In-Field Soil Sampling Summary

The instructions below instructions are a very brief snapshot to encourage samples to be taken with the best chance of representing the paddock avoiding contamination.

  • A comprehensive guide to “fit for purpose” soil sampling can be found at the Fertcare website.
  • An infographic outlining the key things to know about soil sampling can also be found here.

Sampling practice is the single most important component to getting value from soil testing, and should be taken very seriously. Accurate analysis, interpretation and precise nutrient management can only occur with a quality representative sample.

Choosing where to sample

  • Avoid unusual areas, stock camps, fertilizer dump sites, dam sites, gates, troughs, trees, fence lines (old and new), old burn heaps, sheds and roadways.
  • Sample varying topography (Hills and flats) separately.
  • Avoid poorly drained areas and wet conditions.
  • Avoid headlands.
  • Ensure different fertilizer and rotation histories are sampled separately.
  • Avoid dung and urine patches in pastures.
  • Sample high and low yielding areas separately.
  • Sampling paddocks that have had ameliorants (lime) or fertilizer applied in the past 2-3 months is likely to skew results.

Taking the sample

1. Review your required tests. If guidance is required consult your local advisor/agronomist.

2. Determine an appropriate sampling plan.

3. Ensuring a representative sample is obtained.

   a) Avoid unusual areas listed above.

   b) Ensure all your equipment is clean.

4. Remove debris and plant material from the soil surface.

5. Take the required number of cores, aim for at least 25 cores per site, in an appropriate pattern (see below).

6. As a general rule, 8-10 inch rows and 1-inch corer, 1 in every 8 cores should be taken on a recent seeding row furrow and the remainder between the seeding rows.

7. Pool your cores in a clean plastic bucket, breaking the soil into small crumbs.

8. Mix the sample thoroughly in the bucket.

9. Place your representative sample into soil test bags and fill to the required line.

10. Ensure your equipment and bucket is clean before moving onto your next sample.

11. Shovels are not ideal, but if using a shovel ensure the sample is consistent down to the required depth (e.g. take a slice down the side not a V shaped “hole” sample).

12. If excess sample is collected ensure the sample is well mixed before sub-sampling into the bag, try to reduce the sample to around 250-300 grams to avoid excessive postage charges.

Different sampling patterns

a) Transect

b) Zig-zag

c) Cluster

d) Uniform grid

e) Random

Nutrient
Symbol
Units Used
Adequate Range Expected
Comments
Phosphorus

P

ppm (mg/kg)

15 - 45

Dependent on crop/pasture type and soil type.
Potassium

K

ppm (mg/kg)

40 - 120

Lupins and Canola are less sensitive to K deficiency. Clover and Medic require higher soil levels.
Sulphur

S

ppm (mg/kg)

5 - 15

Dependent on soil type.
Nitrate

NO3

ppm (mg/kg)

up to 30

Very mobile in the soil. May be lost to leaching.
Ammonium

NH4

ppm (mg/kg)

up to 20

Stable in the soil as it is a cation, but converts to Nitrate readily.

Copper

Cu

ppm (mg/kg)

> 0.3

Soil tests for Copper are a guide only.
Zinc

Zn

ppm (mg/kg)

0.12-0.5

Dependent on soil pH. The more alkaline the soil (higher pH) the higher the soil Zinc level needs to be.
Organic Carbon

O.C.

%

1.0 - 3.0

Dependent on soil type and rainfall.
Electrical Conductivity

EC (1:5)

dS/m

< 0.25

A measure of 'salinity'. Highly dependent on soil type with heavier soils having some buffering capability, but generally EC (1:5) values <0.2 are non-saline and >0.7 is of concern and possibly accumulating salt.

A variable conversion factor can be applied so values will fit one scale across all soil types. This is called 'estimated EC' or ECe. In this case ECe threshold of >8 represents highly saline soil.
pH

(CaCl2)

>5.0

Economic responses to applying lime to increase pH above 5.0 are doubtful. If subsoil pH is low, it may be necessary to increase topsoil pH >5.5 (CaCl2)
Aluminium

Al

ppm (mg/kg)

<5.0

As pH declines (becomes more acidic) aluminium can increase in soil solution. Aluminium is toxic to roots. When roots don't grow, plants cannot explore the soil to access nutrients and soil moisture. Levels above 5 mg/kg strongly impact wheat. Other crops such as barley are more sensitive (Read the article on soil pH here)

PBI

PBI (Phosphorus Buffering Index) is a function of soil type. Generally where soil particles contain more iron, aluminium and calcium such as forest gravels, plus some soils with considerable clay and organic matter, the PBI will be higher and decrease plant-available P  (See article)

Nutrient
Symbol
Units Used
Nitrogen
N
%
Phosphorus
P
%
Potassium
K
%
Sulphur
S
%
Calcium
Ca
%
Magnesium
Mg
%
Copper
Cu
ppm
Zinc
Zn
ppm
Manganese
Mn
ppm
Boron
B
ppm
Sodium
Na
ppm
Iron
Fe
ppm
Nitrate
NO3
ppm
Chloride
Cl
%
Options
Molybdenum
Mo
ppm