Chapter 1 Water Use of Crop EVAPORATION By Li Guangyong,China Agricultural university
Chapter 1 Water Use of Crop By Li Guangyong, China Agricultural university
Outline 1. Concept of Evaporation and Transpiration 2. Water use of crop 3. Factors affecting evapotranspiration 4. Concept of reference crop evapotranspiration (ETo) 5. Crop evapotranspiration under standard conditions (ETc) 6. Crop evapotranspiration under non-standard conditions (ETe adi) 7. Calculation of reference evapotranspiration,ETo 8. Kc and crop 9. a value method for ET.calculation 10.Some results from China 11.Weather station for ET calculation
Outline 1. Concept of Evaporation and Transpiration 2. Water use of crop 3. Factors affecting evapotranspiration 4. Concept of reference crop evapotranspiration (ETo) 5. Crop evapotranspiration under standard conditions (ETc) 6. Crop evapotranspiration under non-standard conditions (ETc adj) 7. Calculation of reference evapotranspiration, ETo 8. Kc and crop 9. α value method for ETc calculation 10. Some results from China 11. Weather station for ET calculation
1.Concept of Evaporation and Transpiration TRANSPIRATION EVAPORATION
1. Concept of Evaporation and Transpiration
Mature plant Young plants ·Transpiration:soil water-→roots→leaf→air 99%water to air,less than 1%keep in plant and become itself Evaporation:from naked soil Deep percolation:when irrigation or rainfall is too much,soil moisture will higher than field capacity. Redundant water will flow out roots zoon
Mature plant Young plants • Transpiration：soil water→roots→leaf→air 99% water to air, less than 1% keep in plant and become itself • Evaporation: from naked soil • Deep percolation：when irrigation or rainfall is too much, soil moisture will higher than field capacity. Redundant water will flow out roots zoon
The partitioning of evapotranspiration into evaporation and transpiration over the growing period for an annual field crop 100% 80% 60% transpiration 40% 20% evaporation 0% sowing harvest time
2.Water use of crop Evaporation Transpiration Evapotranspiration (ET)=Water use of crop For rice: ET deep percolation=water use of field units:mm or m3/ha
2. Water use of crop • Evaporation + Transpiration = Evapotranspiration (ET)=Water use of crop For rice: ET + deep percolation= water use of field units： mm or m 3/ha
Conversion factors for evapotranspiration depth volume per unit area energy per unit area mm day-1 m3 ha-1 day- I s-1 ha-1 MJ m-2 day-1 1 1 mm day-1 7 10 0.116 2.45 1 m3 ha1 day- 0.1 1 0.012 0.245 1 1Is-1 ha-1 8.640 86.40 1 21.17 1 MJ m-2 day- 0.408 4.082 0.047 1 1
Conversion factors for evapotranspiration d e p t h v olu m e p e r u nit a r e a e n e r g y p e r u nit a r e a * m m d a y-1 m 3 h a-1 d a y- 1 l s-1 h a-1 M J m-2 d a y-1 1 m m d a y-1 1 1 0 0.116 2.45 1 m 3 h a-1 d a y- 1 0.1 1 0.0 1 2 0.2 4 5 1 l s-1 h a-1 8.6 4 0 8 6.4 0 1 2 1.1 7 1 M J m-2 d a y- 1 0.4 0 8 4.0 8 2 0.0 4 7 1
Example If ET=5mm/d,then how much water consumed by crop in 1 ha per day? ·ET=5/1000*10000=50m3/ha/d (1ha=10000m2) 。 If irrigation depth 50mm (500m3/ha),then irrigation interval=? Irrigation interval=50mm/5mm=10 days
Example • If ET=5mm/d, then how much water consumed by crop in 1 ha per day? • ET=5/1000*10000=50m3/ha/d (1ha=10000m2) • If irrigation depth 50mm (500m3/ha), then irrigation interval=? • Irrigation interval=50mm/5mm=10 days
3.Factors affecting evapotranspiration Factors affecting evapotranspiration with reference to related ET concepts ET weather ETo parameters crop characteristics management environmental factors ● c adj
3. Factors affecting evapotranspiration
3.Factors effected water use of crop Weather parameters:radiation,air temperature,humidity and wind speed. Crop characteristic:crop type,variety and development stage
3. Factors effected water use of crop • Weather parameters: radiation, air temperature, humidity and wind speed. • Crop characteristic: crop type, variety and development stage