Farm Horizons, April 2013

Disappointed in your soybean yield?

By Dave Schwartz
Certified crop advisor, Gold Country Seed

If you are disappointed in your farm’s soybean yield, you are not alone! I would say most growers are very satisfied with corn yields on their farm, but somewhat disappointed with their soybean yields.

I don’t believe there is one silver bullet that we can rely on that will raise soybean yields 10 bushels per acre.

My feeling is that lower soybean yields may be a result of current management practices including reduced tillage, corn/soybean rotation, and very early planting dates.

Years ago, soybeans were planted toward mid- to late-May in a crop rotation that included small grain and alfalfa. Now, soybeans are planted often in late April, and on a rotating basis with corn, so fields have more disease pressure.

Following are some ideas for growers to consider that may increase soybean yields on their farm.

• Crop rotation. Growers who plant continuous corn report great soybean yields when soybeans are planted on this ground once every five to six years.

The other comment I hear is dairymen who plant soybeans for the first time and harvest 60 to 70 bushels per acre soybeans. When soybeans are grown in following years, yields seem to drop off.

Corn has the ability to come back year after year with strong yields much better than soybeans. With the current grain market, many growers are experimenting with more continuous corn, and this should help their soybean yields.

• Row width. We saw a movement years ago to narrow soybean row widths from 30 inch to 15- to 20-inch-rows. The goal was to increase yields and reduce weed pressure. We had one bad white mold outbreak many years ago, and that seemed to drive row widths back to 30 inches.

What we have learned since is that white mold is often an issue with high soil fertility (more vegetative growth) and high plant populations. Using soybean varieties that stand well, and reducing plant populations so the final stand is 110,000 to 120,000 plants will significantly reduce white mold pressure.

The data I have seen shows soybean yields increase approximately four bushels per acre when growers shift to narrow rows. In good growing seasons, expect more than four bushels per acre; and in poor growing seasons, very little.

• Seed treatment. I don’t believe growers will see as much yield response from seed treatment as they will with narrow rows, but it will usually more than pay for the extra cost associated with treatment.

Again, the environment in which we grow soybeans has changed over the years. It’s not unusual to see soybeans planted before May 1. This was unheard of years ago!

Another change is I see more soybeans mudded-in than I did years ago. The combination of cooler soil temperatures and colder, more compacted soils is a perfect recipe for damping off-type seedling diseases. Seed treatments provide protection from seedling diseases through emergence, when plants are at their most vulnerable stage. The main advantage I see of insecticides in seed treatments is the insecticide holding back soybean aphid populations from economic threshold levels approximately seven days. In other words, fields with untreated seed will need to be sprayed for soybean aphids approximately seven days earlier than fields with treated seed. This can be huge when commercial applicators are busy and not able to get fields sprayed in a timely manner. Soybean aphids have the potential to reduce soybean yields up to 50 percent.

• Soybean genetics. It is important to choose the right soybean product for fields that are unique in that they have very high soil fertility, soybean cyst nematode, soybean disease issue such as phytophthora root rot, or droughty soil. Work with your seed rep to select a soybean line that has the right package for each field.

• Reduce stress at R5 stage. Whatever growers can do to reduce stress at the seed fill stage will improve soybean yield. By reducing stress at this key stage of development, plants will have less pod and seed abortions, and seed size will increase. More seeds per pod and larger seeds increase yield significantly. Good weed and insect control are management practices that will likely create a more stress-free environment.

The information above is food for thought. If you have any questions, feel free to contact me via e-mail at schwartzseed@gmail.com.

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