Plant Larger Seeds for More Competitive Crop

By Brenda Frick, Ph.D., P.Ag.

Wheat and oat plants grown from larger seeds are more competitive with wild oats than plants grown from smaller seeds. Screening seed lots to remove the small seeds can improve crop yield in weedy fields. Combined with other management strategies like increased seeding rate, using larger seed has the potential to significantly improve weed management.

Several studies have looked at the effect of seed size in cereals. Plants from larger seeds are often more vigorous and grow more quickly, especially at the early stages. In some studies, plants from larger seeds produce greater yield. In other studies, the slower growing plants from the smaller seed are able to “catch up”. This is more likely when small seeds are grown in a pure monoculture, where all of the plants are of the slow growing type.

The difference between plants from small and large seeds may be greater under competition from weeds. In the plant world, most resources are available on a first-come-first-served basis. The advantage generally goes to the first plant to occupy the space, creating shade, using the water and nutrients. Weed competition increases the advantage of early vigour.

Steve Shirtliffe and Chris Willenborg of the University of Saskatchewan and William May at the Indian Head Experimental Farm seeded plots with small, medium or large oat seeds. The oats were seeded at two rates, either with or without wild oat competition. When plots were weed free, neither increased seeding rates nor larger seed size was beneficial. Oat seed size had no effect on crop yield and higher seeding rates depressed oat yield slightly.

An entirely different story emerged when plots included wild oats. Both increased seeding rates and increased seed size improved the oats’ ability to compete with wild oats. Management techniques that were of little consequence when weeds are effectively controlled by herbicides were of major importance when weeds were abundant.

Competitive ability of crops includes both their ability to maintain yield in the presence of weeds, and their ability to suppress the weeds. In the plots with wild oat competition, doubling the oat seeding rate increased crop yield by 15% and reduced wild oat biomass by 25-50%. For each mg increase in the individual weight of the oat seeds corresponded to a 21 kg/ha increase in oat yield and a 7 kg/ha decrease in wild oat biomass.

Larger seed may give an advantage in different ways. Shirtliffe and Willenborg found that emergence was similar for small and large seeds, but plants from larger seeds produced more plant material and more flowering stems. For some, but not all of the oat cultivars they tested, larger seeds produced taller plants.

Similar results found in Montana wheat study

A study in Montana found similar results with wheat. Increasing seeding rate 60% reduced wild oat biomass and seed production 12%. Using larger wheat seeds reduced wild oats by 18%. These effects were additive. Combining the higher seeding rate with larger seeds reduced wild oats by 30%. A previous experiment in Montana indicated even greater reductions in wild oats with increased seeding rate and seed size.

Wheat from larger seeds had greater ability to withstand wild oat competition. Wheat plants in all weedy plots were suppressed by wild oats. For wheat from large seeds, this suppression occurred only during early growth stages. For wheat from small seeds, the suppression continued throughout development.

Wheat plants grown from larger seeds were also more effective at suppressing wild oats. Wild oats produced fewer and lighter seeds when suppressed by wheat plants grown from larger seed.

Reducing wild oat seed weight has long term implications. Wild oat plants grown from lighter seed emerged later, and produced fewer leaves, fewer tillers and less seed compared to wild oat plants grown from larger seed. Wild oats from lighter seeds were less competitive.

These studies reaffirm that importance of simple accessible techniques such as increasing seeding rate and seed size for weed management in the absence of herbicides. It also suggests that a strong vigorous crop can have a significant impact on the weeds with which it grows, and the weeds that will follow in future generations.

Brenda Frick, Ph.D., P.Ag., is the Senior Research and Extension Associate for Organic Agriculture Centre of Canada at the University of Saskatchewan. She welcomes your comments at 306-966-4975 or via email at organic@usask.ca.

References

Shirtliffe, S. J., W. E. May, C. E. Willenborg. 2007. The effect of oat seed size on tame oat competition with wild oat. Abstract to WSSA

Willenborg, C.J., Rossnagel, B.G., Shirtliffe, S. J. 2005. Oat Caryopsis Size and Genotype Effects on Wild Oat-Oat Competition. Crop Science 45: 1410-1416.

Stougaard, R.N., Xue, Q. 2004. Spring wheat seed size and seeding rate effects on yield loss due to wild oat (Avena fatua) interference. Weed Science 52: 133-141

Xue, Q., Stougaard, R.N. 2002. Spring wheat seed size and seeding rate affect wild oat demographics. Weed Science 50: 312-320

 

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Posted November 2007