Water Requirement and Irrigation Requirement for Crops
In this article -
- Water Requirement for Crops
- Water losses in Crop water Requirement
- Factors affecting Crop water Requirement
- Consumptive Use of Water
- Factors affecting Consumptive use of water
- Irrigation Requirement
- Factors affecting Irrigation Requirement
- Water requirement of different crops
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Water Requirement of crops - The amount of total water needed for crop from sowing to harvesting , is called water requirement of crop.
Water requirement varies for every crop, that is water requirement varies with the variety of same crop.
other definition-
- The total amount of water required for a crop during its whole life is called water requirement.
- The amount of water required by the plant for survival, growth, development , plant metabolism and to produce crop is called water requirement.
Water requirement of crop varies according -
- Crop
- Period of sowing and harvesting
- Soil moisture
- Evaporation
- Transpiration
Crop water requirement requirement also includes the water losses through leaching, transpiration and evaporation. This water losses continues with water requirement. It can be reduced but can't be eliminated.
Water losses in Crop water requirement -
Water losses can be mainly of four types -
- Evaporation loss
- Transpiration loss
- Other loss like - conveyance loss , percolation loss, runoff loss
- Water required for special purpose, that is - ploughing, leaching, land preparation , weeding and puddling
- Evaporation loss - Evaporation is a main cause of water loss. It makes the upper layer of soil dry and hard. Crop evaporation is a physical process , in this process water turns into gaseous state from liquid state during moving from soil to atmosphere.
- Transpiration loss - This type of loss neither can be eliminated nor can be reduced. Transpiration loss is a necessary evil. It helps the crop to maintain its temprature. It is also a physical process. Transpiration loss occurs through stomata of plants.It pumps water and minerals to leaves for photosynthesis.
Water requirement representation -
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1. WR = E + T + WPM + WL + WLSP
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WR = Water requirement
E= Water loss through evaporation
T = water loss through transpitaion
WPM = water required for plant metabolism
WL = water loss
WLSP= water loss for special purpose
Evaporation loss, transpiration loss and water for plant metabolism can't be separated.
Evaporation loss + Transpiration loss + Water for plant metabolism = Consumptive use of water
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2. WR = CU + WL + WLSP
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WR = water requirement
CU = Consumptive use of water
WL = Other water loss
WLSP = water loss for special purpose
It is not necessary that rainfall distribution is good all over the country and the availability of rain water varies according to season. The good production can't be done only with the dependence on rain water. It is necessary to supply water through artificial means for good production, this supply of water through artificial means is called irrigation requirement.
Water requirement in terms of Irrigation requirement -
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3. WR = IR + ER + S
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WR = water requirement
IR = Irrigation requirement
ER = Effective rainfall
S = water distribution from ground water table
Factors affecting crop water requirement -
There are four main factors affecting the crop water requirement -
- Crop Factor
- Soil factor
- Climatic factor
- Agronomic Factor
1. Crop variety - Crop water requirement varies according to crop variety it means that water requirement can be different for the two variety of same crop.
2. Growth stage of crop - From sowing to harvesting crop goes through many growth stage. The water requirement varies according to growth stage of crop. There are mainly three stage of plant growth -
- seed stage
- Vegetative stage
- Flowering and fruit stage
In seed stage the water requirement of crop is less. With the growth of crop water requirement also increases. The water requirement is higher in fruiting stage with comparision to seed stage and vegetative stage.
3. Duration of crop - The duration of crop also affects the water requirement. For long duration crop water requirement is more and for less duration crop water requirement is also less.
4. Plant population - The density of plant in an agriculture field is called plant population. If density of plant is high water requirement will also be high. If the plant density is less water requirement will also be less.
5. Crop growing season - This also affects the water requirement of crop. In summer , the evaporation and transpiration rate is high and humidity in atmosphere is less thus the water requirement is high.
In rain season the relative humidity is high and evaporation and transpiration rate is also less thus the water requirement is less .
Soil factor - The soil factor includes -
1. Structure - The structure of soil affects the water requirement. Crumby structure of soil needs less water and structureless soil needs more amount of water.
Clay soil particle size is small it needs less amount of water. But the particle and pore size of sand soil is large, it has more water loss through leaching thus it needs large amount of water.
2. Depth of soil - The depth of soil is directly proportional to water requirement. If the depth of soil is large then the water requirement is also large.
3. Topography of soil - It also affects the water requirement of crop. If the soil is levelled it needs small amount of water in comparison to undulated soil topography.
4. Soil chemical composition - It is a main factor that affects the water requirement. The soil with pH value 6 - 7.5 needs small amount of water in comparision to acidic and basic soil.
Climatic Factor - The climatic factor includes -
1. Temprature - It affects the rate of evaporation and transpiration. If the temprature is high then rate of evaporation and transpiration will also be high, thus water loss is high it means that if temprature is high water requirement will also be high. If temprature is high relative humidity will become low. It means that more water is required in high temprature.
If temprature is less the rate of evaporation, transpiration is low and relative humidity will be more, that is, less amount of water required.
2. Sunshine hours - It is direct proportional to water requirement, that is if sunshine hours is more water requirement will also be more.
3. Relative humidity - It is inversely proportional to rate of evaporation and transpiration. If Relative humidity high then rate of evaporation and transpiration will be less, that is water requirement is less. If relative humidity is less then rate of evaporation and transpiration will be high that is, water requirement will be high.
4. Wind velocity - The wind with high velocity carries a large amount of water with itself. If the wind velocity is high then rate of evaporation will also be high that is, water requirement will be high.
5. Rainfall - It also affects the water requirement. If the amount of rainfall is large , the amount of moisture and humidity in atmosphere will also be large, that is , water requirement will be less.
Agronomic Factor -
1. Irrigation method used - There are many methods for irrigation -
- Flooding and furrow system
- Surface Irrigation
- Sprinkler Irrigation
- Drip Irrigation
- Check basin method
Flooding irrigation, Check basin irrigation needs more amount of water.
Drip irrigation and sprinkler irrigation has less water loss, that is , it needs less amount of water.
2. Frequency of Irrigation - It is inversely proportional to water requirement. If the frequency of irrigation is high then the water requirement will be less.
Consumptive use of water - The amount of water that is required for evaporation, transpiration and for metabolism of plant.
It can be denoted -
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CU = E + T + WPM
______________ _____________________________________
CU = Consumptive use of water
E = Evaporation
T = Transpiration
WPM= Water for plant metabolism
Consumptive water used in evaporation and transpiration is greater than 99 percent and water used in plant metabolism is less than 1 percent.
Factor affecting consumptive use of water - There are four main factors that affect consumptive use of water -
- Crop Factor
- Climate Factor
- Soil Factor
- Agronomic Factor
1. Crop factor - it includes -
- Planting Pattern
- Stage of plant growth
- Duration of crop
- Stomata opening and closing
- Rooting depth
2. Climate factor - It includes -
- Radiation
- Humidity
- Rainfall
- Temprature
- Wind velocity
3. Soil Factor -
- Soil water depth
- Infiltration rate of soil
- Water holding capacity of soil
4. Agronomic Factor -
- Mulching
- Time of sowing
- Harvesting
- Fertiliser and pesticides use
- Herbicides use
Irrigation requirement - Irrigation is a process of applying controlled amount of water to crops for good production.
Irrigation is supply of water through artificial means of water supply .
The amount of water applied to land surface in addition to the water supplied through rainfall and soil profile to meet the water needs of crop is called irrigation requirement.
It can be denoted-
________________________ ______________________________
IR = WR - ( ER + S)
________________________ ______________________________
IR = Irrigation Requirement
WR = Water Requirement
ER = Effective Rainfall
S = contribution of soil moisture
Irrigation can be qualified in two parts -
- Net Irrigation Requirement
- Gross Irrigation Requirement
Net Irrigation Requirement - It is the actual quantity of water required in terms of depth to bring the soil to field capacity level to meet the ET demand of the crop. It is represented in terms of meter cube per hectare.
Gross Irrigation requirement - It includes water losses with net irrigation requirement.
Water requirement Measurement -
The method of measuring water requirement -
- Transpiration Ratio Method
- Consumptive use Method
- Field Method
- Aerodynamic Method
- Soil water balance method
Transpiration Ratio Method -
In this method , firstly transpiration ratio is measured.
water used by plant in transpiration
Transpiration Ratio = --------------------------------------------------- Dry matter yield
After measuring TR , WR is measured.
Water requirement is the product of Transpiration Ratio to biological yield.
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WR = TR * Biological yield
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Water requirement of different crop -
Crop Water Requirement
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1. Rice 900 - 2500 mm
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2. Wheat 400 - 600 mm
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3. Groundnut 500 - 600 mm
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4. Cotton 800 - 1300 mm
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5. Onion 500 - 600 mm
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6. Sorghum 400 - 600 mm
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7. Chilli 500 - 600 mm
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8. Castor 500 - 600 mm
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9. Soyabean 450 - 600 mm
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10. Pineapple 650 - 1000 mm
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11. Bean 300 - 500 mm
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12. Tomato 600 - 800 mm
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13. Grapes 500 - 1200 mm
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14. Potato 500 - 650 mm
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15. Cabbage 380 - 500 mm
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