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Farming more sustainably by managing soil acidity

Acid soils are a major cause of land degradation, threatening the productivity of agricultural soils in North East Victoria.  

Nearly half of the five million hectares of Victorian land affected by very acidic topsoil, as  measured by a low soil pH, are found in the North East region.  

Highly acidic soils reduce crop and pasture growth and productivity, decreasing the availability of nutrients in the soil, whilst increasing the risk of erosion through reduced plant cover. 

North East Catchment Management Authority (CMA), in partnership with Agriculture Victoria, Murray Dairy and local community organisations, is implementing the “Securing North East Soils Through Knowledge Exchange” project to promote awareness and change on-farm practices to improve soils by reducing soil acidity and hillslope and gully erosion.  

The project will help farmers and agency staff to better understand the problems and opportunities to improve soil health, manage acidity and reduce erosion  across the region. 

As part of a four-year partnership with Agriculture Victoria over the past year, two land holder groups totalling 24 participants from the Upper Murray and the Ovens Valley have undertaken the GrazFert program. This program has supported landholders develop nutrient management plans through participation in workshops, farm visits and the analysis and interpretation of soil tests. It is understood by participants that implementing these plans will improve soil pH and ground cover management on participating farms. 

Over the next three years an additional partnership with Murray Dairy will help 24 dairy business’s across North East Victoria develop soil nutrient and effluent management plans. 

Over the four year life of this project, North East CMA will provide nine community grants to local groups to increase awareness and promote adoption of appropriate land management practices.  

The first grant will support members of the Ovens Landcare Network to learn about the tools available to maintain and improve ground cover and increase soil health through regenerative farming. 

A second grant to Riverine Plains Inc. seeks to quantify and demonstrate the carbon gains from mixed cropping systems by assessing how increased carbon in soils can reduce on-farm carbon emissions, reduce soil acidity, increase water holding capacity, improve nutrient cycling and enhance the biological function of farm soils.  

Trials will compare soil carbon in paddocks coming out of pasture rotation with those under continuous cropping. The findings from these on-farm trials, to be completed in early 2021, will be presented through field days and network newsletters.  

The four-year Securing North East Soils Through Knowledge Exchange project is supported by the North East CMA through funding provided by the Australian Government’s National Landcare Program. 

Case study 

pHarmers search for their pH 

By Dr Cassandra Schefe, a soil scientist with AgriSci Pty Ltd at Rutherglen, Victoria. 

Imagine. You are a soil scientist standing in a paddock with a farmer, looking at a pasture or crop that’s not growing as well as the farmer expects. 

The first question you ask is, “How much rain have you had? 

The next is, ”So what’s your soil pH?”  

“I’m not sure, I do soil test but don’t understand how it’s measured or effects my farms production? is the farmer’s reply. 

The pH of a soil is a measure of its acidity -  ‘pH’ means ‘power of Hydrogen’, with hydrogen being the element that is measured in a pH test. The more hydrogen measured equals more acidity.  

The scale for pH ranges from highly acid at pH 0 - this equals battery acid. Highly alkaline is pH 14, or drain cleaner, while pH ‘7’ is ‘neutral’. Most soils in North East Victoria vary from pH 4 to pH6.  

An important point about pH is that it is a logarithmic scale. This means that a decrease of one pH unit increases acidity by ten times. A decrease of two units - say from pH 5 to pH 3 - increases acidity by 100 times! 

By now the farmer might be thinking, “Well, all that science stuff is nice, but so what?”  

Well pH is actually one of the most limiting growth factors for crops and pastures in North East Victoria. When we talk about acid soils, we generally talk about values less than pH 5.5 in calcium chloride (pHCa), which is more stable than when we measure it in water.  

A soil pHCa value of 5.5 is a magic number: below 5.5, most soil nutrients are tied up in the soil and are less available to plants, which shows up in plants as deficiencies. Other natural elements in the soil such as aluminium become more soluble, and become toxic to some productive plant species roots. 

“Okay, so soil pH might be something to think about. But do all my soils have the same soil pH value?” 

That is for our next paddock talk. 

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