Building soil health to improve soil function and productivity

Farmers know all too well that yield varies across a paddock. Identifying soil constraints in underperforming soils requires a good understanding of the physical, biological and chemical make-up of soil in the paddock. Soil samples can be taken and tests done both in the paddock and at the lab (e.g. salinity, trace elements, microbial function and organic carbon) to determine these constraints. A few limiting factors may include low organic matter, water repellence, alkaline or acidic soils, soil structure and water holding capacity.

Increasing soil organic carbon can be a step in the right direction to increasing soil productivity. Physically soil organic carbon improves soil structure, lowers its density, improves drainage and water holding capacity, and reduces erosion. Soil organic matter can improve cation exchange, provide a source and release of nutrients and sorption and the deactivation of contaminants. Biological activity and diversity is increased and there is improved suppression of soil borne pathogens.

Critical Organic Carbon (OC) content by clay content of South Australia agricultural soils

Texture                          Low            Moderate          High
Sand                             <0.5             0.5 -1.0             >1.0
Sandy loam                  <0.7             0.7 -1.4             >1.4
Loam                            <0.9             0.9 -1.8             >1.8
Clay loam/clay              <1.2             1.2 -2.0            >2.0

To build soil carbon over the long term paddocks should be managed to minimise erosion, keep cover on soil, grow plants with deep roots and biomass above the ground and address growing constraints such as pH, compaction and improve nutrition. It is more difficult to build organic carbon in sandy soils as they have little clay or small pore spaces. Sands tend to have less protection of organic matter from microbial breakdown and lower soil organic matter build-up. Similarly in sands, micro-organisms have fewer places to survive from predation by other soil organisms and are more likely to encounter dehydration stresses.

Increasing soil carbon using liquid nutrient and strategic tillage

Earlier this year the Buckleboo Farm Improvement Group (BFIG) established two trial sites to combat sub-soil constraints and increase soil carbon, supported through the Natural Resources EP Regenerative Agriculture Program with funding from the Australian Government's National Landcare Program.

The soils targeted during this trial included deep white sands at Solomon, and red sandy soils at Buckleboo (funded by GRDC) and were used to trial the effects of injecting liquid nutrients at depth when deep ripping.

At both sites five different treatments were replicated. The deep white sands were previously clay spread.

The sites will be monitored over the next four years using a combination of methods including; Walkley Black Soil Organic Carbon (SOC), emergence counts, Dry Matter (DM) cuts and normalized difference vegetation index (NDVI) mapping.

The first year monitoring results are in and the difference is evident between the control and the various treatments, particularly with the lower than average rainfall this season.

Soil carbon demonstration grants now open!

The Soil carbon demonstration grants are a new and important part of a long-term project that aims to provide land managers with the opportunity to implement ‘farmer’ scale large plot demonstrations with interventions intended to overcome sub soil constraints and have long term benefits for increased soil organic carbon and productivity across a range of soil types.

'Expressions of Interest' from Agricultural and Farming Groups on Eyre Peninsula to be involved in Soil carbon demonstration grants are open now, so demonstrations sites can be setup early in 2020.

It is intended that interventions to be demonstrated will reference trials and demonstrations that have shown the most promise (from results of other trials and demonstrations) for increasing soil organic carbon and reducing the extent to which soil constraints limit production.

Application forms are available online  www.naturalresources.sa.gov.au/eyrepeninsula/get-involved/grants-and-funding or you can contact Mary Crawford on 0407 187 878.

Soil acidity (EP regional status 2018)

• The estimated value of lost agricultural production due to acid soils in the Eyre Peninsula region is between $16M and $19M per year
• Soil acidity on EP has increased in the past 20 years, in area and severity
• 7% (186,000 ha) of EP’s agricultural land has surface soil acidity (0 - 10cm depth)
• A further 19% (509,000 ha) of agricultural land could become acidic in the next 10 - 50 years
• During the last decade average lime use was around 80% of estimated topsoil acidification rate
• Encouragingly a large increase in lime use was recorded during 2017 and 2018, above the acidification rate
• Soil acidity will continue to increase unless lime use rates are maintained above current acidification rate of 21,000 tonnes per year
• Acidification rate could potentially increase to 80,000 tonnes lime per year in next 10-50 years
• Estimated further 213,000 tonnes lime needed to raise pHCa of acidic surface soils above 5.5, and 9,000 tonnes lime required to treat acidic subsurface soils
• Newly emerging areas affected by acidity and pH stratification are key issues under dryland cropping.

Restoring soil pH balance on your farm

‘Restoring Soil pH 2020' will be the fourth year that Natural Resources Eyre Peninsula and Rural Solutions SA will hold workshops for farmers who would like to develop a program to restore their pH levels. Restoring Soil pH is a program that has given farmers on lower and eastern Eyre Peninsula an insight into how acidic their soils are becoming. 

The program supported by the NREP Regenerative Agriculture Program and funded by the Australian Government’s National Landcare Program, aims to increase land managers awareness and knowledge of techniques and benefits of monitoring, maintaining and treating soil acidity.

In 2019, land mangers mapped 307 ha and 60% was below the target pH of 5.5 (CaCl2), with 29% below the critical pH of 5.0 (CaCl2). Twenty six percent of the area mapped had pH in the range considered best for plant growth (5.5 to 6.5 CaCl2). Each site was  analysed for potential cost savings that could be achieved by pH mapping compared to a uniform lime application rate.

The lime application costs included:

• the cost of lime product ($12/t),
• freight and application ($20/t) and
• $16.50/ha for mapping.

Using variable liming rates, the average forecasted potential savings across all sites for one application was $1,440 (or 38% on the cost of the liming operation). The highest potential savings on one paddock is $2,840 and the lowest pontential ‘savings’ of -$180. Watch a short video (linked here) overviewing some of the soil acidity mitigation work for improved production on lower Eyre'.

For further information about the forthcoming workshops and advanced bookings for the two workshops starting in February 2020 please contact Sarah Voumard 0428 128 684.

Acknowledgement

This Regenerative Agriculture Project is supported by the Eyre Peninsula Natural Resources Management Board, through funding from the Australian Government’s National Landcare Program.