Stubble retention has improved soil health and made it possible to successfully grow crops in an increasingly challenging environment, but come sowing time you are more likely to hear cursing than praise, particularly in high-rainfall environments such as Kangaroo Island, South Australia. Blockages of seeding equipment are the most common challenge, but reduced efficacy of pre-emergent herbicides and poor seed-to-soil contact and emergence can also be problems.
Agriculture Kangaroo Island (AgKI), in collaboration with the MacKillop Farm Management Group (MFMG), worked with growers on Kangaroo Island to see how they were addressing the challenges of stubble-retention in this high-rainfall environment (550 millimetres) with a challenging range of soil types.
As part of the GRDC Stubble Initiative, the learnings were shared through a seeding machinery field day and case studies on growers such as Travis Bell and Ben Pontifex.
Based at Kingscote, Travis Bell uses a DBS tyned seeder with a long knife point and a closer connected to the press wheel via a linkage, enabling both small and large seed to be accurately placed at a consistent depth. The machine can sow all crops ranging from kikuyu grass and canola to broad beans, and performs even in sand and heavy clays. Crops are cut at 250mm high to eliminate long sections of stubble.
The DBS can handle heavy stubble loads going through a five-tonne per hectare wheat crop with no problems even under damp conditions. A GPS guidance system allows the Bells to sow inter-row most of the time to improve stubble flow through the machine, but they use sensors on the seeding bar for this to work perfectly.
The tyned machine provides good seed-to-soil contact and also allows the effective use of pre-emergent chemicals that require incorporation. A key challenge for Mr Bell was getting the speed of sowing right: at higher speeds there is too much soil throw resulting in inaccurate seeding depth and herbicide damage, particularly on sandier soils.
Ben Pontifex, who farms a range of different soil types on Kangaroo Island, uses a Tobin Bullet single disc machine with a much larger disc than usual and seeding boots that he has modified to handle large broad bean seeds. The larger discs allow placement of bean seed to 75mm deep but can also accurately place small seeds.
Hairpinning – a common problem with disc seeders where the disc pushes long pieces of stubble into the ground reducing seed-to-soil contact – is more of an issue when sowing small seed such as canola because there is less pressure from the disc at shallow depth to cut through stubble on the ground. While Mr Pontifex has been able to overcome this issue by burning stubble or aerially broadcasting canola, he has now set up his rotations so that canola is sown into bean stubble where hairpinning is much less of an issue.
Most single disc seeders do not usually provide sufficient soil throw for pre-emergent herbicides that require incorporation. However, Mr Pontifex has found that the larger discs and fast travel speeds (up to 16 kilometres per hour) provide relatively large amounts of soil throw, enabling effective control.
The seeder performs well in all soil types, with the exception of sticky, wet clay, so the sowing of this small area of clay is delayed under these conditions. For Mr Pontifex the main challenge is the weight of the machine, which increases the likelihood of it getting bogged; however, he says this is a necessary evil as the weight is essential for good disc penetration to allow deep seeding and stubble cutting.
GRDC Research Code MFM00006
Felicity Turner, MFMG
0400 299 087