THE CONTINUOUS cropping systems that have formed the bedrock of many cropping enterprises, particularly in low rainfall zones, over the past 20 years can be sustained, but farmers will have to plan meticulously to do so.
This was the finding of research conducted by CSIRO into the opportunities and challenges for continuous cropping headed up by agricultural systems agronomist John Kirkegaard.
Speaking at the Grains Research and Development Corporation (GRDC) advisor update in Bendigo in February, Dr Kirkegaard said continuous cropping would remain functional with careful management.
However, he said not incorporating a pasture phase would mean that farmers’ nitrogen (N) costs would continue to rise, even when including a grain legume in the rotation.
“A larger proportion of plants’ N supply will have to come from fertiliser,” he said.
He said many of the cereal-heavy continuous cropping systems utilised in dry regions were taking N out of the soil at a rate not balanced by fertiliser application, showing a long-term decline in mineral N levels in the soil.
“This ‘mining’ may make sound economic sense in the short-term, particularly as farmers look to cut input costs after a tough year, but in the medium to long term it will not be sustainable.”
Weed management is the other major long-term management issue continuous cropping throws up.
Dr Kirkegaard said herbicide resistance grew faster under continuous cropping while without a fallow or pasture phase, non-chemical control options are also at a premium.
He said legume crops could provide a valuable chemical rotation and also be cut for hay, which works well in cutting down weed numbers by not allowing them to set seed.
“The flexibility of the legume phase, allowing weed control and water conservation if required, combined with the N fixation they provide mean the phase can reduce production risk and provide a significant benefit to the overall crop sequence.”
He said farmers could also look at ensuring their crop out-competed weed species through narrow rows and higher planting rates.
“Crops on narrow rows of less that 250mm cover the ground faster, let less light through the canopy and reduce weed seed set.”
“Plant density is also important, the crop competes better when it is planted at a higher density.”
Growers looking to get an additional advantage should look to sow east-west to get more effective shading than a north-south sowing.
Dr Kirkegaard also said continuous cropping needed to be weighed up in terms of risk management.
While research found the best earning cropping system at Karoonda, in the South Australian Mallee, in a good year with decile 9 rainfall was by far a mixed rotation continuous cropping system, losses in bad years were much lower with pasture or fallow in the system.
A continuous cereal cropping system needed a decile 5 or better season at Karoonda just to break even.
“The research clearly supports the value of maintaining diversity in species and the end-use of the crop.
“A more diverse cropping system can be as profitable with less cost and risk.”
However, he acknowledged the logistics in broadacre farming could not be replicated in trial plots.
He said the best advice for growers was to focus on the old adage ‘do what you do well’.
“Continuous cropping is better able to capture value in good years, but is at greater risk in poor seasons.”
“If you are continuous cropping, however, the data shows clearly that being diverse in your crop choices and management is critical.”