My own interests in long-term studies, or perhaps more correctly my
frustration at the lack of long-term studies, was sparked by own search for
studies that would support decisions whether or not to fumigate [e.g. with
methyl bromide] before planting or replanting orchards or vineyards. The
farmers that I was interviewing in California seemed to be almost evenly
divided in both thought and practice with respect to methyl bromide
fumigation before replanting stone fruits or grape vines. The research and
extension personnel swore by the virtues of fumigation, and scoffed at the
results of those who did not fumigate. However, the farmers themselves did
not share the farm adviser views of their trees or vines as being bad
without fumigation, and seemed perfectly satisfied. Also, about half those
that fumigated were not satisfied with their results. I stopped short of a
large enough sample for statistical validation, as I was more concerned
with generating leads for my subsequent literature searches and researcher
interviews.
The prevailing scientific justification for fumigating trees and vines,
which are long-term perennial crops that can potentially yield for decades,
was that the trees or vines looked better [e.g. bushier, more leaves,
thicker stem diameter] 2-3 years after methyl bromide fumigation, as
compared to no fumigation. Also, more kill of pathogens and nematodes in
the soil can be demonstrated for several weeks or months before the
pathogens recolonize from lower depths in the soil. In essence, the
fumigations provide a window of time for growth with fewer pathogens. The
studies always stopped after 2-3 years [before fruit yields could be
measured]. The implicit assumption was always that this was indicative of
the future, which could be several decades for vines and trees. However, I
never found any scientific basis for this assumption, which conflicted with
observations that sometimes trees got off to a slow start but caught up or
surpassed trees that had faster starts.
I went through the CABI and AGRICOLA databases, looked at thousands of
sources, spent months combing the biomedical library at UCLA and the bio-ag
library at UC Riverside looking through decades of journals, proceedings,
ag experiment station bulletins etc., talking with researchers over the
phone, writing letters and e-mail, etc. It is probably safe to say that
out of several thousand studies, I found only one long-term study [10
years, which is not long compared to the Rothhamstead studies] comparing
fumigation with no-fumigation before replanting.
The one needle in a haystack "long-term" study, from Italy, was hidden away
in an obscure 500 or so page proceeding on stone fruit decline:
Minguzzi, A. 1989. Rootstock effects on peach replanting: A ten years
trial. Acta Horticulturae 254:357-361.
For the first 3 years of orchard development, the peach trees in fumigated
plots grew better in Minguzzi's Italian trials. This is consistent with
other studies, which end after 2-3 years, and seem to be the basis for
recommending that growers fumigate long-lived perennials before replanting.
However, a trend inversion began at year 4 in Minguzzi's study. By year 10,
the trees that had not been fumigated were doing better than fumigated
trees. Minguzzi concluded that "Fumigation gave an advantage only in the
early years of planting; later it negatively affected tree performance
because of excessive sterilisation of the existing microorganisms
[Mychorrizae?]."
Perhaps researchers are just resigned to the impossibility of getting
funding for long-term studies, along with the fact that you don't get the
necessary publications in timely fashion for career promotion with this
approach. But it is troubling to me that such major farming practices as
preplanting fumigation of long-lived perennial crops rest upon assumptions
that go unchallenged by the vast majority of the scientific community. In
the case of the long-lived perennial orchard or vineyard, the yield at the
end of orchard or vineyard life is the better measure of productivity than
how bushy plants are after 2-3 years. Just food for thought.
Joel Grossman
11 April 1995
email(internet): 3216125@mcimail.com