Commonly known as it’s unappealing nickname “dirt“
soil provides the basis for all terrestrial life on earth.
Urban soils provide poor conditions for tree growth. What can be done ?
Walkout your front door and tell me what you see? Probably streets, sidewalks, buildings, a lot of cars and people roaming among it. Tucked away between the pavement are trees growing within confined spaces. While many people recognize the carbon footprint from emitting greenhouse gases the atmosphere, we often overlook the footprint of our construction activities on urban soil and trees. Compaction, elevated salinity from salting the roads in the winter, and removal of nutrient rich topsoil are all negative consequences on soil from creating our cities and towns. Studies of urban forestry have reported that trees in these harsh environments struggle most of their lives. A tree’s full potential for healthy vigorous growth is cut short as its potential to fail increases.
As demand for sustainable solutions to improve urban soil increases, using organically amended soil is being studied as a viable solution. Biosolids, biochar, and leaf compost can have essential chemical and biological properties that mimic natural forest conditions. Every unique tree species also has different preferences for soil properties. So might trees also have preferences for different types of amendments? One goal of this project is to use organic amendments to create soils that improves growing conditions for six different species planted next to a highway in order to increase the diversity in urban landscapes. The outcomes of this experiment can help to set a new standard for tree planting site preparation. Two types of soil amendments will be tested to see if trees display healthy characteristics such as broad green leaves, a healthy stem, and a tall stature if they occur.
How can we evaluate the greenes of leaves, stem health, and tree size if they respond in this experiment? Measuring leaf nitrogen is my main task this summer because it demonstrates an essential nutrient that is provided by the soil which is key for a tree’s leaf and overall success in growth. Measuring leaf nitrogen is not a quick task to accomplish. First I will grind leaves into a powder, intricately wrap the powder into tiny aluminum rolls which is called tinning, and then process those tins through a carbon/nitrogen analyzer. Other standard measurements will be taken to further assess the effects of these amendments. One indicative measurement we will be collecting is the leaf chlorophyll content with a SPAD meter. Chlorophyll is a green pigment in the leaf that allows it to produce energy from sunlight. This is a useful measurement because the leaf chlorophyll content is strongly correlated with leaf nitrogen levels. I collected SPAD data using a handheld tool. SPAD data is collected simply by clipping the device on a leaf for a couple of seconds. I do this five times for every leaf I collect data from to give me an average SPAD ratio. We collected SPAD measurements for hundreds of trees multiple times over two months. This useful handheld device gave me results instantly, and made me develop an appreciation in the sophisticated tools I am capable to use in my research. More data needs to be collected in order to evaluate the characteristics I am looking for. That way I can assess if these experimental organic amendments can bring us closer to change the way trees are planted in site preparations.