Water erosion and soil properties patterns along selected rainfall events in cultivated and abandoned terraced fields under renaturalisation

Current cultivated soils (C) and soils under different age of agricultural abandonment and plant cover like forest (F), meadows (M) and scrubs (S) were surveyed at any high (H) or low (L) rainfall event generating runoff to record erosion and both dissolved and eroded carbon and nitrogen. This survey was conducted from January 2009 to April 2010 and was also addressed to determine soil properties such as surface temperature (ST), moisture (SM), bulk density (BD), shear strength (SS), pH, organic carbon (SOC), total nitrogen (NT), total phosphorus (PT), CO2 emission, glomalin (GRSP), and β-Glucosidase, Phosphatase and Protease activities. The overall data set allowed accomplishing with the objective of the research, seeking differences in soil properties according to the previous land use, land abandonment and repeated fire occurrence. ANOVA of repeated measures showed runoff variance statistically significant within soil uses at L rainfall (p < 0.05). Eroded soil and eroded carbon varied significantly among soil environments (p < 0.05) at both H and L rainfall. However, erosion rates were low when compared to other Spanish sites. Soils under meadows (M) showed higher SOC and GRSP, and higher enzyme activities, and were identified as important natural firebreaks, besides their susceptibility to sediment and nutrient depletion. Similarly, soils F and S, though repeatedly affected by fire, showed satisfactory soil properties. The poorest soil properties were found in cultivated soils (C) that increased their erosion rates by 838%, 733% and 188% with respect to F, S and M soils along the observed period. In general, soils with higher organic carbon content (M > S > F) showed proportionally lesser CO2 emission, indicating their tendency to act as carbon sink. The shallowness of the soil profiles, overgrazing and frequent fire occurrence were found to be soil ecosystems threatening elements in areas deserving special attention for the risk of irreversible degradation processes. Unpredictable and erratic fire occurrence all over the area also suggests environmental protection through prevention plans.