Water Conyenance Efficiency and Water Use Efficiency

Water Conyenance Efficiency & Water Use Efficiency

Water Conyenance Efficiency:

It indicates the efficiency with which water is conveyed from source of supply to the field. It estimates the conveyance losses. It is expressed as

           Wf
Ec = ——— X 100
           Ws

Where,

Ec = Water conveyance efficiency (percent)
Wf= Water delivered at the field
Ws= Water delivered at the source

Water Application Efficiency:

Irrigation water applied to the field is lost due o surface run off and deep percolation. Surface run off occurs due in long furrow or long border strips if ridges are weak. The water moves from one plot to another due to weak bunds giving way to water which may collect in large quantities even to break strong bunds. In furrows, water is allowed most of the time at the beginning of furrow till the flow reaches the other end of the furrow. It results in deep percolation of water in the first quarter of furrow. Water application efficiency is the measure of efficiency with which delivered to the field is stored in the root zone.

                                              Water stored in the root zone
Water application efficiency = ———————————— X 100
                                                Water delivered to the field

Water Storage Efficiency:

This parameter estimates whether the amount of water necessary for the crop is stored in the root zone or not. It is expressed as the percentage of water needed in the root zone prior to irrigation to that stored in the root zone during irrigation.

                                                        Water stored in the root zone
               Water storage efficiency = ————————————- X 100
                                                         Water needed in the root zone

Water Distribution Efficiency:

Water distribution efficiency is defined as the percentage of difference from unity of the ratio between the average numerical deviations from the average depth stored during the irrigation.
 
         Water distribution efficiency = {1-Y/d} X 100

Where,
d = Average depth of precipitation along the run off during irrigation
Y = Average numerical deviation from –d

Water distribution efficiency indicates uniformity in distribution of water over the entire root zone.

Water Use Efficiency (WUE):

Water use efficiency is defined as yield of marketable crop produced per unit of water used in evapotranspiration.

               WUE = Y / ET

Where,

WUE = Water use efficiency (kg/ha/mm of water)
Y = marketable yield (kg/ha)
ET= Evapotranspiration (mm)

If yield is proportional to ET, water use efficiency has to be constant but it is not so. Actually, Y and ET are influenced independently by crop management and environment. Yield is more influenced by crop management practices, while ET is mainly dependent on climate and soil moisture. Fertilization and other cultural practices for high yield usually increase in water use accompanying fertilization is often negligible. Crop production can be increased by judicious irrigation without markedly increasing ET. Under optimum water supply, ET is not dependent on kind of plant canopy provided the soil is adequately covered with crop.

Increasing the amount of plant canopy has there fore little or no effect on ET. Obviously, any practice that promotes plant growth and more efficient use of sunlight in photosynthesis without causing a corresponding increase in ET will increase WUE.

Factors affecting WUE:

1. Nature of the plant:  There are considerable between plant species to produce a unit dry matter per unit amount of water used resulting in widely varying values of WUE.

Water use efficiency of different crops:

There is also difference in WUE between varieties of the same crop. Selection of properly adopted crop, with good rooting habit ,low transpiration rates increase. WUE

2. Climatic Conditions:

Weather affects both Y and ET. Manipulation of climate to any extent is possible at present. However, ET can be reduced by mulching, use of antitranspirant etc. To limited extent , but may not be economical or practical. Weed control is the most effective means of reducing ET losses and increasing the amount of water available to the crop thereby increasing WUE.

3. Soil Moisture Content:

In adequate supply of soil moisture as well as excess moisture supply to the crop have an adverse effect on plant growth and production and therefore conductive to low WUE. For each crop combination of environment conditions, there is a narrow range of soils moisture level at which WUE is higher than with lesser or greater supply of water, proper scheduling of irrigation will increase WUE.

4. Fertilizers:

Irrigation improves a greater demand for plant nutrients. Nutrient availability is highest for most of the crops when water tension is low. All available evidences indicate that under adequate irrigation suitable fertilization generally increase yield considerably, with a relatively small increase in ET and therefore, markedly improve WUF.

5. Plant population:

Higher yield potential made possible by the favorable water regime provided by irrigation, the high soil fertility level resulting from heavy application of fertilizers and genetic potential of new varieties and hybrids, could be achieved only with appropriate adjustments of the population. The highest yields and WUE are possible only through optimum levels of soil moisture regime, plant population and fertilization.