Weed control – false seed bed technique
E. Johnson - Scott Research Farm
Organic producers often use spring cultivation to stimulate weed populations
to germinate. Once weeds have emerged, they can be controlled before or
as the crop is seeded. Seeding is delayed to allow time for weed germination
and tillage. How long should the farmer wait between final tillage and
seeding the crop?
Spring tillage can be used for weed control as well as to prepare the
seedbed. Shallow preseeding tillage (less than three inches) in early
spring can aerate and warm the soil, thus stimulating weed seedling germination.
Harrow-packing following spring cultivation firms the soil and further
encourages weed seed germination. The tillage operation should destroy
weed growth while conserving as much soil moisture and crop residue as
possible. The second tillage operation is delayed until weeds have emerged.
Seeding can then be conducted after the second tillage operation. This
practice can be especially successful at reducing the weed seedbank of
winter annual and early emerging species, such as stinkweed, knotweed,
Russian pigweed, Russian thistle, lambs quarters, wild mustard, wild oats,
and wild buckwheat. Weed control can be very successful with delayed seeding,
but the practice may reduce crop yields either because of increased losses
due to delayed harvest, or from reduced moisture in tilled soils. Seeding
should only be delayed long enough to let weeds emerge.
The study was conducted at Scott from 1997 to 1999 and at Melfort from
1997 to 2000. Both grass and broad-leaved weeds were seeded in the early
spring, and were then cultivated and harrow packed. Field pea, lentil,
canola and flax were sown the same day, and one, two, three, four or five
days later. Our experimental design was a randomized complete block with
Pre-seeding tillage timing did not always have an impact on weed density
or crop yield. When it was important, it was generally better to seed
as close to tillage as possible. Pre-seeding tillage timing appeared to
have more effect under the higher moisture conditions experienced at Melfort.
However, pea yields were improved at Scott in 1998 if seeding was conducted
soon after tilling (Table 1). At Melfort, flax yield declined as seeding
was delayed (Table 1) with field pea and canola yields showing similar
trends. Overall yields were low at Melfort in 1999 but flax showed similar
yield responses to pre-seeding tillage timing with highest yields occurring
when seeding was conducted within one day of the final tillage operation
(data not shown with this article).
There may be yield benefits to seeding soon after the final preseeding
tillage operation. Whether these benefits materialize or not probably
depends on the timing of moisture availability for weed germination prior
to seeding crop, and on conditions that permit adequate crop growth.
Provided by the Canada-Saskatchewan Agri-Food Innovation