Nitrate in the upper groundwater of 'De Marke' and other farms

Abstract

Groundwater-nitrate concentrations were compared between the experimental farm 'De Marke', which was designed to minimize nutrient surpluses -, and farms being representative for the sandy region of the Netherlands. Samples were collected during the period 1991-99 at 'De Marke' and during 1992-95 at 94 representative farms. Between 1991 and autumn 1992, groundwater nitrate at 'De Marke' decreased from 193 mg litre-1 to 115 mg litre-1. No decrease was found at the representative farms. The decrease at 'De Marke' was attributed to new farm management. After autumn 1992, groundwater nitrate at 'De Marke' fluctuated between 30 and 115 mg litre-1. A comparable pattern in time was found at other farms. This variation was attributed mostly to variation in groundwater table and precipitation. After autumn 1992, farm management did not result in a further reduction in groundwater nitrate. Only 9 of the 94 representative farms had an average nitrate concentration lower than that at 'De Marke' during 1992-98. If differences in groundwater table and precipitation were taken into account, it was estimated that only three of the representative farms would have had a lower average nitrate concentration than 'De Marke'.