Sulphur in the soil - Soil Essentials: Managing Your Farm's Primary Asset - page 53

The plant available test will show how much sulphur a plant could access at the
time the sample was taken. This amount could change over time depending on the
rate of organic matter breakdown, waterlogging conditions (less available) or
warm, moist, well-aerated conditions (more available). Soils sampled as 0-60 cm
samples may give a better prediction of likely responses to sulphur applications
than topsoil sampling only.
Total sulphur is measured by x-ray f luorescence, and available sulphur by the
ICP or CPC methods and may be quoted in micrograms/gram (µg/g) or
milligrams/kilogram (µg/kg). Both of these are equivalent to parts per million
(ppm). Pivot and Agplus analyses give different results due to different testing
methods, so they need to be interpreted differently (see Table 13).

What do the tests mean?
Soil test results can be compared as shown in Table 13 where levels of plant
available sulphur for two soil tests are used to decide the sulphur status of the soil.

Table 13 Assessing sulphur test results from two laboratories

(Source: Soil Sense C-04)

Level in soil
(Blair)

Agplus analysis Pivot analysis

Available S µg/g Available S µg/g

Low <4 <6

Marginal 4-8 6-10

Moderate 9-12 11-50

High >12 >50

If sulphur levels in soil are less than 9 µg/g, then the soil would probably
benefit from the addition of sulphur fertiliser. If the soil is in a temporary state,
such as containing rotting crop residue, or is waterlogged, then the problem may
be self correcting over time when these adverse conditions disappear. Deep-rooted
crops may also be able to access sulphur from the subsoil, and so may not respond
to sulphur fertiliser.
A number of fertilisers and soil conditioners contain sulphur, as shown in
Table 14.