Cropping systems for stubble retention
News story from 'Climate Change, A NSW Department of Primary Industries special feature', in The Land, October 2008
Phil Bowden, Cootamundra
New designs are enabling implements to handle cropping residues well while at the same time increasing soil-moisture-holding capacity.
Eighty per cent of farmers would prefer to retain crop residues for a sustainable farming system but, according to a recent survey by I&I NSW, 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.
Most farmers in the Murrumbidgee catchment deal with high stubble loads using a combination of grazing and burning.
However with the recognition of the value of stubble retention, new designs and systems are addressing these problems.
There are many advantages to production such as increased moisture holding capacity of soils, increased soil microbial activity that assists recycling nutrients and greater protection of soil from increased ground cover.
Trying to sow through thick stubble with unsuitable equipment can cause blockages and a sub standard sowing job. Research has found that trying to sow into stubble greater than three tonnes per hectare can cause problems and this is compounded if it is long, has not broken down sufficiently, or if soil is wet. Machinery that has low vertical and lateral clearance or inappropriate tine layout and shape can add to the difficulties.
Many things can be done to deal with heavy stubble loads. At harvest, the straw should be spread evenly across the paddock rather than in windrows and 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 tines.
When buying or modifying machinery, several basic factors should be considered. The vertical clearance and the rank spacing should be at least 500 millimetres. The tine layout should be a minimum of five ranks, allowing tines to be one row space and two ranks apart or vice versa.
The drawbar should be long enough to add an extra rank at the front, so that the turning radius is not compromised, and if the seeder is too long it can compromise precision depth placement.
Wheel positioning can also affect the tine 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 tines.
An alternative is to increase row spacing, which will reduce tine and point numbers but may affect crop yield. Using press wheel to control seed depth usually provides distinct advantages here.
Research has shown that the best tine cross-section is circular with a diameter of at least 40 mm. Diameters as large as 100 mm are OK. A curved (rounded) leading edge is better than a plain rectangle and flat-on tines are better than edge-on. The tine should be straight for at least 500 mm above the soil or at least have minimum curvature. The tine should be vertical or tilted backwards from the point in the working position to avoid pinning residues against the soil.
Machinery that is 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 and 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 issues all need research before this technology will be acceptable in many areas.
A research project is planned for the Southern NSW cropping zone that will look at the effects of different stubble loads on stored moisture in the soil profile and how farmers can deal with stubble efficiently.
The project is being funded by Murrumbidgee Landcare through the Woolworths Sustainable Farming Drought program with support from the Murrumbidgee Catchment Management Authority and the I&I NSW.
Stubble management demonstrations will be set up on paddocks at Harden, Junee Reefs, Henty and Mirrool Creek with different tillage systems, to monitor soil moisture, stubble load, effect of grazing and other issues that impact on stubble management.
These demonstrations will give farmers some comparison of different farming systems and will assist in the transition to full stubble retention. An important aspect of the project is that it is community initiated and community driven. It is aiming for local data, local knowledge and local support for change.
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