Eighty per cent of farmers would prefer to retain crop residues for a sustainable farming system.

However, according to a recent survey by NSW Department of Primary Industries (DPI), many current tillage and seeding implements do not handle cropping residues very well at critical times of the year, when there is no time to waste.

Trying to sow through thick stubble with unsuitable equipment can cause blockages and a sub standard sowing job, according to DPI conservation farming officer, Rashid Qaisrani.

"Sowing into stubble greater than three tonnes a hectare can cause problems," he said.

"This is compounded if it is long, has not broken down sufficiently, or if soil is wet.

"Machinery with low vertical and lateral clearance or inappropriate tyne layout and shape can add to the difficulties."

In a research project he is conducting at Wagga Wagga, Dr Qaisrani is analysing effects of different stubble loads on stored moisture in the soil profile.

He says several factors, well considered, can assist transition to full stubble retention.

"At harvest, the straw should be spread evenly across the paddock rather than in windrows," Dr Qaisrani said.

"The cutting height could be adjusted, with the possibility of using a second cutter bar.

"Sowing will be easier if stubble is left standing and with a GPS auto-steer, the job can be done inter row.

"Using a tram track system will also help and use of trash gaiters or residue managers will reduce build up on tynes," he said.

When buying or modifying machinery, several guidelines will help.

The vertical clearance and the rank spacing should be at least 500 millimetres.

The tyne layout should be a minimum of five ranks, allowing tynes to be one row space and two ranks apart or vice versa.

"We found that a curved shape on the leading edge of the tyne is best with a diameter of 40 to 80 millimetres and that flat-on tynes are better than edge-on".

A shank angle, vertical or tilted backwards with a high "C" shape above the stubble flow, will work best.

The drawbar should be long enough to add an extra rank at the front, so the turning radius is not compromised.

Wheel positioning can also effect the tyne mounting as blockages can occur if the residues flow onto the wheel.

"If wheels are mounted outside the frame there will be greater flexibility for changing position of tynes," Dr Qaisrani said.

"If the seeder is too long it can compromise precision depth placement.

"An alternative is to increase row spacing, which will reduce tyne and point numbers but may effect crop yield.

"A press wheel to control seed depth may have advantages here as well."

Machinery well designed with no catch points is less likely to cause residue stoppages.

Recessed bolt heads, and use of knife points will streamline trash flow.

Operating the equipment at shallower depth and lower speed gives less clumping and soil throw.

The use of disc seeders and coulters increases the capability of handling heavy stubble loads, minimises soil disturbance reduces draft requirements, but they are not without their problems.

The initial cost, use in wet or rocky conditions, compaction, ‘hair pinning’ and seed and fertiliser placement all need research before this technology will be acceptable in many areas.

However with the recognition of the value of stubble retention, new designs and uses are addressing these problems.

Dr Qaisrani’s project is funded by the Murrumbidgee Catchment Management Authority and covers several sites including Ardlethan and Junee Reefs.

Contact Rashid Qaisrani, Wagga Wagga, (02) 6938 1857, rashid.qaisrani@dpi.nsw.gov.au