Spatial relationships between soil properties and land use change after agricultural land abandonment

During the last few decades significant amount of agricultural land in Latvia have been abandoned and overgrown, due to various factors. It is considered that abandonment is strongly influenced by socioeconomic and political factors, however, soil quality should be taken into consideration, as it plays a very important role in the development of vegetation. The aim of the research is to clarify spatial relationship of soil properties with different land use change scenarios.The study was conducted in the polygon (310 ha) characterized by slightly undulated topography in the southeast part of Latvia, where over the last 60 years, abandonment of agricultural land and overgrowth with forest has been observed.For the spatial assessment of land use change, aerial photo materials between 1954 and 2014 were digitized, where three types of land use were determined: arable land, grassland and forest. From 1954 till 2014 land use in the study area has changed significantly, therefore several scenarios were distinguished: a) arable land → forest; b) grassland → forest; c) arable land → grassland; d) grassland → grassland. In the study area 36 soil profiles were established, samples were collected and physical and chemical analyses (soil texture (sand, silt, clay (%), pHKCl, total carbon (%), total nitrogen (%), exchangeable cations (Ca2+, Mg2+, K+, Fe3+, Al3+) (cmol(+) kg-1)) according to standard methods were conducted in the laboratory. To estimate statistically significant (p<0.05) differences between land use scenarios and soil properties was used One-Way ANOVA.The study results shows that the area covered by forest increased from 11% to 62%, between 1954 and 2014, but arable land decreased from 33% to 0,1% and grassland area decreased by 20%. In 2014 agricultural lands are mainly overgrown with Alnus incana (48.6%), Salix caprea (19%) and Betula pendula (14%), as well with Populus tremula and Picea abies. Statistical analyses showed significant differences of soil textural classes: content of sand and silt fraction, pHKCl value, and exchangeable cations (Ca2+, Al3+) between former arable land that changed to forest and arable land that changed to grassland. Arable land overgrows faster in areas of poorer soil and lighter soil textural classes, in contrast longer agricultural activity was found in areas, characterized by relatively heavier soil textural classes. Soil was more acidic and concentration of Al3+ was significantly higher in areas that have been overgrown by trees. Statistical analysis revealed that soil texture, acidity and nutrient availability significantly influence further development of land, either area will be transformed to forest or kept as grassland. Although, overgrowth is considered as reasonable land use option of abandoned agricultural lands, preliminary results showed that investigated marginal lands are suitable for farming. Further study will be conducted in a wider region for deeper understanding of mechanisms responsible for land use changes.