The selection of soybean varieties that will yield well under any given set of conditions has been one of the most elusive challenges in agriculture. Dr. Edgar Hartwig, USDA soybean breeder at Stoneville, established the foundation for most of the soybean genetics we have today, but I doubt that even he could have imagined how complicated this subject would get.
Only a few years ago soybean varieties came as “Group 4, 5, 6, 7, or 8.” You did not often hear people talking about decimal parts of a maturity group.
It’s hard to believe now, but we actually planted a few MG 8 varieties in this area, and more in the southern part of Mississippi. Group 6 and 7 were probably the most common maturities planted. Only a few Group 5 and even fewer Group 4 varieties were planted.
We knew our soybeans by name. Most of them had the names of Confederate leaders like Lee, Davis, Bragg, Forest, Pickett, Semmes, and others. The majority of varieties released during this period were Group 6 and 7. Only one Group 4 was released around that time, and it was named for General A.P. Hill. There was one named for Stonewall Jackson, but it did not gain the wide acceptance of its contemporaries.
Following the era that Dr. Hartwig released all these named varieties the industry moved to “company” or proprietary varieties. The great improvements in genetics that have been achieved since then have been amazing, and today we expect sixty bushel yields instead of thirty. We grow mostly Group 4 varieties that we once considered too early for this region, and we plant a month or more earlier than in earlier times. Group 5 varieties are also popular and are the choice of growers who feel they fit their systems best.
I will cut to the chase here and express my own opinion that the most consistent high yielders under dryland culture in this region are usually those ranging from MG 4.5 to about 5.1. We could talk about differences in determinacy and other things, but for now let’s leave it there.
Some people stick to the early to mid-maturity Group 5 varieties, and they are great, but over the long haul they just don’t yield quite as well in most situations as the late Group 4 varieties.
The mid to late maturing Group 4 varieties are usually the best performers in dryland yield trials.
We’ve tried late Group 3s, but it seems that they don’t have enough time to produce the yields that the Group 4s can. The late Group 4s seem to have it timed about right in most cases.
Why does this happen? I’m not sure of course, but in my opinion it’s largely because of a principle called “avoidance.” The MG4 varieties are not exposed to stress as long as the MG5s are. You can probably name the stresses better than I can, they include heat, moisture, insects, nematodes, diseases, etc. The more exposure the crop has to stress the more negative effect there may be on yield, so “avoid” them whenever possible.
I have no intention of changing anyone’s mind about which soybean to plant, especially if they are pleased with their yields.
I know there will be comments that I have overlooked some things here, and that will be true, but from the last few years of experience I have noticed that when the “proven” mid to late MG4 varieties are planted in the sweet-spot window around the last of April or the first two weeks of May, they can be expected to fill the combine just a little faster in the dryland (or rain-fed) fields of Central Mississippi. I believe that’s what we are looking for.