Natural native soils are the result of thousands of years of biological, chemical and physical weathering (erosion of bedrock). Geologically, soils are dominated by the parent material within a given region. The ideal soil for the growth of trees and plants is composed of 50% solids, 5% to 10% of which is organic matter, and 50% pore space for oxygen and water infiltration and percolation.
Urban soils however, typically contain 10% to 20% pore space and very little organic matter. It’s no wonder we have so many problems with the trees in our urban environments. It has been said grow soil and the trees will take care of themselves. Indeed there is merit to that statement.
Another factor influencing the health of a soil, is the abundance or lack of the various microbial populations (i.e. mycorrhizae, soil arthopods, nematodes, worms and various protozoa).
Over time soils develop layers called horizons due to rainfall, heating and cooling, chemical reactions and biological activities. These horizons collectively make up the soil profile.
In natural forest settings, the soil profile is usually not disturbed to the point of serious compaction. Trees and soils are so ecologically interdependent, that it is hard to imagine separating them from one another. Truly the soil is the foundation on which a tree lives and grows. If we can grow healthy soil the trees will take care of themselves.
All these factors combined serve to compress and compact soil particles into tighter and tighter arrangements thereby squeezing out available oxygen. Pushed to the extreme an overly anerobic situation is created, where growing conditions range from unfavorable to antagonistic or marginal at best. Although certain trees have a habit of developing root systems close to the soil surface, many times this is caused by the trees reaction to growing in compacted, less then favorable soil.
The first year or two after planting is the most important time for watering and fertilizing. By this time, a young tree is getting its roots established and developing it’s limb structure. Providing care at this critical time will ensure bountiful rewards in the future with stronger, better shaped, more pest and disease resistant trees and shrubs. A good root system is the key to a healthy tree, and there should be a fairly balanced ratio between shoot growth and root growth.
Fertilizers come in a wide array, but there are two basic types that is organic (natural) and inorganic (chemical). All organic compost and fertilizers are derived from living material and contain the most essential building block of life carbon. Many people have become confused over the relative merits of organic versus inorganic aids for trees and shrubs. Most organic aids are generally longer lasting, and are considered more to be soil builders and thus they improve soil quality over time. Compost and manure, are good examples of organic soil builders. Working this organic matter into the soil before planting is the best basis for ensuring good growth and a healthy start for young trees.
The results you achieve with your trees, is directly related to the degree of fertility in the soil, which is influenced by the type and amount of nutrients available. For instance, approximately 1/7 of protein is nitrogen, which is the element most used by all trees and green plants. It is important for both growth and development.
Leaving the leaves where they fall is a great way to keep the soil healthy.
A micorrhizal root under magnification.
Excess fertilizer salts transported by storm water run-off is one of the major causes for ground water contamination.
Interaction between tree roots and mycorrhizae
Man Testing Soil There are many fertilizer manufacturers that produce chemical fertilizers with added mycorrhizal inoculants.
Like air and water, the soil is a precious resource, but it is not an unchanging resource. On the contrary, the quality of the soil in any one location can change dramatically in a relatively short time. Our urban environments are a good example of this. Soils in natural undisturbed forest areas generally contain robust and diverse populations of mycorrhizal fungi. In urban areas however activities such as site development, tilling , topsoil removal, grading, digging, and soil compaction destroy many of these beneficial fungi.