Notes from the Pod Doctor  - April 20, 2010

Hello again from somewhere deep within the recesses of the Rabbe Companies.  I am emerging once again from what has seemed to be a very long winter, to bring you a few thoughts regarding soybean genetics and production.  A few of you, (well ok, most of you) are probably asking what the heck I do all winter long, since soybean does not grow around here below three feet of snow in the winter time!  In fact I have continued to be very busy.  Besides spending a week harvesting and replanting my winter nursery in Puerto Rico in late January (yes Joel, I was working VERY hard that week!), I have spent my time in the lab analyzing seed protein and oil characteristics of lines harvested last fall.  I have crunched numbers from last year’s yield trials and lab analyses in order to generate reports and make selections for the next round of testing and development in 2010.  From those selections, made at each stage of our 5-year development program, I have prepared seed entry lists and experiments for testing selected lines in 2010.  Seed for these experiments must be inventories, precisely packaged, randomized, put into planting order, and boxed before ever going to the field to plant.  We do this for over 10,000 lines from our proprietary breeding program each year.  Thousands of man hours are required in seed preparation in the seed lab during the winter and spring in order to plant all these experimental soybean lines in multiple locations and reps in a timely manner in May.

Planting rates

Every year growers ask questions about what is the best planting rate for each variety of soybean.  Although some genetic variability exists for population response, these variety differences are small compared to differences in population response of various corn hybrids.  In other words, most all soybean varieties will perform up to their own yield potential across a fairly wide range of populations ranging from final stands of 120,000 plants per acre up to 200,000 plants per acre.  Keep in mind that final stands are on the average about 90% of the number of soybeans planted.  This translates to 133,000 – 222,000 seeds dropped per acre. 

If a soybean variety is more prone to lodging, reducing the population by about 10% will help reduce the amount of lodging that will occur.  Lowering the population slightly can also improve air circulation and lower humidity and moisture condensation within the canopy.  This in turn helps reduce development of white mold and possibly other disease-causing molds.  However if final populations go below 120,000 plants per acre, yield loss can occur despite the reduction of lodging and/or disease development.  If soil conditions or other environmental factors are a concern for achieving a high percentage of uniform emergence, then the planting rate should be increased somewhat in order to achieve acceptable final stands.

Row spacings

One of the surest ways of increasing soybean yield is to reduce rows spacing.  Research from universities and private companies across the upper Midwest for over 40 years has shown consistent yield improvements of 10 – 20% going from conventional 30 inch rows to narrower row spacing all the way down to 12 - 14 inches.  Row widths narrower than 12 inches generally show little or no additional yield improvement.  Most all soybean varieties will show a yield response to row spacing.  Despite the conventional wisdom that “thin-canopied” varieties yield better in narrow rows and “fat-canopied” varieties yield better in wide rows, most research indicates that most varieties respond to narrow row spacing about the same.  Differences in disease resistance and lodging resistance are more important than canopy width in determining how well a variety will be adapted to narrow row spacing.

Should plant population be increased with narrow row spacing?  Surprisingly the results to this question are much more inconsistent.  Increased population in narrow rows can probably increase yield slightly, if white mold and other fungal diseases are not a concern.  Otherwise plant populations should probably not be increase significantly.

A big concern in planting in narrow rows, especially in 7-inch drill spacing, is the quality or degree of seed-soil contact and uniformity of planting depth achieved during planting.  In the past, grain drills or other narrower-row planting equipment did not achieve the same level of seed-soil contact and depth uniformity as conventional 30-inch planters, causing poor or uneven emergence and considerable stand reduction.  Newer types of narrow-row planting equipment, even many grain drills, provide improved seed-soil contact and uniformity of planting depth.

Obviously, cost and maintenance of multiple planters must be taken into account when considering the purchase of narrow-row planters.  However significant yield improvements may justify additional capital costs.  As older planting equipment wears out and requires replacement, narrow-row planting options should be one of the considerations in equipment updating decisions. 

Choice of Maturity

Another question I often hear regarding soybean production is “What is the best soybean maturity to grow in my area?”  Before answering that question, a short explanation of the reasons for genetic differences in soybean maturity is in order. 

 Soybean flowering, development, and relative maturity are primarily determined by day length during the growing season, although other environmental factors can also play a role.  Soybean responds to differences in day length through the reaction of two different forms of a light-sensitive chemical called phytochrome.  The phytochrome system has nothing to do with the photosynthesis or energy storage system in the plant.  Rather, the phytochrome system signals the plant to transition more slowly or more quickly from vegetative development to flowering and then to reproductive development and finally maturity. 

In the Midwest soybean growing region of North America, day length (about 45 minutes longer than the time from sunrise to sunset in the summer) lengthens as you move north.  Longer days cause later maturing varieties to mature even later or more slowly because they are more sensitive to the longer days.  Earlier maturing varieties are less sensitive to the longer days and will mature in a timely fashion.  At least eight identified genes, and probably many minor, unidentified genes in the soybean genome code for differences in maturity through their interaction with the phytochrome system.

Soybean breeders and growers have developed a general soybean maturity zone map of North America, used to provide general guidelines regarding where soybeans of different maturities are usually grown.  This map is divided into maturity zones from zone VIII in southern Louisiana and the gulf coast up to zone 00 in far northern Minnesota, northern North Dakota, southern Manitoba, and northwestern Ontario.  Ormsby, MN is generally considered to be located approximately on the border of zones I and II.  In order to more precisely distinguish maturity differences among soybean varieties, maturities are identified using a single digit after the decimal point.  For example a variety with a 2.0 maturity would be earlier than a variety with a 2.4 maturity. A 0.5 maturity (note the single zero “0” before the decimal) would be later than a 00.8 maturity (note the double zero “00” before the decimal).

Back to the original question “What is the best maturity to grow in my area?”  In the Ormsby, MN area, the answer would be 2.1.  However since no two years are exactly alike, and since soybean harvest does not all happen on the same day, I advise growers to spread the risk in their operations, and plant 2 or 3 or 4 varieties with a modest range of maturities, or a range of about 0.6.  For example in Ormsby, MN, I recommend a maturity range of about 1.8 to 2.4.  The earlier varieties will allow harvest to get started earlier.  In the meantime, the slightly later varieties, which generally possess higher yield potential, will have opportunity to mature.

Weed control options for conventional soybean

I wrote some information regarding conventional soybean herbicide options in this column back in early January.  I think it is useful to review those options here.  If you already have recent experience growing conventional soybeans, you know that some of the traditional herbicide options are becoming more difficult to obtain.  However, options are available.  The key is to let your local chemical supplier know well in advance so that orders can be made to the manufacturers for the specific chemicals that you want.  Since relatively small quantities of many conventional soybean herbicides are being used across North America, manufacturers prefer not to stock pile too much product unless they know that it will be sold.  Therefore early ordering of some of the conventional herbicides is important to allow time for manufacture and shipment.

I have listed here some commercially-available herbicides that should be available if ordered early.  The commercial names are followed by the generic chemical name in parentheses.

Flexstar (fomesafen),

Fusion (fluazifop+fenoxaprop),

            Prowl, Pendant, Pendulum, etc. (pendimethalin)

Poast plus (sethoxydim)

Thunder, Pursuit (imazethapyr)

Pursuit Plus (imazethapyr + pendimethalin)

            Select, Section, Shadow, etc. (clethodim)

Treflan, Tri-4, Trust, etc (trifluralin)

Dual, Dual Magnum, Dual II, etc. (s-metolachor)

Sharpen  {Kixor} (saflufenacil)

Optill {Kixor + imazethapyr} (saflufenacil + imazethapyr)

This is NOT a comprehensive list and I am not endorsing any particular products on this list at the expense of any other products.  If you have been successfully using conventional herbicides that are not on this list, by all means talk to your supplier about obtaining more for 2010.

Please note that imazethapyr, previously sold as Pursuit, may only be available as Thunder in 2010.  So if the chemical rep tells you that Pursuit is no longer being made, impress him or her with your knowledge that it is now available as Thunder.
Kixor is the base of a new family of conventional herbicides manufactured by BASF, which is available for use in 2010.  It is an interesting new product to control broadleaf weeds in soybean.  It can be used either pre-plant or post-emerge for control of broadleaf weeds.  Sharpen is the formulation of Kixor used for broadleaf weed control in soybean.  Optil, a packaged mixture of Kixor and imazethapyr, can be used for control of a wide range of both broadleaf and grassy weeds.

Please consult your chemical rep for more detailed information regarding Kixor products or any of the other products listed above.

Identity-preserved purity

All Galena Genetics soybean seed products are being contracted as identity-preserved products in 2010.  Therefore purity of the soybean crop following harvest next fall is critically important.

When it comes to maintaining genetic purity, one of the most effective, but often overlooked, practices is proper planter cleanout when switching from one variety to another.  This is true regardless of whether switching from one IP variety to another IP variety, or whether switching from a commodity variety to an IP variety.  If the planter is not properly cleaned out when switching to a new variety, contamination will occur regardless of how carefully the combines and trucks are cleaned out during harvest.

If using planter boxes, make sure each box is individually emptied and spun out to remove seed remaining in the metering unit, before the next IP variety is put into the box.  Likewise if an air-delivery planting system is used, make sure the tank and all lines are completely cleaned and blown out before switching to the next IP variety.

Safety

You may get weary of me repeating myself, but planting season can be a very busy time of year on the farm.  The pressure to get the crops planted quickly can lead to inherently dangerous situations.  Please use caution when working around all your power machinery.  Make sure to budget time for rest and sleep during planting season.  Fatigue is a major contributing factor to all farm-related injuries.  Remember, safety first!

Grant Metz, PhD
Research Director
Galena Genetics, LLC
501 Main St.
PO Box 548
Ormsby, MN 56162
(grant_metz@rabbeusa.com)