Nitrous Oxide Production from Injected Liquid Dairy Manure

Injection of liquid organic wastes into soil promotes conditions that may be conducive to denitrification by creating an anaerobic environment abundant in inorganic N and readily oxidizable C. To quantify gaseous N loss, we measured N 2 O emissions from simulated waste injections applied to soils in large wooden containers (71 by 42 by 44 cm). These containers were equipped with headspace covers for gas entrapment, soil‐atmosphere wells, C 2 H 2 ‐dispersion tubes, soil moisture‐temperature cells, and end‐entry doors for soil sampling. Soil type was a Plano silt loam (fine‐silty, mixed, mesic Typic Argiudoll) packed to a bulk density of 1.1 Mg m −3 and maintained at a constant temperature of 12.0 ± 1.4 °C. Liquid dairy manure was injected into the soil at rates commonly used for crop production (79 000 L ha −1 ). The nitrification inhibitor nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] was used to further evaluate nitrification‐denitrification losses. Nitrous oxide emissions, with and without C 2 H 2 treatment, were estimated by passing air across the soil surface above an injection zone and trapping emitted N 2 O onto a molecular sieve. The largest emission of N 2 O occurred shortly after injection, followed by a shift to N 2 . Maximum gaseous‐N loss occurred 5 d after injection and corresponded with maximum CO 2 concentrations in the soil atmosphere. Nitrapyrin was effective in controlling nitrification, but did not consistently influence the rate of denitrification. When we simulated 190 mm of precipitation at 25 d after injection, increases in N 2 O production were minimal, possibly due to a limitation in readily oxidizable C. Total measured gaseous‐N loss in the presence of C 2 H 2 over 40 d accounted for 2.5 to 3.2% of the slurry's NH 4 ‐N, or 1.0 to 1.3% of the total N added.