Manage seeps to ensure cropping land future

01 December 17

Practice changes such as continuous cropping combined with effective summer weed control could be contributing to an emerging problem across the South Australian and Victorian Mallee districts.

Winter-focused cropping systems where months of summer rain can go underutilised could be contributing to waterlogged and unusable areas of paddocks, known as Mallee dune seeps.

Researchers say growers need to be more aware of the issue to really learn the cause of the seep areas.

Seeps are becoming more prevalent across sandy soils in Mallee regions owing to sub-optimal water use by plants.

Deep sandy soils are the main culprit, contributing disproportionately to water leakage beyond the plant root zone.

Insight Extension for Agriculture consultant Chris McDonough says more seeps are being observed across the central and southern SA Murray Mallee, as well as a few northern Mallee locations.

“It’s becoming a bigger problem in new areas from Mannum through to Karoonda,” he says.

“We’re also seeing seeps growing in the Lameroo districts right through to Ouyen and Manangatang, particularly since the wet season of 2010.”

Mallee dune seepage is a phenomenon caused by excess water in sandy Mallee landscapes.

Saturated areas are caused by the formation of perched water tables at depth, the lateral movement of this excess water, and then its surface expression.

These have increased in occurrence, extent and severity in recent years.

This has resulted in the loss of valuable farmland, and a range of environmental, economic and social consequences – which can include the degradation via erosion and salinisation of bare seep areas.

A preliminary survey of 73 farmers by Mallee Sustainable Farming (MSF) has already reported approximately 730 hectares of seep affected land across the region indicating while the area affected per farm is relatively small, the issue is expanding and its impact on farm operations is increasingly broad.

Research conducted by Mr McDonough and Juliet Creek Consulting’s James Hall was prompted when 12 farmers from across the SA Murray Mallee expressed concern to the local Natural Resources Management (NRM) Board about seeps appearing on their properties.

These research efforts at sub-catchments near Wynarka, Mannum East and Karoonda are supported by the SA Murray-Darling Basin NRM Board through funding from the Australian Government’s National Landcare Programme and the NRM levies.

Field-based work at these sub-catchments has focused on understanding the landscape processes involved in seepage and the formation of seeps.

This has included the characterisation of soils at selected sites, land unit mapping, EM38 soil mapping measuring soil electrical conductivity and deep drilling.

Soil moisture probes and piezometers within the catchments have helped reveal which rainfall events on which soil types are contributing most to leakage of water beyond plant root zones, and the movement of perched underground water.

Practical farm-scale trials have also been established to look at improving overall plant water use, including the strategic planting of deep-rooted perennials (such as lucerne, saltbush and native trees).

Trial work has also focused on the use of organic soil ameliorants (spaded chicken manure) which has helped break compaction, double crop yields and utilise far more moisture from these non-wetting deep sands.

“We have also begun preliminary work using NDVI, drone and satellite imagery to enable the early detection and management of potential seep areas” said Mr McDonough.

Mr Hall says Mallee dune seeps are usually thought to be areas of salinity formation, but this is not often the case, at least initially.

“Certainly the evidence is that the distribution, extent and severity of seeps is worsening in the sandy Mallee areas of Victoria, the SA Murray Mallee, the Mid North, Yorke Peninsula and Eyre Peninsula,” he says.

“Seeps occur in these sandy areas where clays or similar material is near the soil surface, forcing perched groundwater and seepage waters to the soil surface.

“The groundwater and seepage systems investigated so far that are associated with Mallee dune seeps are local groundwater systems.

“This means that local action to increase overall water use by productive plants can have a positive impact and non-arable saturated seep areas can potentially be returned to productive agricultural use.”

“Good quality farming land is going out of production because it’s getting too wet and often it’s the best land on the farm,” he says.

“The bigger issue is what that’s telling us about water use on these farms and how overall water use by productive plants is well below what is optimal.”

A Wynarka seep formed since the wet year of 2010 illustrating the loss of valuable farming land in affected areas.

 

He says water balance and economic modelling is needed to better understand the water and economic losses associated with current farming systems in sandy Mallee districts and to model different farming systems that might utilise more rainfall.

“Many landscapes now have continuous cropping across whole farms where there’s nothing growing for more than six months of the year,” Mr Hall says.

“Once the soil is filled to capacity any extra rain goes through and drains to depth beyond the root zone.”

Mr Hall says the excess water would either contribute to seepage and seeps or drain to depth and recharge deeper regional ground water if there is no impeding clay layer present.

“Even in areas where there aren’t seeps appearing at the soil surface, there is likely to be the same issue of sub-optimal water use,” he says.

“It would be better to make productive use of this water rather than allow it to join seepage waters or drain away to depth.”

Growers who have never experienced seeps are encouraged to seek advice and act early to manage the possible development of areas of permanently to semi-permanently saturated soil.

Mr Hall says the risk of soil degradation is an issue, with salinity levels increasing if seeps remain bare.

Erosion can also occur unless vegetative cover is established and maintained.

He outlines three possible approaches:

  • Do nothing but risk increasing degradation of existing seep areas and possibly the formation of new seeps on productive farmland
  • Manage seep areas separately to the rest of the paddock (preventing further degradation but not tackling the cause) or
  • Manage the whole sub-catchment to increase overall water use and minimise seepage, and bring seep areas back into production.

He says a change to farming systems and land use was required to succeed with the third option where “matching land use and management to land type” was required.

This could include introducing new or additional species to the farming system such as lucerne or other deeper-rooted perennials.

It could also include growing summer crops on sandy soils.

“Summer cropping is more risky than winter cropping – however, the risks are likely to reduce as more experience is gained,” he says.

“Given suitable initial soil moisture conditions, there is potential to try and grow summer crops, especially on deep sandy soils.

“Of course, erosion risks need also to be managed.”

Mr Hall says the solution for the individual farmer will take some trial and error, similar to the inception of minimum till and no-till farming, which took many years for techniques to be optimised and to become widely established.

Mr McDonough says solutions need to be economically viable for farmers and suggests that while summer crops have been tested by some Mallee farmers in the past, there is a lot more work needed to develop them into practical solutions for seep control.

He suggested strategies targeting the specific problem areas on a property such as growing lucerne strips for either grazing or cutting in key areas may achieve the desired water use to prevent waterlogging.

“However, we do need to come up with more options that suit different farmers’ systems, as well as ways of clearly identifying the most efficient methods of remediation to achieve maximum benefit,” Mr McDonough says.

“These are still the unknowns we are working through.”

 

A seep area in a lupin crop in Karoonda rendering part of a paddock unusable due to waterlogging.

 

Mr Hall says there is strong evidence the trend towards continuous cropping for short-term profitability and ease of farm management has consequently decreased farm water use in comparison to systems based on crop-pasture rotations.

He says there is presently an unknown amount of rainfall not being utilised for productive agriculture and an unknown amount of potential income being lost.

“There are many things to consider to alleviate this leaching and sub-optimal water use issue, including how to manage and operate farms on the basis of land type with modern methods and machinery,” he says.

In the parts of the SA Murray Mallee Mr Hall has conducted deep drilling revealing groundwater (saturated soil) perched upon clay at the majority of sites, at depths of up to 10 m below the land surface.

Constraints to crop production on sandy soils, including seeps is rated highly by members of the Grains Research and Development Corporation (GRDC) Low Rainfall Regional Cropping Solution Network.

As a consequence, a large research and development project led by CSIRO has been funded and is currently in its second year.

It is examining a range of constraints to crop production on sandy soils and cost-effective methods to mitigate or ameliorate these.

The initial strategy is increase winter crop production and water use to reduce the occurrence of seeps.

 

Useful resources

A range of useful reports on Mallee dune seeps including a summary report by James Hall is available on the Natural Resources SA Murray-Darling Basin website (see http://www.naturalresources.sa.gov.au/samurraydarlingbasin/land-and-farming/soils/soils-resources).

 

Source: https://grdc.com.au/news-and-media/news-and-media-releases/south/2017/11/manage-seeps-to-ensure-to-ensure-cropping-land-future

Author: Rachael Oxborrow | Date: 15 Nov 2017