Features Agronomy Soybeans
Are soybean genetics improving?

In the past few years, Ontario's average soybean yield has been quite variable,
even though there is considerable effort put into genetic improvement and new
variety development. Now, many farmers are concerned about what appears to be
stagnating provincial soybean yields.

The numbers confirm what growers already know – provincial average yield
has not increased over the past 10 years. From 1996 to 2005, average provincial
yield actually went down on average about 0.2 bushels per year. Even if you
disregard the devastating 2001 year (21bu/ac), the trend is still declining,
at about one-tenth of a bushel per year. This is in contrast to the previous
10 years; from 1986 to 1995, average provincial yield increased about 0.45 bushels
per year. However, there is considerable year-to-year variability during the
entire 20 year period.

Soybean yield in Ontario has been affected by drought, disease and insect pressure
in recent years. In spite of these challenges in the growing environment, the
question is often asked: are we making genetic progress? Are the new soybean
varieties marketed in Ontario better than the ones they are replacing?

Answering these questions can often be difficult, but there are a couple of
places to go in the search for this information. Soybean variety trials have
been conducted in Ontario for several decades to compare variety performance.
Varieties are grown in replicated plots under the same management program in
several locations across the province to compare agronomics, disease resistance
and quality for current and new soybean varieties. Each year, new varieties
enter the variety trials and old varieties are removed. Most varieties remain
in the trials for several years, creating an overlap from year to year that
allows a comparison of performance over time. Varieties in the performance trials
are often a good indicator of the genetics available to growers at that time.

Each variety in the Ontario Soybean Variety Trials receives a ranking in the
form of a yield index. The yield index indicates a variety's performance as
a percentage of the average yield of all varieties grown in a test area over
two to three years of testing. A yield index of 100 means the variety was equal
to the average yield in the trial. A yield index of 110 means that the variety
yielded 10 percent more than the average yield in the trial.

A comparison of the yield index of any variety over several years in the Ontario
soybean variety trials can provide an indicator of genetic change in varieties
available in Ontario. OAC Bayfield, a very popular soybean variety in recent
years, is still grown on significant acreage in some parts of the province.
OAC Bayfield has been tested in the 2500CHU to 2800CHU zone of the Ontario variety
trials continuously for more than 10 years. The 1997 publication of the Ontario
Variety Trials shows OAC Bayfield had a yield index of 112, in trials that averaged
54.2bu/ac across all varieties in the test. During the next 10 years, OAC Bayfield's
yield index decreased to 101 in the 2006 publication (see Table 1). Since yield
index is calculated relative to other varieties in the test, this means new
varieties are outperforming OAC Bayfield. In 1997, OAC Bayfield yielded 12 percent
higher than the average variety, while in 2006 it yielded one percent higher
than the average variety. One could consider this evidence that new varieties
are better than the older varieties, even though the absolute year-to-year yield
is not increasing.

A look at published papers from soybean researchers reveals another perspective
on yield trends and genetic change. A search of scientific literature shows
a few papers were published in recent years to examine yield trends. Malcolm
Morrison and colleagues at Agriculture and Agri-Food Canada published the results
of a study in 2000 that involved growing 14 soybean varieties released between
1934 and 1992. Results showed that over 58 years of breeding, yield increased
about 0.45 percent per year. At an average of 40bu/ac, this is an increase of
0.18 bushels per year. They determined the yield increase could be attributed
to increased rates of photosynthesis and partitioning of resources to seed growth
rather than vegetative growth. They also reported reduced protein and increased
oil content. It would appear that from a scientific perspective, 10 years might
not be enough time to accurately assess genetic trends, but a longer time horizon
shows significant yield improvement.

Yield is a complex trait that can be determined by many factors. The final
yield in the bin is influenced by many minor traits depending on the year, farm
and growing conditions. New technologies such as DNA markers are now providing
researchers and breeders with more tools to pinpoint the genetic makeup of new
varieties, resulting in more precise breeding ability. These tools have been
in development for several years but the results have not been fully realized
to-date, since it takes several years to develop new varieties. Perhaps future
varieties will contain genes that allow soybean varieties to withstand the impacts
of variable climate, disease and insect pressure to produce high yield more
consistently.

Despite the appearance of stagnating provincial soybean yields, all signs indicate
that provincial yield potential is improving. Growers and researchers alike
are optimistic that yield potential is improving, thanks to both public and
private soybean breeding efforts. -30-

*Crosby Devitt is the research manager with Ontario Soybean Growers.