Mechanical management of weeds - Ecological Management of Agricultural Weeds - page 168

The false seedbed procedure works in a manner similar to the stale
seedbed. In this technique, preparation of a seedbed is followed by one or
more superficial cultivations at about one-week intervals prior to planting the
crop. This reduces the pool of germinable seeds in the surface soil and can
reduce weed density in the crop.Usually the cultivation is kept shallow so that
few additional seeds are brought within emergence distance of the surface.
Because firming the soil of a prepared seedbed promotes weed emergence
(Roberts & Hewson, 1971), the soil should be rolled after all cultivations
except the final one before planting.
Although the false seedbed procedure is widely used by organic growers
(Wookey, 1985; Stopes & Millington, 1991), it has received little scientific
study. Johnson & Mullinix (1995, 1998) found that two shallow passes with a
rotary tiller equaled two applications of glyphosate for reducing weed pres-
sure on subsequent peanut crops, and two cultivations before planting were
better than glyphosate for weed control in cucumber.In a study on rapeseed in
Alberta, Darwent & Smith (1985) compared delayed seeding and preplanting
removal of Avena fatua with cultivation or nonresidual herbicides to use of tri-
fluralin and early seeding. Although weed density and biomass were statisti-
cally lower with trifluralin, control with delayed planting and cultivation was
sufficient to give consistently good yields. In contrast, Robinson & Dunham
(1956) found no advantage to cultivation prior to seedbed preparation in the
production of soybean in Minnesota. Apparently, weed seeds were protected
from germination in clods worked up by sweep cultivation of firm soil.
The false seedbed technique has several limitations. First, it can only be
effective if the soil is warm and moist enough to allow germination of weed
seeds. For example, Baumann & Slembrouck (1994) spring-tine harrowed two
and three weeks after plowing a grass sod,then one week later prepared a final
seedbed and planted carrots. They found no difference in weed density
between this treatment and one that was plowed and planted on the same
schedule but without the preplant harrowing, probably because the soil was
dry and not conducive to seed germination prior to harrowing.A second limi-
tation of the procedure is that the soil is kept bare and loose for an additional
period, and this may promote erosion. A third limitation is that yield may be
lost if planting is delayed by the preplanting cultivation. A fourth problem is
that although cultivations prior to planting may greatly reduce one set of
species,if planting is delayed,a new set of species may become physiologically
ready to germinate.In this case,weed composition may shift without a change
in total abundance. The first and second of these problems should be least in
irrigated agriculture, since in these systems soil moisture is controlled by the
grower and the land is flat. The third and forth problems are likely to be least