Ground Cover South : Ground Cover 056 June-July 2005 - South
11 clay site is close to the sandy paddock. Increasing soil firmness and thus available moisture by rolling the paddock at sowing time, particularly in sandy paddocks, can also reduce frost damage. "Using a heavy roller on the soil immediately after sowing reduces the surface area of the soil. This in turn conserves soil moisture, and therefore heat," says Ms Rebbeck. "This is because the release of moisture and heat overnight is slower and more even." It also appears that sowing plants less densely on dark soil helps to conserve moisture and provides a larger surface to absorb heat during the day and release heat at night, although it may carry a yield penalty. However, this is not yet proved in trials. Later in a crop's maturity, the less dense canopy allows airflow and prevents cold air pockets from forming. ConsultAg director and farm consultant Garren Knell says that results in WA field tests support the SA findings. In particular, soil colour and texture seems to be important for the level of heat capture. WA field trials to test the effect of doubling the spacing between rows did not improve frost tolerance on white, sandy soils. "The soil needs to be dark in order to absorb the sun's heat during the day," says Mr Knell. "The light-coloured soil on which we did our trials is reflective, so not only did we find that the wider spacing reduced wheat yield by 10 to 12 per cent, but it did not protect against frost." Additionally, Mr Knell says it is important that growers identify frost-prone paddocks and suggests adopting the following principles: n don't aim for maximum yield: sow later at a lower seed rate and apply a moderate rather than high level of nutrients such as phosphorus and nitrogen -- inputs saved on frost-prone paddocks can be applied to paddocks with a low frost risk; n sow longer-season varieties, or more tolerant cereals such as barley or oats; n sow a mix of two wheat varieties (for example long and medium maturity) to give two flowering times in the one paddock and reduce potential frost damage; n consider removing or reducing stubble on dark, heavy soil paddocks, to try to maximise heat capture and release by the soil; and n avoid applying nitrogen late in the season, as this seems to make the crop more susceptible to damage. Although nutrition is essential in helping a crop combat frost, if the crop has a sufficient level of nutrients adding excess nutrients is simply a waste. "We have found that unless a grower's soils are marginal for elements like potassium, adding extra nutrition provides no extra frost protection," Mr Knell says. GRDC Research Codes DAV0006, DAN360, CAG00002, S00017 For more information: Dr Peter Hayman, 08 8303 9729; Melissa Rebbeck, 08 8303 9639; Garren Knell, 08 9881 5551 SOME SUGGESTED STRATEGIES Minimising frost on prone paddocks 1 DON'T JUST AIM FOR MAXIMUM POTENTIAL. CONSIDER: n Delaying seeding; n reducing seed rates (50 to 60 kilograms); and n using conservative phosphorus (eight to 10kg) and nitrogen rates (30 to 40kg). 2 SOW MORE TOLERANT SPECIES AND VARIETIES n Barley 2ºC more tolerant than wheat; and n oats the most frost-tolerant cereal. 3 DON'T SOW CEREALS ON WIDE ROWS TO MINIMISE FROST ConsultAg trials show: n Wide row sowing can cost 10 to 12 per cent yield; n no differences in temperature at head height; and n no difference in percentage of frost damage. 4 BLENDING WHEATS HEDGES YOUR BETS n Long and short season; and n tall and short straw. 5 ENSURE ADEQUATE POTASSIUM SUPPLY n Adequate potassium results in stronger tissue and thicker cell walls. 6 CONSIDER REMOVING STUBBLE ON HEAVY SOIL PADDOCKS n Stubbles act as a mulch that can reduce heat absorbed. 7 CONSIDER CLAYING SANDY SURFACED SOILS n Overcomes non-wetting; n retains more moisture in soil surface; and n increases heat absorbed by soil. 8 AVOID LATE NITROGEN APPLICATIONS. n Late nitrogen applications may increase exposure to frost; and n stem stores of carbohydrate reduce freezing point, and carbohydrate is mobilised when roots uptake nitrogen. 9 FOR EXTREME AND RARE FROST EVENTS n Cannot farm to avoid exceptional and rare climatic events, so n have in place a sound business structure -- off-farm investments, farm equity and farm management deposits. THE SEARCH FOR FROST TOLERANCE GENES JUNE/JULY 2005 GROUND COVER Frost By HELEN OLSEN n The frost protection mechanisms used by a species of grass in the same family as wheat may give scientists a mechanism with which to improve wheat's frost tolerance. A research group at the Leslie Research Centre in Toowoomba is using conventional breeding techniques to try to introduce frost tolerance from these related grasses. Crop physiologist Troy Frederiks travelled around Australia's east coast in search of these grasses. "We have developed a substantial collection of this grass species and all tested types show good tolerance to natural frosts of temperatures as low as minus eight degrees Celsius," says Mr Frederiks. "In fact in an earlier study the type tested showed good frost tolerance to -12ºC." However, he says the genetic mechanisms and their suitability to wheat have not yet been determined. The team has also tested synthetic wheats characterised as frost-tolerant from the International Wheat and Maize Improvement Centre (CIMMYT), and lines developed by Dr David Woodruff (now retired from the Queensland Department of Primary Industries and Fisheries). However, none of the lines showed useful increases in frost resistance compared to controls. "The CIMMYT lines tested are very long-season wheats, and therefore may have been classified as frost tolerant simply because they were not in head during the frost danger period," says Mr Fredericks. He says wheats with just a few degrees more resistance would allow early sowing in northern growing regions. This would lead to dramatically increased yield potential by more effectively using stored soil water and reducing the chances of a hot finish to the season. Another research team, led by associate professor Grant Daggard at the Centre for Rural and Environmental Biotechnology (CREB) at the University of Southern Queensland, is exploring novel ways of introducing frost tolerance into wheat plants. "One problem with frost is its randomness," says Dr Daggard. "Growers can delay sowing wheat to avoid spring frosts, but that's estimated to cost one per cent of yield for each day's delay. This yield penalty is particularly frustrating when there isn't a frost that season." Given the difficulty in identifying variation for frost resistance within wheat, Dr Daggard's group has introduced new genes into wheat plants, including one that produces an 'antifreeze' protein that is active in the transformed plants. Some of the newly engineered plants are being prepared for whole-plant testing in artificial frost environments. Dr Daggard points out that the research is mainly proof-of-concept, and there will need to be more acceptance of genetically modified organisms before these wheats become viable alternatives. A research team at the University of Adelaide has had greater success, identifying two genetic locations expressing the frost tolerance trait in barley using molecular marker technology. Postdoctoral fellow Dr Nigel Long says the first lines developed from an aggressive breeding strategy to incorporate these frost tolerance genes into commercial barley varieties will be evaluated in screening nurseries in 2005. "We're testing about a dozen lines derived from a cross between Australian barley lines and a Japanese barley variety Haruna nijo, which has shown a greater level of frost tolerance than commercial Australian varieties," says Dr Long. GRDC Research Codes DAQ00002, USQ00002, UA00063, UA00073 For more information: Troy Frederiks, 07 4639 8876; Dr Grant Daggard, 07 4631 2228; Dr Nigel Long, 08 8303 6738 Measuring frost Developing advice for growers: consultant Garren Knell checks a field trial.
Ground Cover 057 August-September 2005 - South
Ground Cover 055 April-May 2005 - South