E. Lugato

What are the effects of agricultural management on soil organic carbon (SOC) stocks

BackgroundChanges in soil organic carbon (SOC) stocks significantly influence the atmospheric C concentration. Agricultural management practices that increase SOC stocks thus may have profound effects on climate mitigation. Additional benefits include higher soil fertility since increased SOC stocks improve the physical and biological properties of the soil. Intensification of agriculture and land-use change from grasslands to croplands are generally known to deplete SOC stocks. The depletion is exacerbated through agricultural practices with low return of organic material and various mechanisms, such as oxidation/mineralization, leaching and erosion. However, a systematic review comparing the efficacy of different agricultural management practices to increase SOC stocks has not yet been produced. Since there are diverging views on this matter, a systematic review would be timely for framing policies not only nationally in Sweden, but also internationally, for promoting long-term sustainable management of soils and mitigating climate change.MethodsThe systematic review will examine how changes in SOC are affected by a range of soil-management practices relating to tillage management, addition of crop residues, manure or other organic “wastes”, and different crop rotation schemes. Within the warm temperate and the snow climate zones, agricultural management systems in which wheat, barley, rye, oats, silage maize or oilseed rape can grow in the crop rotation will be selected. The review will exclusively focus on studies conducted over at least 10 years. Searches will be made in 15 publication databases as well as in specialist databases. Articles found will be screened using inclusion/exclusion criteria at title, abstract and full-text levels, and screening consistency will be evaluated using Kappa tests. Data from articles that remain after critical appraisal will be extracted using a predefined spreadsheet. Subgroup analyses will be undertaken to elucidate statistical relationships that are specific to particular type of management interventions. Meta-regression within subgroups will be performed as well as sensitivity analysis to investigate the impact of removing groups of studies with low or unclear quality.

Which agricultural management interventions are most influential on soil organic carbon (using time series data)

BackgroundLoss of soil organic carbon (SOC) from agricultural land is identified as one of the major threats to soils, as it influences both fertility and the production of ecosystem services from agriculture. Losses of SOC across regions are often determined by monitoring in different land use systems. Results from agricultural field experiments can reveal increasing SOC stocks after implementation of specific management practices compared to a control, though in time series experiments the relative rate of change is often negative and implying an overall loss. Long-term agricultural field experiments are indispensable for quantifying absolute changes in SOC stocks under different management regimes. Since SOC responses are seldom linear over time, time series data from these experiments are particularly valuable.MethodsThis systematic review is based on studies reporting time series data collated in a recently completed systematic map on the topic restricted to the warm temperate climate zone and the snow climate zone. These 53 studies were identified and selected systematically according to CEE guidelines. An update of the original search for studies will be repeated using Web of Science and Google Scholar to include newly published academic and grey literature in the time since the original search was performed in September 2013. Studies will be subject to critical appraisal of the internal and external validity, followed by full data extraction (meta-data describing study settings and quantitative study results). Where possible, studies will be included in a quantitative synthesis using time series meta-analytical approaches. The implications of the meta-analytical findings will be discussed in terms of policy, practice and research along with a discussion of the nature of the evidence base.