Summary: Final Report of the ERTDI-funded project 2000-LS-184.108.40.206-M2
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This farm-scale study, carried out at the Teagasc, Moorepark (Curtin’s) farm, examined the effect of four managements (treatments) on nitrate-nitrogen (NO3-N) leaching between 2001 and 2004. The soil on the grassland farm is a free-draining sandy loam overlying Karstic fissured limestone.
Leaching was measured using 24 ceramic cups at 1 m deep in each the four treatments - (T1) plots receiving dirty water and nitrogen (N) fertilizer which were grazed; (T2) two-cut silage and grazing plots receiving slurry and fertilizer N; (T3) grazed plots receiving fertiliser N and (T4) one-cut silage and grazing plots receiving slurry and fertiliser N. There were 33, 37 and 26 sampling dates in the 2001/2002, 2002/2003 and 2003/2004 drainage seasons, respectively. The NO3-N and ammonium- N (NH4-N) concentrations (mg/l) were determined in the water samples. The annual average and weekly concentration of these parameters was analysed using a repeated measures analysis. The aggregated data were not normally distributed. Effective rainfall (drainage) was different in each of the three drainage seasons.
The mean N direct inputs for the four treatments in 2001, 2002, 2003 were 311, 309, 326 kg/ha with mean stocking rates of 2.12, 2.47, 2.47 cows/ha, respectively. Fertiliser N constituted 72-90 % of the total N input to the dirty water plots and was 92 -94 % of the total input to the silage plots in those years.
The NO3-N and NH4-N concentrations recorded from the ceramic cups during the monitoring of an intensive dairy farm on a vulnerable soil give cause for concern. The level of concern will depend on the water quality targets required. However, the results must be put in the context of the soils which were selected on the basis of their high vulnerability in terms of leaching. Secondly, management options to reduce the pressure from the intensive dairy system monitored are evident. These can be implemented to reduce the N loading from the system without requiring changes in the production potential of the current management system. Their impact on water, however, remains to be evaluated.
Estimated annual losses, based on the weighted annual mean concentrations of NO3-N and effective rainfall plus irrigated dirty water were 34.8, 22.6, 36.2 kg/ha N, for drainage years 1, 2 and 3, respectively. The mean losses were 11%, 7% and 11 % of applied N in years 1, 2, 3, respectively. Estimated annual N losses in leached NH4-N were 1.6, 1.8, 1.1 kg/ha N, for drainage years 1, 2, and 3, respectively, based on the weighted annual mean concentrations of 0.345, 0.317, 0.275 mg/l NH4-N and effective rainfall plus dirty water irrigation amounts. The amounts of NH4-N leached were low i.e., 0.5, 0.6, 0.3 % of applied N in years 1, 2 and 3, respectively. <...>