The logic presented is that organic matter mineralizes in
ways/rates/timing which a) is not controllable, and b) is not easily
predictable, and hence, c) has the potential to continue to pump out
labile N long after the crop has been harvested. On this basis, they
discount the merit of long-held organic farming wisdom, namely, "feed
the soil" as a source of immobilized and slowly released mineralized
nutrients to feed the crop. The next dimension to this logic is that
perennial forages, which enhance soil OM, are hazardous to the
environment because when they are plowed under, they mineralize and
release copious amounts of N - with again, the potential to pollute.
In response, I can only agree with their logic **if** one continues
to crop in conventional ways - with the land bare or under dead
stubble for 7- 10 months of the year. However, a great deal of the
rationale behind organic field crop agriculture is to keep the land
covered with a live - and predominantly, growing - crop year-around.
This practice, in addition to supplying a sink for labile nutrients,
also keeps the soil colder longer and enhances the synchrony between
such T-sensitive processes as microbially-based mineralization and
plant-based uptake.
I would be interested in the comments of SANETers on these issues,
particularly as they pertain to the definition of soil quality, and
ultimately, the attributes of the "ideal" soil that we should be
shooting for. 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