Effects of excretal returns and soil compaction on nitrous oxide emissions from a cattle overwintering area

Excretal returns and physical disturbance due to treading can greatly influence nitrogen flows in grazed pastures. Dung and urine depositions stimulate microbial transformations, while soil compaction and poaching change the physical environment in which these transformations take place. In this study, a cattle overwintering area in the Southwest Czech Republic was characterized with respect to bulk density, porosity, water-filled pore space (WFPS), organic C, total N, pH, microbial biomass C and denitrifying enzyme activity (DEA). Carbon dioxide and nitrous oxide (N₂O) emissions were measured on four different dates between October 2001 and May 2002. Sampling took place along a transect away from an open barn with access to feed. Soil chemical and biological properties showed that deposition of excreta declined with distance from the barn. In contrast, N₂O emissions were highest at intermediate positions along the transect. At the section with the greatest animal impact, the ratio of N₂ versus N₂O produced was five-fold higher, and the soil pH was 2 units higher, compared to the section with the least animal impact, which indicated that soil conditions favoured production of N₂ rather than N₂O in the area where excretal returns and treading was intense. A multiple linear regression was conducted using data from the last sampling. There were significant effects of WFPS and pH on log-transformed N₂O emissions, while effects of NH₄⁺ and NO₃^?, and interactions between NH₄⁺ and, respectively, WFPS and pH were nearly significant. The observations indicate that, whereas pasture management to achieve a better distribution of animal impact may improve N retention in the soil, it is not clear whether this will reduce N₂O emissions.