Spatial distribution of soil health indicators at different depths after 30 years of changes in land use in a small catchment of NW Spain

Preservation and recovery of soil health have become one of the priorities of European environmental policies. In this context, the EU Soil Protection Strategy sets concrete targets to be achieved by 2030, including improving soil quality in those agricultural systems that have been impacted by intensive agricultural practices. Aforestation of agricultural land is usually considered an approach with positive effects in many soil indicators, e.g., soil carbon stocks, since it is usually consider a viable carbon sequestration strategy in carbon stock markets. However, long-term effect of afforestation on soil properties can vary from place to place, according to differences in environmental conditions like soil types or climate. Moreover, an increase of carbon stocks does not necessarily lead to an improvement of other soil health indicators. Typically, soil health indicators are often measured only at the upper 10 - 20 cm, while deeper layers are rarely evaluated. Thus, the objective of the present work was to analyze long-term effects of land use transformations from a grazing pasture to eucalyptus plantations on diverse soil health indicators including C content, enzymatic activity and soil respiration.

The study was conducted in a small catchment located in Galicia (NW of Spain), and covers an area of 10.7 ha. During more than 30 years, some plots were dedicated to cattle grazing, while other were cultivated annually with maize. In 1999, part of the catchment was transformed into a eucalyptus plantation, while other part was dedicated to the annual cultivation of maize for forage using conventional methods. As a result, 4 treatments were identified in the catchment, including the two historical dedications and the two current ones. In 2024, soil samples were collected in 72 locations inside the catchment, at three different depths: 0-30 cm, 30-60 cm and 60-90 cm. Measured soil health indicators included enzymatic enzymatic activities, soil respiration and total soil carbon. These properties were interpolated for the whole catchment using geostatistics, in order to identify their spatial variability and their relation with past and present land uses. Results will provide a deeper understanding of the impact of long-term changes in land use at different depths.

 

Acknowledgements:

This study was funded by the Ministry of Science, Innovation and Universities of Spain under the project “Gesta Race” (TED2021-130315B-I00) and the “Ramón y Cajal” fellowship (RyC 2021-615 033370-I), and by the Regional Govermnent of Galicia (project ED431F 2024/024 Xunta de Galicia).