Ground Cover Supplement : GC Supplement - No-till
GROUND COVER NO-TILL 8 NO-TILL TODAY A green approach to weed control SCOTT McCALMAN WAS SO TAKEN WITH THE IDEA OF SOUTH AMERICA'S GREEN MANURE ROLLING TECHNOLOGY HE BUILT A UNIT OF HIS OWN AND FOUND THE IDEA REALLY WORKS BY BERNIE REPPEL IT SOUNDS TOO good to be true: a green manure crop that controls broadleaved weeds and grasses without herbicides, mulches soil to a depth of 75 to 100 millimetres, has soil moisture, nutritional and agronomic benefits and is relatively cheap to plant. Yet it works, which is why central New South Wales no-till growers Scott and Jo McCalman have 350 hectares planted this year to a manuring mix of oats and field peas on their properties ‘Jedburgh’ and ‘Drungalear’ outside Warren. When the oats – saia variety, with a large biomass – reach the milky dough stage, the crop will be rolled down with a home-built roller whose strips of angle iron (20mm apart) crimp and crush the green material to a mulch that totally covers the soil. It will deliver excellent weed-kill and a reasonably long-lasting ground cover that cools the soil, increases microbial activity and improves infiltration of rain. The cover crop is sown early, ready for rolling by May or June to minimise the impact on crop rotation and the farming system, and to optimise the chance of conserving enough moisture for a sorghum, cotton or pulse crop the following summer. Mr McCalman first heard about the South American-developed green manure rolling technology at a Western Australian No-Tillage Farmers Association (WANTFA) conference and came home convinced of the range of benefits it promised to his farming system. Over 15 years, the McCalmans moved progressively to an all-cropping, controlled-traffic, no-till system. In an area with a highly variable annual rainfall of 455mm, they see moisture conservation, improved soil structure and profitability as the main benefits of conservation farming. With the ‘highly variable’ rainfall pattern oriented slightly to winter falls, crops on ‘Jedburgh’ and ‘Drungalear’ include wheat, canola, chickpeas, broadleaf lupins, sorghum and cotton. “We have found the zero-till system to be more secure, particularly in dry years,” Mr McCalman says. “It allows us to grow a harvestable crop even in the tougher dry seasons. We believe a full zero-till program and maintenance of maximum stubble cover leads to a harsh inter-row environment for weed development, thus suppressing inter-row weed germination, growth, and development. “The whole thing is soil-cover-driven and, even after a zero-tilled dryland cereal crop that might have gone three tonnes to the hectare – leaving about six tonnes to the hectare of stubble – you can still see the soil through all that stubble, and I want to cover the soil totally. “We get this – as well as excellent weed control – when we roll a green manure crop. We had to come up with a smarter way of controlling weeds, because the cost of inputs is killing us, and this seems to be it.” Mr McCalman built his 12.2-metre roller on an existing tool bar in 2002 – matching the width to his existing planters – and tried it first with saia oats alone, then with a mixture of oats and vetch (dropped for its ability to persist as a weed) before settling on the mix with field peas. He found peas will grow on most soils, fix a lot of nitrogen and have a well- sized, competitive seed. He also found the crimping action caused by the blunt angle iron will kill the crop in nearly all cases, while cutting is likely to make it grow again. So far – with the residual nitrogen benefits in mind – the McCalmans have limited their application of green manure rolling to particular problem paddocks, mostly those earmarked for a rotation crop, not a cereal. Last year, with a late seasonal break, they did use it on ‘good Knife rolling mustard in the mid-north of SA.
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