Intensity and duration of denitrification following application of manure and fertilizer to soil

Denitrification and nitrous oxide production rates were determined in a field/laboratory study following application of N fertilizer (255 kg N ha -1 as NH 4 NO 3 ) and liquid (450 kg N ha - 1) and solid (600 kg N ha -1 ) cattle manures. We measured the three proximal regulators, O 2 supply (water content, air-filled porosity), NO 3 - concentration and C supply (CO 2 production, extractable-C content) along with denitrifying enzyme activity (DEA) and NH 4 + concentration, using a soil core technique. Part 1 of the study involved measurements with soil cores collected from the 10-, 20-, and 40-cm depths following N-fertilizer and manure applications in the fall 1991 and spring 1992. At the 40-cm depth, denitrification rates and DEA were very low, indicating that little soluble C was leached from the manured soil. Air-filled porosity, CO 2 production and NH 4 + concentration were most closely related to denitrification rates at the 10- and 20-cm depths with the manure treatments. Denitrification rate with different manures depended on time (season) of application and was influenced by soil water content. Solid manure promoted denitrification for a longer period than liquid manure. In Part 2 of the study, denitrification and nitrous oxide production rates in the tilled (0-15 cm) layer were measured over a 49-d period. Both were most closely related to soil water content, but neither was related to NO 3 - content. Peak rates of denitrification and N 2 O production occurred early in the sampling period with liquid manure but later with solid manure. Cumulative production of N gases was greater with solid than liquid manure, which, in turn, produced more N gases than with the fertilizer or control treatments.