Producers and Educators Conducting Soybean Population Research

Producers and Educators Conducting Soybean Population Research

Photo of Brandy Vanderwalle
Extension Educator Brandy Vandewalle of Fillmore County takes a soybean population stand count as part of an on-farm research project.

June 15, 2007

 

Extension educators in Clay, Fillmore, Hamilton and York counties have been getting down on their hands and knees to count soybean plants for producers involved in the Quad County On-Farm Research Projects.

The Research Project combines the efforts of producers and Extension educators in these four counties and in surrounding counties to pool resources and conduct on-farm research. Projects use technologies such as yield monitors and weigh wagons to collect data from replicated research plots. By pooling data from many sites, the power of the research and results is amplified. The project also gives producers an opportunity to find answers to questions not currently under research in Nebraska and allows University findings to be tested on local farms.

Each year research projects are selected by the group and particpating producers. The goal is to have one or two studies that are conducted by many of the members. Members' equipment is used to establish, manage and harvest field-size research comparisons. Producers, consultants, and educators monitor the fields and record relevant data. University personnel analyze results and the information is shared in group meetings.

This spring 10 producers in Clay, Fillmore, Hamilton, Seward and York counties undertook a study to determine the optimum plant population for peak economic return under field conditions. They planted replicated soybean plots at a population rate of 90,000, 120,000, 150,000 and 180,000 seeds per acre.

In general we have a good idea of what that ideal population should be, however a number of factors can affect soybean emergence and final stands.

In 2006 a similar study was conducted by four producers. It showed an average yield increase of only two bushels per acre when comparing the 90,000 seeds per acre rate with the 180,000 rate; however, the seed cost was nearly double. The plots planted at 90,000 averaged 65.4 bu/ac while the plots planted at 180,000 yielded 67.4 bu/acr

A similar study in 2006 by a producer in the Nebraska Soybean and Feed Grains Profitability Project showed that increasing seeding rate resulted in a small but significant yield increase; however, the increase was not enough to cover the increased cost of seed.

For more information about the Quad County On-Farm Research Group or other on-farm research being conducted, visit this Web site at http://farmresearch.unl.edu/ and watch for yield results this fall.

Gary L. Zoubek
Extension Educator

 

What's the Best Seeding Rate? Check the Discussion . . .

Other University researchers and extension specialists also are addressing the question of what's the best soybean seeding rate, given today's quality seeds and higher costs. Following is a contribution from UNL Agronomy Professor James Specht and links to on-line articles he cites.

When many of the old studies on plant population were done, the seed quality and vigor of the offered varieties were often not up to snuff and though the warm germination test might indicate good viability, the seed might not perform as indicated when exposed to cold soil stress. Now with warmer springs in recent years and well-conditioned seed sold by proprietary seed companies, there is less to fear about planting too few seed than there was 20-30 years ago.

From my own perspective, if you are shooting for 75 bu/ac or more yield, you can probably ensure achieving a high yield if you have at least 100,000 plants per acre at harvest, the plants are uniformly distributed, and there are no weeds. We've seen this in our on-campus eco-intensification experiment, but we always ensured that the stands were uniform and weed-free. Variability of with-in row seed spacing can be a yield-killer if the plant stands are "patchy."

Others also use the 100,000 figure. See Profitability of Cutting Seeding Rates: Fact or Fiction (PDF 239 KB) by Shawn P. Conley and Greg Shaner, and published by the Purdue University Agronomy Department.

There may be some years when there are only 100,000 plants per acre at harvest and the yield is 95% or better than the yield at 150,000. In fact, 75,000 plants per acre (uniformly distributed and weed-free) may yield on average at least 90% or more of the 150,000 yield. (See "What is the best soybean seeding rate," an article by Keith Whigham, Iowa State University extension agronomist, in the April 27, 1998 issue of Integrated Crop Management.)

While the Roundup Ready™ technology fee has stimulated the new interest in seeding rates, the key element that must be resolved by each producer is a bottom-line one: "Can I plant 100,000 seeds per acre in early May and still be sure that by mid Septemer I will have 100,000 plants per acre?" Only the producer with long-term experience with conditions on his or her farm and who has tracked the difference between seed per acre dropped at planting and mature plants per acre at harvest will know how to evaluate the economics of the question (and it must be re-evaluated each spring).

One person who has done substantive research on this subject in recent years is Palle Pedersen of Iowa State University. See one of his recent articles, "Soybean seeding rates: The balance between cost and yield," which was published in the April 2, 2007 edition of Iowa State University's Integrated Crop Management.

James Specht
UNL Agronomy Researcher and Soybean Breeder

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