Soil Science: Soil Matrix and Phases

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Questions and Answers

What is the primary function of a tensiometer?

To measure soil pH levels

To assess soil temperature

To analyze soil nutrient content

To record soil moisture tension (correct)

Which component is NOT part of a tensiometer's construction?

Hollow metallic tube

Ceramic or clay cup

Capacitance sensor (correct)

Vacuum gauge

When should a soil be irrigated according to the tensiometer readings?

When the soil is saturated

When the soil reaches field capacity

When the vacuum exceeds 1 atm

When desired tension is reached (correct)

What is a limitation of using a tensiometer in certain soil types?

Sensitivity is limited to 0.85 atm while available moisture can exceed this Signup and view all the answers

For which type of soil are tensiometers least effective?

Clay soils Signup and view all the answers

What is the primary purpose of the gravimetric method in soil moisture measurement?

To measure soil moisture by weighing dried soil samples Signup and view all the answers

Which of the following limitations is associated with the volumetric method of measuring soil moisture?

It can lead to significant errors due to handling and transport Signup and view all the answers

At what tension do plaster of Paris blocks function most efficiently?

Between 1 and 15 atm Signup and view all the answers

What is a critical consideration when placing gypsum blocks in soil?

They must have close contact with undisturbed soil Signup and view all the answers

Why are nylon and fiberglass resistance blocks not suitable for use in saline conditions?

They lose their moisture sensing capabilities Signup and view all the answers

What term describes the attraction between soil particle surfaces and water?

Adhesion Signup and view all the answers

Which pore size is categorized as macropores?

Size greater than 100 µm Signup and view all the answers

Which type of soil water is NOT available to plants?

Hygroscopic water Signup and view all the answers

What is the primary method used to measure moisture content directly in the soil?

Gravimetric method Signup and view all the answers

Which type of water moves freely downward in the soil due to gravity?

Gravitational water Signup and view all the answers

What is the tension range at which capillary water is held in soil?

1/3 atm to 31 atm Signup and view all the answers

Which of the following is an indirect method of measuring soil moisture?

Resistance blocks Signup and view all the answers

What effect do large pores have on soil properties?

Enhanced aeration and infiltration Signup and view all the answers

What is the primary purpose of the pressure membrane apparatus?

To measure soil moisture up to 100 bars Signup and view all the answers

Which method is used for a practical estimate of moisture content based on touch?

Appearance and feel method Signup and view all the answers

What is the first step in the gravimetric method for determining moisture content?

Determine the weight of an empty moisture can Signup and view all the answers

How is water content calculated in the gravimetric method?

Mass of pore water divided by mass of dry soil solids Signup and view all the answers

Which method is classified under the direct measurement of discharge?

Weirs Signup and view all the answers

What coefficient is applied to the surface velocity to determine the mean velocity of flow in open channels?

0.80 Signup and view all the answers

What equipment is necessary for performing the oven-drying method in determining soil moisture content?

Hot-air oven Signup and view all the answers

Which method is NOT associated with measuring the flow in pipes?

Weirs Signup and view all the answers

What was the estimated net irrigated area in India in 2015-16?

140 million ha Signup and view all the answers

Which state had the highest groundwater potential among the listed states in 2015-16?

Uttar Pradesh Signup and view all the answers

How much average annual precipitation does India receive?

4000 km3 Signup and view all the answers

What percentage of water resources in India is considered utilizable?

36% Signup and view all the answers

Which state reported a groundwater resource availability of 4233 km3/year for the years 2013-14 to 2015-16?

Gujarat Signup and view all the answers

What was the average annual surface flow reported?

1869 km3 Signup and view all the answers

Which method is NOT mentioned as a way to enhance water resources potential?

Desalination Signup and view all the answers

What was the groundwater share available for irrigation?

325 km3 Signup and view all the answers

In which state was the groundwater resource measured to be 13 km3 in the year 2015-16?

Sikkim Signup and view all the answers

Which of the following states showed a decrease in groundwater availability from 2014-15 to 2015-16?

Telangana Signup and view all the answers

Which option correctly lists the net irrigated area percentages?

NIA %, GW %, SW % Signup and view all the answers

What is the total net groundwater resource in the listed years for India?

432 km3 Signup and view all the answers

In the state of Bihar, what was the groundwater resource availability in 2013-14?

2933 km3 Signup and view all the answers

Study Notes

Soil Matrix

The solid phase of soil, known as the soil matrix, governs the distribution of liquid and gas phases.
Interaction between the soil matrix and water is influenced by adhesion (attraction of soil particles to water) and cohesion (attraction of water molecules to each other).
Adhesion occurs due to surface tension, while water is held tightly at the soil-water interface.

Pore Size Distribution

Micropores: Smaller than 30 µm.
Mesopores: Ranging from 30 to 100 µm.
Macropores: Larger than 100 µm.
Large pores enhance aeration and infiltration; medium pores facilitate capillary conductivity; small pores increase water holding capacity.

Soil Water Forms

Gravitational water: Moves freely downward under gravity; also known as free water.
Capillary water: Held in capillary spaces between tensions of about 31 atm and 1/3 atm; available for plant use.
Hygroscopic water: Bound to soil particles by adsorptive forces; not available for plants, held at tensions greater than 31 atm.

Methods of Soil Moisture Measurement

Direct Methods: Measure moisture content directly.
- Gravimetric method: Weighs soil samples, dried at 105°C.
- Volumetric method: Uses core samplers; accurate but labor-intensive.
Indirect Methods: Measure water potential or tension.
- Tensiometers, resistance blocks, neutron probes, and pressure plate apparatus.

State-Wise Ground Water Resources (2013-16)

Andhra Pradesh: 3014 - 2743 km³, trend downwards.
Gujarat: Holds steady at 4233 km³.
Uttar Pradesh: Highest availability, ranging from 14027 - 14231 km³.
Overall ground water resources in India: 68117 - 67300 km³ over three years.

India's Water Resources Overview

Total net sown area: 141 million ha; rainfed area: 86 million ha; irrigation potential: 140 million ha.
Average annual precipitation: 4000 km³; average annual surface flow: 1869 km³.
Groundwater resources available for irrigation: 361 km³; net utilizable: 325 km³.
Water conservation methods include watershed management, rainwater harvesting, and pollution prevention.

Soil Moisture Measurement Techniques

Gravimetric Method:
- Weigh dried soil to determine moisture content.
- Comparison of moist sample and dry sample weights gives moisture percentage.
Volumetric Method:
- Uses known volume of soil; calculates water content through drying.
Resistance Blocks:
- Different types sensitive at varying tensions; gypsum blocks are suited for saline conditions.
Tensiometer:
- Direct measurement of soil moisture tension; effectively used in sandy soils.

Soil Moisture Characteristics

Tension levels vary based on soil type: sandy (0.06 atm), loamy sand (0.3 atm), clay (0.6 atm).

Water Measurement Techniques in Irrigation Engineering

Hydrometry encompasses methods such as the velocity-area method, direct discharge measurement using weirs, notches, and flumes.
Float method applies a coefficient to surface velocity for flow calculations.

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Description

Explore the concept of the soil matrix and its role in the distribution of liquid and gas phases within soil. This quiz covers fundamental interactions between soil particles and water, focusing on adhesion and cohesion phenomena. Test your understanding of these key principles in soil science.