Seed Rate

Increase Seeding Rate – Austen Preet

            In general, increasing the seeding rate of a crop is not a weed control practice that can be used solely to inhibit weed populations. On the other hand, it is a technique that can reduce the number of individuals within those weed populations because interspecific competition limits the availability of nutrients. This technique lowers the breakout of weed infestations by in-taking more water, nutrients, and sunlight due to the increased amount of sown plants per square metre. If the crop is able to emerge earlier and produce a strong stand, the majority of the incoming weed population will be out-competed and not survive past the critical weed free period. Increasing seeding rate is especially effective when the crops being sown are more competitive such as rye, oat, barely, wheat, or canola. Within these species, a grower can increase effectiveness by selecting a cultivar that competes well in the specific field it is going to be seeded into. Also, research shows that taller cereals tend to be more competitive than semi-dwarf varieties, and hulled barely is more competitive than hull-less strains (Agriculture Canada. 2006).

When using an increased seeding rate to limit weed biomass, it is important to avoid planting uncompetitive crops, such as flax or lentils, because the higher rate of plants per square metre may not be able to combat the weed populations. Therefore, this strategy may result in unwarranted intraspecific competition between the crop species which may result in a lower total yield (Seeding Rate. 2006). Extra costs can be avoided by implementing this strategy on crops that have relatively cheaper seeds, such as barley and wheat, compared to using a crop like peas. It is important to adequately fertilize the fields that are going to receive the higher seeding rate because with low fertility the increase in plant population will actually decrease the total yield (Hall. 2004).

Figure 4: The yield of a cereal, like barely, will only be positively affected under increased seeding rate if the plants are adequately fertilized. Barley yield was lower, even with increased seeding rate, when the rate of nitrogen was not sufficient to support extra growth. Source: Image Link$department/deptdocs.nsf/ba3468a2a8681f69872569d60073fde1/75f6e66c5df1cacb87256eba005d8587/Information/0.7302!OpenElement&FieldElemFormat=gif

Ecologically the plants themselves will be effected due to the increased rate of individuals in a given area. For example, phenotypic plasticity is demonstrated in a dense wheat canopy because each wheat plant will produce fewer tillers, but more plants and heads in the same amount of space will result in a higher yield (Western Producer. 2006). The financial cost of increasing seeding rate for weed control is obvious. More seed will have to be purchased to increase the amount of plants that will germinate. This cost is highly dependent on the crop that is being planted because the price of seed varies greatly between species. A grower does not want to plant too many seeds, and experience yield loss due excessive intraspecific competition. This will result in a cost of purchasing more seed, as well as the cost of losing profit due to the decrease in yield.

            This technique, like many other control options, displays both negative and positive aspects. It depends on the grower’s specific needs to determine if this is an appropriate measure. For example, high seeding rates can have additional benefits, such as reducing fleabeetle damage to canola and lower root maggot infestations (Dosdall et al. 2005). However, a denser stand will increase the susceptibility to sclerotinia. In general, test results will showcase that the effect of seeding rate on weeds is variable. Results in a given field will depend on cultivar choice,

Figure 5: Increased seeding rate increased canola yield, while slightly decreasing the weed biomass in the trial. This exhibits that increasing seeding rate is a productive strategy that can also help with weed control when used in proper situations. Source: Image Link

environmental conditions, and the types of weeds present (Western Producer. 2006). Increasing the seeding rate is altogether an effective practice in certain species that are competitive and produce less expensive seed. In terms of weed control, it is a method that can benefit the grower when conditions are suitable, and the downfalls to increasing seeding rate are relatively minor. This technique is a useful practice, and a capable secondary means of controlling weed populations.


Agriculture and Agri-Food Canada. 2006. Weed Management Options Which Reduce Pesticide Risk.

Agriculture and Agri-Food Canada. 2006. Seeding Rate and Row Spacing.

Dosdall,L.M. and F.C. Stevenson. 2005. Managing flea beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) in canola with seeding date, plant density, and seed treatment. Agron. J. 97:1570-1578.

Hall, M. 2004. Integrated Weed Management Principles: Reducing the Risk of Failure.   $department/deptdocs.nsf/all/agdex8712

The Western Producer. 2006. Boost seeding rate for weed control in spring wheat- Organic Matters.