Twenty six farmers and consultants recently attended a workshop at Reedy Creek to discuss production constraints on alkaline soils of the South East. Many of the alkaline inter-dunal plains were represented on the day with farmers coming from Keith, Conmurra, Avenue, Millicent, Naracoorte, Kingston and Reedy Creek.

The day commenced with Dr Melissa Fraser (PIRSA Rural Solutions SA) providing an overview of the geology of the SE and how and when the numerous dune ranges and inter- dunal plains formed over the last 800,000 years. The resultant soil types of the plains were then discussed, from shallow dark clay loam over limestone to deep cracking clays.

A bit of soil chemistry followed with the basic concepts of pH, salinity, sodicity and dispersion presented. Phosphorous availability on clay-rich alkaline soils was also a key talking point.

Next on the agenda were two paddock visits to inspect soil pits and discuss soil test results, the first to a dryland pasture at David Lloyd’s, followed by a flood irrigation bay at Josh Hancock’s. The pits had been dug to intercept areas of ‘good’ and ‘poor’ pasture growth; it became quickly evident that the ‘good’ actively growing pasture occurred on seams of deep soil or where the underlying shallow limestone rock was fractured, allowing root access to the watertable below (within 0.4m).

Key differences between the sites included lower salinity in the soil at Hancock’s, owing to the lower EC of the irrigation water used there (in comparison to the EC of the shallow unconfined aquifer water). Despite this, the salinity of the soil at both sites was still high enough to impair the production of salt sensitive crops and pastures such as beans and
some clover species. Phosphorous availability was also low to moderate as indicated by both the Colwell P and Diffusive Gradients in Thin-films tests (DGT). Exchangeable sodium percentages were greater than 6% in most cases at both sites, indicating that the soils may be prone to dispersion and waterlogging (sodicity) in some years and seasons.

The key take-home messages from Hancock’s was that irrigation should be scheduled to meet the needs of the driest parts of the paddock to reduce the development of bare patches of soil that are prone to evaporation and the accumulation of salts.

An afternoon brainstorming session was then held to identify production constraints and project ideas. The common themes presented by each of the small groups included:

• Alternative grass and legume pasture species – particularly Messina and summer active brassicas (fodder beets and tillage radish)
• Optimising pasture productivity and utilization – nitrogen use
• Forms, rates and timing of phosphorous fertiliser and P tie up in the soil
• Trace elements and foliar fertilisers
• Shallow limestone rock – how to break it without bringing it to the surface
• Gypsum – how, when, where, rates

Dr Fraser is currently working through these ideas and will host a follow-up meeting at the Reedy Creek hall on Wednesday 12 April from 4.30-7pm; sodicity and gypsum, Messina and rock breaking will be the main focus of discussions.

Mel was supported on the day by Daniel Newson (Natural Resources SE) and Tiffany Bennett (Rural Solutions SA) in addition to the Reedy Creek Mid South East Irrigators and Mackillop Farm Management Groups. Financial support for the day was provided by PIRSA and Natural Resources South East through the Australian Governments National Landcare Programme; thanks must also go to participating landholders for their assistance and input on the day.

Photo 1: The trench dug in the irrigation bay at Hancock’s showing the shallow unconfined water table within 0.4m of the surface.


Photo 2: a zone of ‘poor’ pasture growth (left) owing to the shallow soil in that area.  ‘Good’ pasture growth is seen on the right, overlying a deeper black friable clay. The water in the trench is sitting at the top of the underlying limestone.

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