Recent CSIRO field studies on the cost-effectiveness of grazing grains in high rainfall areas have been further analysed, with the results of summer 2004 trials now included.
These studies were reported in the last issue of Groundcover (June 2004), and the main message was that the incorporation of dual-purpose wheats into grazing systems in higher rainfall areas could lead to a large increase in productivity and profitability.
CSIRO Plant Industry lead researcher Dr Hugh Dove points out that the positives of using dual-purpose wheats have to be balanced against the loss of grazing between the time pasture is sprayed out and the time stock can graze the wheat. In wetter areas, some of the grazing lost by pasture removal can be recouped by sowing a brassica forage crop in spring.
This issue was researched near Canberra in spring-summer 2003-04, and the results update the earlier findings.
Areas destined to be sown to winter wheat or to forage oats were either left fallow over spring-summer, or sown to Hunter hybrid brassica in mid-September. Crossbred lambs began grazing the plots mid-December. “By the end of grazing (16 January), the brassica crop had provided over 2100 grazing days/ha and the weight of lamb produced was 637 kg/ha,” Dr Dove says. “In terms of lamb carcass gain over the period, and the net costs of producing the crop, this amounted to more than $840/ha.”
However, this gain may come at a cost, - the impact of the brassica"s use of water from the soil profile.
"By mid-December, there was about 120mm less water in the first metre of soil under the brassica crop,” Dr Dove says. “Assuming that every reduction of 1mm in soil water content potentially costs 20kg grain yield, valued at $160/tonne on-farm, this extra water use... had the potential to cost the system $384/ha.”
But, “by mid-March, the difference in soil water content to one metre depth under the brassica crop, compared with adjacent fallow areas, was only 30mm. At most, this would cost the system only $100 in foregone crop yield.
“The difference between the net value of animal gains ($840) and the potential reduction in grain yield due to the brassica"s water use ($100-$384) suggests it is profitable to include the brassica crop in the rotation, but the calculations assume that the wheat crop has been successful.”
For more information:
Dr Hugh Dove, 02 6246 5078, firstname.lastname@example.org
GRDC Research code: CFP 00009, program 4