Linking Soil Carbon and Soil Acidification with Farm Management Practices


Year of study: 2010 to 2013

Project Manager

Westernport Catchment Landcare Network and Cardinia Environment Coalition

Partner Organisations

Tarago Catchment Sustainable Farms, DEDJTR Ellinbank, Bass Coast Landcare Network, South Gippsland Landcare Network, Port Phillip & Westernport Catchment Management Authority

Project Objectives

To link soil carbon and soil acidification with farm management practices, leading to increased knowledge of farmers and an increased uptake of sustainable farming practices.

Linking soil carbon field trip
Linking soil carbon farm


Benchmarking soil carbon levels across multiple soil types and land uses and relating this information to land management practices.

The utilisation of current soil acidification knowledge across the region, the review of management practices at a local farm scale level through training, monitoring and mapping.







109 sites have had Soil Carbon benchmarking undertaken on multiple soil types. Soil acidification was also monitored on each of these 109 sites.

140 soil tests had been taken throughout the region to measure soil acidification.

Carbon benchmarking was conducted to Australian standards.

Collected at 0-10cm, 10-20cm, 20-30cm depths and sent to EAL Norsearch for analysis. Collection was across 8 strategic soil groups, with multiple land uses and management practices situated throughout the Westernport Catchment (central, eastern & southern areas).

These soil types comprise 68% of all soils within the whole of the Westernport catchment. (calculated using data from Soil Survey I.J. Sargeant Soil Survey report No.52).

Location of carbon benchmark properties
Collecting soil


Results for total organic carbon are benchmark results only and do not reflect management over
time. These levels of soil carbon however, may over time (5 years or more), indicate the effect that the enterprise activity has had on them.

Slightly lower levels of carbon from 0-10cm occurring in cropping may indicate the disturbance of soil aggregation through ploughing and oxidation of organic matter.

Other than the horse enterprises all other enterprises had similar organic carbon levels from 0-10cm.
What perhaps is interesting is that the highest levels of organic matter are seen in the horticultural enterprises. Almost all research indicates that cultivation depletes organic matter (Hunt 1980, Burke, Yonker, Parton, Cole, Flach, and Schimel, 1989). The suggestion is that site selection on an organic carbon rich soil (Kooweerup peat soils) and/or soil mixing through cultivation may explain such results.

The lowest levels of organic matter are seen in horse enterprises. Does this reflect a lifestyle property where perhaps poorer quality land class may have been available or is it illustrative of an overgrazed poorly managed enterprise? As this is a benchmark figure for organic carbon only retesting over time would perhaps indicate a positive or negative trend in carbon levels.
Given that more than 75% of Australian farming soils have organic carbon contents less than 1.75% (CSIRO) which equates to levels of 63 tonnes per hectare the levels seen across most enterprises in Gippsland compare quite favourably.

The graph on the right, indicates that the highest levels of organic carbon were found in Ferrosols and Vertosols. This is to be expected as Ferrosols (volcanic soils) have strong crumb structure and moderate to high organic matter content. Vertosols (peat soils) also have high levels of organic matter corresponding with high carbon content.
Tenosols in Gippsland tend to occur on rolling to steeper slopes over granite geology and are less developed. They are usually strongly acid throughout with weathered parent material usually encountered above 1 metre depth. They had the lowest total levels over the 30cm with carbon declining rapidly from 10-30cm.




The graph on the right, shows that the more clay dominant soils, ie: light to medium clays and clay loams are some on the better structured soils with good aggregation allowing root penetration illustrating the accumulation and retention of organic matter over the 30cm profile. In comparison the sandy loams tend to be more compact soils with poorer structural development.  Although accumulating reasonable organic carbon in the 0-10cm profile have difficulty allowing plant root access deeper in the profile hence negating organic matter build-up. The geochemistry of sedimentary derived soils would also indicate lower pools of essential plant nutrients.







Although it is hard to reach conclusions on the relationship between total organic carbon and phosphorus from the scatter diagram on the right, research does indicate that not only is organic matter a major contributor to the phosphorus pool but it plays an important role in mobilising this phosphorus (Dalton, Russell & Seiling, 1951). Given that organic matter is an important food source for earthworms it may also be likely that earthworm populations are larger where higher levels of total organic carbon are to be found and hence may play an important role in mobilising
phosphorus from the soil pool (Mackay, Syers, Springett & Gregg, 1982).

Enterprise and total soil carbon graph
Australian soil class and total carbon
Soil type and total carbon
Total organic carbon and phosphorus levels

Overview of findings

The project has assisted individual farmers and also provided pH and soil carbon data across a range of soil types that may assist further researchers in understanding the complexity involved in sequestering soil carbon while accommodating enterprise productivity.
Although no definitive trends were observed or relationships found between carbon and the other major nutrients research does indicate that high labile carbon is active in mobilising a range of important plant nutrients (Pettit, Dalton,1952, Jensen, 1917, DE Koch,1955).

Nutrients were found to be highly variable amongst the different enterprises and this could be influenced by both the nature of the enterprise in terms of demand on nutrients but also more importantly dependant on the soil type with its historical geochemistry.

Farmers tended to manipulate pH and the major nutrients nitrogen, phosphorus, potassium and sulphur to suit their particular enterprise.

The carbon levels were fairly consistent across similar soil types.

It is reported that soils under pasture have higher organic carbon than cropped soils due to the less disturbed state of pastures and the slower decomposition of pasture roots (DPI, NSW, 2010). Perennial pastures with higher shoot to root ratio (S/R) have higher levels of organic carbon. Results from the Healthy soils carbon sampling are consistent with this research with dairy and beef properties demonstrating high levels of organic carbon across the sampled profile.

In the same way that cropped soils generally have decreased organic carbon over time, it is also evident that heavily over grazed pastures that do not allow significant root development also have decreased soil carbon levels.

Building soil carbon levels takes considerable time. Where the use of green manures, legumes and compost additions can add organic matter to horticultural and cropping soils, grazing enterprises rely on rotational strategies, the addition of root biomass through growing hay or silage and the application of organic manures like poultry litter.

The full report is also available.

Western Port Catchment Landcare Network
Tarago Catchment Sustainable Farms Logo
Bass Coast Landcare Network Logo
South Gippsland Landcare Network logo
CFoC logo


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