A Comparison of the Leachable Inorganic Nitrogen Content in Organic and Conventional Farming Systems

Abstract

Soil samples collected from 26 organic and 550 conventional farms during autumn 1990 through the national Grid Net Survey (GNS) and a simultaneous supplementary survey on 8 organic farms have been analyzed in order to estimate the risk of nitrogen leaching. The average nitrate N (nitrogen) content in the soil (0–75 cm) was very similar in samples from organic farms (31kg/ha) and conventional farms using manure (29 kg/ha), but superior to that of conventional farms not using manure (22 kg/ha). Samples collected from fields on organic farms cultivated with grass with clover or alfalfa were very small (12 kg/ha) compared to samples from fields cultivated with cereals (57 kg/ha) and samples from bare fields following cereals (48 kg/ha). The average nitrate N content was higher in samples from clayey soil (40 kg/ha) than from sandy soils (15 kg/ha). The nitrate N content in samples from regions with a high percolation level during the autumn (August to December 1990) was lower than in samples from regions with a low percolation level.