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This article in SSSAJ

  1. Vol. 75 No. 2, p. 669-677
    Received: May 28, 2010

    * Corresponding author(s): upendra.sainju@ars.usda.gov
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Soil Nitrogen Dynamics under Dryland Alfalfa and Durum–Forage Cropping Sequences

  1. Upendra M. Sainju * and
  2. Andrew W. Lenssen
  1. USDA-ARS, Northern Plains Agricultural Research Lab., 1500 N. Central Ave., Sidney, MT 59270


Forages grown in rotation with or without cereals to sustain dryland soil water content and crop production may influence N dynamics. We evaluated the effect of alfalfa (Medicago sativa L.) and durum (Triticum turgidum L.)–annual forage cropping sequences on above- (stems + leaves) and belowground (roots) biomass N, dryland soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4–N, and NO3–N contents at the 0- to 120-cm depth in northeastern Montana from 2002 to 2005. Cropping sequences were continuous alfalfa (CA), durum–barley (Hordeum vulgare L.) hay (D-B), durum–foxtail millet (Setaria italica L.) hay (D-M), durum–Austrian winter pea (Pisum sativum L.)/barley mixture hay (D-P/B), and durum–fallow (D-F). From 2002 to 2005, total above- and belowground biomass N was 20 to 97 kg N ha−1 greater under CA than other treatments. In 2005, STN, PON, and PNM were 7 to 490 kg N ha−1 greater under CA than D-M, D-B, and D-P/B at 0 to 30 cm but varied by treatment at other depths. In contrast, MBN at 0 to 15 cm and NH4–N content at 30 to 90 cm were 23 to 37 kg N ha−1 greater under D-B than D-M and D-F. The NO3–N content at 0 to 120 cm was 65 to 107 kg N ha−1 greater under D-P/B than other treatments. Even though haying removed a greater amount of N, alfalfa increased surface soil N storage and mineralization and reduced the potential for N leaching compared with durum–annual forages, probably due to increased root growth or N2 fixation. Durum–pea/barley hay, however, increased N mineralization and availability in subsoil layers, probably due to greater root N concentration or downward movement of water-soluble N.

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