establishment in excess of crop ET. Establishment irrigations
are used to either keep plant foliage wet by overhead sprinkler irrigation
(to avoid desiccation of leaves) or to maintain high soil moisture levels
until the root systems increase in size and plants start to actively grow and
develop. Establishment irrigation practices vary among crops and irrigation
systems. Strawberry plants set as bare-root transplants may require 10 to
14 days of frequent intermittent overhead irrigation for establishment prior
to irrigation with the drip system. The amount of water required for crop
establishment can range widely depending on crop, irrigation system, and
climate demand. Adequate soil moisture is also needed for the uniform
establishment of direct-seeded vegetable crops.
CROP GROWTH AND DEVELOPMENT
Irrigation requirements to meet the ET needs of a crop depend on the
and crop growth stage. Crops vary in growth characteristics that result in
different relative water-use rates. Soils differ in texture and hydraulic characteristics
such as available water-holding capacity (AWHC) and capillary
movement. Because sands generally have very low AWHC values (3% to
6% is common), a 1% change in AWHC affects irrigation practices.
Table 3.1.
Irrigation system
Overhead 60-80%
Seepage1 20-70%
Drip2 80-95%
1 Ea greater than 50% are not expected unless tailwater recovery is used
2 With or without plastic mulch
WATER APPLICATION (IRRIGATION REQUIREMENT)
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ciency (Ea), which is the fraction of the water that has been applied by the
irrigation system and that is available to the plant for use (Table 1). Applied
water that is not available to the plant may have been lost from the crop