Fiona Tomney, SARDI
|Contributor||SARDI Minnipa Agricultural Centre|
Site 3, Piednippie, SA
The broad aim of this 3 year SAGIT funded project was to investigate if current management tools for medic based pastures, such as herbicides, fertilisers and rhizobial inoculants, are affecting N fixation by medic pastures under field conditions typical of the upper Eyre Peninsula. These results should also be relevant to other low rainfall Mallee systems where medics are used.
Annual medics (Medicago spp.) are self-regenerating legumes that are well suited to crop rotations on neutral to alkaline soils in the low to medium rainfall areas of southern Australia. They provide highly nutritious feed for livestock, act as a disease break for many cereal root pathogens, and improve soil fertility through N fixation. However, it appears that some of these pastures are not providing sufficient N reserves (as mentioned at local farmer meetings) for the following cereal crops, even where the medic has been quite productive. The longer term decline of protein levels in cereal crops are of concern. Medic pastures are now often sprayed with a range of herbicides and pesticides, both to ensure its productivity as pasture for livestock, and to ensure that minimal weed seeds are carried into the following cereal crop. This project examined if commonly used management strategies reduced N fixation by the medic pasture, and consequently mineral N supply to the following crop.
|Lead research organisation||
SARDI Minnipa Agricultural Centre
|Host research organisation||N/A|
|Trial funding source||SAGIT 515|
Thank you to Greg Scholz, Brent Cronin and their families, for allowing us to conduct the trials on their properties and their support of research; and Andy Bates (Bates Ag Consulting) for his valuable input.
|Other trial partners||Not specified|
|Sow rate or Target density||10 kg/ha|
Two replicated field trials were established on the Eyre Peninsula in 2017. One on a red sandy loam, representative of typical Mallee environments in SE Australia (Minnipa Agricultural Centre Airport) and the other on a grey highly calcareous sandy soil (Brent Cronin’s property at Piednippie).
The 2017 medic trials were dry sown with inoculated Herald strand medic at 10 kg/ha, on 6 June (Minnipa) & 7 June (Piednippie). The GSR at Minnipa was only 155 mm, with most of that rain falling in July and August. All nutrition treatments (Table 1) were applied at sowing. Treatments to simulate herbicide residues were imposed immediately after sowing.
The early post emergent herbicide treatments were applied when the medic plants reached their third trifoliate leaf stage on 21 August (Minnipa) & 24 August (Piednippie). Due to the lack of early season rainfall and poor seasonal conditions this was much later on the cal
|Sow date||7 June 2017|
|Harvest date||Not specified|
|Plot size||8m X 1.5m|
|Paddock history||2016 Mace wheat, 2015 Mace Wheat, 2014 Pasture Oats|
|Rainfall avg ann (mm)||379mm|
|Rainfall avg gsr (mm)||304mm|
|Rainfall trial total (mm)||247mm|
|Rainfall trial gsr (mm)||199mm|
SILO weather estimates sourced from https://www.longpaddock.qld.gov.au/silo/
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.