--------- Begin forwarded message ----------
From: Michael Russelle <email@example.com>
Subject: N scavenging plants
Date: Wed, 17 Mar 1999 13:51:58 -0600
A colleague of mine sent me a copy of the note you had submitted on
You may wish to share this with others in the discussion group.
The USDA-ARS Plant Science Research Unit in St. Paul, MN, has developed a
couple of alfalfa types that form ineffective nodules with rhizobia and
cannot fix N symbiotically. They were developed for research on N2
fixation, but a few years ago, we found that they are 30-40% better in
absorbing nitrate from the soil than regular alfalfa.
We are using these in field trials to clean up excess nitrate. In one
in North Dakota, Ineffective Agate removed twice as much N as corn
even though above ground dry matter yields were the same.
There is very little seed available for these two alfalfas. Even if seed
were readily available, however, we would not recommend that farmers
them, since they either have to be fertilized or seeded in soil with very
high inorganic N supply. It turns out that even regular, N2-fixing
do a pretty good job at removing inorganic N from the soil.
Incidentally, planting a crop that has 'an aggressive root system' is no
guarantee that it will remove N efficiently. Nitrogen removal is a
of dry matter (yield) and N concentration. If the crop will not yield
particularly well at the location, it will not be especially effective in
removing N. Those crops with higher N (or protein) concentration will
remove more N than crops with lower N concentration, given the same
Of course, the crop needs to be able to produce roots at the depths where
the nitrate is found in the soil -- one advantage of alfalfa is that it
be very deeply rooted (roughly 4-6 feet per year) and can get to nitrate
the deep subsoil that other crops cannot reach. Perennial crops are
generally better than annuals, in that they use water over a longer part
the growing season and have higher yield potential. The water use
is important, because nitrate moves through the soil with excess water.
One concern in using crops to remove excess nitrate is that herbage can
develop high concentrations of nitrate-N, too. If the forage is to be
for livestock feeding, it should be ensiled to reduce nitrate
concentrations, or the hay or green material should be tested for
Concentrations above 2000 to 3000 mg nitrate-N/kg dry matter may be
Such feed can be used if mixed with other materials to effect dilution of
Hope this is of some help.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Michael P. Russelle voice: 612-625-8145
USDA-Agricultural Research Service FAX: 651-649-5058
439 Borlaug Hall e-mail: firstname.lastname@example.org
University of Minnesota
St. Paul, MN 55108-6028
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