Kristina Wolf has organized data from the first 20 years of UC Davis’s long-term agricultural experiment (now in its 24th year), as a dataset paper titled “The Century Experiment: The first twenty years of UC Davis’ Mediterranean agroecological experiment” in the journal, Ecology. I directed the experiment from 1993-2002, as a professor at UC Davis.

All the data are available through this web link.  You can download an 83-page PDF describing the data and a zip file containing the actual data files.

Some of the data have also been graphed on the project website.  For example, tomato yields were more consistent with organic than conventional management, but corn grain yields were lower in the organic system, partly due to planting delays from use of a winter cover crop. We showed that, given cover-crop delays, the shorter-season corn we used in the organic system had higher yields (Fig. 2 in Denison et al., 2004)*, but apparently the project has abandoned this system-specific fine-tuning in the interests of consistency.  So either the organic or the conventional system is forced to use varieties that underestimate that system’s full potential.  I wonder which system they sacrifice.

Organic corn had a possible downward trend over years, at least through 2007, when the graph ends.  Later data should be available in the zip file, but I don’t have time to look at it now.

Andy McGuire, who did his MS research as part of the long-term experiment, has published an opinion paper titled “Agricultural science and organic farming: time to change our trajectory” that should be worth reading.  I’ll try to comment on it soon.

*Denison, R. F., Bryant, D. C., Kearney, T. E., (2004) Crop yields over the first nine years of LTRAS, a long-term comparison of field crop systems in a Mediterranean climate. Field Crops Research 86:267-277