-
Define field capacity (FC), wilting point (WP) and available water for plants.
- FC = when the soil pores are so full of water that the next drop will leach downward out of the rooting zone (0.1 to 0.3 bars of suction)
- WP = the level at which plant roots can no longer take in water (15 bars of suction)
- Available water = FC - WP
-
What is meant by soil texture? Draw a suitable soil texture classification chart.
- the relative proportion of sand, silt and clay
- indicates the relative proportion of sand, silt and clay
- see USDA soil textural classification chart (12 textural classes)
-
What is soil structure, what are the properties effected due to soil structure?
- indicates the arrangement of individual particles with respect to each other into a pattern
- Soil structures may be grouped as
- • Cube-like
- • Columnar
- • Platy
- • Angular and/or sub-angular
- • Granular, etc
-
Why is loam most suitable for plant growth?
because they hold more available water and cations than sand and are better aerated and easier to work than clay
-
What are the variables we limit to classify our irrigation water quality? How can we improve soil drainability?
- Na with carbonate – alkali soils
- Na with chloride (salt) or sulphate – saline soils
- Boron – necessary in small quantities, toxic in large quantities
-
What is meant by soil-water potential? What are the components in soil-water potential? Why does finer particle soil have higher soil-water potential?
- it is the energy status of the soil water
- Components:
- gravitational potential (force of gravity pulling on the water)
- matric potential (force on water by soil matrix. Also called soil-water tension
- osmotic potential (difference in salt concentration across plant root)
- Finer particle soils:
- have a larger number of small pores
-
What is osmotic pressure? Why we can not apply saline water for irrigation purpose?
- When solutions of different concentrations are separated by a semi-permeable membrane (e.g. plant root)
- salt decreases the total available water in the soil profile. As salt increases in soil-water, the energy expended by a plant to extract water must also increase, even though the soil moisture tension remains the same
-
What equipment we use for measuring soil suction? How it works? What is the usual unit of soil suction measurement?
Tensiometer for measuring soil-water potential?
-
Explain different soil-water measurement techniques, their advantages and disadvantages.
- Gravimetric: Measures mass water content (θm). Advantages: accurate; multiple locations, Disadvantages: labor; time delay
- Feel and appearance: Advantages: low cost; multiple locations, Disadvantages: experience required; not highly accurate
- Neutron scattering (attenuation): Measures volumetric water content. Advantages: samples a relatively large soil sphere, repeatedly sample same site and several depths, accurate
- Disadvantages: high cost instrument, radioactive licensing and safety, not reliable for shallow measurements near the soil surface
- Dielectric constant: A soils dielectric constant is dependent on soil moisture.
- Primarily used for research purposes at this time
|
|
