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A follow-up survey by Vanclay and Hely (1997) foundthe number of drills that could handle more than2 t ha1 of stubble had almost doubled to 28% over the3-yr period. Of more concern was that only 7% of drillsin the Central West of New South Wales could handlestubble of 3 t ha1. A considerable disincentive toincreased stubble retention is the high cost of tillageand sowing machinery to handle stubble densitiesgreater than 3 t ha1. This amount of stubble can beleft after just 2 t ha1 of wheat have been harvested.Adoption of stubble retention will continue to be slow,notwithstanding acknowledged benefits to resourceconservation, while there are real and perceived financialdisincentives such as cost of machinery changeover aswell as uncertain benefits for their farmprod uctionsystem. Farmers are reluctant to commit additionalscarce funds to purchase new machinery suitable forhandling high stubble densities during the testing phaseof the practice on their farm. Farmers will only purchasenew equipment if the practice is found to be better thanwhat they are currently doingto rotate around the shank. Factors contributing to stubblerotation are: a large vertical clearance of at least 600mm; ashank of circular cross-section of 50mm diameter; shortstubble length; and tines with a 708 rake angle.The findings of Slattery and Riley (1997) demonstratethe opportunities for improving the stubble handlingperformance of tillage and sowing equipment. Thisinvestigation examines the effect of these factors on theflow of wheat stubble through a scarifier and a combinedrill that are typical of the implements owned by manyfarmers in central NSW.The study involved assessing the effects of strawlength, tine spacing, placement and shape on the abilityof implements to handle stubble levels exceeding 3 t ha1where 80% of the standing stubble exceeded a strawlength of 400 mm. The implements used for the studyinvolved a Napier Grasslands scarifier with ‘edge-on’tines with a vertical clearance of 500 mm, and a JohnShearer combine drill that was fitted with Primary SalesAustralia ‘C-shaped’ coil tines with a vertical clearanceof 400 mm.
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