For this study two fertilisation assays were carried out in an experimental field. The first assay (F1) used a sheep manure amendment, following the stipulations of European regulations concerning organic agriculture practices, and the second assay (F2) followed conventional agricultural practices of the area using inorganic fertilizers (313; 37 and 566 kgha-1 of N, P and K, respectively). Over a three-year period, samples of the arable soil layer were taken monthly in order to analyse the soil properties as indicators of soil quality (organic carbon, total Kjeldahl nitrogen, C:N ratio, Olsen P, electrical conductivity, pH in water and 1M KCl, cation exchangeable capacity, and exchangeable bases (Mg, K and Na).
The experimental plot managed using organic agriculture techniques showed significantly better conditions for crop development than the conventionally managed plot: higher quantities of organic matter (22.4 and 17.4 gkg-1, respectively) and nitrogen ( 3.0 and 2.5 gkg-1, respectively), a higher cation exchange capacity(14.4 and 12.2 cmol(+)kg-1, respectively) and greater availability of phosphorus ( 45.4 and 27.1 mgkg-1). No significant differences were observed as regards pH (8.0 in both plots) or the C/N ratio (7.7 and 7.1, respectively). Despite the short trial period of only three years, these results suggest that the agronomic model based on organic agriculture has a beneficial effect on soil properties and contributes to the function of soil as C sink.