Nitrous Oxide Flux from Solid Dairy Manure in Storage as Affected by Water Content and Redox Potential

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Abstract
The current global N2O budget estimates that animal production contributes one third of agricultural emissions. A study was conducted on solid dairy manure to determine the potential for N2O emission during storage. A laboratory flow‐through chamber and tunable diode laser analyzer were employed to continuously quantify the N2O flux in a temperature‐controlled environment. Water, NO3‐N and NH4‐N contents and redox potential (Eh, using a platinum and Ag‐AgCl reference electrode) also were monitored. In Experiment 1, manure samples were collected (4.3 kg wet weight) from three layers near the surface of the pile (0–15, 15–30, and 30–45 cm) and incubated at 22°C for 20 d. The mean daily N2O‐N fluxes were between 0 and 0.33 g N m−2 d−1, and N2O was only generated in samples from the top two layers of the pile. In Experiment 2, samples from the 30‐ to 45‐cm depth were adjusted by amendment with chopped straw to 70, 75, and 80% water content (WC). These samples showed less variable fluxes and produced twice as much N2O‐N as the unamended samples. Levels of straw‐amendment had no significant effect on N2O emissions. Combined results from both experiments revealed that fluxes were highest at 55 to 70% WC and 150 to 250 mV Eh. The N2O emission was limited by low NO3‐N levels in samples with high WC and low Eh. Increasing WC and decreasing Eh with depth and increasing levels of NO3 in the surface layer over time revealed that the exterior of solid manure piles is crucial to the flux of N2O.

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