Previous high N surplus levels on Dutch dairy farms have stimulated investigations into more efficient ways of farming. Increases in N efficiencies are especially relevant for the Pleistocene sandy soils where nitrate concentrations in the upper groundwater have exceeded the EU 50 mg/l threshold in the past. On the northern fringe of the Dutch coversand area, several farmers have reduced N surpluses from over 300 kg per ha per year to about 120 kg per ha per year over a period of 10 years. Reduced surplus levels were especially reached through reduced use of fertilizer N. A field survey into soil nitrate levels was performed in spring 2007 on 29 dairy farms on sandy soil. This followed a previous survey in 2006 focusing on soil mineral N levels in autumn. On the farms, land use was dominantly grassland with a small percentage of silage maize. During the survey of 2007 measurements were done on 300 locations selected by stratified random sampling with combinations of soil type, groundwater level and land use as strata. During the 20 days sampling period, continuous monitoring was performed on two locations. It was found that almost 70% of the observations were below the detection threshold of 1.5 mg/l Nitrate-N although locally much higher concentrations were observed. For further analysis we preferred to use 90th percentile points and areal proportion where a specified threshold is exceeded. When distinguishing between two contrasting types of N-management among the farms we found that the relative area where the NO3-standard is exceeded was 6.3% for high N-input farms and 8.7% for low Ninput farms. Our results confirm some national forecasts where regional average nitrate concentrations in the upper groundwater in the northern sandy regions are expected to stay below the established EU threshold.
|Title of host publication||Eurosoil 2008: Soil - Society - Environment; Book of Abstracts, Vienna, Austria, 25-29 August 2008|
|Editors||W.E.H. Blum, M.H. Gerzabek, M. Vodrazka|
|Place of Publication||Vienna, Austria|
|Publisher||University of Natural Resources and Applied Life Sciences (BOKU)|
|Publication status||Published - 2008|
|Event||Eurosoil 2008: Soil - Society - Environment, Vienna, Austria - |
Duration: 25 Aug 2008 → 29 Aug 2008
|Conference||Eurosoil 2008: Soil - Society - Environment, Vienna, Austria|
|Period||25/08/08 → 29/08/08|
Sonneveld, M. P. W., Roelsma, J., & Brus, D. J. (2008). Nitrogen management and nitrate leaching on some Dutch dairy farms. In W. E. H. Blum, M. H. Gerzabek, & M. Vodrazka (Eds.), Eurosoil 2008: Soil - Society - Environment; Book of Abstracts, Vienna, Austria, 25-29 August 2008 (pp. 149-150). University of Natural Resources and Applied Life Sciences (BOKU).