Chapter 3 - Soil

1. A storehouse of nutrients

2. A habitat for soil organisms and plant

3. A reservoir of water to meet the evatranspiration (ET) of plants

What are the Functions of Soil?

1. Dissolves soil nutrients

2. Regulates temperature

3. Facilities field operations

4. Facilitates soil biological processes

What are the Functions of Water in the Soil?

1. Adhesive Force

2. Cohesive Force

3. Gravitational Force

4. Osmotic Force

What are the Forces acting on soil water?

Adhesive Force

Causes the dissimilar particles and/or surfaces to cling to one another.

Cohesive Force

Causes the similar or identical particles/surfaces to cling to one another.

Gravitational Force

Due to the effect of gravity. Water in the soil flows from points with high soil water potential energy to points of lower potential energy.

Osmotic Force

Caused by salt or io concentration differences or gradients.

Available Moisture (AM)

Is the difference in moisture content of the soil between field capacity and permanent wilting point.

Readily Available Moisture (RAM)

Is the portion of the available moisture that is most easily extracted by plants; approximately 75% of the available moisture.

Allowable Moisture Depletion (AMD)

Is the amount of water that is allowed to be depleted usually expressed in percent

Potential Evapotranspiration (PET)

Introduced in the late 1940s and 50s by Penman.

Potential Evapotranspiration

Defined as "the water loss which will occur if at no time there is a deficiency of water in the soil for use by vegetation" - by Thornthwaite (1943).

Actual Crop Evapotranspiration (ETc)

Also known as the crop water requirements (CWR) or consumptive use (CU).

CWR (Crop Water Requirement)

Defined as "the depth of water needed to meet the water loss through evapotranspiration (ETc) of a disease-free crop, growing in large fields"

1. Indirect methods

2. Lysimeters

3. Catchment water balance

4. Empirical Equations

What are the Estimating Evapotranspiration?

1. Non-weighing, constant water table type

2. Non-Weighing, percolation type

3. Weighing type

Types of lysimeters:

Non-weighing, constant water table type

Used in areas where high water table normally exist

Non-Weighing, percolation type

Used in areas of high precipitation

Weighing type

Provide the most accurate data for short time periods

Irrigation Efficiency

Is a critical measure of irrigation performance in terms of the water required to irrigate a field, farm, basin, irrigation district, or an entire watershed.

1. Water conveyance efficiency

2. Water application efficiency

3. Water distribution efficiency

4. Water use efficiency

5. Water storage efficiency

6. Consumptive use efficiency

What are the Irrigation Efficiencies?