Year	N fertilizer Use	NO3-N mg/l
1955	0.8	0.9
1956	0.88	0.82
1957	0.96	0.74
1958	1.04	0.66
1959	1.12	0.58
1960	1.2	0.5
1961	1.42	0.5
1962	1.64	0.5
1963	1.86	0.5
1964	2.08	0.5
1965	2.3	0.5
1966	2.7	0.57
1967	3.1	0.64
1968	3.5	0.71
1969	3.9	0.78
1970	4.3	0.85
1971	4.44	0.92
1972	4.58	0.99
1973	4.72	1.06
1974	4.86	1.13
1975	5	1.2
1976	5.38	1.22
1977	5.76	1.24
1978	6.14	1.26
1979	6.52	1.28
1980	6.9	1.3
1981	6.9	1.38
1982	6.9	1.46
1983	6.9	1.54
1984	6.9	1.62
1985	6.9	1.7
1986	6.94	1.66
1987	6.98	1.62
1988	7.02	1.58
1989	7.06	1.54
1990	7.1	1.5
1991	7.08	1.48
1992	7.06	1.46
1993	7.04	1.44
1994	7.02	1.42
1995	7	1.4
1996	7.05	1.46
1997	7.02	1.44
1998	7.08	1.5
1999	7	1.68
2000	7.01	1.56
2001