Reducing agroecosystem vulnerability to weed invasion - Invasive Plants: Ecological and Agricultural Aspects - page 173

Careful seed placement
For crop seedlings to occupy space early and successfully compete with weeds
[45], careful placement of seed in the soil is essential . Careful seed placement
is a management technique that requires little or no additional costs.
Nevertheless, it makes little sense to purchase seed and other physical inputs
such as fertilizer and fail to give crop seed the best possible chance of defend-
ing itself against weeds.
Careful placement of seed in the soil may involve several compromises.
Seeding depth must be sufficient to place the seed near soil water, but shallow
enough to facilitate rapid crop emergence. Packing should be substantial
enough to favour adequate seed-soil contact but not cause “hard-pan” or crust-
ing. Packing should also be over the crop row and not extend too far into the
inter-row space so as not to favour weed emergence. Crops should be seeded
as soon as possible after weeds are removed with pre-seed tillage or herbicides
to get a competitive edge on and avoid yield losses from early-emerging weeds
[53-55], but care should be taken to avoid leaving excessive spaces between
drill passes since this can provide safe sites for weeds to proliferate and com-
pete with the crop (Fig. 1). It is also important to ensure that sufficient physi-
cal separation exists between crop seed and fertilizer salts, since close prox-
Figure 1. Mature barley with extra space between seeding drill passes. The space (niche) is filled with
spiny sowthistle [ Sonchus asper (L.) Hill]. The picture was taken in 2000 near Lacombe, Alberta,
Canada