Växtnäring, produktion och miljö

Two field experiments with different crop rotations and one conventional plant nutrient experiment are reported. In the crop rotation experiments nitrogen of different origin, organic or inorganic, was compared. In the plant nutrient experiment effects of different levels of NPK and lime were investigated. Annual off-take of nitrogen were strongly correlated with the crop, N-leve1 and climate. Over the reported period which lasted 13-17 years the off-take varied from 50 to 160 kg ha-' yr-'. It was the lowest in a rotation with cash crops fertilized with 50% of optimum N-rates. The highest value was observed in a rotation with grass leys and supply of manure twice during a six year period. The N efficiency was 65 to 120% in systems based on both organic and inorganic N supply. In systems based solely on air-fixed N the N efficiency could not be satisfactory estimated. Over a 20-year period the yields declined to 50% when no NPK was applied in relation to normal NPK fertilization One of the experiments with different crop rotations and the NPKIlime experiment were placed on a nutrient deficient field. Immediate increase in soil P and K status was observed when fertilizer measures were taken. After 5 years with application of 32 kg P ha-' yr-' soil P status was improved from very poor to medium according to Swedish classification systems. Soil mineral N in autumn after ley harvest was 30% of that after cereals. When the leys were ploughed the difference was levelled out. After luzern, however higher soil mineral N values were observed than after cereals. Each cropping system was drained separately. Annual transport of NO3-N was strongly influenced by the precipitation. The transport from the luzern was small but increased considerably when the ley was ploughed. Transport from the grass ley was similar with the transport from cereals. A low N input reduced the leaching to 50% or less