How to sample soils used for flower, fruit, grape and vegetable production
Note Number: AG0376
Published: May 1998
Updated: May 2009
The usefulness of soil analysis depends on representative samples being supplied to the laboratories. Even in small areas and apparently uniform paddocks, soil properties can vary. The standard sampling procedures outlined below are designed to minimise the effects of soil variation and help you collect a representative sample.
Soils are generally sampled by driving a sampling tube into the soil, usually to 150 mm depth, and extracting a soil core. To obtain a representative sample, soil cores are combined from a large number of places within the sample area. The more cores that are combined, the more representative the final sample will be and the better the advice that can be given.
Where a coring device is not available the soil can be sampled using a spade. Simply dig a hole with a vertical side and cut out a column of soil to the required depth. Ensure that the column is uniform all the way up and that the same amount of soil is taken from each hole. Combine these columns in the same way as the cores would be combined to make your sample.
Depth of sampling
In sampling soils it is important that the standard sampling depths are used. In orchards cores are taken from 0-300 mm depth, but in crops such as vegetables and cut flowers the surface 150 mm of soil is generally sampled. Shallower sampling will often result in higher values for chemical tests because the amount of nutrients is usually greater near the soil surface.
Sampling areas prior to planting a new crop
When sampling soil proposed for use in establishing a new crop it is recommended to sample at a time when the seedbed is as close to final preparation for planting as practical; allowing time for soil analysis and reporting and the ordering and delivery of fertiliser.
Selecting areas for sampling
Soils are tested for many reasons and there is no single rule for determining which areas should be sampled. When seeking a total farm fertiliser program it is often best to sample every block on your property, but this can be both time consuming and costly. A good alternative is to select blocks or sections of blocks that represent the major range of conditions present, for example, high - low fertiliser sites, flats - slopes, black - red soil, sandy - clay soil, granite - basalt, or areas with different cropping histories or fruit varieties. In subsequent years different areas can be sampled and the results combined to provide a profile of the entire property.
An alternative strategy is to sample a set portion of a farm annually, for example, 30%. As blocks are re-sampled the effects of land management on soil fertility can be assessed.
Sometimes soil testing is used to investigate specific problems. In these cases it is often helpful to contrast the situation by taking a sample from a non-problem area as well, for example good and poor sections of a block.
Soil sampling from under established woody perennial crops such as grape vines and citrus trees should only be performed when a specific problem requires investigation. In such circumstances it is best to consult an agronomist to determine whether additional tests such as Plant Tissue Analyses are required for a correct diagnosis. To determine the fertiliser requirements of these established crops, Plant Tissue Analyses are often more helpful than soil tests.
General sampling guidelines
- Take cores from at least 30 sites evenly distributed over the block or section of a block. A grid pattern should be used to determine the site locations (see Figure 1).
|Figure 1: Recommended sampling sites - regular shaped blocks||Figure 2: Recommended sampling sites - irregular shaped sections|
- Cores should be taken from spots of average growth or poorer spots if they predominate. Remember that you are trying to get an "average" sample that is representative of the entire area. Fertiliser takes a little while to be incorporated into soil so it is also best not to sample soils which have been fertilised or limed within the past six weeks.
- For most horticultural crops cores should be taken from 0-150 mm (0-6 in) and 150-300 mm (6-12 in) depths separately and later combined into one sample. For row crops such as vegetables and cut flowers, cores should be taken from 0-150 mm (0-6 in) only. Remove each core carefully from the sampler using a clean screw driver or similar tool and place it in a clean plastic sample bag or other suitable container. If only part of the core comes out with the sampler discard that core and re-sample the site.
- At least 30 cores should be taken from the area being sampled and placed in a clean bag or other suitable container. The more cores that are taken the more representative the sample will be.
- If you have more than the amount of sample required by the laboratory it will be necessary to sub-sample. Place the sample in a clean container, break up the clods and spread the total sample evenly on a clean bench. Divide the sample into four quarters, discard the two diagonal quarters and place the remaining sample in a clean container.
- Transfer the cores or sub-sample into a clean sample bag if you have not already done so and seal the bag. Mark the bag with the block or section name, the number of cores taken and the depth of the sample.
Your samples are now ready for dispatch to the laboratory. Be sure to provide all the information requested by the laboratory processing your samples to ensure that the best possible recommendations can be made.
Modifications to the general guidelines
Sampling cultivated soil
When sampling cultivated land or new crops the soil may be "fluffed-up". Ensure that you get cores that are a full 150 mm (6 in) depth by firming the soil with your foot prior to sampling.
Sampling soil under crop
For woody perennial crops such as fruit trees, vines or proteas it is recommended that samples be taken at
0-150 mm (0-6 in) and 150-300 mm (6-12 in) depths and the samples analysed separately. Cores from woody perennial crops should be taken from areas where the fertiliser has been evenly spread and not from where it has been concentrated. Avoid sampling directly into fertiliser where it has been banded.
It is recommended that when sampling these areas cores are taken from within the plant row and about one third of the distance between adjacent trunks (see Figure 3).
For row crops such as vegetables and cut flowers soil samples should be taken from the 0-l50 mm (0-6 in) depth. Take cores approximately 75 mm (3 in) either side of drill or planter rows but avoid sampling directly into fertiliser where fertiliser has been banded (see Figure 4).
For cover crops soil samples should be taken from the 0-100 mm (0-4 in) depth using the procedure recommended for field crops. See Agriculture Note (AG0375); Sampling Soils Used for Growing Pastures, Field and Fodder Crops.
|Figure 3: Recommended sampling sites for established crops - orchard/vineyard crops||Figure 4: Recommended sampling sites for established crops - row crops|
Figure 5. Recommended subsoil sampling depths - showing a marked change in colour or texture and soils showing a gradual change in colour or texture
Sub-surface soil sampling
Sampling of the sub-surface soil may be required where:
- soil structural problems may exist;
- deep rooted plants are not growing well; or
- salt is suspected of being a problem.
It is recommended that at least two subsoil depths are always sampled. Examples of the depths to sample are presented in Figure 5. Each composite sample should consist of soil cores from at least 15 sites evenly distributed across the paddock. Where the depth to the clay layer in a soil varies, sample to the top of the clay layer and then sample the clay layer as a separate sample. When collecting subsoil samples be careful not to contaminate them with scrapings from other soil layers. Because the chemical properties of soils vary dramatically with depth, even minor contamination of subsoil samples can make the interpretation of chemical results very difficult.
It is recommended that soils are sent to a certified laboratory for analysis. A list of certified laboratories is available from the Australasian Soil and Plant Analysis Council (ASPAC).
Contact us for more information on soil analyses and sampling.
This agnote was developed by David Nash, May 1998.
It was reviewed by David Nash, May 2009
Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
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