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Nitrification and Denitrification in Cattle Manure-Amended Soil¹

ABSTRACT

Dry cattle manure was mixed with soil at a rate of 45 and 90 metric tons/ha and amended with K¹⁵NO₃, and (¹⁵NH₄)₂SO₄ in separate treatments. The greenhouse experiment included an uncropped and a sorghum (Sorghum vulgure Pers.) treatment. Soil atmosphere was analyzed for CO₂, N₂, O₂ + Ar, N₂O, and enriched ¹⁵N₂. The energy-rich manure created a high biological oxygen demand and caused low O₂ and high CO₂ concentrations in the soil environment. Evidence for denitrification was obtained by the presence of N₂O and ¹⁵N enriched N₂-in the soil gases for the manure treatments amended with ¹⁵NO₃^– and ¹⁵NH₄⁺. The ¹⁵N enriched N₂ in the soil gases in the uncropped soil decreased to background levels after 10 days in the NO₃^–-amended manured soils, whereas ¹⁵N₂ enrichment from ¹⁵NH₄⁺-amended manured soils existed at 39 days. The recovery of NO₃^–-¹⁵N in the uncropped soils was 90.2% without manure, 9.4% with 45, and 8.1% with 90 metric tons/ha of manure. Recovery of NH₄⁺-¹⁵N in the uncropped soil was 92.2% without manure, 60.3% with 45, and 57.0% with 90 metric tons/ha of manure. Higher concentrations of added fertilizer N were recovered in the cropped system. In this study, where manure was mixed thoroughly with soil, water was added daily to field capacity, and O₂ concentrations were never below 3.1%, denitrification must have occurred in anaerobic microsites in a predominantly aerobic system. The results for the NH₄⁺-manure treatment demonstrated that both nitrification and denitrification occurred simultaneously.

Key Words: N₂O • ¹⁵N • N recovery

¹ Contribution from ARS-USDA, P. O. Box E, Fort Collins, CO 80522, in cooperation with Colorado State Univ. Exp. Stn., Sci. J. Ser. no. 226.

² Soil Scientists, USDA.

³ Chemist, USDA.

Received for publication June 15, 1977.