Influence of an injection system on the effect of activated soil steaming on Brassica juncea and the natural weed seedbank.

Soil steaming is a promising preventive method for weed control in high-value cash crops, such as vegetables and flowers. A 2-year experiment (20052006) was carried out to test the effect of five different systems of steam injection (surface or deep steam injection bar and three mixed systems at different steam distribution ratios between the surface and the deep bar: 1:2; 1:1 and 2:1) on an artificial infestation of Brassica juncea and on the natural weed seedbank. Treatments were carried out using steam alone or in association with two different exothermic compounds (KOH and CaO), distributed at two different rates (1000 and 4000 kg ha-1). The effects of treatments on the seedbank were analysed by the seedling emergence technique at three different soil depths (07, 714 and 1421 cm). Non-linear dose-response curves were used to correlate weed emergence with soil temperature sum. Surface steaming was the most effective treatment (up to 100% weed control) at 07 cm depth. Deep steaming depleted the weed seedbank up to 95% in the deepest soil layer. The most homogeneous weed control effect across the soil profile was obtained with mixed systems, with differences depending on their distribution ratio. The new steam injection systems increased the versatility of this innovative soil steaming machine and confirmed its efficiency in reducing the weed seedbank, making it a promising replacement of methyl bromide fumigation before growing high-value crops.