Did you realize that approximately 80% of all plant problems can be traced to the soil/environmental effects? How many of us spend 80% of our efforts trying to fix the problem? Traditionally, we have spent the majority of our time applying first aid to treat the symptoms. Rex A. Bastian, Ph.D., vice president, Field Education and Development, The Care of Trees, Wheeling, IL, brought forth valuable and practical information regarding soil and more specifically soil biology during a forum at the Pro Hort 2006 conference. “We need to think (and do) more “soil management” in our landscape management programs,” says Bastian. “Tradition keeps us from looking at new ways and old methods do not equal new results. There are options for improving our soils even in mature landscape situations,” he added.
Bastian reiterated that soil has three properties: physical (structure), chemical and biological. The physical aspects (sand, silt, clay) are widely recognized. We often attempt to enhance the structure with various amendments at planting time and core aeration. Fertilizers are commonly used to correct chemical deficiencies and provide needed nutrients throughout the life of a plant. We all know “organic matter” (mushroom compost, cow manure, leaf compost) is good for the soil and we use it to help improve soil structure and provide nutrients for our plants. But there is much more to it. Organic matter plays an important in soil biology, an often overlooked component of a healthy soil.
Here is a summary of some of the important facts of organic matter and soil biology Bastian presented.
Organic matter in the soil is made up of fresh plant or animal residue, decomposing residue, stabilized (fully decomposed) organic matter (humus) and living organisms.
Healthy soil is loaded with living things which aid in the decomposition process. Living organisms include:
• Bacteria
• Fungi
• Microathropods
• Earthworms
• Protozoans
• Nematodes
The soil foodweb is a term used to describe how these organisms interact with animals and plants (both living and dead) in the soil.
Benefits of a healthy soil foodweb include:
• Retention of nutrients
• Cycling of nutrients in the correct to the plants under culture
• Improvement of soil structure
• Suppression of pathogens
• Improvement in plant root systems
• Decomposition of soil toxins
All soil foodwebs are not the same. Grasses prefer soil foodwebs that are high in bacterial content while deciduous and coniferous trees and shrubs grow best in soils that are more populated with fungi. This fact helps explain why grass does not grow well under trees; it is not just the shade.
“The soil’s biological component can be manipulated through the use of mulch, microbial foods and compost or compost tea. The soil can be inoculated with desirable food web organisms,” says Bastian. Using quality biological foods and compost teas are effective in rebuilding the numbers and diversity of desirable soil organisms.
Bastian gives some practical approaches to rebuilding the soil’s natural biology. “Using large mulch rings around trees can increase the beneficial fungal component of the soil. The decomposing wood provides food for the beneficial organisms.”
“Applications of compost or compost tea over the top of the soil can help change the soil biology,” he adds. Compost can be broadcast over the soil during the dormant season. Core aerating or slicing the soil with air spade or air knife prior to applying compost is ideal.
Using compost tea may be more cost effective than dry compost. “Compost tea can be a very inexpensive soil and foliar amendment,” says Bastian. “You can purchase a brewer and make it yourself. Finding a good source of compost for tea is much easier than finding a source of good quality bulk compost.” It takes a small amount of compost to brew tea rich in microbes. The brew cycle creates 1,000 pounds worth of microbes from 10 pounds of compost,” he commented. Compost tea can be applied through conventional spray equipment and is much less time consuming than spreading dry material.
Bastian described one situation where a Japanese maple tree was suffering from Verticillium wilt. A national tree company had been treating the tree for years with various fungicides yet the tree kept declining. Bastian’s treatment plan composed of radial trenching within the root zone. The trenches were filled with compost and compost tea was applied regularly. Within two years following this treatment the trees has shown significant improvements.
The above article written by Cathy Bilow was published in Growing Trends magazine 2007