Soil testing is cheap or free. Your county extension agent will give you what you need. How can you know what to add until you know what is there?
Drilling 2" holes will cut some roots, and glaze the soil so nutrients won't spread laterally. Using a post hole digger will cut many roots, and putting fert in those holes will burn the rest.
The trunk, branches and leaves are the most obvious parts of the plants to examine, but the landscape below ground is equally important. Armed with $100 in tools and following a few basic principles, arborists can learn a lot about how the earth surrounding a tree’s roots is affecting tree vitality.
A pH meter is a very useful soil-measuring tool, reading the soil’s reaction (pH), as described in the December 2006 CEU article in Arborist News. A soil probe is a simple T-shaped tool that is pressed or twisted into the earth and extracts a core of soil. This core of soil typically contains an A horizon below the mulch, turf, or groundcover; a B horizon below that where the organic matter blends into the native soil; and a C layer of less permeable subsoil, the parent material from which the soil was formed. Many of the nonwoody roots are typically found in the A horizon. White roots extending into the B horizon indicates a high level of oxygen there, where the tree can harvest enough resources fuel its various functions.
Urban soils are often disturbed, with a jumble of material from different horizons interspersed. Touching the soil also can reveal much about its properties. For example, if moist soil is rolled into a cylinder and it crumbles easily, it may be low in clay. A sour smell indicates anaerobic, low-oxygen conditions hostile to root growth, while a sweet smell can signify that beneficial, aerobic bacteria and fungi are at work. A hand lens is useful in finding fine roots, mycorrhizal strands, and other interesting things, such as soil insects.
Earthworms, arthropods, and other organisms aerate the soil and convert organic matter and minerals into forms more available to the tree. A number of references have reported that one cup of undisturbed native soil may contain the following: 200 billion bacteria, 20 billion protozoa, 100,000 meters of fungi, 100,000 nematodes and 50,000 arthropods. There are ways to encourage beneficial soil organisms:
• Use organic mulches for weed control, and amend the soil with composted organic material to provide a food source for soil organisms.
• Avoid over irrigation and **excessive use of fertilizers**, so the organisms do not drown or burn.
• Irrigate during periods of drought. Soil organism activity may be reduced due to dry soil conditions that are common in certain times of the year.
• Avoid unwarranted pesticide applications. Some fungicides, insecticides, and herbicides are harmful to various types of soil organisms.
• Use organic mulches to reduce soil compaction forces, moderate temperature, and maintain soil oxygen levels needed by beneficial soil organisms and roots.
Uncompacted soils have less root rot because they have better drainage, thanks to more pore space that air and water travel through. This pore space helps define the soil’s structure.
