| Year | Value (kg/ha) |
|---|---|
|
1990 |
1030 |
|
1989 |
950 |
|
1988 |
940 |
|
1987 |
930 |
|
1986 |
920 |
|
1985 |
910 |
|
1984 |
900 |
|
1983 |
900 |
|
1982 |
890 |
|
1981 |
880 |