GRAINGROWERS AND breeders have produced better yields than generally acknowledged with a new study finding significant increases occurring in wheat yields in many parts of Australia.
The nationwide research was conducted by David Stephens of the WA Department of Agriculture, who said that a previous study by Hamblin and Kyneur (1993) had found that between 1950 and 1990 the average annual rate of increase for wheat yields was only about 8 kg/ha.
He told the recent Australian Agronomy Conference, "more recent data show that, in the 20 years to 2002, the nationwide annual increase has been an average 25 kg/ha, a three-fold increase over the previous study".
Dr Stephens said the trend toward higher per hectare productivity began some years ago and was influenced by:
- changes in farm management with growers addressing a range of issues such as sowing crops on time, controlling weeds and diseases, overcoming soil-related constraints to production, improving crop water-use efficiency levels, and utilising new and improved varieties
- higher levels of nitrogen fertiliser applications to crops and more crop diversity assisting with soil nitrogen fixation and cleansing the soil of root diseases
- much greater investments in crops research.
Dr Stephens initially did a national study of four major crops for the National Land and Water Resources Audit using agricultural census data for the period 1982-1996, but has subsequently updated the analysis for wheat using the recently released 2000-2001 full agricultural census and industry interviews.
Where the action is
Dr Stephens said that large wheat yield increases had occurred in south-eastern and north-eastern NSW, north-western and southwestern WA, the wetter districts of SA and the south-eastern edge of the Darling Downs in Queensland.
Yields had not kept pace in areas where rainfall was particularly variable, such as large parts of Queensland, northern regions of SA, the mallee country of western NSW and the northern Wimmera of Victoria.
He said farmers in the best-performing shires consistently increased nitrogen fertiliser applications and crop diversity by growing crops such as pulses, oilseeds and sorghum in rotation with cereals. However, in areas where rainfall was seasonally unreliable, farmers tended to adopt risk-aversion practices such as applying less nitrogen and not planting as much non-cereals in rotations.
Dr Stephens said the most profitable farm businesses in the 1990s had high productivity increases, low yield variability, and high cropping intensity.
"As well, farm business profits appear linked to the adoption of new farming technology and the amount of inputs applied," he said.
"Water supply to crops and nitrogen deficiencies appear to be the most limiting factors to crop production but acidity, sodicity and plant diseases are also major limitations.
"To maintain the yield trend increases, improvements must continue in varieties, management and nutrient use. However, future developments should also focus on the unique regional pattern of climate and soil constraints.
"The importance of accurate long-range weather forecasts has increased with the switch to a higher-input farming system that has higher input costs."
Contact: Dr David Stephens 08 9368 3346