Year	metric tons
1961	50
1962	50
1963	30
1964	18
1965	20
1966	30
1967	30
1968	25
1969	25
1970	21
1971	25
1972	30
1973	31
1974	35
1975	35
1976	35
1977	35
1978	35
1979	35
1980	0