Managing bare soils following a fire
The Pinery fire in November 2015 has decimated some of the best grain growing land in South Australia, burning 85,700 hectares of crops and grassland across the state’s Lower North region.
However, in the wake of the fire, the attention for many growers has turned to what the ramifications are for their farming operations, particularly around managing bare soils and future crop rotations.
Here, experts answer questions about how growers can manage their land following the fires.
Should I be cultivating to stop wind erosion?
To add insult to injury, two separate severe wind events have already shifted some lighter topsoils in the fire zone. To minimise losses, a number of growers – many of whom have been practicing no-till or zero-till farming for 20 years – have been out cultivating to bring up clay clods and minimise topsoil losses.
Primary Industries and Regions SA (PIRSA) soil and land management consultant David Woodard says growers who have undertaken “emergency tillage” have been cultivating just deep enough to bring up clods of clay to cover the furrow.
“For many growers, particularly the ones who have already had sand drift, it’s very hard to sit there and do nothing,” he says. “In very shallow sands over clay it may be possible to bring up sufficient clay clods to hold the topsoil.”
Is clay spreading or delving an option on sandy soils?
On deep sands, cultivating may be a futile exercise unless growers are able to bring clods to the surface.
In previous years, trials have been conducted on sandy soils in the Lower North region to look at the benefits of clay spreading and clay delving. While the price tag of about $430 per hectare to $740/ha (depending on proximity to a clay pit) to spread clay may seem prohibitive, the reality is that many growers may only be doing 10ha to cover a sand hill to immediately stop the current drift, but there would also be long-term benefits.
“Clay would be worked into the sand pre-seeding in 2016 which would have long-term benefits in better nutrient holding capacity, better water holding capacity, reduced issues with non-wetting sand and be more resistant to erosion in normal situations,” Mr Woodard says.
“If growers with sandy soils have clay within reach of the surface, about 20 centimetres below, you could use deeper tillage such as delving to bring it up, and then leave it on the surface to spade in before the 2016 growing season.”
“You could clay spread the orange sandy clay under the sandy ridges if nothing better is available.”
Mr Woodard says there are certain types of clay to avoid if growers choose to practice clay spreading or delving on sandy soils to stop erosion.
“You really want to avoid clay with high carbonate as that will create problems later on,” he says.
Is there anything I can do to protect dwellings from sand drift?
It is important to stop drifting so houses and towns are not affected by the drift. Mr Woodard says areas around houses and sheds can be watered down in an effort to get something to germinate and grow.
“Some people might also consider using straw bales or shade cloth fences to provide barriers to drift,” he says.
Is it possible to sow a cover crop to reduce drift?
There are many factors that will depend on sowing a cover crop such as forecast rain, subsoil moisture and cost of seed. One option being floated by growers is to sow a high rate of low quality F3 barley to provide cover over summer, which could be done at a cost of $18-$20/ha.
A key message from AGF Seeds sales and marketing manager Tim Brown is for the summer cover crop not to hinder the following winter crop.
“For example, don’t sow barley as a cover crop over summer in a paddock where you are planning to sow wheat as the winter crop,” he says.
Growers wanting to grow a cover should choose a crop with a good fibrous root system to stabilise the soil, with buckwheat, millet, sorghum and ryegrass all potential options. Cereal rye is also a worthy option as it has a good sandblast tolerance.
Mr Brown says plants with fibrous roots will do a good job of holding the top 10 centimetres of soil together but have a limited ability to access deeper moisture. He says the vigour and toughness of brassicas, particularly tillage radish in a mix with millet or sorghum, could be a good fit in the areas affected by fire. Sorghum and millet plants and any ungerminated seeds will not cause problems with winter crop rotations.
“Tillage radish, with a deep taproot, is able to establish quickly and gain access to subsoil moisture to sustain its quick growth,” Mr Brown says. “Among other things, tillage radish will quickly get the soil covered and protected from the sun and wind. It also breaks down quickly during winter so cycling of nutrients is rapid and nutrient tie-up is limited compared to more lignified plants.
“I think a combination of the two plant types maximises the potential success of a cover crop. I would suggest people very carefully consider using their winter crop species as summer cover crops and maybe consider using varieties with strong vernalisation requirement like winter wheat or winter canola.”
A cheaper option to provide cover over summer is to let summer weeds such as melons germinate and grow out to a stage before the winter crop then spray them out.
David Woodard, PIRSA, 08 8568 6412, firstname.lastname@example.org
Brian Hughes, PIRSA, 08 8568 6411, email@example.com
Tim Brown, AGF Seeds, 0403 264 995, firstname.lastname@example.org
Bill Long, GRDC Southern Panel, 0417 803 034, email@example.com