Soil water movement

Soil water movement
Soil water movement
Soil water movement
Soil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movementSoil water movement

1. Soil water movement-saturated flow, unsaturated flow-infiltration-hydraulic conductivity, percolation, permeability and drainage K. Maheshwaran, Asst.Prof . (SS&AC) Sethu Bhaskara Agricultural College & Research Foundation

2. Movement of soil water Saturated flow Unsaturated flow Water vapour movement There are three types of movement

3. Saturated flow Water moves because of water potential in the soil caused by gravity, salt content, water usage and the direction of flow Water moves is from zone of higher to zone of lower moisture potential Soil water moves mainly due to gravity, moisture potential is greater than -1/3 bar is called as ‘Saturated flow’

4. Saturated flow Its start with infiltration of water Movement of water in soil by rainfall or irrigation when soil is saturated with water The movement of water in saturated soil is termed as ‘Percolation’

5. Saturated flow Two major factors is determined in saturated flow Hydraulic force driving the water through the soil Soil permits the water movement V= Kf V=Total volume of water moved in given time K= Hydraulic conductivity of the soil f= Water moving force

6. Factors affecting saturated soil Texture Sandy soil has more saturated flow than fine textured clay soil Structure Granular structure conduct more saturated flow than unstable soil structure Organic matter OM helps in increase the proportion of macro pores so increase the saturated flow Exchangeable cation Sodium reduces the saturated flow due to dispersion of soil and reduces the hydraulic conductivity Fluidity Depends on the salts and viscosity which affect the hydraulic conductivity

7. Unsaturated flow Moisture potential is lower than -1/3 bar is called as ‘Unsaturated flow’ Movement occurs in soil pores are not occupied with water In this condition, Macro pores with only air and Micro pores with air and water Water moves towards the region of lower potential

8. Unsaturated flow Water moves from wetter to drier region The movement may be in any direction Two forces responsible for this flow Attraction of soil solids for water Capillarity (Micro pores) Due to presence of air phase unsaturated flow is occur

9. Water vapour movement Movement of water in soil by vapour form in two ways Internal movement : Change of water into vapour state take place in within the soil pores External movement : Formed water vapour lost to atmosphere by diffusion and convection take place in land surface

10. Law responsible for water movement Poisevilles law Darcy’s law

11. Poisevilles law Rate of flow a liquid though a narrow tube is proportional to the 4 th power of radius of the tube and the pressure difference and inversely proportional to the length of the tube and viscosity of the liquid Q= P¶r 4 8LZ Q=Volume of flow (cm 3 /sec) P=Pressure difference (dynes/cm 2 ) r=Radius of the tube (cm) L=Length of the tube (cm) Z=Viscosity of the liquid (dynes/cm)

12. Darcy’s law The velocity of flow of liquid through a porous medium is proportional to the force causing the flow and hydraulic conductivity of the medium Q= CKAP Z Q= Velocity of flow (ms -1 ) C=Proportionality constant K= Hydraulic conductivity (cm hour -1 ) A=Cross sectional area of the pores (cm 2 ) P=Pressure gradient (dynes/cm 2 ) L=Length of the porous medium (cm)

13. Permeability Ease of soil transmit water Expressed as cm/sec Intrinsic permeability Flow of water is dependent only on soil characteristics Expressed as K= k’f K=Hydraulic conductivity (cm s -1 ) k’=Intrinsic permeability (cm 2 ) f=Fluidity ( 1 /cm s -1 )

14. Permeability

15. Infiltration Downward movement of water into soil The rate of infiltration is initially high and decrease the value slowly attain constant value

16. Infiltration rate under different soil

17. Factors affecting infiltration rate Time Initially high later it will slow Surface soil condition Porous soil IR is high, Crusted soil IR is slow Texture IR of sandy is rapid than clayey soil Decrease with increase in clay content IR of Montmorillionate is lower than the kaolinite clay Structure Spheroid type has highest IR than plate like structure Block like and prism like has intermediate IR Organic matter IR increase with increase in OM content Compaction IR decrease with increase in soil compaction Impervious layer Reduce IR Water content IR reduce in soil with water Soil reaction If soil is sodic , IR is decease due to dispersion of soil aggregates and its block the soil pores

18. Percolation Downward movement of water after attain saturation Saturation is a pore space is filled with water Due to the gravity force water percolate into the soil

19. Drainage Management of excess water from the agricultural lands Management includes removal and disposal Excess water in soil may be cause aeration, soil temperature, tillage operations Water carries excess salts so drainage is a necessary operation

20. Classification of drainage system Surface drainage Subsurface drainage

21. Surface drainage Removal of excess water from the land surface through the land shaping or constructed channels Soil with low infiltration rate is very susceptible to surface drainage Soil with heavy texture more susceptible to surface drainage because no more infiltration

22. Surface drainage system Collection system Disposal system Outlet

23. Subsurface drainage Removal of excess water from the below surface Sub surface drainage provides better root zone environment

24. Subsurface drainage system Tile drains including perforated pipes Mole drains Drainage wells Deep open drains Combination of tile and open drains

25. Tile drains including perforated pipes

26. Mole drains

27. Drainage wells

28. Deep open drains

29. Thank you……