(1) What Is Soil Salinization?
Salinization of soil is an excessive accumulation of water-soluble salts. Typically, it is table salt NaCl. The list is far more extensive and includes various compounds of sodium, potassium, calcium, magnesium, sulfates, chlorides, carbohydrates, and bicarbonates. In general, salt-affected earths are categorized as saline, sodic and saline-sodic, depending on the content.
The major soil salinity effect on plant growth is tampering with water absorption. Even with sufficient soil moisture, crops wade and die due to the inability to take up enough water. At a global span, according to the report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) of 2018:
about 190 million acres are completely lost;
150 million acres are damaged;
2.5 billion acres are impacted by salinization.
(2) What Causes Soil Salinization?
Soil salinization occurs when soluble salts are retained in the earth. It happens either naturally or because of improper anthropogenic activities, particularly farming practices. Besides, some earths are initially saline due to low salt dissolution and removal. Soil salinization causes include:
dry climates and low precipitations when excessive salts are not flushed from the earth;
high evaporation rate, which adds salts to the ground surface;
poor drainage or waterlogging when salts are not washed due to a lack of water transportation;
irrigation with salt-rich water, which amplifies salt content in earths;
removal of deep-rooted vegetation and a raised water table as a consequence;
leakage from geological deposits and penetration into groundwater;
sea-level rise when sea salts seep into lower lands;
breezes in the coastal areas that blow salty air masses to the nearby territories;
seawater submergence followed by salt evaporation;
inappropriate application of fertilizers when excess nitrification accelerates soil salinization.
(4) Indicators Of Soil Salinity
Salinization can be noticed visually by analyzing the soil surface, speed of water infiltration, and vegetation state. As salinization proceeds, signs get more severe. For example, slight whitening on the surface changes into distinct salt crystals. Apart from visual changes, there are indirect indicators of extra salt concentration. These are poorer water quality or animal behavior when livestock refuses to drink water due to its salty taste.
(5) Surface Changes Because Of Salinization
damp areas and waterlogging;
ground whitening at early stages and salt crystals at late ones;
increased water level in furrows;
bare soils (where plants fail to grow due to salinization);
deterioration of roads, buildings, etc.;
white or dark circles around water bodies.
(6) Soil salinisation can be divided into primary and secondary salinisation according to its causes.
Primary salinisation refers to soil salinisation caused by changes in natural environmental factors, such as climate, geology, geomorphology, hydrology and soil conditions, etc.
Secondary salinisation refers to the process of continuous accumulation of salt in the top layer of the soil as a result of regional water and salt imbalances caused by human activities that make irrational use of land and water resources.
(7) Soil salinisation is mainly distributed in the north-west, north China, north-east and coastal areas of China. Typical distribution areas include the North China Plain, the Hexi Corridor, the Ningxia Plain, the Hetao Plain irrigated agricultural area in the north-west and the oasis agricultural area in Xinjiang.