Abstract
Timely sowing and effective weed control are essential for dry season cotton production in tropical Australia. This study was conducted during the 2003 dry season to assess whether a weed and bed management system can be developed which would allow sowing to occur as soon as fields were trafficable after the wet season. The use of Roundup Ready® technology was also assessed as a potential management system for weeds after the crop has emerged. Minimum tillage cotton sown into a wet season cover crop and into a retained dry season sorghum stubble, were compared with conventionally cultivated cotton sown into tilled fallow in the Ord River Irrigation Area (ORIA) in northern Western Australia. Treatments included with and without the residual pre-emergent herbicide pendimethalin and glyphosate application was split across all treatments. Weed and cotton biomass were compared and lint yield and quality determined at the end of the season. Both pendimethalin and glyphosate effectively controlled those weeds present in the year this study was conducted, and the combination of both herbicides was not required. Cotton seedlings in the minimum tillage treatments tended to be more vigourous than those from the conventionally tilled treatments 32 days after sowing (DAS). The weeds in the fallow treatment suppressed the growth of the cotton seedlings compared to the fallow+ pendimethalin treatment when glyphosate was not applied. However, 61 DAS, the effect was more obvious and the biomass of cotton was almost double that of weeds. Application of glyphosate increased lint yield through better weed control (1864 c.f.1728 kg ha-1, P = 0.020), although interaction with various treatments was highly significant (P = 0.008). Only the fallow treatment demonstrated a significant weed control and yield increase from the application of glyphosate. The application of glyphosate also increased fibre length, although this appears to be related to a reduction in weed competition rather than an intrinsic association. This experiment indicates that a minimal tillage system utilizing Roundup Ready® technology as part of a dry season cotton production system in the tropics shows potential, as effective weed control could be achieved without the use of residual pre-emergent herbicides.
