Biochar amendment for enhanced infiltration and aggregation of compact urban soils

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University of Delaware
Urban development results in soil compaction and conversion of pervious lands into impervious surfaces, which decreases soil infiltration and increases stormwater runoff volume and associated pollutants. To alleviate the problem, biochar – a porous carbonaceous material – may be amended to existing soils next to impervious surfaces such as parking lots and roadways to increase stormwater infiltration. To assess the impact of biochar amendment at the field scale, a commercial wood-based biochar was amended with soil adjacent to urban impervious surfaces at four sites- two sites receiving stormwater runoff from parking lots and two sites from Interstate-95. The effectiveness of biochar to enhance stormwater infiltration in test sites was assessed periodically up to 1.5 years by measuring saturated hydraulic conductivity (Ksat). Factors affecting soil Ksat such as soil compaction, vegetation density, soil water retention capacity, water-stable aggregate fraction and organo-mineral content were measured in undisturbed field soil cores at different ages (up to five months for highway soils and up to 15 months for parking lot soils) of the treatment systems. Results showed that despite the spatial (soil texture) and temporal (season) variability, the geometric mean Ksat of 4% (w/w) biochar amended soils was 1.8 to 4.6 times greater than that of undisturbed soils. The building blocks of water stable aggregates, the organo-mineral content, in 4% biochar amended soils were on average 1.7 times and 3.9 times higher than undisturbed soils after five months and 16 months, respectively. Consistent with these data, water stable aggregate fractions in 4% biochar amended soils were on average 27.2% and 47.3% greater than in undisturbed soils after five months and 16 months, respectively. For the first time, this study showed that biochar is effective in enhancing infiltration in compact roadway soils causing increased hydraulic conductivity, improved water retention and improved soil structure through biochar mediated aggregation.
Biochar, Organo-mineral association, Soil aggregation, Stormwater infiltration, Urban soil