Concentration of nitrate in upper groundwater

Over the last few years, the amount of nitrate in the upper groundwater layer of agricultural sandy soils has declined to the extent that the target value of 50 mg per litre has been achieved. In regions with clay and peat soil in particular , concentrations have been below the target for some time, mainly due to stricter fertiliser standards. Groundwater concentrations under agricultural loess soils are just above the target value.

Nitrate concentrations in groundwater in agriculture areas
	Loess (fall) (mg/l)	Sand (summer) (mg/l)	Clay (winter) (mg/l)	Peat (winter) (mg/l)	Target value (mg/l)
2000		94	55		50
2001		76	35		50
2002	81	64	25	3.2	50
2003	85	55	23		50
2004	94	78	58		50
2005	85	85	41	7.3	50
2006	95	66	43	0.71	50
2007	87	77	37	13	50
2008	77	63	28	5.3	50
2009	81	58	27	5.5	50
2010	71	66	29	11	50
2011	76	55	20	5.4	50
2012	74	47	19	4	50
2013	77	53	17	6.5	50
2014	70	56	20	9.3	50
2015	62	54	25	12	50
2016	54	46	19	6.3	50
Source: RIVM, LMM

Nitrate concentrations in groundwater in agriculture areas
	Loess (fall) (mg/l)	Sand (summer) (mg/l)	Clay (winter) (mg/l)	Peat (winter) (mg/l)	Target value (mg/l)
2000		94	55		50
2001		76	35		50
2002	81	64	25	3.2	50
2003	85	55	23		50
2004	94	78	58		50
2005	85	85	41	7.3	50
2006	95	66	43	0.71	50
2007	87	77	37	13	50
2008	77	63	28	5.3	50
2009	81	58	27	5.5	50
2010	71	66	29	11	50
2011	76	55	20	5.4	50
2012	74	47	19	4	50
2013	77	53	17	6.5	50
2014	70	56	20	9.3	50
2015	62	54	25	12	50
2016	54	46	19	6.3	50
Source: RIVM, LMM

The issue

Green growth requires a healthy balance between economy and natural resources. Groundwater is used in the Netherlands to prepare drinking water. Leaching of nitrogen from farmland to the groundwater threatens its quality. High concentrations of nitrate can lead to closure of drinking water abstraction points or to higher purification costs. A key determinant of nitrate concentration in the groundwater is the nitrogen surplus in the soil balance of farms. In order to reduce the load of nitrogen to soil and groundwater, the standards for nitrogen fertilisation on agricultural land have been tightened in stages. The effect of this on nitrate content has become visible in recent years (CBS, PBL, RIVM, WUR, 2016 and LMM, 2018).

Analysis

There is a large spread in nitrate concentrations between agricultural sectors, farm types and regions with regard to soil type. Soils under arable farms generally have a higher nitrate surplus than soils under dairy farms. In the southern part of the Netherlands, with sandy soils, concentrations are generally higher, among other things because crops are cultivated on soil types that are susceptible to leaching.