Submitted to: Nitrogen Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/22/2003
Publication Date: 9/22/2003
Citation: Powell, J.M., Kelling, K. 2003. 15n labeling and use of dairy manure components for N cycling studies. In: Proceedings of the Sustainable Land Application Conference, January 4-8, 2004, Buena Vista, Florida. p.117. Interpretive Summary:
Technical Abstract: Indirect estimates of manure nitrogen (N) availability to crops are highly variable, but can be improved by using 15N-enriched manure. The objective of this study was to compare total corn 15N uptake and the amount and forms of soil 15N remaining in field plots amended with manure from dairy cows fed costly 15N-labeled forage or less costly 15N-labeled urea. Forage manure (FM) was fabricated by feeding dry cows 15N-enriched alfalfa hay and corn silage to label urine N, fecal endogenous N (consisting mostly of microbial products), and fecal undigested feed N. Urea manure (UM) was fabricated by direct feeding 15N-enriched urea to cows with unlabeled forage. This labeled only urine N and fecal endogenous N. Over a two-year period, we applied 15N-enriched FM or UM field plots and determined corn 15N uptake and residual soil nitrate- and total-15N. Of the total labeled manure N applied, 14 to 18% was accounted for in corn harvested the first year, and 4 to 8% the second year after manure application. No significant differences were noted in total corn N uptake, and total soil 15N levels due to year of application or manure enrichment method. On average, 67% of applied manure 15N was accounted for, either in crop uptake (22%) or in the soil (45%). Most (72 to 98%) 15NO3-N and total 15N was found in the upper 30-cm of soil suggesting either relatively little downward movement of applied manure N, or that leached N moved out of the 0- to 90-cm layer. Our results suggest that the less laborious and less costly urea method of labeling dairy manure may be adequate for evaluating short-term studies. The N contained in the undigested feed in feces did not apparently affect crop N uptake during this 2-year study to a measurable extent. However, this manure N component should likely be labeled using the forage method to produce manure for use in long-term N cycling studies.