It's chilly in the bottom paddock


We know that some of our paddocks are colder than others, but how much colder? Do some paddocks have more frosts? And, if so, are frosts heavier in those paddocks? How does the cold air move around our farm? Researchers are comillg up with some answers.

PLANTING LATE - and accepting lower yields - may be helping you avoid some frost damage, but do you need Results from a project supported by growers and the Federal Government through the GRDC suggest some farmers may be penalising themselves unduly by planting late in paddocks where the risk of frost damage is small.

"We are looking at increasing yield potential by identifying less frost-prone areas that allow earlier planting than the current conservative planting dates," said University of Western Sydney researcher Frank Kelleher.

Dr Kelleher's research team from both the University of Western Sydney and the University of New England monitored temperature variation from 1999 through 2001 wheat crops in undulating crop land at 30 sites on two farms at Spring Ridge, in northern NSW.

They found that the lowest-lying sites had the lowest temperatures, with the highest total hours of temperatures lower than 2°C and O°C, as well as the longest duration of frost events and the lowest degree day temperatures over the wheat season. Plant development in commercial wheat crops and in sown plots was delayed at lower sites, reflecting the lower temperatures.

They found that differences in aspect, slope and altitude caused variation in temperature and frost incidence, even where the country was not particularly hilly. Temperatures were always lower further down the slope, indicating probable air drainage down-slope, irrespective of whether the slopes were long or steep.

However, they found relative position within the total length of a slope may be a key determinant of cumulative drainage effects and resultant temperature. Some results suggested that position in the slope may have an important influence on date of last frost, but that was so mainly on the steeper slopes.

The researchers found that farmers tended to underestimate frost frequency and severity, particularly in 1999, which was a relatively wet year and regarded by the farmers as largely frost-free. Frosts in that year in fact ranged from 15 minutes to several hours.

Mapping frost on your farm

The project indicates that incorporating frost risk into cropping strategies may require temperature data specific to individual farms. Continuous monitoring could help establish patterns of frost incidence on individual farms and then enable farmers to map variation in frost risk across their own farms.

Dr Kelleher said there was considerable scope to use readily available topographic data in a Geographic Information System (GIS), incorporateTemperature data and then map variation in frost risk across the farm. This approach offered the potential to segment landscapes into zones, enabling farmers to integrate frost into crop management strategies more effectively than at present.

Program 4 Contact: Dr Frank Kelleher 02 4570 1387 email

Region National, North, South, West