Title: Soil quality assessment of cultivated volcanic soils of South-west Iceland

Good soil quality is the basis for human, plant, animal and microorganism life as well as for environmental sustainability. Bad cultivation practices deteriorate soil quality and volcanic soils are particularly sensitive. This study aimed to evaluate the impact of cultivation on the soil quality of volcanic soils in South-west Iceland, and to compare the quality of cultivated soils that have received different managements. The hypothesis was that there was a measurable difference in soil quality between cultivated and non-cultivated soils. Soil quality indicators were measured on soil samples from five sites: land that had been cultivated for 17 years;13 years; grass covered land (all wetland soils); erosion spots; and a birch tree cluster (dryland soils). The results showed that 17 years of cultivation had lowered carbon content and reduced aggregate stability. The erosion spot soil was structureless and had lower aggregate stability but a higher clay content than the soil under birch trees. The birch site, however, showed signs of improved soil quality with a higher carbon content, better structure and stronger aggregation compared to the erosion spot site. Total carbon, aggregate stability and soil colour seem to be the most sensitive indicators for cultivated versus non-cultivated soils, and for wetland versus dryland soils. Structure and C/N ratio are also usable indicators. For comparison of wetland and dryland soils, bulk density, porosity, water holding capacity, total nitrogen, CEC and clay % are also very sensitive indicators. Soil pH, consistency, and texture were less sensitive indicators of soil quality in this study. It is important to monitor organic content and aggregate stability of soils under cultivation in Iceland. In order to build up good soil characteristics it may be necessary to rest cultivated areas periodically. The methods applied here may be applicable to volcanic soils in Ethiopia.