Swedish soil fertility experiments

Twelve long-term soil fertility field experiments in south, central and north Sweden were started in the period 1957-1969. Five of the experiments, two in south and three in central Sweden, were situated at favourable sites, the other seven were placed at sites with less favourable climatic conditions and natural soil properties. Two crop rotations, one with and one without livestock and 16 combinations of inorganic NPK (nitrogen/phosphorus/potassium) fertilizers were compared in the south and central Swedish experiments. In north Sweden, there was one rotation with livestock and 30 NPK combinations. There was a four-course rotation in the south, a six-course in central Sweden and a seven-course rotation in north Sweden. The ordinary fertilizer treatments in the rotations without livestock almost doubled the yields of cereals compared with the unfertilized plots; with more fertilizer yields were even larger. In the livestock rotations the mineral fertilizer effects were smaller owing to positive effects of the manure. N responses were always considerably greater than PK responses. In north Sweden yield responses were of the same magnitude as in south and central Sweden. With no fertilizers, in the livestock rotations the uptakes of N, P and K were 50-90, 10-15 and 30-100 kg ha(-1), respectively, depending on the crop. In the non-livestock rotations corresponding values were 25-40, 7-10 and 10-25 kg. In north Sweden the N removal was even higher owing to the large proportion of ley in the rotation. In zero N treatments in south Sweden, over a 24 year period, losses of organic matter were nearly 10 t ha(-1) in the non-livestock rotation and about half as much in the livestock rotation. With 100 kg N ha(-1) losses were negligible. Levels of AL-extractable P were not maintained where P additions equalled offtakes in the crops, but decreased by about 1 unit during the period. P dynamics differed between sites; on some, P fertilizer had no effect on either yields or soil P, whereas in other cases P fertilization increased yields and kept soil P in plant-available forms. The cadmium content in sugar beet roots increased with increased NPK fertilization, but the increases were smaller than differences between sites. The cadmium content varied from 128 to 288 ppb.