Soil Sampling Quick Guide

To ensure that you get the most applicable information out of your soil test, it is important to collect the sample correctly.  The following section will outline the procedure for the collection of an indicative sample from a given area, and ways to eliminate sample contamination. 

To collect a soil sample from a block, take a minimum of 15 sub-samples randomly across the block, (For Precision Ag, and variable rate, please contact us on 07 4132 5000) so that all areas of the block are included in the bulk sample.  The sampling depth is usually 10-15cm (4-6”).  The sampling tool must be made of either stainless steel or plastic.  Always ensure that the instrument used has not been contaminated with any chemicals or fertilisers in any way.  Tools made of mild steel or galvanised steel can cause contamination of the sample and must be avoided at all costs.

Take the bulk sample (made up from all sub samples), mix thoroughly and collect a sub sample of approximately 500g from the bulk sample and place in the sealed plastic bag provided.  Send this sample with the completed Analysis Request Form (via AgPro Technology online).  Always use a clean plastic bucket to collect and mix the sample in and never use old fertiliser bags when sending the sample to the laboratory.       

1.        Contour and slope:

 Consider where there may have been any erosion or accumulation of nutrients.  If there are serious erosion patches, then it is advisable to sample those areas separately so that they can receive the extra fertiliser they may need to bring them up to balance with the remainder of the block.  If the erosion patches are small, then include a sample from these areas in the bulk sample.  The number of sub samples from each area should be in proportion to the size of the area. For example if there is a problem with erosion over approximately ¼ of the block, then ¼ of the overall sub samples should  be taken from this area. This same principle applies for any accumulation of silt or nutrients in areas down slope or in low lying areas.

2.        Fertiliser history:

The major consideration for fertiliser history is the placement of fertiliser and residues of fertiliser left at the sampling sites.  It is recommended that a period of 4-8 weeks be left after an application of fertiliser/lime etc before a test is taken.  This is to reduce the risk of sample contamination.

However, if a sample has to be taken within this period, then the previous fertiliser history needs to be noted so that it can be taken into account when making the fertiliser recommendation.

3.        Change in soil type:

If the block you are to sample has a range of soil types in it, then each soil type must be represented in the bulk sample.  The ratio of the number of sub sites per soil type must be equivalent  to the proportion of each soil type within the  block.  If there are major differences in the soil types, then it may be necessary to sample the soil types separately and treat them accordingly.

4.        Land use:

For most crops the sampling depth is 10-15cm (4-6²).  For shallow rooted crops, the sampling depth is recommended at 8-10cm (3-4²).  For some crops that are very deep rooted (trees/grapes), a separate deep sample may be required to assess any possible toxicities (Na, Cl etc) or accumulation of soil mobile elements (N, S, B etc.).

5.        Special considerations:

When selecting a sampling site, make sure that it is not where previous crop residues were burnt, or a site that may have received extra fertiliser or water etc.  If there is organic matter on the surface it should be removed until you have clean soil from which to sample.

Sending your soil test ?

            The soil sample should be placed in a clean plastic bag with the air removed and mailed to the following address.  It is best not to let the sample get exposed to extreme heat as this may alter some of the readings.  Select a courier that will guarantee prompt delivery with the minimum of cost.  The laboratory will process all soil samples that arrive before 5pm Friday or 5pm Tuesday.  Any samples received after this time will  not be processed until the following run.  Because of the time required to complete a soil test, there are only two batch’s of soil tests per week.