Soil Structure and Plant Available Water Influenced By Biochar Application to Urban Soil Ecosystem.

Urban trees are under severe stress such as soil compaction and drought. Biochar has been suggested as a useful soil amendment by increasing soil water holding capacity, nutrient retention and chemical adsorption. We suggest that biochar application to soils of urban tree system would alleviate stressful condition by improving soil structure. The objective of this study is to investigate the effect of biochar application on soil aggregate distribution and on plant available water (PAW). Pot experiment was conducted with 22 L of soil mixed with biochar made from peanuts shells and twigs at 2.5% (by weight) application rate. Control pot was also prepared with no biochar addition. Ginkgo trees (Ginkgo biloba), most common street trees in Korea, were planted and all treatments were triplicated. Soil water content was adjusted to 60% water filled pore space (WFPS). After 20 d of incubation, soil samples were fractionated into orgno-mineral complexes (< 53 μm), microaggregates (53-250 μm) and macroaggregates (250-1000 μm) using wet-sieving method. In the biochar treatment, the amount of macroaggregates was increased by 7% compared to the control. Soil hot-water extractable (HWC) content was increased in the biochar treatment due to the high labile C content of biochar itself. Soil CO2 and N2O emissions were increased in the biochar treatment. The higher N2O emission from the biochar treatment might be related to relatively higher N content in our biochar. During the 20 d of incubation, biochar played as a nucleus for macroaggregation probably due to the combined effects of higher labile C content and microbial activities in the biochar treatment. After 70 d of incubation, soil aggregation and pore size distribution will be further analyzed to examine the relationship between the changes in soil aggregation and pore size distribution (PSD), which will further influence plant available water (PWA). Our results imply that biochar application could be a promising strategy for management of urban soil-plant system to mitigate soil compaction and drought condition.