Open Access
Multi-modelling predictions show high uncertainty of required carbon input changes to reach a 4‰ target
(Wiley, 2022) Bruni, Elisa; Chenu, Claire; Abramoff, Rose Z.; Baldoni, Guido; Barkusky, Dietmar; Clivot, Hugues; Huang, Yuanyuan; Kätterer, Thomas; Pikula, Dorota; Spiegel, Heide; Virto Quecedo, Íñigo; Guenet, Bertrand; Ciencias; Zientziak
Soils store vast amounts of carbon (C) on land, and increasing soil organic carbon (SOC) stocks in already managed soils such as croplands may be one way to remove C from the atmosphere, thereby limiting subsequent warming. The main objective of this study was to estimate the amount of additional C input needed to annually increase SOC stocks by 4‰ at 16 long-term agricultural experiments in Europe, including exogenous organic matter (EOM) additions. We used an ensemble of six SOC models and ran them under two configurations: (1) with default parametrization and (2) with parameters calibrated site-by-site to fit the evolution of SOC stocks in the control treatments (without EOM). We compared model simulations and analysed the factors generating variability across models. The calibrated ensemble was able to reproduce the SOC stock evolution in the unfertilised control treatments. We found that, on average, the experimental sites needed an additional 1.5 ± 1.2 Mg C ha−1 year−1 to increase SOC stocks by 4‰ per year over 30 years, compared to the C input in the control treatments (multi-model median ± median standard deviation across sites). That is, a 119% increase compared to the control. While mean annual temperature, initial SOC stocks and initial C input had a significant effect on the variability of the predicted C input in the default configuration (i.e., the relative standard deviation of the predicted C input from the mean), only water-related variables (i.e., mean annual precipitation and potential evapotranspiration) explained the divergence between models when calibrated. Our work highlights the challenge of increasing SOC stocks in agriculture and accentuates the need to increasingly lean on multi-model ensembles when predicting SOC stock trends and related processes. To increase the reliability of SOC models under future climate change, we suggest model developers to better constrain the effect of water-related variables on SOC decomposition.
Open Access
A fertilisation strategy combining mineral fertiliser and biosolid improves long-term yield and carbon storage in a calcareous soil
(MDPI, 2023) Zaragüeta, Armelle; Enrique Martín, Alberto; Portell Canal, Xavier; Antón Sobejano, Rodrigo; Virto Quecedo, Íñigo; Orcaray Echeverría, Luis; Ciencias; Zientziak; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD
At a strategic moment for agricultural soils, which are expected to contribute to climate change mitigation through carbon storage while safely feeding a growing world population, the fertiliser strategies used will be key. In a calcareous soil with extensive rainfed agricultural use and straw removal, different fertiliser strategies were evaluated with the aim of determining their effects on crop yield, nitrogen agronomic efficiency, and the storage of organic carbon and total nitrogen in the soil. Different doses of mineral fertiliser, expressed as kg of mineral nitrogen ha−1 year−1 (0, 60, 120, 180, and 240 nitrogen fertilising units (NFUs)), were applied to plots with and without biosolid amendment. The biosolid, applied at a rate of 40 Mg ha−1 every 3 years for 18 years, complied with national and European regulations to be applied on agricultural soil. The use of combined fertilisation reduced the amount of mineral fertiliser applied between 33 and 67% and the total fertiliser units between 7 and 40%, while maintaining similar yields to the reference mineral fertilisation (180 NFUs). These results could be related to a higher nitrogen agronomic efficiency in the combined fertilisation treatments that do not exceed the total NFUs required by the crop. Combined fertilisation was also an effective fertiliser technique to store total nitrogen and organic carbon in the soil. However, compared to the reference mineral fertilisation (180 NFUs), no significant changes in the soil organic carbon were observed, probably due to the crop management method in which the straw is removed and to higher gas emissions. Our results support the need to assess the efficacy of each agricultural technique at local scales in order not to overestimate or underestimate the potential of each agricultural technique to store soil organic carbon.
Open Access
Soil organic carbon monitoring to assess agricultural climate change adaptation practices in Navarre, Spain
(Springer, 2021) Antón Sobejano, Rodrigo; Arricibita Bidegáin, Francisco Javier; Ruiz Sagaseta de Ilurdoz, Alberto; Enrique Martín, Alberto; De Soto García, Isabel Sonsoles; Orcaray Echeverría, Luis; Zaragüeta, Armelle; Virto Quecedo, Íñigo; Zientziak; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Climate change adaptation strategies are needed for agriculture, one of the most vulnerable human activities. In Navarre, North of Spain, ongoing adaptive management practices were identified and promoted in the framework of a regional adaptation strategy. Most include practices aiming to increase topsoil organic carbon (SOC) in agricultural land. In this work, the effectiveness of these practices (conservation agriculture, crop rotations, additions of organic matter, irrigation, and controlled grazing management) was assessed by means of monitoring SOC in a network of 159 agricultural fields across the region. These fields were selected across bioclimatic zones, where soil vulnerabilities and land-uses were previously assessed, to represent the most widespread conditions in the region. A sampling protocol designed to compare SOC stocks in plots with equal soil conditions within each zone, and with or without adaptive practices, allowed the determination of their effect size (measured as response ratios, RR). Exogenous organic matter addition was the most effective practice for SOC storage (RR 95% confidence interval (CI) [1.25–1.37]) across the region. Controlled grazing also resulted in net SOC gains (RR CI [1.13–1.42]) in temperate and semiarid grasslands. Conservation agriculture seemed to be more effective in the driest zone (RR CI [1.30–1.53]) than in the more humid ones (RR CI [0.98–1.21]). Irrigation also displayed a net positive effect (RR CI [1.17–1.34]), modulated by irrigated crop management, whereas crop rotations had an overall negative impact vs. monoculture (RR CI [0.84–0.96]), likely by their interaction with irrigation. These results confirm the variability in SOC responses to changes in management, and SOC as an indicator for assessing regional adaptation practices, although other biophysical, agronomic, and socio-economic factors also need to be accounted for.

Virto Quecedo, Íñigo

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