Meta-analysis of organic matter amendments for urban soil carbon sequestration and soil health improvements

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Zachary Malone, Environmental Systems, University of California, Merced, Merced, CA, Asmeret Asefaw Berhe, School of Natural Sciences, University of California, Merced, Merced, CA and Rebecca Ryals, Life and Environmental Sciences, University of California, Merced, Merced, CA

Background/Question/Methods
Organic matter amendments are used to improve soil properties, increase plant production, and to reduce organic waste streams. Urban settings produce large quantities of waste in the form of organic resources that could be transformed for land application aiding in creating a circular nutrient economy. Past literature reviews on organic matter amendments have focused on the impacts of soil amendments in agricultural settings, but few have assessed their effects in urban settings to help inform urban amendment use. The purpose of this meta-analysis is to determine whether organic matter amendments increase urban soil carbon and soil health indicators of a diverse set of urban environments. Studies included in this meta-analysis were identified using literature searches via Google Scholar and Web of Science, using criteria location in urban settings, application of one or more organic matter amendments, and reporting of data on one or more interested soil properties: carbon (C), nitrogen (N), phosphorus (P), potassium (K), bulk density, or pH. Specific questions for this study include how these amendments influence soil organic matter concentration (OM%) and other soil properties in a diverse set of urban systems, over varying application amounts, and by varying amendment type. Data analysis was conducted in R primarily utilizing ANOVA, regression, and effect size calculations.
Results/Conclusions
There was a positive and significant relationship for organic matter amended soils and reported OM%, with an increase of 4.24% OM ±.78 for amended sites. Positive and significant relationships were also seen for soil nitrogen and potassium. In terms of physical soil characteristics, we observed a negative and significant relationship with bulk density. In addition to significance, relatively large effect sizes were present for OM%, nitrogen percent, phosphorus, and potassium, and a negative effect size for bulk density. By amendment type, only compost and biochar were statistically significant for OM% while biosolids showed more promise in nutrient-focused application with significant relationships to influence soil nitrogen and potassium levels. The application of amendments could have many possible positive externalities on public health by reducing waste landfilling and pollution, increasing urban greenery, and increasing urban garden food production with application, to name a few. Our analysis indicates a lack of data in some soil properties, such as soil potassium, as well as settings and amendments lacking study such as urban parks and biosolids, respectively. Overall, organic matter amendments show promise as a means to increase urban soil carbon and soil health.