Macro-nutrient availability in surface soil of urban tree pits influenced by land use, soil age, and soil organic matter content

Abstract

An adequate supply of plant-available nutrients and an appropriate chemical composition of soils in tree pits are important factors affecting the health and life span of trees in urban environments. We used Multivariate Adaptive Regression Splines (MARS) to explore relationships between nutrient availability, soil organic matter (SOM), soil pH, land use, soil age (time since tree transplanting from nursery to the tree pit), street width, and tree pit cover material in Montreal, Quebec, Canada. Soil was collected to a depth of 20 cm from tree pits along commercial and residential streets and analyzed for concentrations of plant available K, Ca, Mg, P, and N, concentration of Na, SOM content and soil pH. Mulching with wood chips and soil age influenced the availability of K, P, and N in the tree pit soils. Sodium concentration was positively correlated with soil pH, possibly due to the displacement of H+ by Na+ originating from de-icing salt. Soil organic matter content was positively correlated with Mg and Na concentrations in tree pit soils in commercial zones, and with K and Ca concentrations in those of residential zones. Soil from tree pits located along wide streets in commercial zones had high concentrations of Na and Ca, possibly due to higher volumes of traffic on those streets splashing more de-icing salt, and increased weathering of buildings and sidewalk by de-icing salt. The information presented here can be a valuable baseline for managing nutrients in tree pits, in order to mitigate the stresses that can shorten the life of street trees.