Effect of an Agri-environmental Measure on Nitrate Leaching from a Beef Farming System in Ireland

Agricultural Nitrogen (N) management remains a key environmental challenge. Improving N management is a matter of urgency to reduce the serious ecological consequences of the reactive N. Nitrate (NO3 --N) leaching was measured under suckler beef production systems stocked at two intensities: 1. Intensive, 210 kg organic N ha-1 with two cut silage harvests; and 2. Rural Environmental Protection Scheme (REPS), 170 kg organic N ha-1 with one cut silage harvest. Three replicate plots of each treatment were instrumented with ceramic cups (8 per plot), randomly placed within each plot at a depth of 1 m to collect soil solution for NO3 --N at 50 kPa suction to collecting vessels one week prior to sampling. Samples were taken on a total of 53 sampling dates over 3 winter drainage periods (2002/03, 2003/04 and 2004/05). Over the course of the experiment the mean annual soil solution NO3 --N concentration exceeded the MAC twice out of 15 means (5 treatments over 3 years). The REPS grazing and silage sub treatments had significantly lower mean annual soil solution total oxidized N (TON) concentrations than the respective intensive treatments in years 2 and 3. Annual total NO3 --N losses over the three years in Intensive and REPS systems ranged from 55 to 71 and 15 to 20 kg N ha-1, respectively. Mean N surpluses in Intensive and REPS systems were 210 and 95 kg ha-1, respectively with the corresponding mean N inputs of 272 and 124 kg N ha-1. The reduction in N inputs under the REPS system results in lower N leaching losses and contributed to a significant reduction in pressures on water quality