Water Management in Horticultural Crops

Frequency and interval of irrigation

• The terms, frequency of irrigation and interval of irrigation are closely related and are often interchangeable. With higher frequency of irrigation, the interval between two irrigations decreases in a given period, while with lower frequency the interval between two irrigations increases.
• The term, interval of irrigation indicates the time gap, usually expressed in days, between two subsequent irrigations. The total amount of water required by a crop for producing an optimum yield is termed as delta of water and it is synonymous with water requirement of crop.
  
• Immediately after irrigation when the soil is wet, evapotranspiration occurs at a potential rate. It starts declining some days after irrigation as the surface soil dries up. Dry and loose soil surface helps to reduce evaporation.
  
• Since soil water declines progressively owing to continuous evapotranspiration, the rate of evapotranspiration also declines progressively with the advance of time after irrigation.
  
• Therefore, the longer is the interval between irrigations, the greater is the saving of water. Besides, a longer interval between two irrigations cuts down the number of irrigations during the growing season. Care should, however, be taken not to cause any water stress beyond a certain limit by making the irrigation interval unduly long unless compelled to do so for reasons of water scarcity.
  
• Irrigation is usually advised at the lowest limit of the optimum water regime, as already stated earlier. The interval between two irrigations should normally be the time taken by crops to reduce the soil water from field capacity to the lowest level of optimum soil water regime.