Weed control – false seed bed technique

E. Johnson - Scott Research Farm

Problem
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?

Background
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.

Study description
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 four replications.

Major findings
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).

Conclusions
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.

Funding:
Provided by the Canada-Saskatchewan Agri-Food Innovation Fund


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