Better management and economy of the N resource in Ireland.

Abstract

The project, which was carried out at Johnstown Castle, was concerned with measuring denitrification at depth in grazed grass plots receiving 362 kg fertiliser N per ha. Reports in the scientific literature had indicated that such was likely, given the conditions necessary for the denitrifying microbial reactions to take place. In one experiment, denitrification was detected in measurable amounts to 90cm soil depth in spring-summer, using the acetylene block technique. A second more extensive experiment carried out under similar conditions within one year from March to August and from October to March looked at denitrification in greater detail to 50 cm deep. Results showed the importance of soil water and soil ammonium (NH4) to rate of denitrification. The rate was much greater in the 0-10 cm layer than in the lower layers in both time periods. Of the total denitrification occurring in the 0-50 cm layers in the year, which was 16.6 kg N per ha, 80% occurred at 0-10 cm with 62% occurring in the second time period, October to March.