THE EFFECT OF TEMPERATURE ON VIABILITY OF IMBIBED WEED SEEDS

Imbibed seed of 10 common arable weeds were placed in trays in initial ly moist soil and, after imbibing for 2 h, heated in ovens/incubators set to 31 degrees C, 42 degrees C, 56 degrees C, 75 degrees C or 100 d egrees C for 0.5, 1, 2, 4, 8 or 16 days or at 102 degrees C, 155 degre es C, 204 degrees C or 262 degrees C for 0.5, 1, 2, 5, 7.5 or 10 min. After heating, seeds were incubated for 28 days at 10/20 degrees C or 20/30 degrees C on a 12 h dark/light regime, depending on species, and germination recorded. At the lower temperatures, germination of all s pecies was prevented by temperatures of 75 degrees C or higher for per iods of 0.5 days or more. Germination was lower after treatment at 56 degrees C than at 31 degrees C or 42 degrees C for all species except Rumex obtusifolius. The maximum temperature required to prevent germin ation varied among species and was of greater importance than the dura tion of heating. Germination was variable with duration of heating. At the higher temperatures, there was very little germination of any spe cies after heating at 204 degrees C for 7.5 min or 262 degrees C for 5 min or more. Seeds were greatly buffered from the air temperature by 3 mm of soil, throughout the shorter duration of heating. The average temperature of the soil, over the 10 min heating required to prevent o ver 90% germination, varied among species and ranged from 48 degrees C for Avena fatua to 65 degrees C for R. obtusifolius. This work implie s that composting systems maintained at 65 degrees C are unlikely to p rovide an efficient method of weed control. Recommendations for improv ement of the laboratory technique are suggested.