Graham Centre research examining what's going on underneath the surface of clovers, medics, lucerne and newer legumes such as biserrula and serradella has been presented at the Grassland Society of NSW annual conference.
Dr Belinda Hackney outlined the results of a pasture legume nodulation survey of 225 paddocks across the Central West, Central Tablelands, Monaro and Riverina at the conference on Wednesday 26 July.
"More than 90 per cent of pasture paddocks have inadequate nodulation and in some regions up to 20 per cent of paddocks had no nodules at all," Dr Hackney said. "Key factors affecting nodulation were soil pH, nutrient availability and in some cases the use of residual herbicides."
Root nodules on legumes provide a home for symbiotic nitrogen-fixing bacteria called rhizobia.
The survey is part of a wider research 'Pasture legumes in the mixed farming zone of WA and NSW: shifting the baseline' which is a collaborative project with Murdoch University.
"Nodules are the canary in the mineshaft - a symptom of a much bigger issue, and it's something that must be addressed to improve legume and therefore overall pasture production," Dr Hackney said.
"Adequate nutrition in terms of phosphorus, sulphur and molybdenum is essential in supporting nodulation, nitrogen fixation and legume growth but application of these nutrients does not substitute for correction of soil acidity."
Dr Belinda Hackney is a senior land services officer - mixed farming with Central West Local Land Services and adjunct lecturer at Charles Sturt University (CSU).