Long-term changes in extractable soil phosphorus (P) in organic dairy farming systems

摘要: On five farms that have been managed organically for several years, all cultivated soils were sampled on two occasions. The time span between the first and second soil sampling varied from 6 to 12 years. At had 3, 4, 6, 11 or 53 average phosphorus (P) concentrations in topsoil (0-20 cm) extracted by ammonium-acetate lactate solution (P-AL) decreased farms. sampling, P-AL 50, 64, 65, 75 119 mg P kg−1, which is characterised as medium (26–65 kg−1) high (66–150 kg−1). decrease occurred mostly with very (>150 at sampling. In these samples, value 100 87 188 151 respectively. subsoil (20–40 cm), an increase 15 27 kg−1 (P<0.01) concentration was found samples low (0–25 This indicates transfer subsoil. pattern of fairly well explained farm level balances. below values comparable conventional farms, but still a acceptable crop production. Crop yields acceptable, general shows future, some should be supplied external sources avoid further decrease, especially fields lowest concentrations.