Iowa Farmer Today
12-15-07
Bean yields affected by precipitation
By Tim Hoskins
Looking over the soybean yields in the Iowa State University soybean variety
yield trials, Jim Rouse has noticed something unusual.
The yields, with a few exceptions, ranged from 49.7 bushels an acre to 54.6
bu./acre, a relatively small range.
“I thought that was unusual,” says Rouse, project leader for the ISU corn and
soybean variety testing.
He says the yields were a direct of result of what fields received timely rains
during flowering.
Rouse says test sites that had lower yields like the site near Rossie that had an
average yield of 40.8 bu./acre was due to the dryness around flowering.
Other test sites that had higher yields such as the site near Missouri Valley that
had 58.5 bu./acre got timely rains.
While some people note Iowa had average rainfall for the year, Rouse says the
timing of rains affected yields.
“The beans were not in an average environment,” he says.
Rouse says the summer was one of extremes of the amount of rain.
“Most area got just enough rain at the just the right time,” he says. “Yield is a
function of that.”
However, all the test sites were able to provide useable data.
Other than the yields, Rouse says this year’s test had a conventional soybean
test at selected sites.
Most of entries in the conventional test were low linolenic soybeans and some
from ISU soybean breeder Walt Fehr.
“This year we had an interest,” he says.
Most of the conventional tests were in the eastern locations of Walker, Clarence,
Melrose and Crawfordsville.
Rouse divided the soybean yield tests like he has in the past few years based on
early and full-season varieties and soybean cyst nematode resistant and nonsoybean cyst nematode-resistant varieties.
However, that way to divide the test might be changing over time.
Rouse says the trend is for less non-soybean cyst nematode-resistant varieties
to be entered into the yield trials.
“We are seeing fewer and fewer non-cyst-resistant varieties,” he says.
The ratio used to be was 55 percent soybean cyst nematode-resistant varieties
and 45 percent non-soybean cyst nematode-resistant varieties. This past year,
70 percent of the entries were soybean cyst nematode-resistant and 30 percent
non-soybean cyst nematode-resistant varieties.
Rouse believes the yield drag that used to be associated with soybean cyst
nematode-resistant varieties is no longer there.
“I don’t think there is one,” he says about the possibility there is a yield drag.
As normal, the ISU soybean variety yield trial included Iron Deficiency Chlorosis
(IDC) scores.
Rouse says the fields that they used were “hot.” He had three locations to
develop the IDC score.
“Scores we get is what a guy can expect under the worst conditions,” he says.