1. Introduction
Soil salinity is defined as the accumulation of salts in the soil
(Rengasamy, 2010). Soil salinity is a major environmental catastrophe
caused by both natural and anthropogenic reasons (Rapp, 1986). Nearly
20% of all land globally is salinity affected and has raised huge
concerns for governments bodies worldwide to introduce timely land
reclamation measures (Ringler, Bhaduri, & Lawford, 2013). Land
reclamation for salinity affected areas requires timely monitoring of
salinity status of soil and its indicators in an efficient manner to
curb the causative factors (Vogt et al., 2011). Though not as damaging
initially as other hazards like earthquake, volcanic eruption or floods,
soil salinity can take a heavy toll on lives in the long run (Dumanski
Samuel Pieri, Christian Agriculture and Agri-Food Canada, 1998).
Today food security is a highly debated topic and with increasing
salinity in soil for areas which depend upon artificial irrigation
sources, soil salinity is causing stunted plant growth and crop failure
at times (García-Tejero, Durán-Zuazo, Muriel-Fernández, &
Rodríguez-Pleguezuelo, 2011; Koevoets, Venema, Elzenga, & Testerink,
2016).
Increase in soil salinity causes decrease in moisture intake capacity of
plants since their root nodules get blocked by salts (Egamberdieva, Li,
Lindström, & Räsänen, 2016; Etehadnia, Waterer, De Jong, & Tanino,
2008; Franzini, Azcón, Ruiz-Lozano, & Aroca, 2019). Moreover, high
concentration of salts in water causes reverse osmosis resulting in the
wilting of plants causing their perishing(Arora et al., 2018). This in
turns affects the crop yield and causes heavy loss to farmers. Salinity
in soil happened mainly due to natural causes such as frequent flooding
but over the years, unscientific and improper irrigation management(Baig
& Shahid, 2014). Figures indicate that the soil salinity has become a
highly serious phenomenon. Primary salinity affected areas globally
account for 955 M ha and secondary salinity affected areas are some 77 M
ha and out of these 58% is irrigated area that shows the major cause of
salinity is anthropogenic(Amin, 2004).
Increasing human population and the competition for resources has posed
a heavy threat on all-natural resources including water and soil
(Cassman, Dobermann, Walters, & Yang, 2003). Since soil supports almost
all life on earth, proper management of soil in a scientific way becomes
very important (Miltner, Bombach, Schmidt-Brücken, & Kästner, 2012).
Salinity can occur out of a number of other factors apart from improper
irrigation- engineering problems, soil erosion and soil
dispersion(Qadir, Ghafoor, & Murtaza, 2000). For areas with a history
of water logging, the soil salinity becomes more acute(Bhutta &
Smedema, 2007; Shah, Molden, Sakthivadivel, & Seckler, 2001). The
plants intake the moisture leaving behind the dissolved salts in
water(Konukcu, Gowing, & Rose, 2006). After a period of time, this salt
accumulates around the root nodules making further water intake
impossible(Streeter & Wong, 1988). Salinity in soil can be determined
by estimating the electrical conductivity of soil(Rhoades, Shouse,
Alves, Manteghi, & Lesch, 1990; Rhoades & van Schilfgaarde, 1976). The
electrical conductivity measured in milli-siemens per meter is a measure
of the ionic concentration of the soil (Susha et al., 2018).
In agriculture science, soil is considered to be saline in conditions
when there is sufficient amount of salts dissolved in root zone soil
moisture to adversely affect the plant growth (Rengasamy,
Chittleborough, & Helyar, 2003). Some studies claim soils to be saline
in cases when soil electrical conductivity is more than
4dSm-1 at 25oC (Igartua, Gracia, &
Lasa, 1994). Different plants have different tolerance for soil
salinity levels beyond which their growth is adversely affected, as
shown in Table 1(Xie et al., 2009)-
Table 1 . GENERAL SOIL SALINITY TOLERANCE RATE FOR PLANTS