Water Management in Horticultural Crops

2. Subsurface irrigation methods

• Subsurface irrigation, also designated as sub irrigation, involve irrigation to crops by applying water from beneath the soil surface either by constructing trenches or installing underground perforated pipe lines or tile lines. Water is discharged into trenches and allowed to stand during the whole period of irrigation for lateral and upward movement of water by capillarity to the soil between trenches.
• Underground perforated pipe or tiles in which water is forced , trickle out water through perforations in pipes or gaps in between the tiles. Water moves laterally and upward to moist the root zone soil under capillary tensions. Pipelines remain filled with water during the period of irrigation. The upper layers of soil remain relatively dry owing to constant evaporation while lower layers remain moist. The essential pre-requisite for sub-irrigation are: (1)existence of a high water table or an impervious sub-soil above which an artificial water table can be created (2) highly permeable root zone soil with reasonably uniform texture permitting good lateral and upward movement of water (3) irrigation water is scarce and costly and (4) soil should not have any salinity problem.


• It might be ensured that no water is lost by deep percolation. The artificial water table is created to a depth of 30 to 120 cm depending on crops to be grown, nature of soil capillarity and the depth of impervious soil layer. Uniform topographic conditions and moderate slope favour sub-irrigation. In places where sprinkler irrigation is expensive, sub irrigation is adopted. Sub-irrigation is made by constructing a series of ditches or trenches 60 to 100 cm deep and 30 cm wide, the two sides of which are made vertical. Ditches are spaced 15 to 30 m.
• The crops, particularly with shallow root system are well adapted to sub irrigation. Sometimes, sub irrigation is made to high priced vegetable crops by installing a perforated pipe distribution system below the soil surface but within the crop root zone. This is often termed the artificial irrigation. A good quality water supply must be available throughout the growing season and an outlet for drainage is provided, particularly in high rainfall areas.
Advantages and limitations

• Advantages of this method of irrigation are (i) soil water can be maintained at a suitable tension favorable for good plant growth and high yields (ii) evaporation loss from soil surface is minimized (iii) cost of water application is very low and (iv) it can be used for soils having a low water holding capacity and a high infiltration rate where surface method cannot be adopted and the sprinkler irrigation is expensive.