sampling tips

Soil Sampling Instructions     

Here we explain how, when and where to extract soil samples, as well as discussing the importance of adequate preparation, and a small list of tips to remember

Download Submission Forms

Soil submission form (pdf)

Herbage/Leaf submission form (pdf)

Viticulture Soil submission form (pdf)

The Importance of Planning

The following describes some of the basics of soil sampling. Sampling variation causes the biggest variance in soil test results. Even within short distances soil fertility can change drastically. It is very important to make sure that soil sampling variation is minimised.

With proper sampling techniques, the sample variation can be restricted to approx. 15%. In other words if the test found an Olsen P level of 20 it is likely the true levels lies within a range of plus or minus 15% (17-23) if sampled properly. If sampling has not been carried out a larger variation can be expected.

Small differences between one years test and the next do not automatically mean fertility has gone up or down.

Unexpected results may be due to sampling error, if you have not followed strict sampling protocol. It is best to avoid this confusion as much as is possible by following the sampling protocol.

It pays to sit down with your consultant or fertiliser rep to discuss the available options. If you are both serious about soil testing, it will take time to establish the what the best approach is. Both the consultant and the farmer are in there for the long run.

Choose an approach that is going to serve you not only this year, but also in years to come when retesting. This means selecting areas to be tested carefully, and determine exactly which parts are going to be sampled and how.

Generally it is best to sample along predetermined and documented transects or lines which can be found the next time a retest is required.

Where to Sample

When sampling a farm, first establish how many different soil types occur on the farms. It is generally not good practice to do one overall or composite test incorporating significantly different soil types. For instance one soil type may be naturally high in potassium, another naturally low. The composite test result will probably show an adequate potassium level. The result: no potassium will be recommended on the areas where it is needed. On the high potassium area some of the other elements may need to be lifted to maintain a good ratio between the elements (e.g. salt may be required for animal health reasons to counteract high potassium levels). Take one test per soil type.

Obviously your budget and economics play a role also. Also important is the past history e.g. has any area been cropped, been used regularly for hay/silage, any areas getting flooded frequently and so on. All these factors will have to be taken in account when deciding how many samples to take, and where to sample. Select three typical paddocks within each block (Block comprises an area with similar characteristics including use, topography, soil type etc.)

How to Sample

As mentioned before, significant differences exist between soil types, but they also exist within one field. Areas of dung patches, urine patches, camp areas etc. can show considerably different nutrient levels on a micro scale. To "even out" any irregularities, a number of plugs (generally at least 15 but preferably 20 or more) are taken to provide a statistically reliable "average soil sample".

It is important to document exactly which area was sampled, when retesting in the future, the same areas can then be sampled. In moist cases the best approach is to walk a number of transects and take samples every 10, 15 or 30 m whatever is the most practical depending on the length of the transect. In most situations use one transect for each of the three paddocks in each block tested.

The transect can be recorded by using markers on fences or using permanent pegs. Please be aware that pegs tend to attract stock so don't sample close to the peg. Special spring loaded fiberglass pegs are available for this purpose, they don't injure stock and cannot be broken. One method particularly useful in hill country is to use transects of approx. 100-m length. Use a rope or tape with markers at 10-m intervals and sample at the markers. This way variability is kept to a minimum. The transects should run across slopes in hill country, and avoid gates, stock camps, tracks, hedges, water troughs, sheds and any other obvious area that may not be representative for the whole area.

The depth of sampling depends on a number of factors. Generally for pasture samples are taken at 75 mm (3 inches) and 150 mm (6 inches) for cropping/horticulture. Where new plantings are considered a subsoil test should be considered. This applies to deep rooting crops like grapevines. Subsoil tests can show potential problems with acidity or high soluble salt levels. They do not need retesting every year,

When to Sample

During excessively dry, wet, cold or hot conditions, some elements may become either less or more available (depending on the element and make-up of the soil). Obviously there is a pattern throughout the seasons. Some of the elements that tend to be more sensitive to these external influences are sulphate, phosphate, potassium, boron and molybdenum.

Seasonal effects are taken into account when the lab results are interpreted and recommendations made. However when retesting an area after one or two years, it is good practice to do it at the same time of the year, as this would make it easier for the client to compare the results without having to take into account any seasonal effects.

If practical, try to avoid taking samples under extreme conditions, or at least make a note of such conditions when sending in the samples so we can take the circumstances at the time of sampling into account.

Important Tips

• If necessary remove vegetation before sampling, but be careful not to remove topsoil.
• Use a plastic or stainless steel probe, and the bags provided. In one case a farmer used a galvanized iron pipe as an extension of this stainless steel probe, resulting in very high zinc levels. In another case the samples were stored in a used but thoroughly rinsed sheep drench container. The results were very high copper and sulphate levels.
• Do not expose the samples to direct sunlight or excess heat as some plastic bags release sulphur.
• Do not sample areas that recently have been fertilised or limed until at least 50-70 mm rain has fallen. If recently limed make a note of this please.
Record all necessary information on the soil bag label and submission form. Don't forget to record your own information regarding where the news were taken (details of transects etc.)

Special instructions should be followed when sampling cropping areas, greenhouses or orchards.

Please contact us if more details are required.

Download Submission Forms

Soil submission form (pdf)

Herbage/Leaf submission form (pdf)

Viticulture Soil submission form (pdf)

sampling tips
preparation | where to sample | how to sample | when to sample | tips | home