Soil steaming effects on weed seedling emergence under the influence of soil type, soil moisture, soil structure and heat duration

Soil steaming applied in bands is a new technology with the potential to radically lower the burden of hand-weeding intra-row weeds in non-herbicidalvegetable cropping. Preliminary studies with band-steaming have shown effective control of viable weed seeds when the maximum soil temperatures reach 60–80◦C. This temperature range has a particular agronomic interest,and the present study aimed at investigating the influence of soil factors and heat duration on weed seed mortality of soil steaming targeting 60–80◦C. Two soil types (sand versus sandy loam) and two moisture levels (moist versus dry) were studied in one experiment (expt) while two levels of structure of a sandy loam (coarse versus fine) were included in a second experiment. A third experiment was focussing on the significance of heat duration expressed as the speed of cooling-down after steaming had been stopped. Weed control efficacy was generally greater in sand than in sandy loam and soil irrigation further improved weed control. Steam application to the finely structured soil improved weed control efficacy relative to that obtained with the coarse soil of larger aggregate size. The rapidity of cooling from the maximum temperature did not affect the efficacy of the treatment on weed seed mortality. Based on these experiments, a maximum soil temperature of 80◦C should ensure satisfactory weed control under moist soil conditions, especially if the soil is cultivated prior to steaming.