Large On-Farm Study Confirms Organic Recommendation

By Roxanne Beavers and Brenda Frick

The OACC (Organic Agriculture Centre of Canada) and organic farmers in Saskatchewan, Manitoba, Ontario, Quebec, PEI and Nova Scotia recently completed the largest on-farm organic field experiment conducted in Canada. They compared seeding rates of spring wheat in 25 fields on organic farms and in research plots at the Nova Scotia Agricultural College.

Higher seeding rates may be used to compensate for poor germination or when seedbed preparation has been challenging. Manuals for organic production often recommend that spring wheat be seeded at a rate 25% higher than that recommended for conventional farmers in the area. This may give greater competition to weeds or compensate for losses from post emergence harrowing. Prior to this study, the effects of higher seeding rates on crop yield and on weeds had not been documented on organic farms.

A trial was conducted at the Nova Scotia Agricultural College. Seeding rates included the usual recommended rate, an increase of 25% (1.25X), an increase of 50% (1.5X), and double the usual rate (2X). Half of the plots were fertilized with compost to encourage weed growth.

In both years of the study, weeds were smaller and took up less nitrogen when the crop was seeded more heavily. In fertilized plots, higher seeding rates (1.5X or 2X) reduced weed competition. In plots that were not fertilized, the 1.25X rate was as effective at competing with weeds.

At a higher seeding rate, the wheat canopy was denser when the stems began to extend, and this reduced the light reaching weeds below. Wheat plants matured slightly faster and grew taller at higher seeding rates. These factors gave the wheat an advantage over the weeds, resulting in better crop yield. At higher seeding rates each wheat plant produced fewer tillers but there were more plants and heads in a given area. Wheat quality, including protein content and kernel weight were unaffected, while test weight increased at higher seeding rates.

The experiment was also conducted across Canada by interested and enthusiastic farmers. These participating organic farmers seeded strips of wheat at each of four different seeding rates. The farm scale trial assessed what actually happens in the field, allowing for the different management practices and variable conditions on different organic farms.

The on-farm results were similar to those observed in the plot trial. When all organic farm trials were assessed together, yield was similar at the three highest seeding rates. The use of 1.25X seeding rate provided a yield benefit at the least cost. There were no differences observed between seeding rates in protein content, kernel weight or test weight.

Weed biomass was lower at high seeding rates overall, but this difference was not statistically significant. Increased seeding rate did not reduce weed biomass at several of the farms in Ontario and Quebec where there were many grassy weeds. The effect of seeding rate was variable. Results in a given field will depend on factors like cultivar choice, environmental conditions, and the types of weeds present.

Researchers are interested in assessing the kind of approaches that organic farmers have been using to see if they are effective, to determine how they work and to help improve techniques where possible. This study determined that the use of a 25% higher seeding rate for organic spring wheat was effective at increasing yield and reducing weeds at most sites, but in very weedy conditions this rate may not be high enough!

Roxanne Beavers recently completed a M.Sc. (Agr) at the Nova Scotia Agricultural College and is now a Consultant for the Organic Agriculture Centre of Canada. She acknowledges the cooperation of farmers and researchers across Canada (especially Jennifer Bromm in SK and Wendy Asbil in ON). Please send comments or questions by phone to 902-893-7256 or by email to oacc@nsac.ca.

Brenda Frick, Ph.D., P.Ag., is the Prairie Coordinator for the Organic Agriculture Centre of Canada at the College of Agriculture, University of Saskatchewan. She welcomes your comments at 306-966-4975 or via email at brenda.frick@usask.ca .

Posted on the OACC website, February 2006