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Nitrogen Budget and Soil N Dynamics after Multiple Applications of Unlabeled or 15 Nitrogen‐Enriched Dairy Manure
Author(s) -
Muñoz Gabriela R.,
Powell J. Mark,
Kelling Keith A.
Publication year - 2003
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2003.8170
Subject(s) - manure , loam , agronomy , soil water , fertilizer , environmental science , nitrogen , silage , nitrogen balance , zoology , chemistry , soil science , biology , organic chemistry
Repeated N applications to field crops, either as inorganic fertilizers or animal manures, can lead to N buildup in soils with potential long‐term environmental hazards. The objective of this 3‐yr field study was to monitor total‐ and mineral‐N levels in soil after repeated fertilizer or single or repeated dairy manure applications, and to compute an N balance for the soil‐crop system. Unlabeled and 15 N‐enriched dairy manure were used. The experiment was conducted on a Plano corn silt loam continuously cropped to corn ( Zea mays L.) Manure increased total‐ and NO 3 –N levels in soil, especially in the 0‐ to 30‐cm depth and in plots receiving frequent and recent manure applications. Manure increased NO 3 –N in the 0‐ to 30‐cm soil layer more than fertilizer N, whereas the opposite was true in the 30‐ to 60‐ and 60‐ to 90‐cm layers. There was a clear NO 3 –N buildup with repeated manure treatments. Unlabeled N measurements were not accurate enough to track trends in soil total N levels, hampering the calculation of an N balance. 15 Nitrogen‐labeled manure allowed for direct measurement and provided more accurate estimates of N recovery in soils and crops. During the 3‐yr study period, an average of 18% of applied manure 15 N was recovered in corn silage and 46% remained in the soil. Unaccounted‐for 15 N (36%) was assumed to be lost mainly by NH 3 volatilization and denitrification. Most (82%) of the 15 N remaining in soil was present in the top 30 cm, irrespective of frequency of manure application. Although costly and time‐consuming, the use of 15 N‐labeled manure provided a much better approach to study the fate of manure N within the soil‐crop system, compared with unlabeled manure.