Soils in urban areas may have a nutrient imbalance. If there are inadequate nutrients, tree growth and development will be affected. Nutrient imbalances are often caused by high pH levels, low soil fertility, or high salt content.
High or Low Soil pH
|Effects of soil pH on nutrient availability
From: Clemson Cooperative Extension
Urban soils may have a high or alkaline pH because construction materials, such as mortar and concrete, are often spilled or left on the soil. The addition of this calcium-based material, which is alkaline, raises the soil pH. Some species of trees need an alkaline soil, but other species can not tolerate a high pH level. A high pH may also cause chemical reactions with nutrients in the soil that render the nutrients unavailable to the tree. Iron, for example, becomes unavailable for a tree’s growth processes when soil pH is alkaline. Sulfur may be added to soil to lower the pH. Tolerance to the local soil conditions needs to be considered when selecting a tree to plant in an urban area.
Low Soil Fertility
Soil fertility can be low in urban environments. Common causes are:
High Salt Content
The salt level in soils may be elevated because of de-icing salts, excess fertilizer, or irrigation water high in soluble salts. This can be a problem, particularly in areas with low rainfall and extensive use of irrigation and fertilizer (Harris 1992). A soil that is high in salts has less water available to the roots. Sometimes salts can even draw moisture out of the roots. High salt levels can sometimes be reduced by leaching the salts with proper watering techniques. A symptom of high salt content in the soil is browning of leaf edges. If the soil does have a high salt content, select a species that is tolerant to high salts.
Tree damage caused by salting roads.
Photo Credit: USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org
To learn this content and more for ISA and SAF credit, go to cfegroup.org!
To learn this content and more for volunteer hours and a certificate of completion, enroll in eLearn Urban Forestry at campus.extension.org!
Harris, R.W., 1992. Arboriculture: Integrated Management of Landscape Trees, Shrubs and Vines. Englewood Cliffs, NJ: Prentice Hall. 674 p.
By: Ed Macie, Regional Urban Forester, USFS Southern Region