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Uniformity of Nitrogen-15 Enrichment in Different Plant Parts and Subsequent Decomposition Monitoring of Labeled Crop Residues¹

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 % ¹⁵N in all N compounds within the plant. Our objective in this study was to estimate the uniformity of ¹⁵N labeling by comparing the ¹⁵N content of different plant parts of winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench]. Labeling with ¹⁵N 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 ¹⁵N enriched fertilizer into the initial crop and for following decomposition in subsequent years. At crop maturity, recovery of the initial K¹⁵NO₃ application avg. 71.9% for all soil texture-crop combinations. Data from the ¹⁵N labeling study indicated that relatively uniform enrichment of various plant parts was obtained when K¹⁵NO₃ was applied to the soil at the jointing and eight-leaf stages for wheat and sorghum, respectively. On average, atom % ¹⁵N 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 ¹⁵N-labeled plant material into various plant parts for use in subsequent crop residue decomposition experiments is unnecessary.

¹ Contribution 84-433-J, Dep. of Agronomy, Kansas Agricultural Experiment Station. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Kansas State Univ.

² Former Research Assistant and Professor, Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506 and Soil Scientist, USDA-ARS, Durant, OK 74701. Senior author is presently Assistant Professor, Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695.

Received for publication November 20, 1984. Accepted for publication May 6, 1985.

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