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[Display omitted] • The role of temporary grasslands as negative emission technology was assessed. • A new approach to account for bias in bulk density is developed. • C-deficit in croplands decreases linearly with the increase of temporary grasslands. • SOC storage potential in top and subsoil are equivalent. • SOC storage potential corresponds to 1 year of GHG emissions from the same region. Atmospheric C sequestration in agricultural soils is viewed as one of the most promising negative emission technologies currently available. Nonetheless, it remains unclear how strongly soil organic carbon (SOC) stocks respond to agricultural practices, especially for subsoil. Here, we assess the SOC storage potential in croplands and how the presence of temporary grasslands (TG) in the crop rotation affects SOC stocks. We developed a new approach to correct for bias in bulk density (BD) induced by sampling conditions and land-use effects with a data-driven model to predict the BD of fine soil (<2 mm) for reference condition. Using 54 permanent grassland and cropland sites with various proportions of TG from a monitoring network in Switzerland, we showed that SOC stock differences down to 50-cm depth between cropland and permanent grasslands (maximum: 3.0 ± 0.8 kg C m−2) depend on the TG proportion in the crop rotation, regardless of clay content and pH. An increase of the TG proportion by 10% would induce a SOC gain of 0.40 ± 0.13 kg C m−2. The responses of topsoil (0–20 cm) and subsoil (20–50 cm) SOC stocks to TG proportion were linear and equivalent. The effect of TG on SOC storage would have been underestimated by 58% without accounting for subsoil stocks response and by 16% without BD corrections. The conversion of all croplands to permanent grasslands in the study region would potentially store a quantity of SOC equivalent to the anthropogenic greenhouse gas emissions generated by the same region during one year. Although the potential of agricultural soils as negative emission technology is relatively modest compared to former expectations, the findings demonstrate the potential to manage SOC and its associated ecosystem services at large scales and down to deep soil layers. [ABSTRACT FROM AUTHOR]

Background and aims: Uptake of Sr and Cs in plants varies widely between soil types and between plant species. It is now recognized that the radionuclide uptake in plants is more influenced by site-specific and plant-specific parameters rather than the bulk radionuclide concentration in soil. We hypothesized that the stress which Alpine plants experience because of the short growing season may enhance the phylogenetic effect on the Cs and Sr transfer factors as well as the dependency of the uptake by plant to the concentrations of exchangeable Ca and K of soils. Methods: We carried out a field study on the Sr and Cs uptake by 11 species of Alpine plants growing on 6 undisturbed and geochemically different soils in the Alpine valley of Piora, Switzerland. Results: Results show that a strong correlation exists between the log TF and the log of exchangeable Ca or K of the soils. Conclusions: Cs uptake by Phleum rhaeticum (Poales) and Alchemilla xanthochlora (Rosales) is more sensitive to the amount of exchangeable K in the soil than the corresponding uptake by other orders. Moreover, the Sr results indicate a phylogenetic effect between Non-Eudicot and Eudicots: the order Poales ( Phleum rhaeticum) concentrating much less Sr than Eudicots do. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mineral-associated organic C deficits in croplands and grasslands were estimated. • The relationship between soil C-saturation and soil physical quality was assessed. • Challenges to the C-saturation concept and the SOC:clay ratio were highlighted. • C-saturation in grassland was positively linked to SOC accrual history. • SOC accrual is more beneficial for soil physical quality in croplands. Reliable estimations of soil organic carbon (SOC) deficits in agroecosystems are crucial in evaluating the atmospheric C sequestration potential of agricultural soils and supporting management decisions. Nonetheless, the co-benefit on soil quality resulting from SOC accrual is rarely considered. Here, we assessed SOC saturation and soil physical quality in permanent grasslands (PG) and croplands (CR) by applying the C-saturation concept and the SOC:clay ratio as an indicator of soil physical quality to a set of long-term monitoring sites in western Switzerland. For this goal, we produced a new relationship between the silt + clay (SC) particles and the C stored in the mineral-associated fraction (MAOM C) and we assessed the assumption that grasslands can be used as C-saturated reference sites. The saturation in PG was not coincidental as it depended on the C accrual history. Hence, PG with the lowest MAOM C have not reached their C-saturation level and present a potential SOC storage under optimal management. The MAOM C saturation in CR was low (62 ± 4%) and corresponded to a deficit of −8.8 ± 1.2 mg C g−1 soil as compared to the current level in PG. The saturation was mainly affected by the proportion of temporary grassland in the crop rotation. The relative distribution of C between MAOM (∼80%) and the fine and coarse particulate organic matter (POM) was not affected by land-use types. The MAOM C saturation in this study (MAOM C = 0.372 × SC + 4.23) was similar to that reported in the litterature, but discrepancies appeared when the silt and clay contents were considered separately. SC was by far the main factor explaining MAOM C amount in PG (semi-partial R2: 0.66). In contrast to other studies, the C content of MAOM in PG (43 mg C g−1 SC) was not related to the SC content, suggesting a fixed maximal value in C-saturated soils. Nonetheless, MAOM C saturation may be underestimated as the least saturated PG might still accumulate MAOM C. Finally, the SOC:clay ratio was correlated with MAOM C saturation level in CR, but not in PG suggesting that targeting SOC accrual in CR optimizes the benefits between soil C storage and soil quality. [ABSTRACT FROM AUTHOR]

• The role of land-use change, crop rotation and site conditions were elucidate. • SOC was depleted in croplands compared to grasslands and mountain pastures. • SOC dynamics was more influenced by land-use changes than management practices. • P excess in soils enables C sequestration without additional P sequestration. • SOC balancing budget is a realistic approach to encourage C sequestration practices. Increasing soil organic carbon (SOC) in agroecosystems enables to address simultaneously multiple goals such as climate change adaptation and mitigation as well as food security. As croplands are depleted in SOC, they offer a great potential to sequester atmospheric carbon (C). Nonetheless, croplands are still losing SOC under most of the current agricultural systems. Although many factors driving SOC dynamics have already been identified, their relative importance has not been quantified yet. Using one of the densest European soil monitoring networks with 250 sites established in western Switzerland, in the present study we (i) assessed long-term (over 30 years) SOC dynamics in croplands (CR), permanent grasslands (PG) and mountain pastures (MP), and (ii) prioritized the importance of land use, soil characteristics and sites conditions in driving SOC dynamics. The SOC levels in PG and MP were similar when clay content was accounted for, whereas CR were depleted in SOC by 3.9 mg C mg−1 clay as compared to PG. The majority (61 %) of CR had SOC:clay ratio below 1:10, but only 16 % of PG and MP sites reached this threshold. By contrast, soil organic matter stoichiometry (C:N:Porg ratios) was similar in CR and PG for comparable SOC content. The increase of C:Porg ratio with SOC content (dilution effect) and the high total P in CR and PG (legacy effect) indicate the possibility to sequester atmospheric C at reduced nutrient sequestration costs. SOC changes ranged from -0.61 to 1.32 mg g-1 soil yr−1 and were the highest in sites that experienced land-use changes. No PG were losing SOC, while CR sites exhibited both SOC gains and losses. Because of the predominance of the initial SOC content on SOC dynamics, land-use history must be accounted for when assessing the effect of management practices. The main manageable factors driving SOC dynamics were the time under temporary or permanent grasslands along with the soil total P. As PG already are rich in SOC and total P, organic amendments should be partly redirected to CR. [ABSTRACT FROM AUTHOR]

Increasing soil organic carbon (SOC) in agroecosystems is a promising solution to simultaneously address climate change mitigation, adaptation, and food security. Yet, the best management practices that could achieve these goals remain to be identified. Here, we analyze the long-term effects of application of green manure, cereal straw, farmyard manure, and cattle slurry on SOC in a 37 year long field experiment in Switzerland. The treatment effects were compared against control conditions that received only optimal mineral fertilization. More specifically, this study aimed at evaluating the effect of organic amendments on SOC accumulation and distribution in different soil particle-size fractions by means of a set of indicators about organic matter quality (biological reactivity, humification index) and microbial activity (extracellular enzyme activities). In the absence of organic matter input, application of mineral fertilizers alone resulted in the lowest SOC content and the highest humification index of the bulk soil organic matter. Among the organic amendments, cereal straw, farmyard manure, and cattle slurry promoted a higher SOC content and a lower humification index due to an increase of SOC in the clay-size fraction. The annual C accrual reached 4.4‰ per year over 37 years with farmyard manure. The higher biological reactivity measured for the green manure and cereal straw amendments was associated with higher soil enzymatic activities, while C retention coefficients decreased by at least 2.5 times compared to animal-derived amendments. The low availability of nutrients in green manure and straw amendments as suggested by the high phosphatase and N-acetylglucosaminidase activities may indicate a reduction in C retention of organic matter inputs due to nutrient microbial mining with plant-derived amendments. [ABSTRACT FROM AUTHOR]