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The spatial representation of the soil properties for agricultural areas is necessary to implement precision agriculture management practices. This can currently be obtained by extensive sampling of soil or plants, which is laborious and not economical. An alternative procedure is presented in this study, where a digitized soil map was constructed for the regional unit of Kastoria. This digitized soil map has provided a useful electronic database for the spatial representation of the soil variation of the region, based on in situ soil sampling, laboratory analysis, GIS techniques and plant nutrition mathematical models, coupled with the local land cadastre. The novelty of these studies is that local agronomists have immediate access to a wide range of soil information by clicking on a field parcel shown in this digital interface. Thus, differential fertilization management can be applied at a large scale, such as for example, the whole regional unit of Kastoria, while precision is not compromised. The software (provided on CD) automatically calculates the fertilization needs for each farm, displays and prints a detailed two-page guideline to the farmer, namely: • on the first page there is a map of the farm as well as information regarding the farm's nutritional status according to soil analysis (see Figure 1). • on the second page the fertilization advice is provided for the particular crop, based on the soil nutritional status. The current study examined the spatial patterns of soil texture, pH, CaCO3, organic matter, EC, soil nitrate, P, K, Mg, B, Mn, Fe, Cu and Zn in the regional unit of Kastoria and 883 field parcels were sampled for the scopes of this work. A characteristic finding was that potassium distribution in the area was structured and thus delineation zones were provided for differential potassium fertilization management. The interest and acceptance shown by the farmers for these pilot scale studies have been extremely positive, so that the Soil Science Institute of Thessaloniki went on further upgrading of the existing software in order to transform it into a dynamically evolving tool for the Internet. Further research is currently carried out to incorporate in the same software other factors, such as meteorological data, irrigation, plant protection, etc. The final aim is to provide a common online platform with a uniform, integrated user - friendly interface in order to facilitate the management of the agricultural land. [ABSTRACT FROM AUTHOR]

• A P-fertilization experiment (+P or –P) was conducted in two olive groves. • P fertilization influenced soil properties, P fractions and its mineralization. • Acid and alkaline phosphatase activities were significantly higher in the –P plots. • P fertilization did not significantly influence trees' foliar P nutrition. • It is useless for the olive growers to provide P every year in their groves. Often, from soil and plant tissue analyses, over-sufficient foliar P levels in olive trees, grown under low Olsen P availability, are determined. In order to deepen our knowledge in this topic, a field P fertilization experiment (with or without supply of the fertilizer 0-46-0) with 25-year-old olive trees was conducted, in order to investigate if: i) soil organic P was a sufficient 'pool' to satisfy the P nutritional needs of mature, fully productive, olive trees under low Olsen P availability and sufficient organic matter content, ii) the activities of acid and alkaline phosphatase were enhanced under low Olsen P availability, iii) soil chemical properties were significantly influenced by P fertilization, iv) significant differences in foliar nutrition of olive trees existed between P-fertilized (+P) and unfertilized (-P) trees. Our results indicated that in the -P plots 48 % of the total soil P was in organic fraction, while in the + P ones approximately 23 % of the total P was in organic form. In contrast, Olsen, inorganic and total P fractions were significantly higher in the + P plots. In addition, in the + P plots significantly lower: i) soil Fe, Mn and Zn, and ii) foliar Ca, Mg and Mn concentrations were determined, while, in contrast, iii) higher leaf K concentration was found. Foliar P was not influenced by P fertilization, while at the same time, both the activities of alkaline and acid phosphatase were significantly higher in the –P plots, compared to those received P fertilization. Overall, the kind of management of olive groves (sufficient organic matter levels, with or without inorganic P fertilization inputs) significantly influences P dynamics and modifies its fractions in soils, while it also affects organic P mineralization and supports P nutrition for olive trees. It is believed that these data reveal the crucial role of organic matter to sustain P uptake and contribute towards a sustainable management of olive groves to support and sufficiently satisfy the P nutritional needs of olive trees, by also significantly reducing the unnecessary annual P fertilizer inputs. [ABSTRACT FROM AUTHOR]