The Most Important Aspect of a Tree's Future Health and Potential Lies in the Soil Analysis

Article by Rick Caldwell, ISA arborist and lifelong tree climber      4/26/2015
Formerly a tree crew leader and bucket operator/climber for numerous different East Coast and West Coast companies, Rick is currently a sales arborist for Trout Brook Landscaping LLC
Check out additional pictures and stories at www.troutbrooklandscapingct.com

DEFINING SOIL STRUCTURE

Before planting trees and when examining existing tree soils, a homeowner should be aware of what type of soil they are working with. A healthy soil is generally made up of 45% mineral, 5% organic matter, 50% pore space (25% air/25% water). This is not always the case with backyard, garden or even commercial property soils, quite often they are lacking in necessary nutrients, organic matter and adequate pore space. Soil structure is composed of a variable combination of sand, silt, and clay particles (ranging from largest size sand to the tiniest clay particle. A mixture of all three including air/water pore space and organic matter is the optimum soil structure. The soil texture is a description of the degree in which the soil particles are combined; sandy loam, silt clay, clay loam, etc. The ability of the soil to retain a balanced pH (measure of acidity) and nutrient content is known as its buffering capacity. The tiny particles of the clay component of soils holds the colloidal ions responsible for CEC or Cation Exchange Capacity which attract, hold, and release nutrient ions for plant uptake. However too much clay will prevent adequate drainage and result in water pooling, this can destroy beneficial aerobic microorganisms as well as drowning the plant roots. This also allows for an easily compacted soil, which further reduces pore space required for root growth. With soils containing too much sand, the result is excess drainage or low water retention. This affects the pH balance and reduces nutrient content due to the water leaching through the soil, as well as poor root anchorage in the soil.

   Compacted soils can be aerated mechanically relatively quickly or naturally over a longer period of time (with no further compaction). Sandy soils can be remedied with the amendment of organic matter or the type of compost recommended by the soil analysis.

SOIL LAYERS

There are four basic levels in a soil profile (C,B,A,O) in a natural soil environment. C level is above the rock strata (bedrock) and consists primarily of rock or parent material, this level is well below most root zones. The B level consists of mineral breakdown and is also below the root zone. The A layer is the soil aggregation known as the topsoil; this is the region where root growth occurs, approximately 18”-20” deep on average. The top O layer is commonly known as humus, this is where organic matter is deposited, builds up, broken down by carbon eating microorganisms, and turned into nutrient rich topsoil. These beneficial microorganisms are known as aerobic (air breathing), the anaerobic organisms (non air breathing) are the result of excess water in the soil; this can cause root rot and soil born disease (what causes the heavy sulfur smell in swamps). Typically the organic matter content in topsoil is about 5% and provides the majority of the nitrogen as well as the phosphorus and sulfur required by plants. Organic matter, like clay particles, also has the buffering capacity that holds the pH balance and nutrient availability steady.

"pH" DEFINED

This one is definitely a brain exerciser, the pH is a measure (agreed internationally) of the acidity of a chemical solution (liquid). The pH or potential Hydrogen ion (+) is another very crucial factor in the availability of mineral nutrient uptake for plants. The pH scale, which ranges from 0 (extremely acidic Hydrochloric Acid) to 14 (extremely alkaline Sodium Hydroxide), with 7 being considered neutral (pure water). Plant pH requirements differ slightly, however all plants generally prefer a mid-range pH od 5.5-8 on the pH scale. Most nutrients are also made available to plants at this range; some micronutrients require a slightly more acidic level to become available for plant uptake. If a soil analysis results in a low pH or acidic soil, basic substances such as lime are used to “sweeten” the soil. When the soil is too high in pH or alkaline, sulfur or other acidic materials are used to lower the pH level. A soil analysis report will specify actual pH level and the optimum range for the specific plant species, as well as the action required to correct the pH levels.

ESSENTIAL NUTRIENTS IN SOIL ANALYSIS

The primary nutrients that plants require in larger amounts are Nitrogen, Phosphorus, and Potassium, this is the N-P-K listed on fertilizer bags. The numbers on the fertilizer bags represent the percent by weight of the nutrients, thus a fertilizer bags stating 10-15-10 contains 10% Nitrogen, 15% Phosphorus, 10% Potassium. Other important primary plant nutrients are Carbon, Hydrogen, and Oxygen which occur naturally within the soil, with the air and soil water exchange cycle. Sulfur, Calcium, Magnesium, and even small amounts of Chlorine and Sodium are also used by plants for metabolic processes. Micronutrients required by plants in small amounts including Iron, Manganese, Boron, Zinc, Copper are also included on the soil analysis report. The micronutrients Cobalt, Chromium, Iodine, Selenium, Nickel and Molybdenum are used by plants for various reasons, apparently not as important because they are often not included in soil analysis reports.