Christian, consistency isn't a valid test; some other factors could also be consistent (for example, the roots of plants killed by Roundup may very well decay differently than roots killed by having their stems and leaves abruptly removed). I don't know, there could be other things we haven't thought of. That is the point of the experimental method, to keep us from fooling ourselves by uncontrolled observations. The experiment is easy, and simple, and requires no fancy equipment. And if you are already sure of the effect, then go on to figure out new experiments to answer your further questions. Many really interesting questions have been answered first by simple backyard experiments. (Darwin for example was an inveterate backyard experimenter.) I guess I don't really understand your reluctance to investigate this. Working things out is deeply satisfying. Lou