Feedlot manure, containing seeds of twelve weed species, was composted in a windrow to determine whether composting would kill the weed seeds. The twelve species of weeds included: Thfnpsi arvensc, Polygonum comolzwliis, Aiienn fntua, Chenopodium album, Setarin viridis, Galeopsrs tetrahit, Poly,yoiruiri pcrsicorio, Ainnrnnflius retrojlexus, Kochin scopnrin, Gnlium npnrine, Malm rotundrfolm, and Mntrrcnrrn pevfornta. The windrow was managed to maintain core temperatures between 55°C and 65°C for as long as possible.After two weeks of composting, seeds of Gnlriirii npnrriie, Sctnrm zvrrdis, Kocliin scoparin, Mntricarin pevforatn, Thlapsi amense and Poly~yoniiin cotivolvulirs had 0 percent viability in a tetrazolium test. Seedsof Amnrnnflius retrt$cwis had a viability of 3 5 percent, the highest of the twelve species studied. After four weeks of composting, the viability for all twelve species was 0 percent. Therefore, seed viability was extremely low after even two weeks of windrow composting and four weeks of composting was enough to kill all seeds of the twelve species studied. IntrodtictionThe disposal of cattle manure is a problem for many feedlot operators. Feedlot manure is typically land spread, but this may lead to increased weed problems. For example, Blackshaw and Rode (1991) found that many weed species (including Sctaria viridis, Kochia scoparia, Antaranthus refroflexus, Ckenopodiirnr albtini, Pol!jgonu ttt convolvulus, and Mdva rotzrndifolin) were able to survive rumen digestion. The proportion of the population that was able to survive varied with species.There is a common perception that composting kills weed seeds. However, there has been little documentation of this. A study done in Florida by Shiralipour and McConnell, 1991, reported that certain weed species were killed when placed in a pile of composting yard waste. This only held true when the seeds were exposed to high temperatures within the pile.Egley, 1990, reported that killing temperatures vary inversely with the moisture content of the seed. Consequently, moist seeds within a compost pile should be killed at a lower temperature than dry seeds of the same species. Materials and MethodsTwelve commonly occurring weeds in western Canada, were chosen for this experiment. These species include weeds from a number of different families (Table 1) nd have a range of seed coat hardness. Preliminary StudyA preliminary study was carried out at the Olds College Composting Centre. be maintained within the optimum range to kill the seeds of the twelve selected species of weeds. Windrows of a typical feedlot manure mixed with beddingThe goal was to determine how long the compost windrow temperatures must