The
Mallee Farmer The varieties selected were Mandelup narrow leaf lupins, Pioneer 43C80 imidazolinone tolerant canola and Yitpi milling quality wheat.
Results
(a) Rainfall The average annual rainfall for Ouyen is 331mm, with 215mm falling in the April to October growing season. In 2010, the rainfall to December was 395mm and the growing season rainfall was 270mm, with more than half falling from August to October. (b) Soil water Water content in the top soil was similar for all soil types and increased with depth (P<0.001). The total water content to 100cm depth prior to sowing was 134, 156 and 171mm on the dune, slope and swale respectively. Observed differences in plant growth were not attributable to differences in initial soil water content possible due to the season having above average rainfall. (c) Residue loads Initial stubble load from the 2009 Yitpi wheat crop in the paddock ranged from 1285 kg/ha to 4626 kg/ha with no significant difference between soil types. This retained stubble was important early in the season for ensuring low soil erosion risk under low input break crops. Post-harvest residue load in late January 2011 was 1704 kg/ha, 1914 kg/ha and 1496 kg/ha for the dune, slope and swale experiments, respectively. There was no significant difference between any of the treatments in any of the experiments. However, there was a consistent trend for fallow to have less stubble present that the high input lupin treatment on all soil types whilst canola treatments tended to have more stubble than fallow in select experiments. Stubble in the fallow is attributed to the proceeding 2009 cereal crop.
Key Points
• Several break crop options were evaluated to determine their impact on soil erosion risk within the low rainfall Mallee; • The project assessed above ground biomass and stubble loads of canola, lupins and wheat grown for hay, relative to those achieved by wheat grown for grain, in a replicated field trial at Ouyen.
Unexpectedly, hay production (cut in October) was accompanied by no significant reduction in residue loads within soil types in January 2011 although there were downward trends. Lack of difference can partially be attributed to at least 50% of stubble remaining from the 2009 crop.
Results from the 2010 year showed that break crops can be grown in the Mallee but that their long term viability may be year and soil type dependant. Crop management may also need to be adjusted to meet a specific need of the farming system; such as weed or disease control.
(d) Plant density Most low input break crops had significantly lower plant densities than high input break crops, and most wheat treatments, on all soil types. As the crops grew, yellow leaf spot infected the wheat but there were no visible diseases in the break crops. This highlights the potential advantages of growing break crops to reduce disease incidence.
Within a wetter than average year it was demonstrated that soil erosion risk may be increased early in the season by sowing lupins or canola at low seeding rates, and late in the season by moving from grain to hay production.
(e) Crop biomass On each soil type, the lupin treatments had significantly less biomass than the canola treatments. Differences between high and low inputs for the same crop type were shown for both break crops on the swale and for canola on the slope. All wheat treatments, including hay, had similar crop biomass within the same soil type; except on the swale where the continuous wheat treatment was higher for an unidentified reason. At wheat flowering there were no significant differences in crop biomass (P>0.06) between any of the wheat treatments, including hay, within each soil type. Average above ground biomass was 4123 kg/ha, 4233 kg/ha and 5582 kg/ha for dune, slope and swale respectively. Consistent wheat growth within each soil type in 2010 provides a uniform background for all break crops established in 2011. (f) Harvest Grain yields, grain quality, selling prices around the time of harvest and N prices around the time of application were used to compare the economic viability of each crop. This provides a guide only, as prices change frequently; it does however provide insight into how economically feasible the introduction of these break crops are to Mallee cereal based systems. Overall wheat produced the highest grain yields and wheat, including hay, gave higher returns that the break crops. Hay also provided the added benefit of assisting with weed control.
Implications of the findings
This single year experiment has provided a first step in assessing the viability of introducing canola, lupins or hay production into a cropping system to reduce the impact of disease and weeds in the cereal phase, whilst maintaining ground cover.
Several years of experimentation and monitoring will be required before definitive recommendations on break crops can be made. This project will be continued in the 2011 season using the 2010 wheat as a background for break crops sown in 2011.
Recommendations
• Evaluate low input break crops in a year of different rainfall patterns to determine their viability in more than one season; • Monitor residue load before sowing and shortly thereafter to determine if ground cover from residue compensates for low plant density in break crops; • Measure the seasonal course of light interception to determine for how long break crops are able to maintain 50% ground cover; • Record crop residue immediately after harvesting brassica and hay to determine if early harvest makes the soil more susceptible for soil erosion; • Record crop residue at least three times between harvest and sowing to determine the rate of loss.
Acknowledgements
This project was supported by the Mallee CMA, through funding from the Australian Government’s Caring for our Country and the GRDC and DPI.
Further Information
The information for this article has been taken from “Do break crops improve the soil health of Mallee cropping systems?” -- a report for the Mallee CMA by DPI Victoria Future Farming Systems Research. A copy of the report can be downloaded from the Mallee CMA website: www.malleecma.vic.gov.au
Contact
Angela Clough, DPI T: (03) 5336 6618
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