From aclark@crop.uoguelph.ca Sun Sep 21 21:51:50 1997 Date: Sun, 21 Sep 1997 15:39:09 EDT From: "E. Ann Clark, Associate Professor" To: sanet Subject: Re: soil seed bank Joel: a fascinating area. Have a look at a book by Mary Allessio Leck, V. Thomas Parker, and Robert L. Simpson, called Soil Seed Banks. 1989. Academic Press. All kinds of neat stuff relating to your questions, including species specific predation. Chapter by Cavers and Benoit includes a table on numbers of viable weed seeds in arable soils (range is 250 to 130,000 seeds/meter squared, with most in the range of 15-20,000). Chapter by Baskin and Baskin (major contributors to this literature) discusses one particularly intriguing aspect - that "leaf-filtered sunlight inhibits germination of nondormant seeds". I've looked into this and was fascinated to realize that the ratio of red:far-red light (which affects the function of phytochrome, a key developmental hormone) changes upon filtration through a vegetative canopy. In practical terms, this means that keeping the land covered by living plant material REPRESSES germination of weed seeds - leaving the land open and bare ENCOURAGES weed seed germination. Residue doesn't work - has to be living stuff, I think. Thus, the focus of organic farmers in keeping the soil covered at all times is revealed as having yet another beneficial effect - weed control. This kind of stuff was studied in depth in the UK about 10-20 years ago. H.A. Roberts was a major contributors. Ann ACLARK@crop.uoguelph.ca Dr. E. Ann Clark Associate Professor Crop Science University of Guelph Guelph, ON N1G 2W1 Phone: 519-824-4120 Ext. 2508 FAX: 519 763-8933