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Agronomy Journal Abstract -

Nitrogen Fertilizer Recovery by Grain Sorghum in Monoculture and Rotation Systems


This article in AJ

  1. Vol. 83 No. 3, p. 617-622
    Received: May 22, 1990

    * Corresponding author(s):
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  1. G. E. Varvel  and
  2. Todd Andrews Peterson
  1. U SDA-ARS and Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583
    U SDA-ARS-U.S. Dairy Forage Res. Ctr. and Soil Sci. Dep., Univ. of Minnesota, St. Paul, Minnesota



Grain sorghum [Sorghum bicolor (L.) Moench] has become a major dryland crop for the Great Plains, but information on production in rotations is limited. This study was conducted to determine N fertilizer recovery and use by grain sorghum in monoculture and rotational systems. Grain sorghum was grown under rainfed conditions on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic, Typic Argiudoll) in: (i) continuous grain sorghum monoculture, (ii) a 2-yr soybean [Glycine max (L.) Merr.]-grain sorghum rotation, (iii) a 4-yr rotation of soybean-corn [Zea mays L.]-oat [Avena sativa (L.)] + clover [80% Melilotus officinalis (L.) and 20% Trifolium pratense (L.)]-grain sorghum, and (iv) a 4-yr rotation of oat+clover-corn-soybean-grain sorghum at Mead, NE. Broadcast applications of 15N-depleted NH4NO3 were made at 90 and 180 kg N ha−1 in 1985 and 1986 to evaluate N fertilizer recovery. Fertilizer N recovery determined by isotopic methods was significantly higher for grain sorghum in monoculture (64.9%) vs. grain sorghum in rotation (54.9%). Fertilizer N recovery estimated by the difference method ranged from 118.5% in continuous grain sorghum to 9.1% in sorghum following oat+clover. Differences in N-recovery results by the isotope and difference methods indicated N fertilizer applied to grain sorghum in various cropping systems appeared to be entering different organic soil-N pools. These results substantiate the importance of the mineralization-immobilization turnover (MIT) effect in N-isotope experiments and the necessity for careful interpretation of N-recovery results, especially between complex cropping systems.

Joint contribution of USDA-ARS and the Nebr. Agric. Res. Div., Journal Series No. 9213.

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