I finished my
Master Gardener class and learned something new from every lecture. The class I found most interesting was the
lecture on soils – what they are made of, what is in them, how we can work with
them, etc.
Are you aware
that soil is made up of weathered rock fragments, organic matter and living
organisms? There are components that are
living and some that are not living.
Minerals and dead organic matter make up one portion, and microorganisms,
invertebrates, and plant roots make up the living part. “Soil provides nutrients, water and physical
support for plants and air for plant roots.”
The temperature of the soil has
a huge impact on “seed germination, root growth, microbial activity, and
nutrient availability and uptake.” Soil
in Alaska is cold and must be warmed to garden successfully. Many Alaskan gardeners use raised beds in
order to garden successfully; others use black plastic or other covering to
warm the soil.
For successful gardening soil
must “be both permeable to water and able to supply water to plants. These two characteristics depend on the
network of pores in the soil. Large
pores are made by insects, earthworms, and roots and allow water to rapidly drain
with gravity. Small pores are responsible
for increasing the soil’s capacity to hold water against the force of
gravity. Plants need sufficient water
but not too much water.
Whether or not soil has large or
small pores depends on its “texture, structure, compaction, organic matter and
living organisms” in it. Texture
describes when the soil is more fine or coarse, and this depends on the mixture
of sand, silt, clay in the soil. You can tell the quality of the soil by the
feel of it. Sand feels gritty, silt
feels smooth like flour, and clay feels hard when dry but can be molded easily
when moist. The difference is made by
the size of the individual particles.
Sand particles are the largest; silt particles are smaller than sand,
and clay particles are the smallest.
“Although all of these particles seem small, the relative difference in
their size is quite large. If a typical
clay particle were the size of a penny, a sand particle would be as large as a
house.” A good garden soil crumbles in
your hand when it is ready for tilling.
“Nearly all soils contain a
mixture of particle sizes, giving them a pore network containing a mixture of
pore sizes…. A soil with roughly equal
influence form sand, silt and clay particles is called a loam. Loams usually make
good agricultural and garden soils because they have a balance of macropores
and micropores. They usually have good
water- and nutrient-holding capacity, along with moderate permeability.”
Sandy loams are similar to loams
but will drain water more quickly. Silt
loams will hold more water. Clays and
clay-loams are hard when dry and sticky when wet; they have the greatest
capacity to hold water and nutrients.
“Almost any texture of soil can be suitable for gardening, as long as
you are aware of the soil’s limitations and adjust your management to
compensate…. Many soils can benefit from
additions of high-quality organic matter….”
Besides the texture of soil a
gardener needs to be aware of the slope, the aspect (direction of exposure),
and the depth of the soil. Slope determines
the availability of water because water flows down with gravity; there is
usually more water in a valley than on the mountain ridge. “Site aspect also is important. South- ad southwest-facing exposures collect
the most heat and use the most water.”
Depth is important because deeper soil holds more water than shallow
soil.
Soil is alive. “Besides the plant roots, insects and
earthworms you can see, soil is home to an abundant and diverse population of
microorganisms. A single gram of topsoil
(about ¼ teaspoon) can contain as many as a billion microorganisms.” Most of the microorganisms are located in the
soil surrounding the roots of the plants – an area known as the
rhizosphere. The organisms break down
plant remains and other organisms and make energy, nutrients, and carbon
dioxide available to the plants. This
also helps to stabilize the soil more.
Soil supplies 17 essential plant
nutrients. There are macronutrients and
micronutrients. The primary nutrients
are nitrogen (N), phosphorus (P), and potassium (K). Secondary nutrients are sulfur (S), magnesium
(Mg), and calcium (Ca), carbon (C), hydrogen (H),
oxygen
(O), and nickel (Ni). Micronutrients are
zinc (Zn), boron (B), iron (FE), manganese (Mn), copper (Cu), molybdenum (Mo),
and
chlorine
(Cl). If the soil is deficient in any of
these nutrients, the plants will be affected.
For example, soil that is deficient in nitrogen will produce plants with
yellow leaves, and soil that is deficient in phosphorus will have red
leaves. I found it interesting to learn the
plant will take the nutrient from the older leaves and supply it to the newer
leaves; therefore, it is the older leaves that change color first.
Nutrient deficiencies can be
corrected by adding organic or non-organic fertilizers. Processed fertilizers work faster and make
their nutrients available to plants quicker.
Organic fertilizers release their nutrients more slowly, making the
nutrients available to the plant over the growing season. There are some organic fertilizers, such as
fresh manure and fish meal, which contain available nutrients. Some nutrients are not even available for the
plants until the next growing season.
“Repeated application of organic fertilizers builds up a pool of
material that releases nutrients very slowly.
In the long run, this nutrient supply decreases the need for
supplemental fertilizer.”
Gardeners can determine the need
for fertilizer and how much by having their soil tested every few years. If the pH level is too low, lime can be
added. If the pH level is too high,
elemental sulfur or iron sulfate can be added.
I have learned a lot about soil
and its effects on plants and realize there is much more knowledge to gain as
well as how to apply it in my garden.
The Master Gardener course is very interesting and worthwhile to me.
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