Trials study impact of strategic tillage
Research at five sites across northern New South Wales and Queensland is showing that one or two cultivations in a no-till farming system cause little damage to biological activity, organic matter levels or crop yield. A once-off tillage is also helping with weed control and, in some years, disease management.
Research looking into the effects of occasional tillage in a zero-till or no-till system has been a high priority for growers lately, especially with the emergence of hard-to-kill weeds, such as fleabane, and increased crown rot (Fusarium pseudograminearum) in drier years and leaf disease problems in wetter years. Also wet harvests in recent years have caused considerable compaction and soil unevenness from wheel tracks, requiring some restoration work.
To gauge whether a tillage intervention will undo the gains built up under no-till, the GRDC has supported trials by Dr Yash Dang, Dr Ram Dalal and Dr Phil Moody from the Queensland Department of Science, Information Technology, Innovation and the Arts (DSITIA), together with Vivian Rincon-Florez, Clement Ng, Dr Mike Bell and Professor Peer Schenk from the Queensland Alliance for Agriculture and Food Innovation, and Suzette Argent from the Queensland Department of Agriculture, Fisheries and Forestry. The trials have also involved several farm consultants and state agency personnel.
Research sites are located near Biloela, Condamine, Moonie and Warwick in Queensland and Wee Waa in NSW. The Condamine site has medium clay loam duplex soil, the Moonie trial is located on a hard setting loam, and the other three sites are heavy clay soils.
On all sites one tillage resulted in slightly higher grain yield, although the differences were not statistically significant except at Condamine.
Dr Dang says the potential negative effect from tillage – reduced soil moisture – did not adversely affect productivity in 2012, most likely because of good rainfall between tillage and seeding and during the growing season. Dr Dang says this highlights the importance of timing of tillage and taking the seasonal forecast into consideration.
At all the sites, one tillage treatment significantly reduced weed densities in the no-till farming systems. Common weeds were sowthistle, fleabane, wild oats and turnip weed. A second tillage at the Biloela and Condamine sites further significantly lowered weed densities. Differences between tillage implements – chisel, offset disc and Kelly chain – were not significantly different in their impact on weed populations.
Tillage treatment slightly lowered soil bulk density, soil carbon and available phosphorus in the surface soil (0 to 10 centimetres).
One or two tillage treatments had no significant effect on soil organic carbon mass at the Biloela, Condamine and Warwick sites. However, at the Moonie and Wee Waa sites one tillage with either chisel, disc or Kelly chain significantly reduced soil organic carbon at depths of 0 to 10cm.
Dr Dang says it is important to note that at all sites in 2012 all tillage operations were conducted later in the summer fallow period, after 3 March. Tillage earlier in the fallow period could have had a far greater impact on fallow efficiency and water storage for the following crop.
Dr Dang and his colleagues’ research findings are supported by one of Australia’s best known long-term tillage research studies, conducted at Biloela in central Queensland (24.37º S, 150.52º E).
Dr Bruce Radford, formerly a research scientist with Queensland DSITIA and now retired, led the research with funding from several sources including the GRDC.
In this study, conducted on a deep alluvial clay soil capable of storing a lot of fallow water, 20 years of no-till on average out-yielded full tillage (disc and scarifier) by 30 per cent.
The long-term impact of tillage is well illustrated by one treatment, where even after six years of no-till, yields were still down by 30 per cent because the no-till period followed two decades of full cultivation.
However, by the seventh year of no-till following 20 years of full cultivation the yield gap began to close; the difference in the previous two crops (sorghum and chickpeas) being relatively small compared with crops on long-term no-till soil.
Minimum-tillage (stubble mulching) treatments involving the periodic use of a chisel plough, blade plough and/or rod weeder, and reduced-tillage using the same stubble-mulching implements and appropriate herbicides was also assessed against no-till and full tillage (all crop residues were retained in all comparisons).
Stubble mulching and reduced tillage over the 20-year tillage comparison phase delivered yields that were close to continuous no-till.
When followed by seven years of no-till the land that had previously been subjected to two decades of stubble mulching and reduced tillage continued to yield close to the long-term no-till. Their fallow soil water storage and soil characteristics were much the same as the long-term no-till treatment.
An overall conclusion from this research is that changes to soil attributes such as porosity and organic matter, when previously a full cultivation system was used, take a long time to be felt, but once this change has occurred the former full-cultivation land can start yielding as well as long-term no-till systems. Also, minimum-tillage and stubble mulching reflect soil characteristics and crop yield close to zero-till farming.Ongoing research
The research by Dr Dang and colleagues will continue to investigate soil attributes and crop performance where occasional strategic cultivation is used in an otherwise no-till system.
The research will include chemical aspects such as soil carbon status (including fractionating soil carbon into pools with differing lability), profile mineral nitrogen and potentially mineralisable nitrogen in labile organic fractions, phosphorus, potassium and zinc, and crop nitrogen and phosphorus uptake.
Physical attributes being studied include soil-moisture storage, bulk density, aggregate stability and soil strength. Biological issues being examined include microbial biomass, enzyme activity and microbial diversity, as well as more targeted measurements such as quantifying soil and stubble-borne pathogens, nematodes, and factors relating to pathogen suppression (for example, inoculum loads and subsequent disease incidence in fields and controlled pot trials).
Dr Dang’s team is assessing all these aspects in the context of profitability: the impact that strategic tillage has in terms of economic returns as well as biophysical and productivity effects.
Further details of Dr Dang and colleagues’ research are available on the GRDC website and in proceedings from the 2013 autumn round of northern GRDC Adviser and Grower Updates.
Dr Yash Dang,
07 4529 1245,
GRDC Project Code ERM00003
Region North, South, West