RESUMO
Agricultural liming improves acidic soils productivity and is considered a lever for mitigating nitrous oxide (N2O) emissions from soils. However, the benefit of liming in reducing soil greenhouse gas (GHG) emissions depends on the evolution of carbon from the calcium carbonate (CaCO3), and on the evolution of soil organic carbon (SOC) after CaCO3 application. The literature, based on limited field data, presents contrasting effects of liming on inorganic- and SOC-derived CO2 emissions, raising concerns that the reduction in N2O emissions could be offset by increased CO2 emissions. Therefore, this study aimed to monitor N2O and CO2 emissions following the application of lime materials to an acidic soil. In situ, we monitored the effect of two liming products (SC = synthetic CaCO3 and MC = marine CaCO3) on soil CO2 emissions and compared this with control plots, during the growing season of a winter rye, using the static chamber method. Soil pH, N2O emissions, mineral nitrogen concentrations, soil moisture and temperature were measured during the experiment, as were plant biomass and SOC (stock and composition) on the day of harvest. Lime addition increased soil pH from 5.7 to around 7.0, kernel yield from 320 to >400 g m-2 and resulted in a significant reduction in soil CO2 emissions by approximately 40 % for both liming materials while it slightly increased N2O emissions, that had nevertheless remained very low during the experiment. SOC at harvest was not significantly affected, while an increase in dissolved organic and inorganic carbon in the soil was observed. Further investigations is needed to clarify the mechanisms explaining these observations and to define conditions where liming application could act as a potential lever for carbon storage. Our results suggest that the IPCC principles, predicting increased CO2 emissions from lime-derived C, may need to be re-examined in the future.
RESUMO
Background: Grasslands are essential for providing vital resources in the livestock sector and delivering invaluable ecosystem services such as biodiversity and soil carbon (C) sequestration. Despite their critical importance, these ecosystems face escalating threats from human disturbances, human degradation, and climate change, compromising their ability to effectively stock C. Restoring degraded grasslands emerges as a pragmatic and cost-effective approach to tackling climate change. However, the successful implementation of grassland management toward this goal, faces significant challenges. A systematic mapping approach will help to compile a comprehensive global inventory of studies investigating the impact of differing grassland management practices on soil carbon. In addition, the potential for trade-offs with other greenhouse gas emissions further underlines the value of a systematic assessment. This approach aims to identify knowledge clusters (i.e., well-represented subtopics that are amenable to full synthesis) for potential systematic reviews and pinpoint knowledge gaps requiring further primary research efforts, all contributing to a better understanding of the evidence surrounding this topic. Methods: Following systematic evidence synthesis standards, we developed the question to address in the systematic map protocol using the PICO framework. We established a preliminary search string by combining search terms for the Population (Grasslands), Intervention (management) and Outcome (soil carbon) categories, as well as with one additional group (Study types-to focus on farm and field experiments). We will conduct a comprehensive literature search of relevant peer-reviewed and grey literature using Web of Science, Scopus, CABI platforms, Google Scholar, and specialised websites (e.g., Agrotrop). Searches will be conducted in the English, Spanish, Portuguese, French, German, and Mongolian languages, as per the linguistic capabilities of the research team. The comprehensiveness of the search will be assessed by comparing the literature collected to a test-list of forty relevant articles. The repeatability of the literature screening process will be ensured by a list of inclusion/exclusion criteria and inter-reviewer consistency statistical tests. Data extraction will be organised into four complementary sections (article information, PICO categories, study characteristics, measurable parameters), on which we will perform queries to produce the tables, figures and evidence maps that will compose the systematic map. The results will identify and describe knowledge gaps and clusters. Supplementary Information: The online version contains supplementary material available at 10.1186/s13750-024-00345-2.