Soil Composition and Physical Features
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Soil Composition and Physical Features

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@PrudentRainforest

Questions and Answers

What is the approximate percentage of pore space in soil?

50%

Which type of soil particle has the greatest capacity for ion exchange?

Colloidal clay

What is the primary characteristic of loam soil?

Equal amounts of sand, silt, and clay

What is the result of having enough sand in soil?

<p>Good drainage</p> Signup and view all the answers

What is the product of the breakdown of organic matter?

<p>Humus</p> Signup and view all the answers

What is the definition of soil texture?

<p>A measure of the proportion of different sized particles</p> Signup and view all the answers

What is the primary characteristic of clay soils?

<p>Poor drainage</p> Signup and view all the answers

What is the composition of warm soil?

<p>Sand (50%), Silt (30%), Clay (20%)</p> Signup and view all the answers

What is the primary cause of sediments being lost from the soil?

<p>Erosion</p> Signup and view all the answers

What type of particles are lost from the soil due to erosion?

<p>Small soil particles</p> Signup and view all the answers

What is the result of sediments being lost from the soil?

<p>Soil degradation</p> Signup and view all the answers

What is the opposite process of erosion?

<p>Deposition</p> Signup and view all the answers

What is the primary factor that contributes to soil erosion?

<p>Water</p> Signup and view all the answers

What is the effect of soil erosion on soil fertility?

<p>It decreases soil fertility</p> Signup and view all the answers

What is the relationship between soil erosion and sedimentation?

<p>They are related but distinct processes</p> Signup and view all the answers

What is the consequence of ignoring soil erosion?

<p>Land degradation</p> Signup and view all the answers

What is the role of vegetation in preventing soil erosion?

<p>It decreases soil erosion</p> Signup and view all the answers

What is the impact of soil erosion on the environment?

<p>It has a negative impact</p> Signup and view all the answers

What is the primary purpose of checking the plasticity of a soil sample?

<p>To identify the texture of the soil</p> Signup and view all the answers

What is the purpose of using muslin cloth and rubber bands in the experiment to determine capillarity and infiltration rate?

<p>To hold the soil in place</p> Signup and view all the answers

What is the advantage of adding cress seeds to the experiment to determine capillarity and infiltration rate?

<p>To demonstrate germination if the water rises enough</p> Signup and view all the answers

Why is it necessary to dry the soil sample in an oven or microwave in the experiment to calculate the percentage water content?

<p>To evaporate all the water from the soil</p> Signup and view all the answers

What is the purpose of using a ruler in the experiment to determine capillarity and infiltration rate?

<p>To measure the water level</p> Signup and view all the answers

Why is it necessary to use a clean, dry beaker in the experiment to calculate the percentage water content?

<p>To avoid contamination of the soil sample</p> Signup and view all the answers

What is the difference between compaction and uncompaction of soil?

<p>Compacted soil is denser, while uncompacted soil is less dense</p> Signup and view all the answers

What is the purpose of measuring the mass of the soil sample before and after drying in the experiment to calculate the percentage water content?

<p>To calculate the loss in mass of the soil due to water evaporation</p> Signup and view all the answers

What is the primary factor that determines the soil texture?

<p>The ratio of sand, silt, and clay particles</p> Signup and view all the answers

What is the term for the clustering together of soil particles to create larger structures?

<p>Flocculation</p> Signup and view all the answers

What percentage of soil pore space is occupied by air?

<p>25%</p> Signup and view all the answers

What is the result of soil compaction on soil structure?

<p>Soil structure is destroyed</p> Signup and view all the answers

What is the consequence of organic matter loss on soil?

<p>Poorer soil structure and less nutrient availability</p> Signup and view all the answers

What is the term for the process of soil particles being carried away by wind, destroying soil structure?

<p>Erosion</p> Signup and view all the answers

What is the result of tillage on soil?

<p>The more land is cultivated, the more soil is eroded</p> Signup and view all the answers

What is the purpose of using cover crops?

<p>To reduce soil erosion</p> Signup and view all the answers

What is the benefit of good soil structure on plant growth?

<p>It provides aeration, water drainage, and root penetration</p> Signup and view all the answers

What is the term for the process of facilitating nutrient retention and exchange in soil?

<p>Cation Exchange Capacity</p> Signup and view all the answers

What is the primary consequence of sedimentation on topsoil?

<p>Loss of humus and organic matter</p> Signup and view all the answers

Which type of soil pore is responsible for water retention?

<p>Small soil pores</p> Signup and view all the answers

What is the term for the thin layer of water formed around soil particles due to their polarized nature?

<p>Hydroscopic water</p> Signup and view all the answers

What is the primary reason for the darker color of fertile soils?

<p>Higher humus content</p> Signup and view all the answers

What is the effect of lower temperature on seed germination?

<p>Decrease in germination rate</p> Signup and view all the answers

What is the primary purpose of the sedimentation method in soil texture analysis?

<p>To separate the soil into different texture layers</p> Signup and view all the answers

What is the term for the removal of carbon dioxide from the atmosphere through plant photosynthesis and storage as organic soil matter?

<p>Carbon sequestration</p> Signup and view all the answers

What is the primary difference between compacted and uncompacted soil in terms of pore space?

<p>Uncompacted soil has more pore space</p> Signup and view all the answers

What is the purpose of the hand testing method in soil texture analysis?

<p>To determine the soil's texture through touch and feel</p> Signup and view all the answers

Study Notes

Soil Composition

  • Soil is composed of 50% pore space (air and water) and 50% solid matter (mineral and organic matter)
  • Mineral matter is derived from parent material, while organic matter is derived from plant and animal remains

Particle Size

  • Mineral matter is classified by size: sand, silt, and clay
  • Colloidal clay particles are the smallest type of clay particles, but they have the greatest capacity for ion exchange

Soil Types

  • Sandy Soils: large air pores, holds water easily, free draining, little leaching, and poor in nutrients
  • Clay Soils: poor drainage, leads to waterlogging, and is cold
  • Loam Soil: contains equal amounts of sand, silt, and clay, is fertile, easy to work with, and has intermediate characteristics of clay and sandy soils

Soil Texture and Drainage

  • Soil texture is a measure of the proportion of different sized particles (sand, silt, clay) in a soil sample
  • Soil texture is a fixed property of soil that cannot be changed
  • The ratio of Sand, silt, and clay determines the soil texture

Determining Soil Texture

  • Hand testing
  • Sedimentation
  • Soil Sieve

Soil Structure

  • Definition: the arrangement of soil particles in a soil
  • Key points:
    • Floccules are formed by clustering together of soil particles
    • Flocculation creates larger structures called floccules or peds
    • Arrangement of floccules determines soil pore space (50%: 25% air and 25% water)
    • Good structure is necessary for healthy plant growth, nutrient availability, microbial activity, water management, erosion prevention, and resilience to stress

Factors Affecting Soil Structure

  • Freezing and thawing
  • Wetting and drying
  • Compaction: destroys soil structure, reduces pore space, increases soil density, and reduces infiltration and drainage
  • Organic Matter Loss: leads to poorer structure, less nutrient availability, and lower water retention
  • Erosion, Sedimentation, and Weathering: can be broken into three areas – wind, water, and tillage, and can be reduced by using cover crops, crop rotation, and reducing compaction### Soil Erosion and Sedimentation
  • Erosion leads to loss of topsoil, which is crucial for fertility, nutrients, cation exchange, and trapping carbon.
  • Sedimentation is the process of transporting and depositing eroded soil particles to a new location, potentially affecting water quality.
  • Sediments can carry excess nutrients (manure) and pathogens.

Soil Structure and Water

  • Large soil pores facilitate drainage, while small soil pores enable water retention for plant uptake.
  • Clay soils have small pores, making them prone to waterlogging.
  • Loam soil is ideal, with a balance of large and small pores.
  • Water is attracted to the negative charges of clay particles, forming a thin layer around them (hygroscopic water).
  • Capillary water and gravitational water are two types of water in soil.

Soil Colour and Properties

  • Dark brown or black soil colours indicate rich, fertile soils with high humus content.
  • Light or grey soil colours suggest low fertility, low nutrients, and leaching.
  • Red soil colours indicate the presence of iron, which can form an impermeable iron-pan.

Soil Temperature

  • Lower temperatures result in lower germination rates and water and mineral uptake.
  • Van't Hoff's Law states that the rate of chemical reactions doubles with every 10°C rise in temperature.

Soil Compaction and Pore Space

  • Compaction affects soil structure, impacting temperature, water, and mineral uptake.
  • An experiment can be conducted to compare the total pore space in compacted and uncompacted soil.

Soil Texture Analysis

  • Sedimentation, soil sieving, and hand testing are methods to investigate soil texture.

  • The sedimentation method involves adding soil to a beaker, stirring, and pouring the mixture into a graduated cylinder to settle.### Soil Texture Analysis

  • Observe layers in a soil sample: clay at the top, silt in the middle, and sand at the bottom

  • Record levels of each layer using a graduated cylinder

  • Calculate the percentage of sand, silt, and clay in the sample

  • Use the soil triangle to classify the soil type

Soil Sieve Method

  • Dry the soil sample in an oven to remove moisture
  • Crush the sample using a pestle and mortar
  • Weigh the empty weighing boat, then add the crushed sample and reweigh
  • Subtract the mass of the empty boat to calculate the mass of the soil
  • Place the crushed sample in a series of sieves with decreasing mesh sizes
  • Shake the sieves and weigh the contents of each to calculate the percentage of sand, silt, and clay
  • Use the soil triangle to classify the soil type

Hand Testing Method

  • Take a dry soil sample and rub it between your thumb and fingers to note its grittiness/smoothness
  • Wet the sample and rub it again to note its grittiness/smoothness and plasticity (ability to be moulded)
  • Use a flow chart to identify the texture of the soil sample based on its grittiness, smoothness, and plasticity
  • Attempt to roll the wet sample into threads and make a ring to further identify the texture

Capillarity and Infiltration Rate

  • Compare the capillarity and infiltration rate of compacted and uncompacted soil using two open-ended glass tubes
  • Cover one end of each tube with muslin cloth and fill with soil
  • Stand both tubes in a water trough and observe the rise in water level over time
  • Measure the level of water risen using a ruler
  • Compare the results of both soils

Percentage Water Content

  • Calculate the percentage water content in a soil sample using a beaker, weighing scales, and a microwave or oven
  • Find the mass of a clean, dry beaker, then add a moist soil sample and find the mass of the beaker and soil
  • Dry the soil in the oven at 105°C until all water has evaporated, then calculate the loss in mass
  • Repeat for multiple soil samples (e.g., sandy, clay, loam)

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Description

This quiz covers the physical features of soil, including its composition and particle size. Learn about the proportion of pore space, mineral matter, and organic matter in soil.

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