Study of the influence of a Bioabsorbent derived from Orange Peel on a filtering soil using seawater irrigation by capillarity

Desertification is the result of climatic changes and human activity, which reduces productivity and the value of natural resources in arid and semiarid conditions (Aubréville, A.; 1949). This is the international definition established by the convention of the United Nations against desertification, approved on 17th June of 1994, and from that day a date has been commemorated as the World Day to Combat Desertification and Drought.

The main causes for desertification are the weather, erosion, ecological factors such as the kind of soil and ecosystem, as well as human activity. Before desertification occurs, there is a erosion of the ground: when the wind removes the excess of soil and dust particles from the ground, the soil then loses the water table and the regeneration of the soil becomes very difficult (Stringer, L.C.; 2008). The low drainage of the soil, torrential rains or drought are other phenomena that cause desertification. Climatic change is a harmful phenomenon, but the most harmful is human activity: fires, logging, overexploitation of aquifers, intensive farming, with massive use of chemicals, and some forestry practices (mountain or forest crops), etc. (FAO 2000).

Worldwide it is considered that a volume above 1.000 m3 per inhabitant and year is normally more than necessary for domestic use, industrial and agricultural. In consequence, it is estimated that a watershed suffers a loss of hydric stress when the water availability per inhabitant is below 1.000 m3/year or when the quotient between water withdrawal and historical annual average runoff is greater than 0.4. There are some basins of this type in North Africa, the Mediterranean region, the Middle and Near East, South Asia, North China, the United States of America, Mexico, Northeast Brazil, and the west coast of South America. The population of those who live in these basins is about 1.400 and 2.100 million people (Vörösmarty et al., 2000; Alcamo et al., 2003; Oki et al., 2003; Arnell, 2004).

Irrigation represents 70% of all the water extracted in the world and almost 40% is for agricultural production (Fischer et al., 2006). In fact, all the irrigated land represents 18% of all agricultural land in the world and produces 1.000 million tons of cereals each year, half of the total world supply. In fact, irrigated crops produce between two and three times more crops than those produced by rain alone. (Alexandratos, N., 2005).

In general, it seems that global warming will benefit the agriculture of developed countries in warm climates. On the contrary, the countries with a tropical or subtropical climate will suffer the effects of climatic change, and the dependence on imports from other countries will increase, as the difference between north and south, of alimentary security, will be accentuated (Canadell et al.,2007)..

Water management tends to improve the quality and quantity of available water regulating the use of water from the surface and underground, developing other sources of water, rationalizing water’sconsumption, or, controlling the contaminants and recovering them from wastewater through a depuration process. The objective of good water quality must be pursued in each river basin, so that measures relating to surface water and groundwater belonging to the same ecological, hydrological and hydrogeological system are coordinated (Directive 2000/60 / EC). From this point of view, the reuse of treated water is an essential element of the natural water cycle and, in fact, is seen as a measure to solve the problems of water scarcity. Agriculture is the main cause of the lack of water around the world, 70% of all the water extracted and in some cases 95% in developing countries (FAO, 2017), is used for this activity, thereby reducing water availability for people. It is expected that between now and year 2050, the demand for food will increase by 60% and the world’spopulation will be around the 9.000 million (FAO, 2013). The actual and future situation will mean agriculture will need more and more water, and consequently lead to an increase in the global lack of water including those areas that currently have enough sources of water.

In order to reduce the agricultural pressure on the hydric sources, one of the possible solutions is the use of brackish or desalinated seawater. The advantage of the use of this type of water is that there are inexhaustible resources and they are not subject to climatic variations. So this type of water is strategically perfect to develop the availability of increased water resources for agricultural irrigation in water deficient areas. However, only the most advanced crops with higher economic margins can bear the costs of desalinated water (Martínez 2014). This desalinated or osmotized water is characterized by its low mineralization and significant imbalances in its composition. So it is not suitable for every type of supply (domestic, agricultural or industrial). In order to adapt the characteristics of the osmotized seawater to the requirements of the different uses, it must undergo post-remineralization treatments.

The depurated water reusability for crop irrigation is another option, and lately it has been used in many countries. Nevertheless, it is necessary to guarantee a minimum quality of water, as well as its functional uses depending on how it is treated.

On the other hand, another technique to address the lack of water and that hasn'tbeen contemplated until now, is the use of seawater for the irrigation and development of crops.

The uses of capillary irrigation systems can offer a solution not only to the problem of water scarcity, but can also contribute substantially to the transformation of arid or desert areas into green areas and fields. It must betaken into account that the water rises in the soil due to evaporation and absorption by the roots of the plants. Water moves by capillarity (especially intense effect in arid climates) and by difference in humidity, (deeper ground levels remain wetter as they are protected, due to their distance from the soil surface, and from water losses due to evaporation and the absorption by plants). On the other hand, the water not only moves vertically, it also moves laterally. Therefore, it can be said that the water in the ground moves in any direction (Duchaufour 1978).

The use of seawater applied to irrigation is not a new technique, there’sevidence that proves that in 1719 the Sestao’s Carmelite monks, located in Vizcaya, made use of this practice. Later, on Oriñon beach (Cantabria) in 1959 a study was made of the use of seawater, without desalination, for irrigation, and achieving it without saturating the soil with salts (Esteban-Gómez, 1968). Recently, there have been some successful investigations into the cultivation of chard using only seawater. One of the main characteristics is the low difference in height between the seawater and the crop (García et al., 2019), which is a good example of how to make a well-functioning irrigation system as well as reducing the costs. However, to successfully develop the cropping with higher yields, it is fundamental to optimize the substrate for the water and mineral supply of the crops. The tolerance conductivity of the soil will be a major parameter to control; otherwise, the salinity may affect the crops. The objective of this study it to determine the influence of a bioabsorbent obtained from orange peel, on the behaviour of a substrate composed of silicon sand in order to reduce the salinity of seawater without a previous desalination, by applying this technique to capillarity irrigation.