Field survey: heavy metals and phosphorus accumulation in the soils of intensive livestock farms of Western Brittany

Abstract

In Brittany (Western France) intensive pig, cattle and poultry breeding involves high amounts of some elements, such as minerals and metals. In particular, theoretical nutrient balance at farm scale level shows important excesses in phosphorus, potassium, copper and zinc. These elements come from chemical fertilizers and animal feed, and excesses affect chemical evolution of soils due to the addition of slurry. To study this enrichment, a survey of 64 breeding farms started in 1973, and 180 fields (3 per farm) were analysed every 3 years. The enrichment in P2O5 (Dyer), Cu-EDTA and Zn-EDTA has been correlated to the amounts of slurry spread on soils, cumulated over the past 20 years. There were no relationships between crops species or rotations and organic fertilization, the amounts of slurry beeing higher than crop requirements. Slurry and mineral phosphates appeared negatively correlated. A classification of fields based on cumulated inputs of slurry was established. Forthcoming analyses on total elements will be carried out to study the conditions of their migration and evaluate the risks of water pollution.