Agriculture Reference
In-Depth Information
Past research and practical experience has shown that irrigation management
practices must be simplistic, useable, flexible within the existing system design
and maintenance constraints, and understandable by growers, in order for them to
be widely adopted and used. Therefore, it is not surprising that the predominant
irrigation scheduling method is decision making by the growers, based on their own
experience (Warren and Bilderback
2004
).
Irrigation Systems
From a spatial point of view and according to Savvas et al. (
2013
), greenhouse ir-
rigation systems can be categorized in: (i) overhead surface, (ii) surface and (iii)
subsurface or sub-irrigation system.
Overhead surface irrigation is based on a top-down principle and involves over-
head nozzles, where the water is sprayed onto the plants. The nozzles are installed
either in static pipes or in rigs, so called automatic irrigation booms, which move
through the greenhouse above the plants. Overhead irrigation is appropriate for wa-
tering plants with low stature and at a similar uniform growing stage. In addition, it
is of benefit for plants that like regular cooling, such as different lettuces and salad
greens, spinach or seedlings. These systems have relatively low installation costs.
The irrigation uniformity and WUE are however low by these systems. In addition,
the risk for residue on leaves and flowers as well as the risk for spreading diseases
is high, because the water is applied to the aerial part of plants.
The most popular irrigation system in greenhouses is the surface system or drip
irrigation (Fig.
10.16
), mainly due to high efficiency and uniformity. In addition,
drip irrigation is easy to install and design, as well as being precise with less run-
off of water. One of the great advantages of drip irrigation is that it can be used to
deliver nutrient solution as well as plant protecting agents. Drip irrigated water with
or without fertilizer is delivered slowly where needed, through the soil or substrate
surface to the plant roots. Apart from low-pressure irrigation, pressure compensat-
ing emitters are used, in order to deliver a constant water-amount per time unit. One
of the disadvantages of drip irrigation is the clogging of emitters.
Subsurface or sub-irrigation systems provide plants with water through the base
of pots and/or other containers used, and include capillary mats, troughs, ebb-flood
benches as well as flooded floors. In this system water reaches the roots mainly by
capillary forces. Ebb-flood benches are generally used for production of pot orna-
mentals and seedling plants, troughs are used for pot plants and vegetables grown
in substrates, and flooded floors for seedling production and large ornamental plant
production. One of the disadvantages of this system is the accumulation of salts in
the upper layers of the soils or substrates. Sometimes pipes that are usually used in
drip irrigation, e.g. porous pipes, are installed in the soil in form of a sub-irrigation
system. By an appropriate use, the WUE could be improved.
