engleski

Soil variation in Grk vineyards of the Korčula Island, Croatia

The knowledge about soils is crucial when dealing with quality productions and their farming practices. In the present study, we focused our attention on the relationship between soil and Grk, a white-berry grapevine variety that has been cultivated for centuries in the Lumbarda area, island of Korcula, Croatia. Since Grk is cultivated in a small area, we did a survey to fully characterize soil and its spatial variability at a very detailed scale with the main purpose of improving farming practices while preserving the quality of Grk wine. The soil survey was done in September 2008 in an area of about 40 hectares located on costal palaeodunes to the south of Lumbarda town. One hundred locations were selected using a sampling design aimed at homogeneously distributing soil observations in the area. In practice, a very thin grid of coordinates was extracted from the raster image of aerial photographs, and sampling coordinates were selected using the standard k-means approach to non-hierarchical cluster analysis (de Gruijter et al., 2006). Auger borings were dug in the field to a depth of 100 cm, recording the vertical sequence of horizons and, for each horizon, thickness, matrix colour, and texture class. Horizons were then sampled and analysed in the laboratory for grain size distribution, pH and soil organic matter content. The multivariate set of data was in the end processed to calculate the probabilistic pairwise dissimilarity of Goodall (Goodall et al., 1987), delineate the soil units present in the area, and draw their spatial distribution in 1:5000 scale maps. The most variable attributes were pH and sand content, which displayed similar spatial patterns, with larger values in the central portion of the area. The pH, in particular, ranged from 5.5 to 8.4 and its higher values looked related to dissolved Ca ions coming from neighbouring limestone outcrops. Godall’s dissimilarities furthermore suggested the presence of two soil units belonging to Eutric Arenosols (FAO, 1998) that mainly differs for pH and Munsell colour. The hydrological behaviour of these highly draining soils, a scarce rainfall in summer, and the restricted availability of nutrients are the most limiting factors for grapevine growth. Only a variety like Grk, which had enough time to suit this particular soil environment, can be successfully cultivated in Lumbarda. In the near future, suitable farming practices shell be implemented to preserve this typical, high-quality production.

coastal paleodunes; soil units; SOM

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