Winter cleaning pays dividends
GroundCover™ Issue: 19
100% legume pastures double $$ returns
Wheat yield increases of more than 3 t/ha above the regional average have been recorded in trials at Rutherglen in north-east Victoria, following removal of grasses from legume pastures.
According to Glen Scammell, pastures and crops research agronomist at the Institute for Integrated Agricultural Development, similar results are being reported by farmers who have adopted 'winter cleaning' pasture renovation techniques.
"I know of district farmers who have achieved wheat yields of 6.5 and 7 t/ha where the regional average is under three tonnes," Mr Scammell said.
The research, supported by growers through the GRDC, has shown that when the legume content of pastures was manipulated to 100 per cent, wheat yields in 1993 and 1995 reached 6.1 tonnes and 6.0 tonnes respectively.
The benefits to producers using the technique include increases in accumulated soil nitrogen, significant reduction in the risk of grass-borne take-all disease and reduced grass-selective herbicide use in the first crop.
Protein up, too
Complementing the yield increases, grain protein received a boost from an average of 11.2 per cent in 1993 and 12.1 per cent in 1995 where there was no winter cleaning, to an average of 13.2 and 12.4 per cent for 1993 and 1995 where winter cleaning was applied.
Mr Scammell winter cleaned the pastures in 1991 and 1992 with Gramoxone® at 1.5 L/ha applied at the subclover plants' six true leaf growth stage. The cost is about $20 per hectare for the chemical. Grass numbers per square metre at the autumn break in 1993 were reduced from 1,177 in the control to 62 in the winter cleaned, and to just two in 1995.
"Annual grasses have similar growth characteristics to cereals, and are difficult and expensive to control in crop," he said. "The continued use of grass-selective herbicides in-crop has led to the development of herbicide-resistant weeds.
"Using non-selective herbicides in the pasture phase to remove grasses reduces the threat of herbicide resistance and retains the availability of grass-selective herbicides for use within the crops."
100% legumes for two years
With 100 per cent legume in the last two years of the pasture, soil nitrogen availability to the following crof increased markedly, said Mr Scammell. "At a soil depth of 110 cm for example, 242 kilograms N/ha was measured in 1995 following perennial legume pastures, compared with 160 kilograms without winter cleaning in the pasture phase."
"We advocate herbicide application at the clover six leaf growth stage (usually late June to early July) for two consecutive years.
"To ensure the herbicide makes contact with all the plant parts growing above the ground, the pasture should be short (two inches or 5 cm); herbicide is applied at a high water rate (100 L/ha) and a high pressure rate (300 kPa). The subclover is tolerant at this growth stage to Gramoxone and will regrow, while the annual grasses are killed." (If you're using Paraquat 250 check spray rates on the label.)
Compared with spray-topping
The Rutherglen trials compared winter cleaning with spraytopping. While the latter did reduce grass numbers, there was a large carry-over into the cropping phase and the soil nitrogen levels were significantly less than the winter-cleaned pastures. Consequently the effect on yield was not as large as that achieved through winter cleaning.
Mr Scammell said that under the winter-cleaning strategy, from 6-8 weeks of grazing was lost following spraying. It is advisable to graze off the sprayed pasture to help remove the dead and decaying litter, which helps the subclovers recover.
"On the trial at Rutherglen, merino wethers were returned onto the plots two days following spraying, and although they lost 5-10 kilograms initially, this was soon recovered during the spring flush through better quality feed."
Care for your pastures
"We often expect our pastures to perform at the same level as a legume crop yet we do not treat them with the same level of management expertise nor with the same level of inputs and commitment.
"Annual top-dressing with fertiliser, a good autumn clover density, regular monitoring, control of weeds and pests and sap tissue tests to determine the nutrient status of legume plants need to become common practices.
"If we want the pastures to grow we need to feed them with fertiliser. If we want the legume pastures to fix nitrogen, we need a high plant density, we need to control the weeds that use the nitrogen, spray for pests and graze to ensure the pastures provide an end product."
Subprogram 3.4.2 Contact: Mr Glenn Scammell 060 304 500