Soil organic carbon (SOC) plays a vital role in the global carbon cycle and is a potential sink for carbon dioxide. Agricultural management practices can support carbon sequestration and, therefore, offer potential removal strategies whilst also improving overall soil quality. Meta-analysis allows one to summarize results from primary articles by calculating an overall effect size and to reveal the source of variation across studies. The number of meta-analyses published in the field of agriculture is continuously rising. At the same time, more and more articles refer to their synthesis work as a meta-analysis, despite applying less than rigorous methodologies. As a result, poor-quality meta-analyses are published and may lead to questionable conclusions and recommendations to scientists, policymakers, and farmers.This study aims at quantitatively analyzing 31 meta-analyses, published between the years of 2005 and 2020, studying the effects of different management practices on SOC. We compiled a set of quality criteria suitable for soil and agricultural sciences by adapting existing meta-analytical guidelines from other disciplines. The set is supported by a scoring scheme that allows for a quantitative analysis. The retrieved meta-analyses were structured according to 11 management categories, such as tillage, cover crops, crop residue management, and biochar application, which allowed us to assess the state of knowledge on these categories. Major deficiencies were found in the use of standard metrics for effect size calculation, independence of effect sizes, standard deviation extraction for each study, and study weighting by the inverse of variance. Only 1 out of 31 SOC meta-analyses, which studied the effects of no tillage/reduced tillage compared with conventional tillage, was found to be of high quality. Therefore, improved meta-analyses on the effects of organic agriculture, biochar, fertilization, or crop diversification on SOC are urgently needed.We conclude that, despite efforts over the last 15 years, the quality of meta-analyses on SOC research is still low. Thus, in order for the scientific community to provide high-quality synthesis work and to make advancements in the sustainable management of agricultural soils, we need to adapt rigorous methodologies of meta-analysis as quickly as possible.

中文翻译：

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土壤有机碳元分析的质量评估

土壤有机碳（SOC）在全球碳循环中起着至关重要的作用，是二氧化碳的潜在汇。农业管理实践可以支持碳封存，因此可以提供潜在的清除策略，同时还可以改善整体土壤质量。Meta 分析允许人们通过计算总体效应量来总结主要文章的结果，并揭示研究之间的差异来源。在农业领域发表的荟萃分析的数量不断增加。与此同时，越来越多的文章将他们的综合工作称为荟萃分析，尽管采用的方法不够严格。结果，低质量的荟萃分析被发表，并可能导致科学家、决策者和农民得出有问题的结论和建议。本研究旨在定量分析 2005 年至 2020 年间发表的 31 项荟萃分析，研究不同管理实践对 SOC 的影响。我们通过改编其他学科的现有元分析指南，编制了一套适用于土壤和农业科学的质量标准。该集合由允许进行定量分析的评分方案支持。检索到的荟萃分析是根据 11 个管理类别构建的，例如耕作、覆盖作物、作物残茬管理和生物炭应用，这使我们能够评估这些类别的知识状况。在使用标准度量计算效应量、效应量的独立性、每项研究的标准差提取以及方差倒数的研究加权方面发现了主要缺陷。在 31 项 SOC 荟萃分析中，只有 1 项研究了免耕/减耕与常规耕作相比的影响，发现其质量很高。因此，迫切需要改进关于有机农业、生物炭、施肥或作物多样化对 SOC 影响的荟萃分析。我们的结论是，尽管在过去 15 年中做出了努力，SOC 研究的荟萃分析质量仍然很低. 因此，为了让科学界提供高质量的综合工作并在农业土壤的可持续管理方面取得进展，我们需要尽快采用严格的荟萃分析方法。迫切需要改进关于有机农业、生物炭、施肥或作物多样化对 SOC 影响的荟萃分析。我们的结论是，尽管在过去 15 年中做出了努力，SOC 研究的荟萃分析质量仍然很低。因此，为了让科学界提供高质量的综合工作并在农业土壤的可持续管理方面取得进展，我们需要尽快采用严格的荟萃分析方法。迫切需要改进关于有机农业、生物炭、施肥或作物多样化对 SOC 影响的荟萃分析。我们的结论是，尽管在过去 15 年中做出了努力，SOC 研究的荟萃分析质量仍然很低。因此，为了让科学界提供高质量的综合工作并在农业土壤的可持续管理方面取得进展，我们需要尽快采用严格的荟萃分析方法。