More than two-thirds of the nitrogen and one–third of the phosphorus load in the Swan Estuary come from the Avon and Mortlock catchments. The Healthy Soils, Healthy Rivers project is aimed at reducing the nutrient load in the Swan Estuary via the Avon River. Round 4 of the project is underway with twenty farmers participating by providing paddock history data and rates of nutrients applied to their trial paddocks.

As part of the NUE R4 project, participating properties had two soil samples collected during the growing season for comprehensive micro-biology analysis. The results appear quite interesting with most observed levels of soil micro-biology significantly lower than those recommended by Microbelabs as a guide to healthy microbial levels. 

Microorganisms, bacteria and fungi make up 75-90% of the living biomass in soil and are the primary decomposers of organic matter. They transform organic molecules into mineral nutrients that are then available for plant uptake. Two standout results from the test included nutrient accessibility and Mycorrhizal fungi (VAM).  These are linked  because Mycorrhizal fungi assists plants to capture and uptake nutrients through increasing and protecting root systems.

Levels of both of these categories were very low in the majority of samples taken with nutrient accessibility averaging 21% compared to the recommended level of 70% and Mycorrhizal fungi averaging 2.16mg/kg compared to the recommended level of 10mg/kg. These results suggest that plants are not able to utilise all of the nutrients present in these soils.

Higher levels of Mycorrhizal fungi should result in significantly increased capacity of plants to use existing nutrients.  This would reduce the amount of fertiliser required to grow a crop and therefore increase overall profitability.
To encourage increases in Mycorrhizal fungi and other microbes there needs to be:

• minimal physical disturbance (minimal or no tillage) to the soil,
• constant ground cover either living or mulch,
• increased soil organic matter,
• rotated crops or mixed species plantings, and
• reduced chemical and inorganic fertiliser use and increased use of organic fertilisers.         

The Healthy Soils, Healthy Rivers Project is funded by the Department of Biodiversity Conservation and Attractions – Rivers and Estuarine Division and the National Landcare Program.