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.
