Agriculture Reference
In-Depth Information
health. Therefore, practices such as zero tillage that retain crop residues and
increase soil biodiversity will sustain crop health [22].
Field borders may be particularly susceptible to weed invasion. The edge of
the field is the first point of contact for equipment that may be carrying weed
propagules. In addition, field borders are usually more intensively disturbed
and degraded than other areas of the field, and may require more careful man-
agement to ensure crop health.
Crop vulnerability to weed invasions can be limited if light, nutrient, and
water resources are rapidly captured by the crop. It is imperative that crop
managers facilitate rapid crop emergence and early crop growth to counter the
invasive characteristics of weeds. Competitive cultivar selection, careful seed
placement, optimum seeding rates, strategic fertilizer placement, and diverse
crop rotations, which favour optimal crop health, will minimize the probabili-
ty of successful weed invasions. Combining some of these factors at optimal
levels will reduce the need for herbicidal intervention and improve efficacy
when herbicides are necessary.
Competitive cultivar selection
Some crop species compete with weeds better than others [23, 24]. For exam-
ple, in central Alberta, barley ( Hordeum vulgare L.) is generally more com-
petitive than canola ( Brassica napus L.), which is generally more competitive
than field peas ( Pisum sativum L.) [25]. In addition, crop species exhibit con-
siderable intraspecific variation in their competitive ability with weeds.
Differences in competitive ability among cultivars of the same crop species has
been demonstrated in narrow-row crops such as barley [26, 27], canola
[28-30], wheat ( Triticum aestivum L.) [31-35], peas [36-38], and rice ( Oryza
sativa L.) [39-44]. Mohler [45] provides a comprehensive summary of litera-
ture documenting genotypic variation in competitive ability among crop spe-
cies.
Intraspecific competitive differences with weeds among row crop cultivars
such as corn ( Zea mays L.) and sorghum ( Sorghum bicolour (L.) Moench.)
have also been documented [46-48]. However, weed invasions appear to be
more ably limited in wide-row crops by simply using narrower row spacings
as opposed to using competitive cultivars. For example, in soybeans ( Glycine
max L. Merr.), weed populations were significantly reduced by combining
decreased row spacing with increasing plant populations [49, 50]. Narrowing
row spacing has also increased the competitive ability of grain sorghum with
weeds [51] and dry bean ( Phaseolus vulgaris ) with hairy nightshade ( Solanum
sarrachoides ) [52]. Cultivar height, leaf architecture and leaf area all con-
tribute to the competitive ability of specific cultivars, but it is probably just as
important to select cultivars that are well-adapted to specific soil zones and
ecoregions as it is to concentrate on competitive plant archetypes.
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