By David Malinda and Rick Darling
A new type of tillage system presents a potential revolution in tillage technology after a six-year project in South Australia found that higher crop yields could result from its adoption.
The novel progressive tillage regime, carried out at Halbury in SA, aimed at increasing root penetration, organic matter and water infiltration, and sustained increase in yield, over a long period by removing the compacted subsoil layer.
The system was named "tillage rotation" (TR), owing to its process of varying the tillage depth each year.
The results have been encouraging at the site. Compared with conventional cultivation (CC) and no-till (NT), tillage rotation proved to be superior in yield increases, improved infiltration, uptake of nutrients and water, improved rooting system and resistance to root diseases. It also significantly changed subsoil chemistry.
For example, tillage rotation in comparison with conventional cultivation increased roots up to 250 percent at depth, reduced penetration resistance by 650 percent in the originally compacted layer of 7 to15 centimetres depth (Figure 1), and increased infiltration between 18 and 10 times in the 5 to 15cm soil layer. No-till results were in between.
Figure 1. Effect of tillage regime on resistance to penetration of a metal probe at Halbury subsoil trial.
It is believed that due to the reduction in soil bulk density and resistance to penetration and increasing roots at depth, tillage rotation crops extracted more water and produced better yields throughout the six years of the trial except in 1998, where tillage rotation barley was sown deeper than other treatments due to the softer soil (Table 1).
Table 1. Effect of tillage and crop rotation on grain yield (t/ha)
These findings demonstrate that subsoil compaction makes cropping less efficient.
However, this may not be extrapolated to all other soils and research is continuing in other soil types.
Tillage rotation is now a new word entering common usage among farmers and scientists in southern Australia, and it is meeting all the requirements of a better tillage system with a gross margin of $50+ per hectare/year above conventional cultivation.
Conventional cultivation (cultivating many times and at seeding) and long fallow (repeated cultivation at constant depth of cut) have been practised in Australia to eliminate weeds and to "conserve moisture" for more than 150 years.
However, long fallow has been doubtful as an economically and ecologically sound farming system in many areas, and has cost Australia"s soil resources through subsoil compaction, erosion, sediment load and nutrient depletion.
We confirmed this during our long-term trial research in the mid-north of South Australia between 1987 and 2002.
In the early sixties, with the advent of herbicides, researchers developed no-till cropping systems to try to save soil resources and increase yield and hence farm profit. In Australia, like many parts of the world, no-till was expected to produce higher yields compared with conventional cultivation.
Some farmers using no-till achieved yield increases relative to conventional cultivation, but others did not. Although no-till is 40 years old, its adoption by farmers in many parts of Australia has been steady and slow - unlike Argentina, where an overall adoption level of 70 percent is reported.
The reasons behind low-level attainment of higher yields with no-till - relative to conventional cultivation by many farmers - were subsoil compaction as we are finding now, diseases, and weed resistance to herbicides. The reason behind low adoption levels of no-till in some cropping regions has been due to low yields, diseases and problems with chemical use.
Evaluating long-term conservation trials in South Australia, Victoria and Western Australia, senior research scientist David Malinda and his team at the South Australian Institute of Research and Development found that no-till did not produce higher yields compared to conventional cultivation, particularly in the Halbury long-term trial. This was because the trial was established in already compacted subsoil.
In 1997, Mr Malinda and his team set out to create a new tillage technology to address subsoil compaction.
A GRDC-funded project was established to develop a novel tillage regime aimed at progressively removing compaction in small soil depth increments each year until the compacted layer was removed. The tillage regime is a one-pass operation during seeding only.
In each of the six years of the Halbury trial, tillage rotation shoot nitrate N was found to be about double that expected based on N applied at seeding. This prompted us to examine the chemical status of the subsoil.
Analysis of the subsoil in 2003 indicates big differences in soil chemistry in the deeper depths. For example, comparing tillage rotation with conventional cultivation, nitrate N of the 0 to 60cm soil depth was up by 42 to 170 percent for different rotations. Most surprising, there were large differences in measured sulphur and conductivity between tillage rotation, no-till and conventional cultivation at 30 to 100cm (but in particular 40 to 80cm) (Figure 2).
Figure 2. The effect of different tillage regimes on subsoil nitrate N, sulphur and conductivity at Halbury subsoil trial.
CC = conventional cultivation; NT = no-till; TR = tillage rotation
In one rotation, higher concentrations of sulphur (206 percent) and conductivity (94 percent) at 30 to 100cm and nitrate N (213 percent) at 0 to 100cm were recorded between tillage rotation and conventional cultivation (Figure 2). We have not been able to find in the literature comparable results and these differences were not expected. They could have implications for soil carbon sequestration, vigorous soil biological activity and/or leaching.
Work at the Halbury site is continuing. During our extension of these initial results to farmers and others, it became quite clear that growers are interested in tillage rotation technology; they want to know how long the benefits of tillage rotation will last and whether it will work in all soils if different seeding points are used.
To find the answer to the first question, in 2003, after six years of the trial, tillage rotation plots in the original Halbury trial changed to no-till with knifepoints so that the longevity and residual benefits from tillage rotation could be tested. The no-till plots changed to rotation so that the impact of tillage rotation after several years of no-till could be assessed.
To find the answer to the second question, we set up trials in different soil types in South Australia and Victoria ranging from sand to heavy clay, to test tillage rotation using different seeding points. The added information with these changes will be vital in underpinning the adoption of the new technology by farmers.
As soon as we began trials of tillage rotation in other soil types, we found that our plot seeder was not suitable in some soils as the depth of seed placement was hard to control.
For example, some points reduced plant establishment with deeper depth of cut. Also, in the sandy Waikerie soil, there was a general delay in plant emergence (Figure 3). All these affected yield to some extent in 2003. Two companies came to our rescue and assisted with the development of improved seeding equipment.
Figure 3. Plant establishment as affected by depth of cut. The bars are plants counted from deeper depths of cut (15cm and 17cm for Halbury and Waikerie respectively) minus those counted from shallower depths of cut.
Tillage rotation has shown to be a sound economic investment, at least in the red-brown earth at the Halbury site.
It is being evaluated at other research sites and commercial properties in southern Australia from the perspective of its functionality in terms of sustained yield and yield quality, carbon sequestration, and biological consequences.
In addition, tillage rotation is being found to encapsulate a potential revolution in tillage technology and changing the meaning of tillage systems that have hitherto been practised and accepted for a long time.
For more information:
David Malinda, 08 8303 9350, email@example.com
GRDC Research Code: DAS 00012
South, North, West