Nutrient Balances and Yields during Conversion from Conventional to Organic Cropping Systems on Silt Loam and Clay Soils in Norway

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Abstract
Conversion from conventional to organic cropping systems was started in 1993 at three sites in Norway: Landvik (Grimstad), Voll (Ås), and Kvithamar (Stjørdal). A six-year crop rotation was designed for each site. At Landvik, the nutrient input was based on compost from plant residues and household waste, and at Voll and Kvithamar, the plant nutrient supply was from cattle slurry. The yields of leys were large at all three sites. At Landvik, large yields of vegetables were obtained. At Kvithamar the yields of cereals were small, while at Voll the growth conditions for cabbage varied between years, causing crop failure in 1995 and a large yield of good quality in 1994. More potassium was removed than applied from the cropping systems at all three sites, but a significant decrease in potassium status of the soil was only found at Landvik. At Voll and Kvithamar, a negative balance was found for phosphorus, and a corresponding significant decrease in readily available P of the soil was found. The nitrogen inputs to the cropping systems were somewhat higher than the amounts of nitrogen removed by the crops. Adjusted for estimated nitrogen leaching, the nitrogen balances were close to equilibrium at Kvithamar and Landvik and negative at Voll. Nitrogen supply seems to be the major factor limiting plant growth in the cropping systems.

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