Impact of Compaction On Ammonia Losses From Urine Deposition.

Management Intensive Grazing (MIG) utilizes high animal stocking rates for short periods of time to efficiently harvest pasture crops.  Unfortunately, MIG also produces relatively high concentrations of livestock excreta, and can result in increased soil compaction, especially in moist areas.  This bench study examined N losses from urine deposition on three soil types (loam, silty loam, and silty clay loam) under three levels of compaction.  Soil cores were extracted at field capacity using 14.8 cm diameter x 30.48 cm deep polyvinylchloride (PVC) pies pushed 15.24 cm into the soil using a Giddings soil probe, leaving a head space of 15.24 cm.  Cores were fitted with a base screen and bottom PVC cap. Bovine urine from lactating dairy cows was applied at a rate of 1120.85 kg/ha.  Any leachate was collected from the bottom of the core, weighed and immediately frozen.  Ammonia volatilization was monitored for 15 weeks using an acid trap.  Soil moisture was monitored every 3-4 days to maintain the cores at 100% field capacity.  Differences between the beginning soil N, N added in the urine, leachate losses, ammonia volatilization, and ending soil N were examined using a mass balance approach.   Nitrogen not accounted for in the soil, acid traps or leachate was assumed to have been lost through denitrification or volatilization of nitrous oxide gasses.  Total ammonia emissions were higher for the compacted soils, and occurred for a longer period of time than for the uncompacted soils.