Uniformity of Nitrogen‐15 Enrichment in Different Plant Parts and Subsequent Decomposition Monitoring of Labeled Crop Residues

Authors:
  • MWM. G. Wagger
    M. G. Wagger
  • DKD. E. Kissel
    D. E. Kissel
  • SSS. J. Smith
    S. J. Smith
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Abstract
In order to accurately evaluate the N mineralization from decomposing crop residue, residue should be uniformly labeled, i.e., it should contain a relatively constant atom % 15 N in all N compounds within the plant. Our objective in this study was to estimate the uniformity of 15 N labeling by comparing the 15 N content of different plant parts of winter wheat ( Triticum aestivum L.) and grain sorghum [ Sorghum bicolor (L.) Moench]. Labeling with 15 N was accomplished by applying a single, highly enriched but low rate of N to the soil early in the growth stage of the respective crops. Small enclosed microplots were used for incorporating the 15 N enriched fertilizer into the initial crop and for following decomposition in subsequent years. At crop maturity, recovery of the initial K 15 NO 3 application avg. 71.9% for all soil texture‐crop combinations. Data from the 15 N labeling study indicated that relatively uniform enrichment of various plant parts was obtained when K 15 NO 3 was applied to the soil at the jointing and eight‐leaf stages for wheat and sorghum, respectively. On average, atom % 15 N values for all plant parts ranged from 6.962 to 8.171 and 2.801 to 3.274 for winter wheat and sorghum, respectively. These results imply that segregation of 15 N‐labeled plant material into various plant parts for use in subsequent crop residue decomposition experiments is unnecessary.

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