Got that sinking feeling?

The La Niña has delivered record rain across the entire south east of NSW and with that, many of us have faced the regular occurrence of getting bogged in paddocks. What were once safe and dry farm tracks and paddocks have become traps for numerous farm utes, tractors and at times even heavy-duty recovery equipment!

Key points

The Monaro long-term carbon sites were set up in 2009 to begin capturing scientific data about the effects of local geology, nutrient management, vegetation type, seasonal conditions, and general pasture management on soil carbon stocks.

Soil carbon is an important component of soil health. It drives many of the soil functions that our production systems rely upon. Soil carbon levels can be influenced by above-ground vegetation and agricultural management practices and is significantly influenced by seasonal conditions. It is also of increasing interest to those in the field of carbon neutral agriculture.

“Whilst the ongoing sampling and analysis of these sites have shown that seasonal conditions have the biggest influence on any increase or decrease in the level of carbon stored in the soil, this current round of sampling has also highlighted just how over-saturated some parts of our landscape are at the moment” said Local Land Services senior agriculture advisor, Jo Powells.

“The mechanics of why so many of us are getting bogged was clearly visible once we began extracting deep soil cores, especially from our granite soil sites.”

Many of our granite derived soils have a very distinct change within their soil profile from a sandy topsoil to a heavy clay subsoil. The sandy topsoil is held together with organic matter and can remain stable. However when excessive amounts of water are added to the soil, the water moves down through the soil profile and can pool on top of the impermeable clay subsoil.

“In a normal season, pastures and other vegetation would help pump out much of this moisture as they grow, and gravity would also assist the water move laterally across the landscape. However, this season there is just too much water in the landscape, and we are seeing significant quantities of soil moisture being held within the soil profile unable to move”.

“Whilst the topsoil may be initially stable, once disturbed the profile collapses around whatever is causing the disturbance, which for many of us is our tyres”.

Photos taken by the soil carbon sampling team show the varying depth of this now unstable, amorphous layer within our soil profiles. Some Berridale sites show these unstable soil layers between 10-30cm depth. Others taken at Mila (south-west of Bombala) are unstable between 20-60cm in profile depth. Remarkably, the basalt derived soils at all sites showed good stability, had not retained excessive moisture, and posed minimal threat to vehicles.

The good news is that most of these soils are under stable perennial pastures which provide good groundcover. Once spring arrives, these will be able to help pump much of this excess water into their spring growth. The bad news is that much of this moisture is likely to stay in the soil profile until spring arrives soil. So that sinking feeling that many of us are currently experiencing is likely to continue through winter.

Meanwhile the over 700 soil samples collected by the soil carbon team are being processed and results will be presented to Monaro landholders at a field day later in the year.

The Monaro long-term soil carbon monitoring sites is a project supported by South East Local Land Services and the NSW Department of Primary Industries with additional funding provided from the Australian Government’s National Landcare Program.

For more information on soil carbon, down the NSW Department of Primary Industries publication A farmer's guide to increasing soil organic carbon under pastures.

Media contact: Jo Powells, South East Local Land Services, 0429 785 986.