Biochar’s effect on the ecosystem services provided by sandy-textured and contaminated sandy soils: a systematic review protocol
Background
Biochar is a relatively new development in sustainable agricultural management that can be applied to ameliorate degraded and less fertile soils, especially sandy-textured ones, to improve their productivity with respect to crop production through improved nutrient availability. However, as the literature has shown, the response of sandy-textured soils to biochar varies in terms of effect size and direction. Therefore, the present study systematically reviewed the available evidence to synthesize the impact of biochar amendments on aspects of the nutrient cycle of sandy-textured soils.
Methods
Both peer-reviewed and gray literature were searched in English in bibliographic databases, organizational web pages, and Internet search engines. Articles underwent a two-stage screening (title and abstract, and full-text) based on predefined criteria, with consistency checks. Validity assessments were conducted, utilizing specifically designed tools for study validity. Data extraction involved categorizing the various properties of the nutrient cycle into nine main Soil and Plant Properties (SPPs), each of which was studied independently. Nine meta-analyses were performed using a total of 1609 observations derived from 92 articles. Comparing meta-averages with and without correction for publication bias suggests that publication bias plays a minor role in the literature, while some indication for publication bias is found when accounting for heterogeneity by means of meta-regressions.
Review findings
According to the results, soil total and available nitrogen [N], phosphorous [P] and potassium [K], plant nutrient level, and potential cation exchange capacity (CEC) increased by 36% (CI [23%, 50%]), 34% (CI [15%, 57%]), 15% (CI [1%, 31%]), and 18% (CI [3%, 36%), respectively, and N2O emission and mineral nutrient leaching decreased by 29% (CI [− 48%, − 3%]) and 38% (CI [− 56%, − 13%). On average, however, biochar had no effect on soil mineral nitrogen and nutrient use efficiency. Publication bias was identified in the response of effective CEC. After corrections for publication bias, the response shifted from 36% to a negative value of − 34% (CI [− 50%, − 14%]). Meta-regression found that the effect modifiers experimental continent, biochar application rate, and soil pH, explain result heterogeneity. Stronger responses came from the continent of South America, higher application rates, and higher pH soils. Overall, biochar is found useful for many SPPs of nutrient cycling of sandy-textured soils, thereby contributing to increased crop yields in such soils.
Keywords
Nutrient cycle, Crop production, Biomass production, Climate regulation, Water cycle, Residual biomass, Soil amendment
Background
Biochar is a relatively new soil amendment method in agricultural practices that can improve the ecosystem services of soils. Biochar has commonly been applied to less fertile or contaminated soils, specifically sandy-textured and contaminated sandy soils, to improve their properties. However, the available literature indicates that not all sandy-textured and contaminated sandy soils show the same response to biochar applications, as the sign and size of the effect vary across studies. More specifically, primary studies show heterogeneous and potentially conflicting impacts of biochar application on a set of ecosystem services provided by these types of soils; namely, biomass production, water cycle, nutrient cycle, and climate regulation. Therefore, the objective of the present study is to systematically review the available evidence base to synthesise the impact and drivers of biochar amendments on four specific ecosystem services provided by sandy-textured and contaminated sandy soils.
Methods
This review follows the guideline of the Collaboration for Environmental Evidence and corresponds to the ROSES (RepOrting standards for Systematic Evidence Synthesis) reporting standard. A comprehensive search strategy will be employed to cover peer-reviewed and gray literature through bibliographic databases, organizational and institutional websites, and web searches. Search terms and strategies have been developed to identify the impact of biochar on the ecosystem services of sandy-textured soils. The search results will be screened first by their title and abstract, and then by their full text. Two literature reviewers will do this based on eligibility criteria. A validity assessment will be conducted to critically appraise and assess the validity of studies using a common validity framework for environmental studies. Data will be extracted from the studies that are found to be valid for the review. Narrative synthesis and meta-analysis will be employed to synthesise the review results.