HDLN Soil & Water Dairy Action Program - Soil Assessment Component June 2008

Introduction Sustainable use of the soil resource underpins the dairy industry in south-west Victoria. Good physical, chemical and biological health of the soil is essential to reaching and maintaining the productivity required for profitable, pasture-based dairy farming. It is also essential that management of the soil ensures that farms have minimal impact on the environment—both on-farm and in the wider catchment. In this research project, we aimed to benchmark the soil health on dairy farms in the Curdies River catchment, through measurement of selected soil physical and chemical properties, and visual assessment of soil structure and biota in the field. These measurements and assessments were undertaken at sampling locations across a range of soils between 2005 and 2007. On each of 24 properties, 2–3 sites within each of 3 paddocks were sampled (0–10 cm). In all, soil chemical analyses were undertaken for 157 samples, soil physical analyses on 561 samples and 87 sites were visually assessed by 2 observers using 2 visual assessment tools.

Summary of findings

The main findings from this soil health benchmarking project include:

• The soil physical conditions in the Heytesbury area during the monitoring period (2005–2007) were generally good, with little evidence of pugging.
• Pastures on soils with low pH and high aluminium levels could profitably respond to application of lime.
• Levels of soil phosphorus were high to very high (>25 mg/kg) at most monitoring sites. These levels are higher than the economic optimum for pastures and are potentially detrimental to the local environment. Farmers could reduce, or temporarily cease, their phosphorus applications and still maintain high pasture productivity, while saving costs.
• Where soil potassium levels are high, potassium inputs can be reduced or deleted from the fertiliser regime. High potassium levels are potentially a concern for farmers, as they are implicated in the occurrence of grass tetany (hypomagnesemia) in near-calving and lactating cows.
• Soil chemical testing was able to identify potential soil health risks which were not detected by visual assessments. In particular, the production and use of whole farm nutrient maps, as supported by the Heytesbury District Landcare Network, would assist farmers to identify and manage soil health issues on their property.

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