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Approaching variable rates of seeding

New air carts and software offer ability to adjust a seeding rate on the fly – and some farmers are doing that – but effectiveness and efficiency are up for debate.

The current common strategy is to reduce seeding rates in high-producing areas of fields, and increase them in low-producing areas. However, the opposite approach may be a better strategy, says Alex Melnitchouck, an independent agricultural consultant in Calgary, Alberta.  

Melnitchouck raises an issue that has substance, according to Stuart Lawrence, Western Canada territory manager with Ag Leader Technology Inc. Lawrence is still active in managing the family farm at Rosetown, Saskatchewan, and has been involved with using precision farming technology since 1996.

On his own farm, using Ag Leader software, Lawrence had a surprise in 2011 when he examined the yield data for his own variable seeding rate trial with spring wheat. For now, he’s treating his old standard rate as at least open to question. But another approach may be better, and he’s looking for it.

Rethink seeding rates
Melnitchouck approaches the subject of variable rate seeding from a European perspective. He holds a University of Reading master’s degree in soil science and a PhD in agricultural sciences from a school in Belarus, his home country. In 2010, Melnitchouck shared his ideas in 2010 at the 10th International Conference on Precision Agriculture in 2010 in Denver, and in 2011 he spoke to delegates at SeedMaster’s Master Seeders Conference in Regina.

According to Melnitchouck, western Canadian seeding rates are low compared to Europe, with lower moisture on the Prairies the primary limiting factor. “An average seeding rate for spring wheat is about 120 pounds of seed per acre,” he says. “If the farmer has an area of the field with higher moisture conditions, he probably can increase seeding rates in that area. And he can decrease that rate in a lower-yielding area that doesn’t have enough moisture.”

In theory, this approach enables the farmer to increase efficiency in using fertilizer and moisture. He also may achieve more even emergence and more even ripening.

“The second strategy is exactly the opposite,” says Melnitchouck. “In dry areas, plants look very weak so you can put in more plants per unit area to use the potential, and you reduce seeding rates in high-producing areas because plants will develop better in these areas.”

Melnitchouck studied the two approaches for four years in southern Alberta using several seeding rates. His general observation was that it requires an on-farm analysis of field performance to determine the best approach for wheat and barley seeding rates. Either approach could work better, depending on the farm.

Increasing seeding rates in high-producing areas usually will lead to more yield because there are more plants, he notes. At the same time, the crop is likely to have a lower kernel weight and slightly lower value or grade. On the other hand, the second strategy reduces seeding rates in high-producing areas and creates more favourable growing conditions.

Crop production technology must be based on crop biology. Reducing seeding rates in high-producing areas and increasing them in low-producing areas does seem to be the better approach for winter wheat, canola, soybeans and other broadleaf crops. The reasons are similar – winter wheat tillers more strongly than spring wheat, while broadleaf crops generally need more space per plant to achieve maximum yield potential from the field.

These differences in approach point the agronomist to assert that it’s time to update basic seeding rate advice on the Prairies with new benchmarks. “Rates used today by growers were developed 40 to 50 years ago for completely different varieties,” says Melnitchouck. “I’m not aware of any serious work to verify those rates for today.”

Rosetown rate trials
Ag Leader’s Stuart Lawrence is passionate about collecting numbers and evaluating results. As a farmer, he says, “Our focus is to collect data on every operation on the farm to help fine-tune management. If we are out cultivating sloughs in the fall, we are out collecting data; if we are seeding in the spring or harvesting in the fall, we are collecting data.”

Lawrence agrees with Melnitchouck that it’s time to re-evaluate seeding rates and consider variable rates for seeding. Current technology on many grain farms makes it relatively easy to run a trial using GPS, yield monitors, new air carts with variable rate options and software.

Working with their crop consultant in 2011, Lawrence and his father Garry set up a small rate trial with hard red spring wheat. They set the rate controller for three different seeding rates before going into a 100-acre field.

“Dad started out seeding with a rate for spring wheat that we were comfortable with,” says Lawrence. “He selected a uniform area in the field that was suitable for the test. We ended up with a trial having our standard seeding rates, 25 percent more and 25 percent less.”

Conditions for the trial were good. The field had ample soil moisture as they had received close to 30 inches of rain in 2010. They hoped that the higher seeding rate, with ample moisture available, would produce more yield. But the results were a little different.

“The thing that surprised us most is that even in a wet year, the 25 percent lower rate yielded essentially the same as the regular rate,” notes Lawrence. “There was less than one percent difference between the two rates. We have a pretty aggressive fertility package and this field is one of our top producers. If we were going to see a response to higher seeding rates, I would expect it on this field.”

Lawrence stresses that his trial was not a scientific test. “This was done on our farm with our equipment and our soil conditions. I do not advocate anyone seeding 25 percent less just because I did. But what I found is that our yields were essentially the same. We found that the 50 percent window – between 25 percent less and 25 percent more – didn’t change our spring wheat yield.”

Lawrence expanded the trial for 2012, and plans to continue in 2013. In 2012, the lower seeding rate gave the best yield. Per acre, the lower rate yielded 6.75 percent more grain than the highest rate, and the highest rate yielded about one percent less than the normal rate.

The evidence is not scientific in any way, but it does support his concept that farmers need to try things out on their own farms. “Go to meetings and conferences, and talk with consultants. Find inspiration and then go experiment with it. Plan it out on paper first, because when the tractor hits the field, there is no time to think,” he says.

Prairie farming does have potential to improve crop returns by adjusting seeding rates. Both Melnitchouck and Lawrence believe that due to natural variability inherent in soils and growing conditions, farmers need to find their own best approaches to getting the best possible returns on investment.


March 26, 2013  By John Dietz


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