GROWERS experiencing poor protein levels in cereal crops following medic pastures could soon have an explanation thanks to SAGIT-funded research happening at the Minnipa Agricultural Centre.
SARDI research officer livestock and farming systems Brian Dzoma said local growers had expressed concerns that while their cereal crops were yielding well following medic, they were not achieving the protein levels they were expecting.
“We expect protein levels to be high in cereal crops following a medic pasture because effective nodulation and nitrogen fixation should mean an increase in nitrogen levels in the soil, however some growers were telling us this wasn’t happening,” he said.
“The main thing we’re looking at is herbicides and whether post-emergent herbicides are having an effect on nodulation and nitrogen fixation.
“We’re also looking at herbicide residues to see if something used in the previous crop could be having an effect on germination, nodulation, dry matter production and nitrogen fixation.
“The third thing we’re looking at is nutrition and whether this plays a part in helping the medics to fix enough nitrogen.”
There are two trial sites in the three-year project aiming to Identify the causes of unreliable nitrogen fixation by medic based pastures. One trial is on a sandy loam soil in a ‘typical Mallee’ environment with average to good nutrition at Pinbong, about 10 kilometres north-west of Wudinna and the other is on a grey calcareous sand at Piednippie, inland from Streaky Bay. Early results indicate soil nutrition can play a role in the amount of nitrogen fixed.
“Just by applying 10 units of fluid phosphorus, we found a 150 per cent increase in shoot dry matter on the grey calcareous sand, and 33 per cent increase on the sandy loam soil,” he said. “More production means more N is added to the soil when the nitrogen rich medic residues break down.
“In terms of pre and post-emergent herbicides, we haven’t found much difference yet on the sandy loam soil which has good nutrition, indicating the medics are doing their job in improving soil N. However, on the grey calcareous sand, in-crop application of Agritone 750 (MCPA amine) was reducing herbage production and N fixation.”
The trial is assessing six post-emergent herbicides, three chemical residues, and nitrogen, phosphorus, zinc, sulphur and manganese applications. Plants are sent to the SARDI lab at Waite for nodulation analysis.