Tillage might be unnecessary for crop production, but no practical mechanised system can avoid field traffic, usually by wheels, often when subsurface soil is moist. Soil damage is rarely obvious in CA, because soil compaction is universal when we 'random wheel' about 50% of crop area in each crop cycle in mechanised systems, and natural amelioration takes several years.Research comparisons between wheeled and long-term non-wheeled soil have consistently demonstrated major wheel impacts on run-off and infiltration, plant available water capacity, soil biota, planting energy requirements and crop performance. Some evidence from Australia and China is summarised in table 1, and is consistent with wheel compaction results from elsewhere, including some with small-scale equipment, when the control was long-term non-wheeled soil.In practical terms, wheel damage can be minimised only by the use of controlled traffic or permanent bed farming (CTF), where all load-bearing wheels are restricted to permanent traffic lanes oriented for drainage. Precise crop management in soft soil from hard compacted traffic lanes also provides a range of 'system' benefits, improved timeliness and cropping opportunities being the most obvious (McPhee et.al 1995). Productivity and sustainability benefits of CTF have been confirmed by surveys of CTF farmers in Australia which have demonstrated increasing yields and cropping frequency, with less time, fuel, fertiliser and agricultural chemicals (e.g.Bowman 2009).CTF will reduce environmental impact by reducing energy requirements, runoff and soil loss, and the emission impact of partial CTF in organic vegetables in the Netherlands has been demonstrated by Vermeulen and Mosquera (2009). The likely magnitude of this effect in Australian broadacre production was explored by Tullberg (2010), and this paper reports a pilot trial of CTF emissions.
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