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Differential Nitrogen‐15 Labeling of Dairy Manure Components for Nitrogen Cycling Studies
Author(s) -
Powell J. Mark,
Wu Zhiguo,
Kelling Keith,
Cusick Paul,
Muñoz Gabriela
Publication year - 2004
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj2004.4330
Subject(s) - manure , forage , agronomy , feces , urea , hay , silage , chemistry , zoology , nitrogen cycle , nitrogen , cycling , fodder , biology , ecology , biochemistry , history , organic chemistry , archaeology
Current estimates of dairy manure nitrogen availability to crops are based on indirect measures and vary greatly. The objective of this study was to differentially label dairy manure N components with the stable isotope 15 N for direct measurement of manure N cycling in soils and availability to crops. Dairy urine and fecal N components (microbial and undigested feed N) were differentially labeled by feeding either 15 N‐enriched forage or urea to mature dry dairy cows ( Bos taurus ). Nitrogen‐15–enriched ammonium sulfate was used to label alfalfa ( Medicago sativa L.) hay and corn ( Zea mays L.) silage. These 15 N‐enriched forages or either single or multiple doses of 15 N‐enriched urea were fed for 2 to 3 d, and feces and urine were collected separately for 8 d after the initiation of 15 N feeding. For both labeling techniques, 15 N appeared first in urine followed by fecal microbial and undigested feed N. For the forage method, the proportionate combination of feces excreted before and after peak 15 N excretion levels would achieve uniform labeling of fecal N components. For the urea method, no undigested feed N in feces was labeled since 15 N‐enriched forage N was not fed. The choice of which labeling method to use depends on the intended use of labeled manure. Manure enriched using the forage method and high levels of manure 15 N enrichments should be used for long‐term manure N cycling studies. Manure enriched using the urea method and lower 15 N enrichments could be used in shorter‐term studies.