Soil testing for pastures
Soil nutrient supply is a critical factor that influences pasture productivity therefore soil testing is a useful tool to help understand what can be done to improve the growth and quality of pastures. This short article summarises the key points when planning a soil test and collecting samples. It is recommended the soil tests be analysed by a NATA accredited laboratory and the interpretation and recommendations be conducted by a FertCare accredited professional. Soil testing laboratories provide sampling guidelines which should be consulted before taking and submitting samples.
Why do a soil test
Soil testing can be used to diagnose pasture productivity issues and is useful when monitoring the ongoing progress of any development or remedial activities. Together with land type mapping, soil testing can also provide valuable information to determine whether a paddock is suitable for pasture development and can help inform how activities like cultivation, fertilising and planting should be done.
What to test for
If soil testing has not been conducted in the past its highly recommended to undertake a comprehensive analysis where multiple parameters are measured, and soil is collected at multiple depths down the soil profile. A comprehensive laboratory soil analysis will cost approximately $150 per sample (one sample per depth, per sampling area) and will include the following:
- Soil colour and texture
- Macro and micro-nutrients
- pH, salt, cation exchange capacity
- Organic carbon, soil organic matter.
When to collect soil samples
Soil testing is best conducted with enough time to plan and undertake the activity, for example purchasing and applying fertiliser. If the aim is to establish a new pasture, soil samples can be collected once the original pasture has been cultivated (or sprayed) and the fallow has already begun. If the aim is to determine whether an existing pasture should be fertilised, soil samples can be collected any time. When timing sample collection, consider paddock accessibility and ease of coring – very wet or very dry conditions can cause difficulties obtaining samples which could compromise results. Do not sample within three months of adding fertiliser or soil amendments.
Who can collect samples
Soil samples can be collected by anyone, including producers, however it is important to follow specific sampling protocols and handle the samples correctly. It is recommended that producers engage the services of a local agronomist (independent or with a reseller) with soil sampling equipment so that samples can be collected at the correct depth and from suitable locations across the paddock(s). The aim is to obtain multiple samples that represent the paddock or the area of interest. An agronomist can also package and submit samples to the laboratory and provide interpretation if required.
Where and how to take soil samples
Soil samples should be taken in each soil type in a paddock. Indicators of soil type changes are colour and texture, vegetation, and the productivity of the current pasture. Take samples in areas that are representative of the whole soil type and avoid areas such as fence lines or cattle camps. In each soil type, take 15 – 30 cores to pool together. Each core should be broken up into 3 depths:
- 0-10cm (top),
- 10cm – depth of colour and/or texture change,
- Remainder of the core depth, preferably to about 1m.
When a soil core is pushed out of the casing, colour and/or texture changes down the soil profile can be visible. Pick an average spot where this changes and use this as the cut off for the second and third depths. If there is no obvious colour or texture change down the soil profile, then cut between depths 2 and 3 at about 50cm. In a bucket, combine all core segments for each depth of each soil type so one representative sub sample can be taken for that depth. Record GPS points where soil cores are taken and make a note of which cores were combined together to produce the sub sample for one soil type.
A 500g sub sample is needed to send to the laboratory for analysis.
Handling and submitting soil samples
Soil testing laboratories have guidelines on how to store and send soil samples for analysis. Soil can be stored in a fridge (approx. 4ᵒC) for a few days if samples are not immediately sent for analysis. If there is access to industrial drying ovens, these can be used to dry the soil at 40ᵒC before submission. Or samples can be air-dried in a cool dry environment. Ensure all laboratory submission forms are fully completed and sent with the samples.
Soil test results
Most soil testing laboratories, or agronomists submitting the samples, offer fertiliser or soil amendment recommendations as part of the service. Sometimes an extra fee will be charged. These recommendations rely on sufficient background information about the paddock which is why completing the submission forms (mentioned above) with paddock production and history is extremely important. If an agronomist hasn’t been engaged in the soil testing process, producers can contact DAF for assistance in interpreting soil test results.
Further information
FertCare has written a great guide on soil sampling. Read it here.
For more information, contact the Queensland Pasture Resilience Program team or call your local extension officer on 13 25 23.
The Queensland Pasture Resilience Program is a partnership between the Department of Agriculture and Fisheries, Meat & Livestock Australia and the Australian Government through the MLA Donor Company. The five-year program aims to help Queensland producers tackle the three big threats to beef production: land condition decline, pasture rundown and pasture dieback.