Setting up for high quality durum
From the March 2009 edition of Agriculture Today.
Ross Durham farms near Mullaley on the western end of the highly productive Liverpool Plains.
Much of the country he farms consists of sloping basalt soils.
An important aim in his rotation planning is setting paddocks up for the production of high quality durum grain.
Rotation crops need to provide a disease break for durum wheat as well as being profitable in their own right.
Maintaining ground cover is also an important goal on sloping paddocks, to prevent erosion and maximise moisture storage.
For this reason Mr Durham double crops chickpeas or faba beans into sorghum stubble when moisture permits as it did in 2008, bringing the added advantage of extra cash flow.
Faba beans stop using moisture sooner than chickpeas and provide the opportunity to begin storing soil moisture sooner than other winter crops.
Mr Durham insists that all rotation crops receive a high standard of agronomy, which can be demanding on management, especially in high disease years like 2008.
Sorghum is an important rotation, although the area allocated to it has been reduced in recent years, in favour of other crops.
He says canola is an excellent break crop to combat cereal disease and is used providing planting rain falls at the right time.
Mungbean and cotton are always on the eligibility list if agronomy, moisture, price and rotation considerations all line up correctly.
Managing crop rotations
Crop rotations have an important role in managing water, disease, weed and nutrient cycles.
Often crop choice is based on economics.
"While economics is important, so are basic principles to enable us to work with natural cycles and not against them," NSW Department of Primary Industries district agronomist at Gunnedah, Bill Manning, said.
"When looking at the profitability of rotation crops, it is important to calculate gross margins over the whole rotation.
"This is the only way to assess the benefits that a rotation crop may provide to other crops in the system."
Water is often the limiting factor in crop production and crop rotation can help maximise water intake by soil.
Surface cover (stubble) is essential here.
Crops such as wheat and barley leave behind relatively large quantities of stubble that will persist for some time.
Pulse crops such as chickpea and field peas produce less stubble and because of the high nitrogen content they break down faster.
Mr Manning says crop rotations should aim to keep stubble cover up and for this reason crops producing low stubble cover should be followed by crops that will restore ground cover.
"After drought, it is important to restore ground cover as soon as possible to get the water cycle working again," he said.
"Crop rotations play an important role in managing some of the diseases that cause significant economic loss."
As a general rule it is better not to plant a crop into its own stubble.
Crown rot causes significant losses in wheat in most years and survives from year to year in stubble.
Crop rotation to non host crops such as pulses and oilseeds reduces crown rot levels in paddocks.
Soil testing services are now available to assist with risk assessment.
Rotation crops allow time for the stubble to breakdown and disease levels to fall.
Rotation crops that produce a large biomass, such as canola, reduce the rate at which stubble dries out after rain and increase the rate of stubble breakdown.
Net blotch in barley survives on barley residues and crop rotation can assist in the management of this disease.
Blackleg in canola is one of many other diseases influenced by rotation.
According to Mr Manning, the high price of fertiliser, particularly nitrogen, (N) has increased interest in using pulse crops to supply N to farming systems.
"While it is unlikely that pulse crops can supply all the N required for cereal grain production, they can make a useful input," he said.
"Pulse crops such as chickpeas are best used at a stage in the cropping cycle when soil N levels are low, for example in a double crop situation after sorghum."
This ensures that the legume derives as much of its N from the atmosphere rather than the soil.
Some legumes such as faba bean are more tolerant of high soil N and will fix N from the atmosphere, even if moderate levels of soil N are present.
A good crop rotation can increase the range of herbicides that can be used throughout the whole rotation and this can reduce the risk of herbicide resistance.
This requires careful planning, however, as the system can become dependent on the same chemical group being used in different crops, which only increases the likelihood of resistance.
Contact Bill Manning, Gunnedah, (02) 6741 8366, william.manning@dpi.nsw.gov.au
