> ----------
> From: Sean Clark[SMTP:msclark@ucdavis.edu]
> Sent: Friday 22 May 1998 7:00 PM
> To: Sheryl N. Swink
> Cc: sanet-mg@shasta.ces.ncsu.edu
> Subject: Re: How does organic differ from sustainable ag?
>
> At 05:32 PM 5/22/98 -0500, Sheryl Swink wrote:
> >How about it, fellow sanet-mg folks? Do you, especially those who are
> >producers (not just consumers, researcher/extensionists, and
> interested
> >digesters like myself), find that this is a generalizable fact? Or
> has it
> >become a myth? What is the current state of affairs in terms of
> yield
> >comparisons between organic and conventional methods? Are there now
> >reliable organic practices by which farmers are regularly attaining
> or
> >surpassing expected conventional yields onece past the transition
> stage?
> >Anyone have any current research data/references to address this
> issue?
> >
>
> Sheryl,
>
> Organic crop yields are sometimes lower than conventional yields due
> to
> inadequate (N) nitrogen availability or excessive weed competition,
> particularly during the transition, but this really depends on alot of
> interacting and site-specific factors. Stanhill (1990) reviewed about
> 200
> studies comparing organic and conventional cropping systems in Europe
> and N.
> America and found that organic yields averaged about 9-10% less. This
> is an
> interesting and important finding but may not tell you much about a
> specific
> region or crop due to geographic differences in soils, climate, pest
> pressures, farmer experience and support, market demands, etc. The
> results
> of studies coming out since then have been variable.
>
> At the Sustainable Agriculture Farming Systems (SAFS) project at the
> University of California at Davis, we've had lower organic corn and
> tomato
> yields (compared to conventional years) in some years due to N
> immobilization by soil biota and weed pressure. However, bean yields
> have
> often been higher under organic management.
>
> Nitrogen mineralization/immobilization is sometimes less predictable
> in
> organic systems and may present problems for crops with high N
> demands, such
> as corn. However, after 10 years of farming organically these soils
> have
> been pretty consistent in supplying adequate N. Last year we had a
> weed
> problem in the organic corn plots. Crow damage at germination
> resulted in
> poor stands in the organic and conventional treatments. Consequently,
> weed
> pressure was high due to the gaps. Herbicides were used in the
> conventional
> system to prevent yield loss but no economically feasible control
> options
> were available in the organic system once the corn was too high to
> cultivate.
>
> Organic tomato yields at the SAFS site have equalled conventional
> yields
> over the last few years. Weeds can be hand hoed out of this
> high-value crop
> and other pest groups (insects, nematodes, and diseases) are not a
> problem.
> This is not the case in the eastern U.S., however, where diseases can
> be a
> real problem in the humid climate.
>
> Overall, the findings of the SAFS project indicate that equal crop
> yields
> can eventually be achieved in this area with organic methods but that
> economic risk may be greater, particularly during the transition, and
> production costs may be higher, depending upon the crop.
>
>
> Stanhill 1990. The comparitive productivity of organic agriculture.
> Agriculture Ecosystems & Environment 30: 1-26.
>
>
> M. Sean Clark
> Research Manager
> Sustainable Agriculture Farming Systems Project
> Department of Agronomy and Range Science
> University of California
> Davis, CA 95616
> msclark@ucdavis.edu
> TEL:(530) 752-2023
> FAX:(530) 752-4361
>
>
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