Cover Crops Affecting Pool Specific Soil Organic Carbon Sequestration in Cropland – A Meta-Analysis

Greenhouse gas emission can be partly compensated by enhancing soil organic carbon (SOC) levels in soils, e.g. in croplands, which have the highest potential due to their losses in SOC by intensive management. This can be achieved by adopting SOC enhancing soil management practices, such as the cultivation of cover crops (CC). So far, only few long-term experimental studies have investigated the effects of CC on a SOC pool level. There are still uncertainties how CC affect SOC fractions and the stability of the sequestered carbon.

By conducting a meta-analysis, we aim to quantitatively summarize studies related to CC effects on SOC pools throughout soil depths (up to 100 cm) in cropland soils relevant for Europe, as such an analysis is not available so far. We included global studies located in the dry, temperate, and boreal climatic zones, as these are present Europe. The pools chosen for this analysis are the microbial biomass carbon (MBC), the particulate organic matter (POM) and the mineral associated organic matter (MAOM) pool, as well as total SOC. Alongside, we study the effects of a broad range of moderators, such as pedo-climatic factors (e.g., climatic zones, soil texture), other agricultural management practices (e.g., effects of tillage, irrigation, liming, fertilization) and CC characteristics and their management (e.g., CC types, species number, frost resistance, residue management).

By searching several scientific and grey literature databases, we identified 64 studies, of which the majority was conducted in North and South America, whereas only five are available for Europe. The MBC, POM and MAOM pool are studied in 24, 44 and 19 of these studies, respectively. The mean experimental duration is eight years, with a maximum of 39 years. 54% of studies were conducted in a warm temperate climatic zone, 32% in a boreal and 14% in an arid zone. Means values for SOC pools, standard deviations and sample sizes for treatments with CC and controls without CC will be extracted from tables and figures. In order to perform a meta-analysis, logarithm response ratio as an index of effect size will be calculated for each study, which will then be summarized across studies by using weighing procedure. This meta-analysis will provide valuable information on the state of knowledge on SOC pool specific sequestration rates influenced by CC, corresponding quantitative summary results and the source of heterogeneity across studies. These results will offer guidance for future research and assist decision-making processes regarding climate friendly management of agricultural soils.