Effect of organic amendment for the construction of favourable urban soils for tree growth

Abstract

Ornamental tree planting and establishment in cities is a great challenge because urban soil physical properties are unfavourable to the development of root systems. Our objectives were to measure (i) the effects of organic matter on soil physical properties and tree development, and (ii) the effects of ensuing root development on soil physical properties. Using twenty-four 600-L planted or bare soil containers, we monitored physical properties such as dry bulk density, aggregate stability and near-saturated hydraulic conductivity of our reconstituted soils over a 5.5-year period. A 28-cm thick top layer of sandy loam amended with 40% (v/v) sphagnum peat or organic composts was laid on top of a 28-cm thick layer of sandy loam. Bare-root Ostrya carpinifolia trees were planted in half of the 24 containers, and we monitored shoot development and root biomass and distribution. After 5.5 years, trunk diameter had increased from 59 mm for the control soil to 66 mm for soil mixed with green waste compost, and 74 mm for soil mixed with co-compost of sewage sludge and wood chips. After 4.5 years, trunk diameter was strongly correlated with the total number of axes (r = 0.94) and fine root length density (r = 0.98), and was confirmed as a good indicator of tree development. Fine root development increased stable aggregate formation in all treatments as compared to bare soil. After 4.5 years after planting, the tree root system induced by a high organic matter input had significantly improved near-saturated hydraulic conductivity and was fit to support fertile urban soils.

Positive long‐term impacts of restoration on soils in an experimental urban forest

“…Over time, we would expect the growth of planted trees to increase in their effects on soil conditions. For example, planted trees can reduce bulk density and increase water holding capacity through root expansion (Vidal‐Beaudet et al 2018) as well as increase soil C stocks as leaf litter and fine root inputs are incorporated into the soil (Six et al 2002). Although we were unable to test these relationships directly with an unplanted (i.e., no trees) experimental treatment since the project was a collaboration with city agencies in a high visibility park with defined public–private tree‐planting goals, we advocate for future work that specifically examines the role that planted trees play in improving soil conditions relative to other site treatments.…”

Assessing Soil-like Materials for Ecosystem Services Provided by Constructed Technosols

“…Today, even a shortlist of microbial indicators within the standardized protocols includes microbial (basal) respiration [41], microbial biomass [75], enzymes activity [76], nitrogen mineralization, and nitrification in soils [77]. Partly, implementation of these microbial indicators in urban soils' assessment is constrained by high temporal dynamics, especially during the first years after Technosols' construction [78,79]. From the other perspective, monitoring dynamics of these indicators can reflect the evolution and pedogenesis processes in the constructed soils.…”