Gippsland - How Now Gippy Cow
October 2010 Edition
Soil testing puts you in control of fertiliser use
Soil tests and in-paddock observations are essential in assisting to make informed fertiliser decisions. Before applying any fertiliser it is necessary to assess which nutrient and how much of each needs to be applied to correct deficiencies or to balance what has been removed.
Soil testing can help to identify areas on the farm where nutrients are accumulating and therefore fertiliser applications can be adjusted to apply the rate that is needed. For example, effluent application areas, night paddocks, and calving paddocks tend to accumulate more nutrients than other parts of the farm. Undertaking a soil test will help to confirm this trend and then fertiliser rates can be adjusted accordingly.
Excessive application rates of nutrients (nitrogen or phosphorus in particular) not only waste money but can have a major impact on the environment. Algal blooms in water storages and high nitrate levels in ground water are two indicators of inappropriate fertiliser use.
Soil testing can take place at any time of year. However because soil nutrient levels vary throughout the year, it should be completed at the same time each year to be comparable.
Late winter to early spring is a good time to soil sample as soils are relatively consistent in temperature and soil moisture levels. Soil testing in summer can be difficult to collect a full 10cm core as the ground can be hard and it might be difficult to distinguish urine patches.
Paddocks should not be tested for at least six to eight weeks after fertiliser applications and three months after lime applications.
The first step when soil testing is determining which areas of the farm should be tested. Soil testing every paddock on the farm is ideal, however it can be costly depending on the number of paddocks you have. Another approach is to group paddocks into ‘management areas’ and taking representative samples from them.
Management areas are paddocks that have similar soil type, fertiliser history and management practices (day paddocks, night paddocks, effluent application paddocks or hay/ silage paddocks).
From these determined management areas, a monitor paddock can be chosen as a representative and, with regular sampling (every two to three years) over the same transect line, an overview of the nutrient levels and what they are doing can be achieved. Soils can vary greatly within a paddock, so a known/marked transect line helps to reduce the variation in results.
Once the areas to be tested have been determined it is time to conduct the tests. It is recommended a proper soil corer is used, ensuring you sample to the correct depth to get the most accurate results.
A minimum of 30 cores should be taken from the paddock, or area chosen, along a transect line, avoiding any gateways, urine and dung patches, stock camps, water troughs, feed out areas and trees.
After sampling, it is essential to place each soil sample into separate, clearly labelled bags and send them off to an accredited soil-testing laboratory. It’s important to note that laboratories might use different report results and/or analyses for many nutrients. Therefore, if comparing results from different laboratories, make sure the test and units of measure are the same, i.e. compare apples with apples, Olsen P with Olsen P. Even laboratories using the same tests will vary slightly so, if you are happy with the laboratory you are using, stick with it.
Accredited soil testing labs can be found at:
http://www.aspac-australasia.com
http://www.nata.asn.au
If you would like some information more please contact the Gippsland Dairy Extension team at
DPI Ellinbank on 5624 2222 or DPI Maffra on 5147 0800.
