1. SOIL-WATER RELATIONSHIPS: MICROIRRIGATION
Unit
SOIL-WATER RELATIONSHIPS:
MICROIRRIGATION

2. Learning Objectives
1. Define infiltration, application rate, and wetted pattern.
2. Describe the relationships between soil texture, infiltration rates, and wetted pattern.
3. Analyze a specific site for inputs into design and management of a microirrigation system.

3. Terms Application rate Capillary flow Emitter Infiltration Tensiometer
Wetted pattern

4. What are infiltration, application rate and wetted pattern?
— Irrigation success is founded on many basic principles.
- Infiltration is the process by which water moves into the soil.

5. Infiltration, Rates, Patterns
- Application rate is the amount of water that is applied expressed as a volume over time.
-Some examples would include 10 gallons per hour or 5 liters per hour.
- Wetted pattern is the shape that is formed below the soil surface of the water that has infiltrated into the soil.

6. How do infiltration rates and application rates affect wetted pattern?
—Water moves through the soil in many ways.
- The soil has properties that determine the movement and storage of water, which affects the availability of the water to the plants.

7. How do rates/ affect patterns
Water moves through the pores (spaces) in the soil.
The water moves laterally and vertically up and down caused by the cohesive forces of water.

8. How do rates/ affect patterns
Soils with large pore spaces have less of a capillary flow, upward and lateral flow caused by molecular forces in some liquids.

9. How does rates/ affect patterns
The soil will have a unique wetted pattern dependent upon its texture.
Sandy soils have larger pore spaces so the wetted pattern will be more vertical since the gravitational forces will affect most of the water.

10. How does rates/ affect patterns
- Clay soils will have a more lateral wetted pattern due to the stronger cohesive forces and the smaller pore spaces.
- Loam soils will have a more rounded wetted pattern since both lateral and gravitational forces will act in relatively equal proportions.

11. How does rates/ affect patterns
The water is applied using an emitter, a device that meters the amount of water discharged.
If the water is applied at a high rate soils tend to have a wider wetted pattern than those soils that are irrigated with a low application rate.

12. How can you analyze a specific site for the management of a microirrigation system with various inputs?

13. Microirrigation
—The movement of water through the soil in a microirrigation system needs to be monitored.

14. Microirrigation
- A tensiometer is a device that can measure water tension and can describe wetted patterns.
- Other methods of monitoring include spot-checking the soil and determining if the water is reaching the root zone.

15. Terms Relating to microirrigation
-Infiltration is the process whereby water moves into the soil.

16. Terms relating to micrirrigation
-Wetted pattern is the shape produced by infiltrated water into the soil.
-Application rates are the amounts of water that are applied to the soil in gal/hr or liters/hr.

17. WETTED PATTERN AT A GIVEN APPLICATION RATE

18. Soil Moisture Curves

19. Available Soil Moisture:
is the difference between the amount of water in the soil at field capacity and the amount of water in the soil at the permanent wilting point.
-Field capacity (FC), permanent wilting point (WP), and available soil moisture (AM) vary by soil texture. See the table of moisture holding capacities of different soils.

20. Moisture Holding Capacities of Soils

21. Water movement in Various soils
Soil Type
Radius Wetted Area (ft)
Coarse sand
0.5–1.5
1.0–3.0
Fine sand
Loam
3.0–4.5
Heavy clay
4.0–6.0