Why Soil Test?
Soil tests enable small area farmers to understand the health of their soils and to plan fertiliser and soil conditioning (lime, gypsum, dolomite) strategies. If you plan to make a living from the land, the soil will be your most valuable asset.
Before purchasing farming land, always request soil tests from the current owner, as this will provide clarity on any underlying soil health problems together with an insight into the farms nutrient bank. If the farm has a number of different soil types, (sand, loam, clay) ideally a soil test should be provided for each. If a farm has already been purchased and has a limited history of soil testing, as the new owner, make it your aim to regularly undertake soil testing. For farms that remove large amounts of nutrients by producing hay, grain or silage, soil tests should be conducted annually. For farms conducting grazing enterprises, soil tests should be conducted every 2-3 years. Soil testing is only part of the process with accurate record keeping just as important in both soil health and fertiliser strategy monitoring.
 
Soil contains physical, biological and chemical properties; each should be examined individually to understand overall soil health. A standard soil test gives an insight largely into the chemical properties of the soil, however, it also provides information on the physical (soil type) and biological (carbon %) properties. A soil test should be used in conjunction with specific crop and pasture requirements to ensure money is well spent and not wasted on unwanted nutrients, click here to view the article Balancing Soil Nutrients on Small Farms.

Collecting Accurate Soil Samples

A soil test is only as accurate as the physical soil samples that are collected. Incorrect sampling techniques, at the wrong time of year, with a low number of samples will result in an inaccurate test result and a poor reflection of the true fertility of the soil. The soil testing process involves a number of steps including:

1. Collection of samples;
2. testing and interpretation; and
3. record keeping and monitoring.

When to Collect Samples

The best time to collect soil samples is immediately prior to growing a crop or pasture. If a winter crop is to be sown like oats, soil samples should be collected in the months leading up to sowing. Generally these samples are collected from January to March, allowing at least 2 working weeks for the samples to be tested and returned from the laboratory. Where the aim is to establish a pasture, ideally soil samples should be collected up to 2 years before the pasture is to be sown, allowing time for soil deficiencies to be corrected. Collecting soil samples at a similar time each year will increase the uniformity of results collected from year to year and improve the overall picture of soil health. If you are unsure of the best time to collect soil samples in your area, consult with a local agronomist or government representative.
 

Where to Collect Samples

Soil samples should be collected to provide representative examples of individual paddocks. Where different soil types (sand, clay, loam) exist in the one paddock, they should be sampled and tested separately as their inherent properties (nutrient levels, pH, water holding capacity) will be vastly different and mixing them together will result in an inaccurate test.

Care should be taken when collecting soil samples to avoid stock camps, fertiliser dumps, burnt areas, headlands or any other areas that may cause a variation in soil results.

How to Collect Soil Samples

In most cases (except for horticulture) soil samples should be taken from a depth of 0-10cm using a soil sampling tube (see figure 1) or soil auger.

Figure 1: Soil probe, an essential tool in collecting accurate soil samples.

This equipment can usually be obtained from your local government agricultural department or rural merchandise store. The top 10cm (top soil) contains the majority of nutrients and inherent soil properties and is usually sufficient for an accurate soil test. Deep (10-50cm) soil samples can be taken where soil nitrogen or pH is required. The sub-soil has less variation than the topsoil; hence less (up to six) soil samples are usually required per paddock or soil type. Deep soil samples are carried out using a hydraulic soil auger mounted to the rear of a utility. These tests need to be carried out by a qualified local agronomist.

Summary

Collecting soil samples and receiving accurate soil test results and recommendations is essential to the success of any farming business, especially those trying to make money. Accurate soil testing enables small area farmers to better understand soil health and monitor the progress of fertiliser and soil conditioning programs. Most importantly, healthy well balanced soil is likely to produce high yielding crops and pastures which in-turn will result in healthy, productive livestock.

Where to From Here?

Read Fertiliser Essentials – a new Australian book covering the basics of fertiliser use for healthy soils and profitable agriculture. Click on the image below to order your copy.

Glossary

Soil test: The analysis of soil to determine its chemical, physical and biological properties.

Soil conditioning: The addition of material to the soil to improve soil health (pH, structure) and increase plant growth.

Headland: Areas, often corners of the paddock which, that overlap when sown, hence receive double fertiliser and seed.