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Quality of groundwater and surface water in the Farming with a Future project, 2002

Kwaliteit van grond- en oppervlaktewater in het project Telen met Toekomst, 2002


In Farming with a Future (FwF) farmers, together with extension officers and researchers, work towards sustainable production systems for arable crops, open air vegetables, flower bulbs and ornamental trees. Systematic measurements of water quality on the participating farms are conducted by RIVM; for the first time in 2002. The results of these measurements are presented and discussed in this report. Special attention is paid to the concentration of several forms of nitrogen (N) and phosphorous (P), and the relationships with land use and the physical environment. The groundwater of 15 of the 37 farms investigated presented nitrate concentrations (farm averages) below the boundary value of 50 mg/l (as NO3). Groundwater of the farms with arable crops on clay soils and of those with flower bulbs presented the lowest nitrate concentrations as compared to groundwater of the other farm sectors. The highest concentrations were found in groundwater of farms with open air vegetables, followed by the farms with ornamental trees. These differences are partly explained by differences in the physical environment. Farms on 'wet' soils, including all flower bulb farms and arable farms on clay, present lower concentrations than farms on naturally well-drained soils with a deep groundwater table. However, when physical environments appear to be comparable (sandy soils), farms with open air vegetables generally present higher groundwater nitrate concentrations than farms with arable crops. With respect to groundwater P-concentrations, among the participating farms, the ones with flower bulbs clearly present the highest values, (average farm average total-P = 7,4 mg/l), followed by those with arable crops on clay soils (average 0,61 mg/l) and a few farms with arable crops on sandy soils. The most important factors determining the high groundwater P-concentrations on the farms with flower bulbs seem to be the small phosphate retention capacity of the sandy dune soils where flower bulbs are produced; heavy applications of manure and fertilisers (especially in the past); the shallow groundwater level and the practice of deep tillage. Ditch water samples were taken on 5 farms with arable crops on clay and 3 farms with flower bulbs. In all cases, farm average total-N concentrations exceeded the FwF goal for surface water (2,2 mg/l). With respect to total-P, farm average concentrations where within the FwF goal (0,15 mg/l) on 3 of the farms with arable crops on clay, but exceeded this goal on all flower bulb farms investigated. It is questioned however, to which extent the FwF goals for surface water may be applied to each farm individually. Differences between the quality of groundwater, drain water and ditch water seem to be primarily related to the period of sampling, as well as to the residence time of the water in the soil.

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