Restoration of Compacted Urban Soil for Tree Growth with Mulches and Fertilizers.

Soil quality and tree growth are hindered by site disturbances in urban settings. A research plot with 60 Acer rubrum and 60 Betula nigra was created mimicking the typical scraping of A horizon soil and compacting of B horizons in urban landscapes. Hardwood mulch, compost, inorganic fertilizer, aerated compost tea, a commercial biological product, and water were applied as treatments for three consecutive years and assessed for their impacts on soil and tree properties. Increases in soil nutrient availability, aggregate stability, and particulate organic matter were observed with compost compared to other treatments. Fertilizer increased available soil nitrogen and also N leaching below the rooting zone. Decreased bulk density and increased plant available water was observed with mulch compared to other treatments. Mean responses across six sample dates did not differ among compost tea, the biological product, and water for the majority of soil properties. Few significant differences were observed for soil microbial properties among these treatments. Tree growth was greater on compost and mulch compared to other treatments. Some increases in tree growth were observed with fertilizer compared to compost tea, the biological product, and water. Significant correlations were observed between tree and soil properties, confirming the hypothesis that tree growth on this disturbed plot was at least in part limited by soil properties. These results confirm the hypothesis that greater improvements in soil quality and tree growth would be observed with organic mulches compared to liquid organic and inorganic fertilizers.  Furthermore, organic mulches are much more cost-efficient compared to the other treatments in this study.