Re: soil seed bank

E. Ann Clark, Associate Professor (aclark@crop.uoguelph.ca)
Sun, 21 Sep 1997 15:39:09 EDT

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