International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage



Deficit Irrigation

Deficit irrigation (DI) is an optimization strategy in which irrigation is applied during drought-sensitive growth stages of a crop. Outside these periods, irrigation is limited or even unnecessary if rainfall provides a minimum supply of water. Water restriction is limited to drought-tolerant phenological stages, often the vegetative stages and the late ripening period. Total irrigation application is therefore not proportional to irrigation requirements throughout the crop cycle. While this inevitably results in plant drought stress and consequently in production loss, DI maximizes irrigation water productivity, which is the main limiting factor. In other words, DI aims at stabilizing yields and at obtaining maximum crop water productivityrather than maximum yields.

 

If crops have certain phonological phases in which they are tolerant to water stress, DI can increase the ratio of yield over crop water consumption (evapotranspiration) by either reducing the water loss by unproductive evaporation, and/or by increasing the proportion of marketable yield to the totally produced biomass (harvest index), and/or by increasing the proportion of total biomass production to transpiration due to hardening of the crop - although this effect is very limited due to the conservative relation between biomass production and crop transpiration, - and/or due to adequate fertilizer application and/or by avoiding bad agronomic conditions during crop growth, such as water logging in the root zone, pests and diseases, etc.

 

The correct application of DI for a certain crop results in the following:

  • Maximizes the productivity of water, generally with adequate harvest quality;
  • Allows economic planning and stable income due to a stabilization of the harvest in comparison with rain-fed cultivation;
  • Decreases the risk of certain diseases linked to high humidity (e.g. fungi) in comparison with full irrigation;
  • Reduces nutrient loss by leachingof the root zone, which results in better groundwater qualityand lower fertilizer needs as for cultivation under full irrigation;
  • Improves control over the sowing date and length of the growing periodindependent from the onset of the rainy season and therefore improves agricultural planning.

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