Bio-drainage technology helps in reclamation of salt affected waterlogged areas. Benefits include increased cropping intensity, increased nutrient use efficiency, growing arable crops including pulses and oilseed, which otherwise is not possible on waterlogged soils, and increased employment generation.The driving force behind the bio drainage concept is the consumptive water use of plants.

In natural environments the components of the hydrological system, i.e. rainfall, evapotranspiration, change in soil-water storage and drainage, are in balance. Periods of high rainfall might temporarily result in increased drainage flows, a rise in the groundwater table and/or soil moisture storage, then over a period of about 5-10 years equilibrium is established. Vegetation plays a vital role in the evapotranspiration and soil-water storage components of this balance.

When natural vegetation is cleared and replaced by crops or tree plantations, the seepage losses to the groundwater table under the new land use system are either higher or lower than under the pre-clearing situation.Plantations of fast growing tree species such as eucalyptus, when grown on previously cleared land, could result in strongly reduced accessions to the groundwater and in the drying-up of wells and springs.

The deep-rooting characteristics of trees make them extremely efficient users of water. While shallow-rooted grasses and crops have limited access to underlying water tables, deep-rooted trees can access water tables down to several metres. Also, in recharge situations with deep water tables, the deep root systems of trees greatly reduce the opportunity for rainfall/irrigation accessions to the water table.

One of the major factors determining the sustainability of plant water use issalt balance. If the salts moving into the rootzone are not either (i) taken up by the vegetation and harvested or (ii) removed from the rootzone by leaching, the vegetation is doomed to succumb to salinity. Where bio drainage results in salt accumulation, engineering assistance is needed to make the system sustainable. Bio drainage management mechanisms can be classified as follows.

Dry land/rain fed systems:

• Recharge control
• Groundwater flow interception
• Discharge enhancement

Irrigated systems:

• Water table control
• Channel seepage interception
• Bio drainage cum conventional drainage systems