1. Common Soil Parameters What are the common parameters of soil that we could test?

2. The 3 soil attributes  Physical attributes Texture, structure, etc  Biological attributes Organic content  Chemical attributes pH, conductivity, cations, anions etc

3. Physical Properties

4. 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.

5. 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

6. 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

8. 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.

9. 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.

10. Class Exercise 1 Finger assessment of soil texture for mineral soils

11. Soil Structure  Described as weak, moderate, or strong depending on how distinct the peds? are.peds  Fine, medium, or coarse depending on the size of the peds.  Shape of the peds - platy, granular, blocky, columnar, or prismatic,

12. 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 = 6000d 2 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)

13. Example 8.1  Calculate how far a 0.05 mm diameter particle would travel in one minute.  v = 6000 x 0.05 2  = 15 cm/min  in 1 minute, particles of this size would have travelled 15 cm

14. 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

15. 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

16. Exercise 8.3 answers a)40 x 2.04 g = 81.6 g b)40 x 0.40 g = 16 g c)81.6-16 = 65.6 g d)Silt 66.8%, clay 16.3%, sand 16.9% e)silt loam

17. 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

18. 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 +, Mg 2+ and Ca 2+, Cl -, SO 4 2- and HCO 3 - ).  Soluble fertiliser may also contribute K +, NH 4 + and NO 3 -.  High EC is undesirable for most plants.

19. 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

20. 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)

21. 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

22. Calcium Carbonate Content - Field Method  Field estimate of CaCO 3 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 CaCO 3 contents above 10%.

23. Biological Attributes

24. Organic content  determined by oxidative digestion (dichromate)  measured by: back titration of excess dichromate colorimetry of green product

25. Chemical Attributes

26. 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

27. 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

28. 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

29. Sodium absorption ratio (SAR)  predictor of salinity  measure Ca, Mg & Na in mmole/L  use eqn or nomogram

30. 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?

31. 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

32. 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.

33. Pesticides  residues left in soils from pesticides or their by-products  analysed by GC-MS for sensitivity and ease of identification