**4. Seawater agriculture**

*Landscape Architecture - Processes and Practices Towards Sustainable Development*

a way that each tree had its own small catchment area, typically less than 100 m, and store it in the root zone of an adjacent infiltration basin where a tree or bush or an annual crop is grown [14, 22–24]. The system can be built on almost any slope, enabling the farmer to use large flat areas [13] that might be a significant advantage for application in the areas where collecting large amounts of runoff is

*Traditionally designed micro-catchment system: (a) schematic of the system and (b) flooded micro-catchment.*

The infiltration basin is usually a shallow depression located at the low end in

The size of the runoff production area directly determines the total amount of runoff water that can be stored in the pit together with soil and rainfall character-

 in Mali [16]. Runoff generation at micro-catchments is also affected by the rainfall characteristics. It was shown that there is a clear relationship between runoff yields and average rainfall intensity and the degree of correlation between them improves with

The rate of water losses by evaporation is mainly affected by radiation, climate, soil texture, soil structure, soil hydraulic properties, etc. [15]. Because of relatively low absolute amount of water collected at micro-catchments, special attention should be paid to the prevention of the stored soil water from

Long-term micro-catchment experiments carried out at Mashash runoff harvesting experimental farm of Ben Gurion University of the Negev showed that the change of collection plot design from a flat surface to a deeper and narrower pit makes the system much more effective. Being collected in the pits, water may infiltrate deeper due to repetitive concentration of relative large water amounts at the limited area and the increased waterhead. Most trees planted inside the pits showed the much higher surviving ability comparing with trees planted at the flat plots.

in Israel,

istics, topography, etc. [25]. Reported sizes of a single plot are 100–250 m2

a decrease in the length of the gap between the rainstorms [18].

in India, and 1000 m2

Runoff generation at micro-catchments is affected both by the total rain amounts and average rainfall intensity [18], while the relatively absolute amount of water collected at micro-catchments is low anyway. In such circumstances, the central idea behind any micro-catchment design should be enhancing infiltration and reducing evaporation of already collected water and thus improving soil moisture storage in the crop rooting zone through the dry season. The second component of the system is the water conservation efficiency at the collection plots, i.e., in the soil profile and its further availability to trees/shrubs. The deeper the harvested water moves in the soil profile, the less part of it is exposed to

the immediate vicinity of the runoff generating area (**Figure 6**).

**148**

not possible.

**Figure 6.**

evaporation [15].

250–400 m2

evaporation.

The increasing deficiency of freshwater combined with the ever expanding world population will exacerbate water use pressure between the different water user sectors (urban, industrial, and agricultural). Solving this problem will undoubtedly be the twenty-first century challenge and is necessitating that marginal quality waters including saltwater and/or seawater are strategically used to meet the water shortage without any detriment to the environment and natural resources for increasing crop production worldwide.

According to the Food and Agriculture Organization (FAO) of the United Nations [26] and World Resources Institute (WRI) in collaboration with the United Nations Development Programme (UNDP), United Nations Environment Programme (UNEP), and World Bank (WB) [27], most of the West Asia and North Africa countries are expected to fall below the water scarcity level (1.000 m3 capita<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) by the year 2030. The most affected countries are Kuwait, United Arab Emirates, Saudi Arabia, Yemen, and Libya where renewable water resources (RWR) per capita will fall well below 100 m3 capita<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> [26–28]. Of course, reverse osmosis factories are blooming in the Middle East and North Africa, producing almost half of the 95 million m3 day<sup>−</sup><sup>1</sup> of desalinated water for human use worldwide [29], but will not be able to meet not in the present nor in the future the growing agricultural water demand. Undoubtedly, nonconventional water use will contribute to partially alleviate water scarcity in regions where renewable water resources are extremely scarce [28].

Halophytes have demonstrated their capability to thrive under extremely saline conditions and thus are considered as one of the best germplasms for saline agriculture [30]. Few researchers have examined halophytes under special topics as sustainable cultivation, saline agriculture, and integrative anatomy [31–34]. Much practical work remains to be done, as well as developing the basic science of halophytology [35]. Apart from the cultural and sometimes the political constraints related to it, we think that there is still a big deal of scientific and technical knowledge to be studied and discovered for a better development of seawater agriculture in desert areas.

Novel approaches to mangrove planting in desert countries have been published [36, 37]. They prove establishing mangrove trees in salty coastal lands is possible providing an appropriate mineral nutrition, i.e., nitrogen, phosphorus, and iron. Based on this finding, they devised a planting method (**Figure 7**) and used mangrove nurseries. This discovery has permitted plantation of about 1 million mangrove trees, chiefly *Avicennia marina*, in the intertidal zone of the Red Sea coast of Eritrea [36]. However, this assumption has not made the unanimity among the scientific community and is contested by some other scientists [38]. Nevertheless, such forests can provide feedstuffs and serve as nurseries for fish reproduction. These important findings deserve to be considered for future mangrove plantings and/or mangrove restoration projects in Africa's desert countries.

**Figure 7.** *Forestation of desert area by mangrove transplants.*

### **Figure 8.**

*Two-year-old mangrove forest (El Gahra, Mauritania).*

Also, other projects confirmed that even with low fertilization amounts, some plant species like *Avicennia germinans*, *Nitraria retusa*, and *Sesuvium portulacastrum* can grow in extremely salty areas as well [39]. As a result, tens of thousands of mangrove trees were planted in the Mauritanian side of the Senegal River Delta and Nouakchott seaport [39]. Two years after planting, the mangrove trees reached a height of about 2 m and constitute already a source of forage foodstuff (**Figure 8**).

Thus, certain parts of the Earth's great deserts and other water-stressed areas might be converted to mangrove forests with seawater irrigation, which might be one of the possible and relatively cost-effective approaches to mitigate desertification under global warming.
