Burning narrow windrows for weed seed destruction

The recently developed technique of burning narrow windrows to kill weed seeds has been extensively adopted by WA crop producers. A chute mounted to the rear of the grain harvester concentrates harvest residues including weed seed into narrow windrows in preparation for burning the following autumn. Preliminary kiln studies determined that temperatures in excess of 400 degrees C for at least 10 s were needed to guarantee the death of ryegrass seeds while 500 degrees C for the same duration was required to kill wild radish seed within their pod segments. The effectiveness of burning narrow windrows of crop residues in killing annual ryegrass and wild radish seed was evaluated over four seasons in the northern wheatbelt region of Western Australia. Burning standing stubble was found to be less effective in killing annual ryegrass and wild radish seed present on the soil surface, than either burning conventional or narrow windrows. Higher biomass levels in narrow windrows increased the mortality of annual ryegrass and wild radish through burning by increasing both burning temperatures and duration of these higher temperatures. Although burning exposes the soil surface, increasing the potential for erosion, strategic burning of narrow windrows significantly reduces the erosion risk where, depending on harvester width, generally less than 10% of field area is exposed by this practice. (C) 2007 Elsevier B.V. All rights reserved.