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 patters

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(salt)
dS/m
Levels <0.2 are="" generally="" considered="" negligible.="" levels="">0.8 can be said to be accumulating salt, and should be investigated further.</0.2>
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
(CaCl2)
5.0

As pH declines (becomes more acidic) Aluminium levels can increase in some soil types. High Aluminium levels will affect root growth reducing their ability to explore large volumes of soil and therefore their access to nutrients and soil moisture. (Read the article on soil pH here)

PBI

PBI is a function of soil type. Generally as a soil contains more iron, clay and organic matter, the higher the PBI. (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