Each year the soybean trend yield is improving by approximately .43 bushel/acre and much of that yearly increase is due to genetic rate of gain or improving soybean varieties. When the first varieties of soybeans were largely grown in the United States for oil and feed meal, it was 1924 and the average yield across the 1.5 million acres grown was 11 bushel/acre. Today, the U.S. grows 88 million acres of soybeans, which will produce about 51.9 bushel/acre. What a jump in production over 98 years! The estimated genetic rate of gain of .43 bushel/acre/year does not seem like much but when it is multiplied over almost a century, it sure adds up.
My Master of Science research thesis project looked at the genetic rate of gain but with a twist – how does current management factors impact varieties from the past. I did not go back to test varieties from the 1920s but did use four different varieties, each from the 1970s, 1990s, and 2010s. For any soybean history buffs out there, I was using varieties such as Conrad, Thorne, Williams, Beeson, etc. The research I completed looked at the genetic rate of gain in a more detailed manner as well, how much seed fill occurs each day across the four decades represented.
The final conclusions from the two years of field research were variable across the management and varietal treatments. Overall, though, those that spent a longer period in the reproductive growth stages, had a larger dry maximum seed weight. When fungicide and insecticides were included in the treatment, the effective filling period (EFP), or seed fill, was lengthened. However, just because the EFP was extended, it did not always equate to a larger seed weight. Sometimes longer EFPs would produce less dry weight each day compared to a treatment or variety that had a shorter EFP but a greater fill rate. There were no consistent trends across treatments looking at different fertility additions or the application of a fungicide and insecticide when it came to the seed fill per day. However, there were numerical trends when looking at the seed fill across the eras of soybean varieties – the beans from the 70s averaged 2.8 bu/ac/d while the 90s and 2010s averaged 2.9 and 3.4 bu/ac/d respectively. The EFP time showed no trends across eras or treatments with an average of 26.8 days. With the increase in seed fill rates, the newer varieties also yielded in a step wise better pattern as they became more modern.
Even though, I could not conclude the fact that different management treatments were enhancing yield consistently, it is important to note that the genetic rate of gain is real across years. Not only is it visible in the bushel totals at the end of the season, but it is also apparent throughout the growing season as the new varieties fill the seeds at a greater rate to hit higher yield goals. As seed companies launch new soybean varieties each year, know that the potential in them should be greater than the previous years. If we continue adding .43 bushels/acre each year, in another century of producing soybeans our average yields could be close to 100 bushel/acre!