common soil parameters n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Common Soil Parameters PowerPoint Presentation
Download Presentation
Common Soil Parameters

Loading in 2 Seconds...

play fullscreen
1 / 33

Common Soil Parameters - PowerPoint PPT Presentation


  • 118 Views
  • Uploaded on

Common Soil Parameters. What are the common parameters of soil that we could test?. The 3 soil attributes. Physical attributes Texture, structure, etc Biological attributes Organic content Chemical attributes pH, conductivity, cations, anions etc. Physical Properties. Colour.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Common Soil Parameters' - major


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
common soil parameters

Common Soil Parameters

What are the common parameters of soil that we could test?

the 3 soil attributes
The 3 soil attributes
  • Physical attributes
    • Texture, structure, etc
  • Biological attributes
    • Organic content
  • Chemical attributes
    • pH, conductivity, cations, anions etc
colour
Colour
  • described by using a Munsell Colour Chart
  • describe colour in terms of Hue, Value, and Chroma.
  • A typical designation is 10YR 5/2. This is the symbol of a greyish brown colour with 10YR hue, 5 value, and 2 chroma
  • The symbol components are always arranged in this sequence.
soil colour determination
Soil Colour Determination
  • Hue - colour of pigment that must be mixed with black and white (or the proper shade of grey) to produce the colour to be matched
  • Soils range in hue from red (R) through yellow-red (YR) to yellow (Y) with some spots of green-yellow (GY) or even green (G).
  • 0-10 prefixes divide the space between the absolute hues
  • eg 7.5YR
  • value - the square root of the percentage of light reflected
  • soils range from 2 to 8
soil colour determination1
Soil Colour Determination

Chroma

  • the amount of pigment that must be mixed with the proper value of grey to produce the particular colour
  • pure grey colours have 0 chroma
  • increasing brightness is indicated by chroma’s up to about 8 in soils
soil texture
Soil Texture
  • Soil Texture is the most commonly used descriptor of a soil.
  • Texture is a property of the fine earth (<2mm) fraction that depends on the particle‑size distribution.
  • Particle size in this fraction varies from 2mm diameter down to less than 0.1mm
  • The distribution of particles over this size range influences many important soil properties such as ease of cultivation and water‑holding characteristics.
soil texture1
Soil Texture
  • Soil is allocated to a textural class, depending on its content of sand‑, silt‑ and clay sized particles.
  • In the field, determined subjectively from the feel of a moist soil molded between the fingers and thumb
  • This is because the particle‑size distribution influences the mechanical properties of the material.
class exercise 1

Class Exercise 1

Finger assessment of soil texture for mineral soils

soil structure
Soil Structure
  • Described as weak, moderate, or strong depending on how distinct the peds? are.
  • Fine, medium, or coarse depending on the size of the peds.
  • Shape of the peds - platy, granular, blocky, columnar, or prismatic,
settling rate lab method
Settling rate lab. method

for the silt‑size particles plus some of the coarse clay,

  • rate of settling is proportional to the square of the diameter of the particles
    • v = 6000d2
    • v is the settling velocity in cm/minute
    • d the particle diameter in mm
  • two sizes needed for determining soil texture; limits between:
    • sand and silt (0.05 mm) and
    • silt and clay (0.002 mm)
example 8 1
Example 8.1
  • Calculate how far a 0.05 mm diameter particle would travel in one minute.
  • v = 6000 x 0.052
  • = 15 cm/min
  • in 1 minute, particles of this size would have travelled 15 cm
exercise 8 2
Exercise 8.2
  • Would larger particles than 0.05 mm travel more or less than 15 cm in this time?
  • More
  • What does this mean about the sand fraction?
  • It would sink faster
  • Calculate how long a 0.002 mm diameter particle would take to travel 1 cm.
  • v = 0.024 cm/min
  • 1 cm in 41.7 minutes
applying this in the lab
Applying this in the lab
  • a uniform suspension of soil in water is allowed to settle for one minute
  • a sample is then withdrawn from a depth of 15 cm
  • will contain no particles larger than 0.05 mm diameter
  • larger particles will have settled beyond that depth even if they started at the surface
  • the sample will contain silt and clay only
  • any particles smaller that had sunk from this level will be replaced from above
  • repeat at a depth appropriate for 0.002 cm
  • eg 3 cm after 2 hours
exercise 8 3 answers
Exercise 8.3 answers
  • 40 x 2.04 g = 81.6 g
  • 40 x 0.40 g = 16 g
  • 81.6-16 = 65.6 g
  • Silt 66.8%, clay 16.3%, sand 16.9%
  • silt loam
soil water
Soil Water
  • The amount of water present in the soil at any one time is most commonly expressed as a percentage of the oven‑dry weight of the soil
  • Percentage is commonly determined for the field capacity of the soil and for air‑dry soil.
  • These two percentages are used as limits to classify the water present in a soil after a rain as gravitational, capillary, and hygroscopic
soil conductivity
Soil Conductivity
  • Determined quantitatively by a conductivity meter.
  • Standard water:soil mix
  • An important parameter when assessing salinity.
  • Used to estimate the concentration of soluble salts in the soil (Na+, Mg2+ and Ca2+ , Cl-, SO42- and HCO3-).
  • Soluble fertiliser may also contribute K+, NH4+ and NO3-.
  • High EC is undesirable for most plants.
stone content
Stone Content
  • affect soil fertility by taking up space
  • reduce ability of a given volume of soil to hold water and nutrients
  • a hindrance to cultivation
  • measured by eye in the field
  • by separation and weighing in the lab
soil ph
Soil pH
  • Tested with a calibrated pH meter.
  • Soil solutions are well buffered – do you remember what this term means?
  • By using a standard, valid comparisons between soils can be made (absolute values are difficult to interpret)
soil ph1
Soil pH
  • Measurements can be made in the surface layer of a moist soil provided sufficient water is present to make liquid contact between the electrodes.
  • Under some circumstances where buffering capacity is not adequate, soils maybe suspended in 0.1M KCl for pH determination
  • There are many ways by which the pH of a soil can be measured – refer to handbook
calcium carbonate content field method
Calcium Carbonate Content - Field Method
  • Field estimate of CaCO3 content is based on the reaction of soil with dilute acid giving both visible and audible effects.
  • Method is only approximate and not sensitive to differences in CaCO3 contents above 10%.
organic content
Organic content
  • determined by oxidative digestion (dichromate)
  • measured by:
    • back titration of excess dichromate
    • colorimetry of green product
nitrogen
Nitrogen
  • wet ashing with conc. sulfuric
  • formation of ammonium ions
  • converted to ammonia (NaOH)
  • steam distillation
  • collection in boric acid
  • titration with std HCl
  • known as the Kjeldahl method – standard for N
  • doesn’t pick up NO2/NO3
  • need conversion by initial reduction
phosphorus
Phosphorus
  • availability vs total a major issue for P
  • various extraction solution to assess availability, eg Olsen 0.5 NaHCO3
  • analysis by:
    • ICP
    • XRF
    • colorimetry
micronutrients
Micronutrients
  • can exist in soils in:
    • water‑soluble
    • exchangeable
    • adsorbed
    • complexed
    • secondary clay minerals
    • insoluble oxides
    • primary minerals
  • extraction with chelating DTPA and ICP analysis
sodium absorption ratio sar
Sodium absorption ratio (SAR)
  • predictor of salinity
  • measure Ca, Mg & Na in mmole/L
  • use eqn or nomogram
exercise 8 4
Exercise 8.4
  • A soil is tested for leachable Na, Ca and Mg, and the results are (in mmole/L: 15, 3 and 2 respectively. What is the SAR?
cation exchange capacity cec
Cation exchange capacity (CEC)
  • relies in the removal of ions with a concentrated solution of an ionic substance intended to drive off the adsorbed ions
  • techniques used to analyse the released ions include:
    • titration with EDTA – Ca & Mg
    • flame AAS – Na, K
    • ICP emission - all
    • Kjeldahl N analysis – all adsorbed ions are replaced by NH4, which are then released by excess K; the ammonium is then analysed
  • some methods use approximations and correction factors to achieve quick result
ph buffering capacity
pH buffering capacity
  • adding known amounts of acid (as HCl) or alkali (as NaOH or lime) to soils
  • allowing a equilibrium period before measurement of pH
  • graph of amount added (per kg of soil) vs pH plotted
  • buffer capacity is the slope of the graph
  • quoted as an amount of acid or alkali (typically millimoles H+ or g CaCO3) per kg of soil per pH unit.
pesticides
Pesticides
  • residues left in soils from pesticides or their by-products
  • analysed by GC-MS for sensitivity and ease of identification