1. High water table- water table within 1.5m is usually not desirable.
2. When water stands on the land surface for long periods.
Tolerances of crops to standing water vary widely.
– 2-4 hrs for sensitive vegetables. Eq. Potato.
1 day – for maize.
4 days for water tolerant grass crops.
3. In the region where the annual evaporation exceeds, annual rainfall soil salinity and alkalinity and rise of ground water levels due to excess irrigation water are the problems of the region.
Drainage aids in leaching of salts, reduce the change of salt accuratation and removes excess irrigation water.
4. Excessive soil moisture content. Soil moisture content above F.C for a considerable length of time is harmful to crops.
5. Humid region with continues or intermitted heavy rainfall.
6. Flat lands with fine textured soil.