What it does

Salinity affects respiration and the photosynthesis of plants. It decreases biological N2 fixation and soil nitrogen mineralization.

Why and where it occurs

The major causes of salinity or sodicity include:

• poor irrigation practice or insufficient irrigation water in seasons/years with low rainfall
• high evaporation
  Salinity is often associated with alkaline soils in inland areas where evaporation is greater than precipitation.
• increased level of saline groundwater
• salt water intrusion in coastal areas (e.g., Mekong Delta, coastal India)

Examples of salt-affected soils include:

• saline coastal soils (widespread along coasts in many countries)
• saline acid sulfate soils (e.g., Mekong Delta, Vietnam)
• neutral to alkaline saline, saline-sodic, and sodic inland soils (e.g., India, Pakistan, Bangladesh)
• acid sandy saline soils (Korat region of northeast Thailand)

How to identify

Check the field for the following symptoms:

• Tips of affected leaves turn white
• Chlorotic patches appear on some leaves
• Plant stunting and reduced tillering
• Patchy field growth
• Symptoms first manifest themselves in the first leaf, followed by the second, and then in the growing leaf

Salinity or sodicity may be accompanied by P deficiency, Zn deficiency, Fe deficiency, or B toxicity

Further effects on rice growth:

• Reduced germination rate
• Reduced plant height and tillering
• Poor root growth
• Increased spikelet sterility
• Excess Na uptake decreases 1,000-grain weight and total protein content in grain, but does not alter major cooking qualities of rice
• Decreased biological N2 fixation and soil N mineralization

Click on images to enlarge

White and browning of leaves are typical of salinity injury

Field damage of salinity

How to manage

To prevent

• Grow salt-tolerant varieties (e.g., Pobbeli, Indonesia; IR2151, Vietnam; AC69-1, Sri Lanka; IR6, Pakistan; CSR10, India; Bicol, Philippines)
• In rice-upland crop systems, change to double-rice cropping if sufficient water is available and climate allows
• Submerge the field for two to four weeks before planting rice. Do not use sodic irrigation water or alternate between sodic and nonsodic irrigation water sources. Leach the soil after planting under intermittent submergence to remove excess salts. Collect and store low saline rainwater for irrigation of dry-season crops (e.g., by establishing reservoirs). In coastal areas, prevent intrusion of salt water.
• Use fertilizers efficiently.
  
  Where possible,
• In temperate climates where rice is direct seeded, coat seed with oxidants (e.g., Ca peroxide at 100% of seed weight) to improve germination and seedling emergence by increased Ca and O2 supply. Alternatively, treat rice seeds with CaCl2 to increase seed Ca2+ concentration.
• Apply rice straw to recycle K. Apply farmyard manure.