Agricultural soil organic carbon stocks in the north-eastern Iberian Peninsula: Drivers and spatial variability

Estimating soil organic carbon (SOC) stocks under agriculture, assessing the importance of their drivers and understanding the spatial distribution of SOC stocks are crucial to predicting possible future SOC stocks scenarios under climate change conditions and to designing appropriate mitigation and adaptation strategies. This study characterized and modelled SOC stocks at two soil depth intervals, topsoil (0–30 cm) and subsoil (30–100 cm), based on both legacy and recent data from 7245 agricultural soil profiles and using environmental drivers (climate, agricultural practices and soil properties) for agricultural soils in Catalonia (NE Spain). Generalized Least Square (GLS) and Geographical Weighted Regression (GWR) were used as modelling approaches to: (i) assess the main SOC stock drivers and their effects on SOC stocks; (ii) analyse spatial variability of SOC stocks and their relationships with the main drivers; and (iii) predict and map SOC stocks at the regional scale. While topsoil variation of SOC stocks depended mainly on climate, soil texture and agricultural variables, subsoil SOC stocks changes depended mainly on soil attributes such us soil texture, clay content, soil type or depth to bedrock. The GWR model revealed that the relationship between SOC stocks and drivers varied spatially. Finally, the study was only able to predict and map topsoil SOC stocks at the regional scale, because controlling factors of SOC stocks at the subsoil level were largely unavailable for digital mapping. According to the resulting map, the mean SOC stock value for Catalan agriculture at the topsoil level was 4.88 ± 0.89 kg/m2 and the total magnitude of the carbon pool in agricultural soils of Catalonia up to 30 cm reached 47.9 Tg. The present study findings are useful for defining carbon sequestration strategies at the regional scale related with agricultural land use changes and agricultural management practices in a context of climate change

Long-term effects of gasification biochar application on soil functions in a Mediterranean agroecosystem: Higher addition rates sequester more carbon but pose a risk to soil faunal communities

17 Pág. Departamento de Medio Ambiente y Agronomía​ (INIA)Biochar applications can have important implications for many of the soil functions upon which agroecosystems rely, particularly regarding organic carbon storage. This study evaluated the impacts of adding a highly aromatic gasification biochar at different rates (0, 12 and 50 t ha-1) to a barley crop on the provision of crucial soil functions (carbon sequestration, water content, greenhouse gas emissions, nutrient cycling, soil food web functioning, and food production). After natural ageing in the field for six years, a wide range of soil properties representative of the studied soil functions were measured and integrated into a soil quality index. Results showed that C sequestration increased with biochar rate (23 and 68% higher than in the control for the 12 and 50 t biochar ha-1 treatments, respectively). Water content was enhanced at the 50 t ha-1 treatment depending on the sampling date. Despite biochar additions neither abating nor increasing CO2 equivalent emissions (carbon dioxide plus nitrous oxide and methane), the system shifted from being a methane sink (-0.017 ± 0.01 mg CH4-C m-2 h-1 at the 12 t ha-1 treatment), to a net source (0.025 ± 0.02 mg CH4-C m-2 h-1 at the 50 t ha-1 treatment). In addition, biochar ageing provoked a loss of nitrate mitigation potential, and indeed ammonium production was stimulated at the 50 t ha-1 rate. The 50 t ha-1 treatment also adversely affected nematode and collembolan functional diversity. Lastly, biochar did not affect barley yield. The results of the soil quality index indicated that no biochar treatment provided more benefits to our agricultural soil, and, although the 50 t ha-1 treatment increased C sequestration, this was potentially offset by its harmful effects on soil faunal communities. Therefore, application of this biochar at high rates should be avoided to prevent risks to soil biological communities.We gratefully acknowledge the funding by the project FERTICHAR (AGL2015-70393-R) of the Spanish Ministry of Economy and Competitiveness. We are also grateful to Dr. van den Brink, P. J., and Dr. Šmilauer, P. for their assistance on PRC analysis interpretation and proper use of CANOCO 5, respectively.Peer reviewe

Reducció de l'erosionabilitat d'un alfisòl mitjançant l'ús de fangs de depuradora o d'adobs minerals per al desnvolupament de la coberta herbàcia

S'ha avaluat la resistència a l'erosió mitjançant pluja simulada (94 L m-2 h-1) d'un alfisòl afectat per un incendi forestal i posteriorment fertilitzat amb (a) fangs de depuradora i (b) un adob mineral N-P. La simulació de pluja s'ha efectuat sobre el sòl nu i també sobre el mateix sòl ja revegetat, als dos mesos de la fertilització. Sobre sòl nu, els dos tipus de fertilitzants donen unes taxes d'erosió comparables en els primers minuts de pluja (1500 i 1359 g m-2 h-1 per al tractament de fangs i fertilitzant mineral, respectivament), si bé apareix un marcat efecte protector dels fangs en pluges de més de 10 minuts de durada (212 i 942 g m-2 h-1, respectivament, als 40 minuts de simulació). La presència d'una coberta vegetal estable constitueix, però, la major protecció del sòl contra l'erosió. Efectivament, amb la superfície revegetada, i amb independència del tipus d'adob aplicat, les taxes d'erosió difícilment superen els 100 g m-2 h-1.We tested soil erosion rates after a wildfire throughout rainfall simulation (94-L m-2 hr-1). The soil was amended by using sewage sludge or mineral N-P fertiliser. Rainfall simulation was done either on denuded or covered soil. For small rain episodes (10 min.), the erosion rates were higher in the mineral fertilised plots (942 g m-2 hr-1) than in the sludge-treated plots (212 g m-2 hr-1). Vegetation cover supplied the highest protection against soil loss. Under vegetation cover, soil erosion was unaffected by the type of amendment, and showed rates of erosion lower than 100 g m-2 hr-1

Aplicación del flujo de C02 como indicador de la calidad de la restauración en actividades extractivas a cielo abierto

Se ha medido el flujo de CO2 para una evaluación retrospectiva de los trabajos de restaración de áreas afectadas por minería de calizas a cielo abierto. Los trabajos de rehabilitación se han tipificado en distintas categorías atendiendo a las opciones más frecuentes (aporte de suelos, enmiendas orgánicas, siembra y plantación). Los flujos de CO2 suelen ser inferiores a 1 g CO2 m-2 h-1. Su evaluación demuestra que el tipo de tratamiento tiene gran importancia en la recuperación biológica del suelo, especialmente en áreas de escasas precipitaciones (menos de 525 mm anuales) y para granulometrías extremas. En estos casos, no aparecen diferencias significativas entre suelos enmendados con lodos de depuradora (1,127±0,227 g CO2 m-2 h-1) y suelos de referencia no perturbados (1,071±0,130 g CO2 m-2 h-1). En estos suelos, la comparación de parcelas de distintas edades sugiere que el efecto de la adición de mate-ria orgánica fresca no es efímero

Biochar Addition to a Mediterranean Agroecosystem: Short-Term Divergent Priming Effects

The goal of this study was to evaluate biochar’s resistance to microbial decomposition and its impact on native soil organic matter (SOM) decomposition. Conducted in a vineyard with a sandy loam Mediterranean soil with neutral pH and low organic carbon content, the experiment involved the application of 6.5 g biochar kg−1 derived from pine (PB) and corn cob (ZB). The monitoring period spanned two years, with soil samples collected at short- and medium-term timepoints (2 and 26 months post-application) and incubated in the lab for an additional 250 days. Soil respiration, the CO2-C isotopic signature, and dissolved organic carbon (DOChw) were assessed to identify potential priming effects (PE) and evaluate their persistence over two years. In the short term, biochar-induced priming effects were feedstock and pyrolysis temperature dependent, exhibiting negative priming in high-temperature wood biochar and positive priming in low-temperature grass biochar. The mechanism behind short-term positive priming was attributed to the higher labile organic carbon (OC) content in ZB compared to PB. In the medium term, initial strong priming effects shifted to slightly negative priming effects in both biochars, indicating the depletion of labile carbon fractions and the emergence of physical protection processes that mitigated priming