Soil issues

The Limestone Coast region is large with various land forms and features which have been shaped over millions of years. The processes that shape this region have produced different soils throughout the region each with their own inherent management strategies and susceptibilities that come with farming these soils.

Acidic soils

Approximately 24,000 ha of cleared land in the Limestone Coast have strongly acidic soil, approximately 613,000 ha of cleared land have acid soil (28%), requiring management to prevent acidity reaching critical levels. A total of 534,000 ha, or 24%, of land is moderate to highly susceptible to rapid soil acidification due to low buffering capacity.

Soil acidification is often associated with nutrient deficiencies and/or imbalances (e.g. molybdenum, calcium, magnesium and potassium) that adversely affect plant growth. Some compounds become soluble at very low pH (e.g. manganese and aluminium), and can be toxic to plants. Acidity also decreases the activity of many micro-organisms, notably nitrogen fixing rhizobia bacteria associated with legumes.

Soil fertility

Approximately 1.34 million ha (61% of total area) of land cleared for agricultural purposes in the region has low inherent fertility and are generally sandy surfaced soils. They are naturally deficient in phosphorus (P) and many have significant trace element deficiencies. Compared with natural ecosystems, agricultural systems require higher levels of nutrition and remove more nutrients. Without fertilisers in some form, to build and maintain soil nutrition, plant growth, agricultural production, water use and profitability decline, and the risk of erosion increases, particularly on susceptible soils.

Dryland salinity

Primary salinity refers to landscapes which were saline in their virgin or uncleared state. Secondary or dryland salinity is mainly a result of historical clearing of deep-rooted native vegetation and its subsequent replacement with shallow rooted annual crops and pastures. Salinity spread in the Upper South East was also accelerated by the demise of extensive Lucerne stands through aphid infestations in the late 1970s, followed by widespread flooding.

As a “one point in time” activity, the National Land and Water Resources Audit (Barnett 2000) estimated secondary salinity (moderate to very high) in the region at 250,000 ha, and primary salinity at 20,000 ha (note that changes in extent and severity will occur in response to such factors as climatic variation). Where salinity is of moderate severity in the Upper Limestone Coast, growth of traditional agricultural crops and pastures is affected, especially when exacerbated by seasonal waterlogging. With increasing salinity, the adverse impact on plant performance becomes greater.

Erosion management

The top centimetre of the soil is the most fertile. Therefore any topsoil loss is most expensive from economic and production perspectives. Wind erosion is a significant problem for the landscape features with high proportions of sandy surfaced soils. These are predominantly the Coastal Landscapes, the Dune-Flats, the Range Country, Shallow Sand over Limestone and the Sand over Clays, particularly in the drier Upper Limestone Coast, and where cultivation is prevalent.

The Deep Sands are also inherently highly susceptible to wind erosion, however, these tend to be under permanent vegetative cover, and so are rarely at risk. The more fertile loamy soils of the Mallee Soils, Range Country, Red Gum Country, Volcanics, and Wimmera Country, while generally a lower risk, can be susceptible if over-cultivated to a very fine tilth.