Water Resources Management - Practices of Irrigation and On-farm Water Management - page 156

maintenance of the borders with sufficient height. Thus, actual need of irrigation
water would be reduced.
Adopting Efficient Irrigation Method/Technologies
This can be achieved through the following measures:
Improving Irrigation Efficiency If crop irrigation is practiced in areas with dry
climates, much of the water use in those areas is for agriculture. Considering world
average, about 75% of the total water use is for crop irrigation. Most of the irri-
gation systems are surface or gravity systems, which typically have efficiencies of
60-70%. This means that 60-70% of the water applied to the field is used for evap-
otranspiration by the crop, while 30-40% is “lost” from the conveyance system, by
surface runoff from the lower end of the field, and by deep percolation of water that
moves downward through the root zone.
Increased irrigation efficiencies allow farmers to irrigate fields with less water,
which is an economical benefit. In addition, increased irrigation efficiencies gener-
ally mean better water management practices which, in turn, often give higher crop
yields. Thus, increasing field irrigation efficiencies also saves water by increasing
the crop production, thus allowing more crops to be produced with less water.
Field irrigation efficiencies of gravity systems can be increased by better man-
agement of surface irrigation systems (changing rate and/or duration of water
application), modifying surface irrigation systems (changing the length or slope of
the field, including using zero slope or level basins), or by converting to sprinkler
or drip irrigation systems where infiltration rates and water distribution patterns are
controlled by the irrigation system and not by the soil. Surface irrigation systems
often can be designed and managed to obtain irrigation efficiencies of 80-90%.
Thus, it is not always necessary to use sprinkler or drip irrigation systems when
high irrigation efficiencies are desired.
Irrigation Scheduling As with increased field irrigation efficiencies, improved
scheduling of irrigation conserves water only if runoff and/or deep percolation from
the irrigated fields cannot be reused. Scheduling of irrigation can be based on soil
water measurements (tensions and/or contents), or on estimates of daily evapo-
transpiration rates using climatological methods, evaporation pans, or lysimeter.
Measurement of the plant water status through remotely sensed plant or crop canopy
temperatures with infrared thermometers shows promise as a technique for schedul-
ing irrigations. Better timing of irrigation could also increase crop yields per unit of
evapotranspiration (for example, through less leaching of fertilizer), thus increasing
crop water use efficiencies.
Water-Wise Cultivation Method
The wet-seeded or direct-seeded technique is an alternative to the transplanting
method of rice crop establishment. This technique increases crop yield and water
productivity, and reduces irrigation need.