|POWELL, J MARK|
|Kelling, Keith - UNIVERSITY OF WISCONSIN|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 15, 2004
Publication Date: N/A
Technical Abstract: Most studies of manure N cycling are short-term and rely on indirect methods, such as apparent N recovery, or the difference method (DIFF), fertilizer N equivalents (FE) or incorporate 15N into ammonium-N fractions. Direct and perhaps more precise measurements may be achieved by long-term studies using 15N incorporated into all manure N components. This paper summarizes results of a 6-year trial that compared indirect and direct measures of manure N uptake by corn. 1st, 2nd and 3rd year estimates of manure N uptake by corn were 25, 6 and 2% in plots amended with manure 15N; 25, 6 and 0% by DIFF; and 55, 24 and 25% by FE. Although manure 15N and DIFF provided similar estimates, the variability associated with DIFF and the FE were much greater, especially for years 2 and 3. Indirect estimates of manure N uptake by plants (i.e. DIFF and FE) are therefore less precise than direct measurements using manure 15N. Long-term manure-soil-plant-N cycling studies require manure 15N derived by feeding 15N-labelled feed; short-term studies may use manure 15N derived from feeding 15N-labelled urea.