From eweigel@juno.com Fri Mar 19 01:02:30 1999 Date: Wed, 17 Mar 1999 19:53:41 -0700 From: Edna M Weigel To: sanet-mg@amani.ces.ncsu.edu Subject: re: N scavenging plants SANETers: The following is an informative Email I received about N scavenging plants. This is only an academic interest for me since I live in a desert with low/moderate available nitrogen (my county agent thinks I need to add lots more nitrogen, but I grow vegetables just fine with a little added compost, mulch, and water). However, I thought it might be of more interest to some of you who live in areas plagued by nitrate groundwater pollution. regards, Edna --------- Begin forwarded message ---------- From: Michael Russelle To: eweigel@juno.com Subject: N scavenging plants Date: Wed, 17 Mar 1999 13:51:58 -0600 Message-ID: <3.0.5.32.19990317135158.0084dcd0@soils.umn.edu> A colleague of mine sent me a copy of the note you had submitted on SANET. 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 trial in North Dakota, Ineffective Agate removed twice as much N as corn silage, 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 plant 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 alfalfas 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 function 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 yield. 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 can be very deeply rooted (roughly 4-6 feet per year) and can get to nitrate in the deep subsoil that other crops cannot reach. Perennial crops are generally better than annuals, in that they use water over a longer part of the growing season and have higher yield potential. The water use question 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 used for livestock feeding, it should be ensiled to reduce nitrate concentrations, or the hay or green material should be tested for nitrate. Concentrations above 2000 to 3000 mg nitrate-N/kg dry matter may be toxic. Such feed can be used if mixed with other materials to effect dilution of the nitrate. Hope this is of some help. Michael Russelle - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Michael P. Russelle voice: 612-625-8145 USDA-Agricultural Research Service FAX: 651-649-5058 439 Borlaug Hall e-mail: russelle@soils.umn.edu University of Minnesota http://www.umn.edu/arspsru/plantsci.html St. Paul, MN 55108-6028 http://www.dfrc.wisc.edu/profiles/mpr.html USA --------- End forwarded message ---------- ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866] To Unsubscribe: Email majordomo@ces.ncsu.edu with the command "unsubscribe sanet-mg". To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command "subscribe sanet-mg-digest". All messages to sanet-mg are archived at: http://www.sare.org/san/htdocs/hypermail