Nitrate leaching in agriculture to upper groundwater in the sandy regions of the Netherlands during the 1992-1995 period.
The Dutch National Monitoring Programme for Effectiveness of the Minerals Policy (LMM) was initiated to allow detection of a statutory reduction in nitrate leaching caused by a decreasing N load. The starting point, or baseline, was taken as the nitrate concentration of the upper metre of groundwater sampled on 99 farms in the 1992-1995 period in the sandy areas of the Netherlands, where predominantly grass and maize grow. We found here that a reduction in nitrate leaching of more than 20% in future would almost certainly be detected with the LMM. Detecting downward trends due to decreasing N load will require nitrate concentrations to also be related to soil drainage, precipitation excess leading to groundwater recharge and to location. Furthermore, we found that about 16% of the N load in the Dutch sandy regions was being leached to the upper metre of groundwater in the 1992-1995 period. The critical N load in approximately 1990 for exceeding the EC limit value for nitrate, NO3, (50 mg L(-1)) in the upper metre of groundwater for the mean situation for grassland, maize and arable land in the sandy area was found to be 210 kg ha(-1) a(-1). Because manure management has been altered, the critical load found will be lower than the current critical load.
Boumans
Leo J M
LJ
Netherlands Environmental Assessment Agency (Agriculture and Rural Areas), Bilthoven, The Netherlands. ljm.boumans@rivm.nl
Fraters
Dico
D
Van Drecht
Gerard
G
D000383:Agriculture / Q000331:legislation & jurisprudence; D004784:Environmental Monitoring; D005308:Fertilizers; D008372:Manure; D008962:Models, Theoretical; D009426:Netherlands; D009566:Nitrates / Q000032:analysis*; D012822:Silicon Dioxide; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014876:Water Pollution / Q000517:prevention & control; D014881:Water Supply
D005308:Fertilizers; D008372:Manure; D009566:Nitrates; D014874:Water Pollutants, Chemical; D012822:Silicon Dioxide