SOIL C AND N AS INDICATORS OF VINEYARD SOIL QUALITY IN THE RAVNI KOTARI REGION OF CROATIA

The effect of soil management methods on soil organic carbon and nitrogen concentrations in vineyard soils is poorly understood. Vineyards generally are situated on poor soils with intense land management techniques that decrease soil organic matter and healthy soil structure. Wine grapes also require a delicate balance of soil nitrogen to ensure fertility and avoid excess vegetative growth. The main objective of this study was to determine how land management methods affected soil organic carbon (SOC) and total soil nitrogen (TSN) in the Ravni Kotari region of Croatia, a dry Mediterranean environment. Soil samples were collected from conventional and organic crushed limestone, conventional and organic tilled, and conventional no till vineyards. A total of 66 pit samples (10 cm deep) were collected from the crushed limestone vineyards, and a total of 77 profiles (18 cm deep) were collected from tilled and no till vineyards with clay-rich soils. The highest median SOC and TSN concentrations were measured in the crushed limestone vineyards, though conventional (32 mg C/g soil and 2.3 mg N/g soil) was not significantly different from organically managed (26 mg C/g soil and 1.7 mg N/g soil). The lowest median SOC and TSN concentrations were measured in the clay-rich vineyards, though tilled vineyards (13 mg C/g soil and 1.3 mg N/g soil) were not significantly different from the no-till vineyard (14 mg C/g soil and 1.3 mg N/g soil). A comparison of grass and abandoned vineyard soils, however, showed significantly higher SOC and TSN concentrations (26 mg C/g soil and 2.4 g N/g soil) than the tilled vineyard soils from the same area, showing the effect of tilling on soil organic matter. Both the grass/abandoned vineyards and no-till vineyards showed a decrease in SOC and TSN with depth, whereas the tilled vineyards did not. The results support prior studies that showed tilled vineyards display lower SOC and TSN concentrations due to the intensity of the management technique. Our findings indicate the possibility of an armoring effect from the use of crushed stone as a protective barrier that keeps the soil cool to reduce respiration of SOM.