Soil interpretation notes 2016

Soil Interpretation Workshop 19/08/2016

Speaker: Don Cook (Farmright soil services)     Centre: MACE 1.00-4.00pm

Soils Results      Low        High      Average

pH (CaCl2)           4.3          5.4          4.7

Phosphorus        5.0          24.0        10.2


Potassium           90.0        320         180


Sulphur (KCl)      4.3          21.4        8.5

OOC                       2.03        4.50        3.07

CEC                        3.65        18.0        7.4

Ca%                       47%        82%        66%

Al%                        <1.0%    28%

Soil texture





Clay has the greatest capacity to have nutrients to cling to because of its ability to attract nutrients (positively charged particles)

Description of terms in the soil test

Sum of Cations – low CEC soil will usually leak more (low cation exchange)

If you have a white colour under the top soil, CULTIVATE WITH CAUTION. Topsoil layer needs to be protected at all times.  In fact probably best not to cultivate as likely to lead to tunnel erosion and then gully erosion.

NPKSCaMg – These are the nutrients required in a productive pasture!!

Nitrogen is often leached and so it is a point of time measurement.  Do I need to use nitrogen?  Low reserves and a low organic matter may mean that you should consider this especially if you are planning to crop.  However….. it is important to have an overall goal of your property so that you do not waste valuable money if the addition of nutrients does not lead you to the outcome that you are looking for.

Organic matter is always overlooked by the fertiliser company.

Organic matter is the OO – Oxidisable organic carbon (sometimes the manure distorts the soil sample, so important not to sample where cattle camps may be).

Covering the soil (growing grass with 100% cover) well is important in making organic carbon.  Cut and drop is as good as anything especially in the lighter soils to increase the amount of carbon that will make it into the soil.

In order to shift the speeding up of organic carbon movement from the top of the soil to the inside of the soil, you need dung beetles or other macro invertebrates.  The dung beetles need more active root zones and could be sensitive to chemical applications.

Phosphorus Olsen (who was a doctor) – is a measure of available P to the plant. It is a relatively stable test.  “Making better fertiliser decisions” is a published article on the depi website which outlines how P relates to growing good pastures and what the ideal level is.

For improved pastures you should look at least a Olsen P of 12.  However, this can be higher depending on the goal of the property.  An increased stocking rate may require more.

Native pastures may need only an Olsen P of 8 ‘s or 9’s so once again your goals are important.  Horses have quite low stocking rates and therefore it is important to maintain good ground cover.  The level of P for cover – if on native pastures then need 8’s and 9’s and 12 if on other pasture.  Horse paddocks don’t need to be high P.  High Olsen P levels for cattle require more like 15 if the DSE is higher than the recommended number for your area

If running over 12 DSE per hectare (for this area) then need a high Olsen P of 15.  We should be looking at an average of 12 Olsen P only.  Depends on intensity of your property and what you want to do with it.

Phosphorus Buffering Index is the ability of the soils to hang onto the Phosphorus.  Chemical make up of the soil helps but if not hanging on very tightly, it will have a low PBI.  7kg of Phosphorus for maintenance to raise it one unit. Low stocking rates for natives pasture is about 4kg.

Always write down the NPKS ratio on anything that you purchase and put on your property.

Sulphur – generally need to put out a little bit of sulphur on your paddocks in order to help the growth.  More about sulphur in the booklet.

Soil Structure – Need a mixture of soil particles, because it helps with the air and the water.  There are positive and negative charges (Ca/Mg ratio – need greater than 2:1) You need to add lime in high rainfall areas it is just about when and how.

Soil acidity – managing soil acidity is one of the main issues you face in high rainfall areas such as ours.   There are two different scales because there is variation in the pH of water (at a certain time of the year) and therefore the pH in water is not as reliable as the pH in CaCl.

Once the pH drops below 4.8 then Al changes form and becomes toxic to plants.

Possibly every 10 years we need to lime if you have a base to work with.  The maintenance of lime should be approx 150-200kg/ha/year.  May need to wait a couple of years before you get a full understanding of the result of your lime application as it takes time and rain to seep into the soil.  To get a shift of 4.5 – 5.0 pH then you would need to have 2.5t/ha.

GRDC (Grains Research Development Centre) – Ground Control magazine

Rock Phosphate – needs sulphur in the first year – gypsum mixed in (lowest rate that you can).  Gypsum on in the first year and then not worry about sulphur until the third year.  The second and third year that you just add the rock phosphate.  Really good option for a horse paddock.  The rock phosphate needs to be accounted for over a number of years.

The plan is to build the phosphate each year – ie. 300kg of rock phosphate over 3 years (110kg/year)

Potassium gets taken up the hill with animals.  Using Potassium sulphate could also solve the sulphur issue as well.  Potash is another option but doesn’t have the sulphur component.  20kg of Potassium