The effects of different types (superphosphate, basic slag and rockphosphate) and quantities (0, 44 and 175 kg P ha(-1) a(-1)) of P-fertiliser application on crop yields and P-CAL/DL-contents in soils were evaluated in three long-term field experiments lasting 40 years. After 20 to 40 years of application of 44 kg P ha(-1)a(-1) as superphosphate and basic slag crop yields increased in comparison to zero P-fertilisation. These differences are statistically significant (Tukey test) for spring barley (at three sites), sugar beet and potato (at one sire each). The omission of P-fertiliser during the whole 40 year period caused great economic losses in these root crops in a conventional cultivation regime. No statistically significant yield decreases were observed when discontinuing P-fertilisation after 20 years of application compared to continuous fertilisation. After 20 years of application of 44 kg P ha(-1) a(-1) the soil P-CAL/DL-contents were at a medium stage (less at one site with heavily textured soil) and decreased only slowly in 20 years of zero application. In the case of zero fertilisation during 40 years the soil P-CAL/DL-contents remained at almost the same level. The correlations between spring barley, winter wheat and sugar beet yields and P-CAL/DL-contents in soils are significant and highly significant, the coefficients of determination show that other factors are also important for crop yields.
