Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 292

In wet years or wet seasons, there is sufficient leaching and dissolving of salts
so that they are not visible on the soil surface and some crop growth may be possi-
ble. However, the excess water received in wet years may contribute to the overall
salinity problem over time. In dry years, increased evaporation dries out the soil and
draws salts up to the soil surface, producing white crusts of salt. In dry years, pro-
ducers become more concerned with salinity because salts are highly visible and no
crop growth occurs.
Saline Soil or Permanent Salinity
In this case, the soil is saline by formation, i.e., geologically formatted from saline
rocks, having deep saline profile, or land deposited from sea loads. For example,
coastal area (southern part) of Bangladesh. During wet season, crops are also grown
here, due to dilution of salt in surface soil. But if the rainfall is low, crops are affected
by salinity.
B: Classification Based on the Development Mode
Based on the mode of development, salinity can be categorized as
1. Primary salinity
2. Secondary salinity
Primary Salinity
This kind of salinity is developed naturally. It results from the long term continu-
ous discharge of saline groundwater. Saline soils due to primary salinity often have
high EC values. These soils are not suited to crop production without special man-
agement. The best course of action for primary salinity is to leave the affected area
in its natural state. If the land has been tilled, salt-tolerant vegetation should be
established.
Secondary Salinity
This kind of salinity is human induced, and is the result of human activities that have
changed the local water movement patterns of an area. Soils that were previously
nonsaline have become saline due to changes in saline groundwater discharge.
Saline soils due to secondary salinity may have lower EC values and may be
improved with management. In order to optimize production in saline, discharge
areas, water must be utilized in the adjacent, nonsaline recharge areas. This will
decrease the movement of excess water from recharge areas to discharge areas.
C: Classification Based on Salt Content or EC
Sensitive crops may exhibit negative effects of salinity at levels <2 dS/m. An EC of
4 was considered in the past as a general salinity rating for traditional annual crops