Manhattan, Kansas
April 29, 2008
When planting soybeans in Kansas,
it can be a good insurance policy to inoculate the seed, said
Kansas State University
agronomy professor Chuck Rice.
"Soybeans are big users of nitrogen, removing about three to
four pounds of nitrogen per bushel of seed," said Rice, who is a
soil microbiologist with K-State Research and Extension.
"Soybeans that are poorly nodulated will have to take up most of
the nitrogen they need from the soil. Since nitrogen fertilizer
is generally not applied for soybeans, a crop that is poorly
nodulated will quickly use up the available nitrogen in the soil
and become chlorotic from nitrogen deficiency."
Soybean inoculant contains Bradyrhizobium japonicum bacteria.
The Bradyrhizobium bacteria forms nodules on soybean roots, and
these nodules fix nitrogen from the atmosphere and supply it to
the plants, Rice explained.
If soybeans have been grown on the field in previous years,
there may be enough Bradyrhizobium bacteria in the soil to
nodulate the soybeans adequately. In that case, an inoculant
will not benefit the crop.
"But if there is not enough Bradyrhizobium in the soil, the
inoculant may increase yields by two bushels per acre or more on
fields that have had soybeans in the recent past," he added. "On
fields where soybeans have never been grown, the inoculant can
increase yields by 10 bushels per acre or more."
Rice said that soybeans should be inoculated in the following
circumstances:
* Where the field has not
been planted to soybeans for the past four years or more;
* Where the soil pH is less than 5.5 or greater than 8.5;
* Where soil erosion has occurred since the last time
soybeans were grown;
* Where soil organic matter levels are less than one
percent; and/or
* Where there has been severe drought or flooding.
If soybean plants are chlorotic
and nitrogen deficient despite being inoculated, that probably
indicates the inoculant has failed, the agronomist said.
"There may be several causes of poor nodulation and inoculation
failure, including: poor quality inoculant; poor storage and
handling; or poor seed coverage with inoculant," Rice said.
"Most fungicide seed treatments should not harm the inoculant if
applied according to directions, but be sure to check the label
of the specific fungicide seed treatment to be used," said Doug
Jardine, K-State Extension plant pathologist.
If the inoculation has failed, producers may need to apply
nitrogen to their soybean crop. Producers may need to apply as
much as 80 to 100 pounds of nitrogen per acre in that case, said
Dave Mengel, K- State soil fertility specialist.
K-State Research and Extension is a short name for the Kansas
State University Agricultural Experiment Station and Cooperative
Extension Service, a program designed to generate and distribute
useful knowledge for the well-being of Kansans. Supported by
county, state, federal and private funds, the program has county
Extension offices, experiment fields, area Extension offices and
regional research centers statewide. Its headquarters is on the
K-State campus, Manhattan. |
|
