Table 3 Overview of eligibility criteria

Population

Sandy-textured soils with 50% or more sand in the soil composition

Other soil textures or soil types not given

X

X

Marginal soils, such as sandy-textured soils, are widely used in agricultural processes and seem to benefit from biochar. The heterogeneity in the results of primary studies is the reason why this review focuses on these soils

Intervention

Biochar obtained by pyrolysis and/or gasification of various biomass materials

Biochar made from materials other than biomass or technologies other than pyrolysis and/or gasification

X

X

In accordance with the definition of biochar adopted for this review, the included biochar samples were specifically derived from biomass through pyrolysis and/or gasification processes

Comparator

Control sites or plots without biochar that correspond to intervention sites or plots

Control sites or plots that do not correspond to intervention sites or plots

X

To ensure comparability between comparator and intervention

Outcome

Positive, negative, or no changes in different soil ecosystem processes of the nutrient cycle of sandy-textured soils

Other soil ecosystem processes of sandy-textured soil

X

These soil ecosystem processes of the nutrient cycle were identified as relevant by the advisory committee of this review, being also the partners in the project funding this review (BASTA, Research Foundation – Flanders, grant S000119N)

Study design

Lab (incubation), greenhouse, and field experiments

Review studies

X

Primary study designs provide observations for qualitative and quantitative synthesis

Publication type

Research articles, research reports, dissertations, etc

Review studies

X

X

In order to consistently account for primary data only, review studies were excluded

Language

English

Other languages

X

X

English was the common language within the review team, so it provided dual consistency at all stages of the screening