Soil sodicity - Soil Essentials: Managing Your Farm's Primary Asset - page 64

What are the symptoms of sodicity?
Symptoms that are typical of a sodicity problem include poor infiltration and
drainage, resulting in waterlogging, increased water runoff and poor water storage;
surface crusting; poor emergence of crops and pastures; and problems with
cultivation and erosion. These symptoms might not always be due to sodicity. They
may also occur on nonsodic soils caused by, for example, cultivation or
compaction, or when exchangeable calcium is low and exchangeable magnesium is
high. Soil tests for sodicity will usually identify the causes.

How to manage sodicity problems?
Sodicity problems can be corrected by the application of calcium salts, normally in
the form of gypsum. In acidic-sodic soils, lime may be applied either alone or in
combination with gypsum. The sodium displaced from the clay particles by
calcium comes back into the soil solution and is likely to move deeper in the soil by
leaching. Once this is achieved, it is a matter of (1) maintaining salt (preferably Ca
salts) concentration in soil solution to a level that will prevent the clay from swelling
and dispersion, and (2) minimising sodium inputs to soil to prevent further
problems. Figure 23 shows how a sodic soil is transformed into a nonsodic soil.

What are the sodium inputs to soil?
Most of the Australian landmass has been under the sea at least once. Following
geological movement the sea f loor has become dry land. Because of this, a great
deal of sea salt is present in Australian soils. Most of this salt has leached down the
soil profile until it reaches a point where there is insufficient soil moisture to leach
it further.

Ca Ca Ca Ca Ca Ca

Calcium (Ca) is
applied either as
gypsum or lime.

Calcium
displaces the
sodium resulting
in better soil
structure.

Na Na Na Ca Ca Ca Ca

Na Na Na Ca Ca Ca

Na Na Na Na

Sodium slowly
moves down
below the root
zone.

Na Na Na

SODIC SOIL RECLAIMED SOIL

Figure 23 Effect of adding a calcium fertiliser to a sodic soil. ( Soil Sense C-12)