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Stepping up soybean yields

Agronomic improvement and genetics have built improved soybean production

Reading Time: 4 minutes

Soybeans yields have continued to increase decade over decade, including a jump of 23 per cent in average yield in Ontario from 2010 to 2020 compared to the previous decade.

A good part of that increase is from genetics, but it’s also agronomic management.

Dr. Dave Hooker, an associate professor at the University of Guelph’s Ridgetown Campus and Horst Bohner, OMAFRA’s soybean specialist focused on the key management areas that affect soybean yield during the recent Ontario Agricultural Conference.

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Hooker and Bohner looked at seven factors that affect yield on today’s soybean farms.

1. Stand establishment

Getting soybeans started depends on planters getting beans to the correct depth based on moisture conditions. Bohner says some farmers have been planting soybeans deeper, trying to make sure they are into enough moisture for seeds to germinate.

However, some recent trials he conducted showed Bohner that sticking with the traditional 1.5-inch depth for soybeans is usually the best choice.

Soybeans planted April 22, May 22 and June 10 at depths of two and 2.5 inches had the lowest plant stands. The deep-planted April stands were down to 95,000 plants per acre from a planted 175,000 seeds, for example. However, yields weren’t as affected as one might think. Also of interest is that in this trial the soybeans planted at one inches yielded the same as those planted at 1.5 inches.

Soybean plant populations based on planting depth and date.
photo: Horst Bohner

“I don’t have any evidence that planting soybeans deeper will give more yield,” he said. “I’m comfortable planting soybeans at 1.5 inches.”

2. Planting date

Like many others this year, Bohner found that early planted soybeans hit by snow did just fine. While early-planted beans may not be showing huge yield advantages, if the land is in good shape and it’s advantageous from an equipment management perspective to get the soybeans planted, then early planting date shouldn’t be a barrier. Variety should also be matched to their ability to thrive under early planting.

Later planting, however is an issue.

Hooker showed a graph that showed a precipitous drop off in yields after late May in the U.S. He says the date is likely May 12 to 15 in southern Ontario before soybeans yields drop.

3. Variety selection

Be aware that soybeans have significant variability in days to maturity even within maturity groups.

Hooker looked at soybean trial data at www.gosoy.ca. He compared the defined maturity group of each variety with its actual days to maturity in the field. He found significant variability within maturity groups, for example, six days difference within .2 of a maturity group and nine days difference within a .3 maturity group.

Variety selection is also important to rotation with soybeans, especially because of the need to plant wheat as soon as the soybeans are off the field.

Hitting optimum planting date for wheat has significant effects on wheat yield, with a loss of 1.1 bushels per acre per day with wheat planted after optimum planting date. At $7 per bushel wheat, that’s $7.70 per acre per day lost when wheat isn’t planted on time. If planting wheat after soybeans, a good guideline is to select a variety that is 0.5 to one maturity group less than the target maturity group for an area.

4. Residue management

Bohner is now strongly on the side of pre-tillage before planting soybeans, especially as corn yields continue to rise.

The crop residue left after 200 bushel per acre corn is significant, he said, and affects soil temperature, dryness and the amount of slug feeding in a field.

“I’m finished with no-till,” he said. Not that the yield difference between conventional and no-till soybeans is huge, he says. It’s only a few bushels.

However, a pass of spring tillage can make a better plant stand, with a more level surface for a combine head.

“The reason I’m doing it is to make your life easier.”

Hooker says it depends on where you farm. North of London, cooler temperatures in the spring mean some tillage can help warm the soil, whereas south of London, the temperature is often warmer, earlier, making no-till more feasible.

5. P and K fertility

“I’m convinced that in order to take a soybean crop from 50 to 80 bu, the fundamental difference is nutrients within the plant available to the plant that helps retain flowers, set the pods and retains seed size,” says Bohner.

Many farmers don’t put much fertilizer on when planting and Bohner says they can get 50 bushel soybeans with that practice. Bohner looked at adding a 2X2 band of 90 to 180 lbs of 6 nitrogen, 28 phosphorus and 28 potassium to a field. If the soil test is low, an extra five bushels of yield can be found. If the soil tests show the nutrients are in the field already, then there won’t be as much of a response. However, there is enough of a difference between fields that are low in fertility and don’t get fertilizer and those that have enough nutrients in the soil that is pays to keep up with fertility throughout the rotation.

6. Crop rotation

Hooker has long talked about the value of wheat in a corn-soybean-wheat rotation and the four to six more bushels per acre of soybean yield available. However, he talked about another long-term rotation at Ridgetown College that only includes soybeans and wheat. Crop yields are good in that rotation.

Farmers could grow more soybeans as long as they keep winter wheat in the rotation, says Bohner.

7. Foliar fungicide

There have been many years of trials conducted in Ontario that show that foliar fungicides will increase soybeans yields by two to three bushels per acre.

“You might say that’s not enough to get me excited, but the fact it is consistent is extremely encouraging,” said Bohner.

There are more foliar feeding options now available that mean that there could be more options to feed soybeans rather than broadcasting fertilizer. Many of those options don’t show as consistent of a response, but he did like the results he saw from a product called K20-S — which includes nitrogen, potash, sulphur, manganese and other micronutrients.

The highest payback for foliar application, says Hooker is foliar fungicide, unless there is an obvious problem in the crop like manganese deficiency.

About the author

Editor

John Greig

John Greig has spent his career in agriculture journalism and communications. He lives on a farm near Ailsa Craig, Ontario. Contact John at [email protected] or follow him on Twitter @jgreig

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