Salinity In Plant Agriculture

1. Introduction

As per the FAO (Food and Agriculture Organization) Land and Plant Nutrition Management Service, in excess of 6% of the world's territory is influenced by either salinity or sodicity [1]. A significant part of the world's territory is not cultivated, yet a critical extent of cultivated area is salt-influenced.

Salinity has existed even before humans and agriculture but has been exasperated due to certain agricultural practices such as irrigation that causes water tables. This results in dissolved salts being accumulated in the soil water to a degree that restrains plant development. Sodicity is the secondary effect of salinity wherein soluble salts are washed into the subsoil through leaching either naturally or by human-prompted

NaCl being the most soluble and abundantly released salt. Other causes include deposition of oceanic salts and rainwater that conrains 6-50 mg/kg of NaCl.

Soil salinity has become one of the major abiotic stresses in plant agriculture worldwide [3]. 50% and 20% of all the irrigated lands and cultivated lands respectively have been affected by soil salinity.

1.1 Measurement of soil salinity

Electrical conductivity (EC) is the term used to measure soil salinity [4]. It is measured by passing electric current between the two electrodes of the salinity meter placed within the sample of soil or water. EC is influenced by the concentration of dissolved salt in the sample. Salts in a solution help conduct electricity through it hence higher the EC value higher is the level of soil salinity.

The SI unit of electrical conductivity is dS/m.

1.2 Effect of soil salinity on plant growth

Soils are said to be saline when they contain high concentrations of soluble salts or when it’s ECe is 4 dS/m or more which equals to 40 mM NaCl and creates an osmotic pressure of 0.2 MPa

LITERATURE SURVEY

2.1 Salinity tolerance in plants

Electrons usually leak out of the electron transport chain (ETC) during normal aerobic metabolism in chloroplasts (mitochondria and peroxisomes). These electrons react with molecular oxygen in the absence of other acceptors. As a result, reactive oxygen species (ROS) such as singlet oxygen(1O2), hydroxyl radical(OH), superoxide(O2-) and hydrogen peroxide(H2O2) are produced.

But there is evidence that ROS are produced excessively in plants in response to biotic or abiotic stresses [5]. Hydrogen peroxide can also be produced in the plasma membrane, cytosol and extracellular matrix by certain oxidases and cell wall peroxidases.

When produced excessively, these ROS can have detrimental effects on a plant’s metabolic activity and can cause oxidative damage (oxidative stress) to proteins, lipids essential to membrane integrity and nucleic acid. Recently it has been demonstrated that ROS have a role in cell signalling such as apoptosis, gene expression and activation of cell signalling cascades [6]. To accomplish salinity tolerance, three interconnected plant activities are paramount:

i. damage must be reduced or prevented ii. homeostatic conditions must be re-built in the stressful