MPRB Soil Amendment Study

Throughout the City of Minneapolis, there has been an increase in young trees planted in boulevards in recent years. The research of soil amendments which can be incorporated into pre-existing soil as a potential method of improving planting practices and reducing mortality by increasing initial tree establishment and success is of particular interest.

Biochar

Biochar is a carbon-rich byproduct of organic materials (such as wood waste) burned at a high temperature in a closed container without the presence of oxygen. The biochar used for this project was produced from sawmill waste and processed in Missouri. Biochar has been shown to improve physical and chemical characteristics of soil such as nutrient availability and retention as well as water-holding capacity which could increase water availability. The Minnesota study hopes that these organic materials will increase the health and success of urban trees and can be used more frequently in the future.

This project examines the effects of two rates (22qt and 44qt) of both composted organic matter and biochar amendments when incorporated into the preexisting soil at a tree planting location. Treatments were randomly assigned to 600 public boulevard trees in the City of Minneapolis. During first year of data collection (summer 2014), tree stem caliper was taken at 15cm and 30cm along with an initial rating of overall appearance and quality. Three years later (summer 2017), the trees were revisited and measured for mortality and given a condition rating.

Click on the map below for access to an interactive web mapping application for the Biochar portion of the Soil Amendment Study:

Biochar Map

Precision Organics Test Product (POTP)

The product tested in this study is manufactured to have a carbon to nitrogen ratio (C:N) of 20:1. Similar C:N ratios, used in other products and in previous trials, is suspected to have reduced mortality by increasing initial tree establishment and success through enhanced water retention and availability and by increasing soil biological activity and nutrient availability.

This project will examine the effects of a Precision Organics Test Product (POTP) when incorporated into the preexisting soil at planting time. POTP was incorporated at two rates - full rate (½ bag) and half rate (¼ bag) and randomly assigned to public boulevard trees in the City of Minneapolis. Ten tree species were used in this study with each species replicated eight times for each POTP treatment as well as untreated controls, resulting in a total of 240 study trees. During the first year of data collection (Summer 2014), tree stem caliper was taken at 15cm and 30cm along with an initial rating of overall appearance and quality.

Click on the map below for access to an interactive web mapping application for the POTP portion of the Soil Amendment Study:

POTP Map