Agronomic actions following fire

After dealing with the immediate challenges of livestock management  following a bush fire, affected producers now need to turn their attention to minimising soil damage and managing weeds, according to a South Australian agronomist who’s helping clients to recover post-fire.

Landmark Advanced Farm Services Senior Agronomist Andrew Parkinson, based at Riverton in the lower north of South Australia, estimated 30% of his clients were affected by the fire in November 2015 which burned 80,000ha in one afternoon and evening.

With the initial agronomic response of remedial cultivation to prevent wind erosion behind them, producers and their advisors are now looking to the learnings of landholders in the Lower Eyre Peninsula region of South Australia after a similar extreme bushfire event in 2015. In the wake of that fire – which burnt approximately 83,000ha – a monitoring program ran for 18 months to assess the impact to soils and their productive capacity. 

“One lesson out of the Eyre Peninsula fire was the need to minimise further soil damage after the fire,” Andrew said.

“A strategy is to plant early canola or long season wheat with opening rains to rebuild soil cover and establish feed for livestock.”

He said producers will need to determine a weed management strategy which reflects their individual priorities, such as:

• grazing weedy paddocks
• rebuilding ground cover
• conserving soil moisture for seeding

“Although the real impact of the fire won’t be known until it rains, producers can start making assessments about how to manage summer weeds now,” Andrew said.

“There is no one-size-fits-all approach and management will depend on soil type and paddock rotations.”

Andrew said the lessons from the Eyre Peninsula fire can guide expectations. For example:

• Seed bank: The loss of pasture seed reserves in a fire and subsequent regeneration can be variable.  Buried seed, such as sub-clover, can survive even intense burns, as the heat of the fire only penetrates to less than 20mm in the soil. Surface seeds, such as medic and grasses, are more vulnerable to fire and high losses can occur.
• Soil health: Direct fire effects on soil physical, chemical and biological properties will vary with the heat that the soil has been exposed to. The most significant changes will most probably occur from subsequent loss of finer topsoil through wind or water erosion of the exposed soil surface.
• Disease: Root pathogen populations at sites tested after the Lower Eyre Peninsula fire were low, with no evidence of a change on burnt ground, but some diseases were still very prevalent after the fire (e.g. blackleg in canola and brown leaf spot in lupins), indicating high survival of inoculum sources through the fire.
• Nutrients: Nutrient loss (organic matter, nitrogen, sulphur and potassium) occurs when the surface stubble cover, pasture residues and accumulated trash are burnt. Nutrients are also lost when ash blows away.
• Weeds: Soils laid bare by fire are very much at risk of invasion of weeds from nearby paddocks, roadsides and native vegetation areas. Reduced competition from regenerating pastures and lack of grazing allow such weeds the opportunity to gain a foothold in burnt paddocks. 
• Pests: Depending on the intensity of the fire, some reduction in insect pests is likely.  Producers on the Lower Eyre Peninsula reported that red legged earth mite, millipedes, lucerne flea, aphids, slugs and snails were all less prevalent in crops and pastures during 2005, following the fire.

Other post-fire management agronomic considerations for March include:

• Monitor and control weeds to prevent long-term problems. This includes confinement feeding to prevent the spread of new weed species from brought-in feed for livestock and by animals returning from agistment.
• Adjust cropping program in response to the fire, such as cropping burnt paddocks to cereals for more rapid early growth and to cover bare soil quickly. Cereal crops will also provide greater biomass production and leave more stubble cover after harvest.
• Test grain stored on-farm for reduced germination as a result of exposure to high temperatures in the fire.
• Inoculate pulse crops (including pasture legumes) sown into burnt paddocks with the appropriate strain of rhizobial inoculum, as a precaution against the heat of the fire having sterilised the surface soil.
• Sow crops with minimal soil disturbance to reduce the risk of further erosion.

More information

Andrew Parkinson E: andrew.parkinson@landmark.com.au

Resources

Technical Resource Manual for Farm Fire Recovery, Jim Egan, Senior Research Agronomist, SARDI