EVOLUTION OF SOIL CHEMICAL VARIABLES IN AN ORGANIC CELERY CROP DURING THE CONVERSION PERIOD TO ORGANIC FARMING

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.