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Fate of Nitrate from Manure and Inorganic Nitrogen in a Clay Soil Cropped to Continuous Corn¹

ABSTRACT

Effects of dairy manure and N fertilizer were studied on plots that had received in a factorial arrangement two levels of manure (0 and 66 metric tons/ha) and two levels of N (0 and 224 kg/ha) applied every spring for 6 years. Laboratory incubation studies using soil profile samples showed potential denitrification to be greater in soil from the manure treated plots than in plots receiving either inorganic N or no N. The amount decreased with depth to 96 cm, below which energy for anaerobic microbial activity appeared to be limiting.

Laboratory analyses of profile samples indicated decreasing nitrate-N/chloride ratios at all depths from fall to spring, suggesting that denitrification rather than leaching was responsible for a significant portion of the nitrate loss during this period. Abrupt decreases in the nitrate-N/chloride ratios from the surface to the 45- to 71-cm depth indicated that denitrification had taken place and that a nitrate bulge at 96- to 122-cm probably was caused by denitrification above that depth.

The results indicate that more nitrate was lost by leaching when N was applied as NH₄NO₃ than when applied as dairy manure, both because there was more nitrate in the profile and because it was less susceptible to denitrification.

Key Words: denitrification • leaching of nitrate • manure • nitrate

¹ Vermont Agr. Exp. Sta. J. Article no. 292. Part of a thesis submitted by the senior author in partial fulfillment of the requirements of the M.S. degree, Univ. of Vermont, 1972. Contribution to NE-39, Regional project on soil nitrogen.

² Graduate Research Fellow, Professor, Associate Professor, and Associate Agronomist, respectively, Dep. of Plant and Soil Sci., Univ. of Vermont, Burlington 05401.

Received for publication January 17, 1972.