This paper reviews different existing systems of seedling microirrigation in afforestation. These systems differ from agricultural irrigation methods since they only pursue the establishment of the planted seedlings instead of achieving good agricultural yields. They, therefore, involve very low irrigation doses compared to the usual irrigation doses found in the agricultural sector. These approaches are nonconventional localized irrigation systems with high efficiency in water application. Based on the water discharge equations they use, these methods can be classified into four groups: direct deep irrigation, irrigation through porous walls, irrigation with wicks, and irrigation with solar distillers. This paper describes a total of sixteen different systems suitable for afforestation. All the systems are compared with each other. To make the comparisons, four key parameters are considered: the cost of acquiring and installing the system, the water application efficiency, the maintenance of the system, and the possibility of irrigating several plants at the same time. The irrigation systems described in this review represent an important technical advance not only for dryland forestry but also for rainfed arboriculture, xeriscaping, and xerogardening. These systems make it possible to widely extend the planting period to almost throughout the year, not only in arid regions but also in less dry or even humid climates, especially when critical areas have to be afforested, including shallow, sandy, saline, or gypseous soils, suntraps, windy and desertified areas, open pit mines, and other areas. Seedling microirrigation is an emerging sector of the irrigation industry that is rapidly developing with new devices and patents. Two foreseeable future trends can be identified: the growing use of new permeable materials and the possibility of connecting individual emitters to irrigation lines.
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