Download Soil Basics - Hampshire Farm Landscaping

1. The Symbiotic Decay-Nutrition
(Continued on next page)
Cycle
The soil works as a dynamic plant-growing system. Good soil is rich in organic matter
and microbes that, together with the atmosphere, precipitation and sunshine, provide
all the needed elements and conditions for strong plant growth.
Plants are known to need at least 16 elements to live, grow and reproduce (See Table
1). Recent research has shown that most plants also require very small amounts of
nickel, and some plants require silicon. Like animals, plants need a certain balance of
nutrients, not just the nitrogen (N), phosphate (P) and potassium (K) that we typically
associate with plant foods. And like animals, plants need different amounts of the
various nutrients at different life stages. How does the soil supply these nutrients in
the right balance, and how can we improve soil properties to maximize plant health
and vigor?
Table 1. Typical Elemental Plant Composition (%)
Oxygen
Carbon (from air)
Hydrogen
Nitrogen
Potassium
Calcium
Sulfur
Phosphorus
45
44.0
6.0
2.0
1.1
0.6
0.5
0.4
Magnesium
Manganese
Iron
Zinc
Chlorine
Boron
Copper
Molybdenum
0.3
0.05
0.02
0.01
0.01
0.005
0.001
0.0001
In the real world of crop and pasture management, two things are very important to
maintaining soil health, and therefore plant vitality: the decay cycle (by which organic
matter is recycled to recover critical elements), and supplemental provision of
nutrients, usually via some kind of fertilizer.
Decay of organic matter that enriches the soil is a cycle – there must be organic matter
present to decay, and there must be microbes present to cause the decay. Organic
matter, plants and microbes have a symbiotic relationship; organic matter enriches the
physical attributes of the soil by holding water, warming appropriately but not baking
in the sun as barren soil would, and providing a food source for the soil microbes.
The microbes breakdown the organic matter and make elemental nutrients available to
the plants. And the plants provide shade to prevent excessive soil warming (which
would be detrimental to the microbes) and provide a continuous supply of organic
matter through fallen leaves, dead grass blades, seed husks, etc. The addition of
complex chemical and biological compounds to the soil via decay substantially
enriches the physical, chemical and biochemical complexity of the soil and helps to
maintain the proper pH (6.0 to 6.8) that allows for a healthy balance of microbial life.
Use of a natural fertilizer such as the Bradfield products contributes to this provision
of organic matter and nutrients. This symbiotic development of a nutrient cycle
results in healthy plants with deep, extensive root systems that are better able to
absorb nutrients and water from the surrounding soil. Use of a straight chemical
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1. The Symbiotic Decay-Nutrition
(Continued from next page)
Cycle
fertilizer interrupts this symbiotic cycle by 1) not contributing organic matter; 2)
depressing natural fixation of nutrients by bacteria living in the soil and in nodules
found on the roots of plants; 3) disrupting the balance of nutrients available to the
plant (much as oversupply of one nutrient may disrupt absorption of another in
animals); and 4) interrupting the normal progress of the decay cycle. Over time, this
results in plants suffering from malnutrition and inadequate root development, thus
increasing the need for extraneous provision of fertilizers.
Nutrient needs are relatively small at the beginning of a crop’s or pasture’s growth, then
increase dramatically during peak vegetative growth and during seed production. If
soil is healthy and the decay cycle is progressing normally, last year’s residues will be
digested and their nutrients released and available to the plant at about the time the
plant is approaching its peak needs. Anything that interrupts or slows the cycle can
result in inadequate nutrition when the plant most needs it.
Healthy soils have far larger amounts of nutrient elements than crops need, but most
of this total soil nutrient supply is unavailable to plants. Most of the nutrients in soil
are initially “tied up”, their molecules chemically bound in mineral particles, or in the
complex organic molecules in humus or the bodies of soil organisms. These nutrients
can be made available through natural processes: weathering, the action of
precipitation and temperature changes; plant root release of acidic substances
(hydrogen ions and organic acids); microbe release of acids and chelating substances;
and microbial decay of organic matter. In a healthy, biologically active soil, these
natural release mechanisms can often meet much of a plant’s nutrient needs. Indeed,
natural nutrient release is one reason that biological farmers can reduce their fertilizer
inputs after several years. Farmers using inorganic sources of fertilizer typically find
that they must increase application rates year after year in order to sustain reasonable
crop growth.
For optimal plant health and production, your soil needs sufficient organic matter (2
to 3% minimum), adequate moisture, a proper balance of all nutrients (not just N, P
and K), and high biological activity in order to provide an appropriate balance of
nutrients and encourage plants to have strong root systems by which to absorb these
nutrients. Bradfield products act as a part of the symbiotic cycle to provide natural
sources of nutrients in a base of organic matter to feed the soil, not just the plants!
REFERENCES
Zimmer, Gary. 2006. Soil Basics: How It Works. Acres U.S.A.
www.answers.com/topic/CNO-cycle
Harrison, John Arthur. The Nitrogen Cycle: Of Microbes and Men.
www.visonlearning.com/library/module_viewer.php?mid=98&l=&c3
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2. Water Uptake
(Continued on next page)
Plants need water as part of their cells. Indeed, plant tissue is about 80 to 90% water.
This water is the substance in which the various molecules and ions that perform
metabolic activities (such as photosynthesis, food transport, cell maintenance, growth
and reproduction) are dissolved and transported. Water is also the substance in which
the soil’s nutrients are dissolved and carried into the plant.
Plants are constantly losing water via “transpiration” through thousands of tiny pores
(“stomata”) in the leaves and by leakage of root exudates through the tips of the roots.
Plants do have some ability to regulate the size of their stomata and slow down water
loss, but obviously water must be continually provided to the plant by absorption
through the roots to maintain optimal health. The constant movement of water
upward from the roots to the leaves serves to carry nutrients from the soil to all parts
of the plant and to help cool the leaves during hot weather. Plants vary in their water
needs – while a cactus will lose only microscopic amounts of water in a day, a corn
plant may lose up to two quarts!
In the soil, water fills pore spaces between soil particles. In moist soil, about half of
the total soil water is able to be absorbed (“available water”) and about half is too
tightly held on soil particles to be used (“unavailable water”). The composition of the
soil is a major factor in availability of water to plants. Soils with a high clay content
hold a higher percentage of the total water as unavailable water, but their total water
supply will be considerably larger than sandy soils. High clay soils are also subject to
compaction, which can impede the development of strong, deep root systems. Sandy
soils will be short on total water-holding capacity and may not have the humus
content necessary to support nutrition and water provision needed by many plants.
Use of fertilizers such as Bradfield products that contribute organic matter to soils can
increase the available water and reduce the compaction of clay soils and increase the
total water capacity and nutrient content of sandy soils.
Salts in soils also affect root water uptake. The higher the salt level, the more difficult
it is for the plant to draw water from the soil. Excessive use of inorganic, high-salt
fertilizers (such as potassium chloride or ammonium nitrate) can increase salt levels so
high that plant growth is negatively impacted. Use of natural fertilizers avoids this salt
build-up and maintains water availability.
The faster the rate of transpiration from the leaves, the faster the plant must draw
water through the roots to keep up. Plants need much more water when weather is
sunny, humidity is low, or the wind is strong. Under these conditions, if the soil’s
supply of available water is low, either due to low capacity or low availability, plants
will begin to wilt. This is one reason why a soil’s structure and humus content are so
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2. Water Uptake
(Continued from next page)
important: to improve water movement and availability. Inorganic fertilizers do
nothing to enrich the organic matter or humus content of a soil and therefore do
nothing to improve the supply of water to plants. Indeed, the potential for salt buildup will result in a negative impact on available water over time. A soil rich in organic
matter will not only be optimal for water availability, it will encourage growth of
dense, deep root systems that are better able to withstand periods of water shortage.
Use of natural Bradfield fertilizers helps to build soil organic matter, ultimately
resulting in stronger, healthier plants!
REFERENCES
Zimmer, Gary. 2006. Soil Basics: How It Works. Acres U.S.A.
Transport in Plants.
www.biologymad.com/PlantTransport/PlantTransport.htm
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3. Ions, Nutrition and all that
“Scary” Chemistry (Continued on next page)
Nutrients that are held on soil particles yet are available to plants for use are called
“exchangeable nutrients”, meaning they can be easily exchanged between the soil
particle and the plant root. These nutrients are in the form of “ions”, atoms or
molecules that have an electrical charge. Ions with a positive charge are called
“cations”; those with a negative charge are “anions”. Common nutrients are shown
here in the form in which they are available to plants:
Positive ions
Potassium
Calcium
Magnesium
Iron
Copper
Zinc
Manganese
Nickel
Negative ions
Nitrogen
Phosphorus
Sulfur
Boron
Molybdenum
Chlorine
The very small colloidal particles in soil, clay and humus have a large surface area
covered by many negative electrical charges. Cations are attracted to and held by
these negatively charged colloids (positive and negative charges attract – similar
charges repel). Anions are mainly found free in the soil solution (the water between
the soil particles). Clay particles generally have a flat, angular shape, while humus
particles are irregular and lumpy. Humus particles have much more surface area and
can hold about three times as many nutrients as clay particles. Scientists have a
means of estimating a soil’s fertility by determining its cation exchange capacity (CEC).
The CEC is only an estimate of a soil’s ability to hold major cations (calcium,
magnesium and potassium), but it has proven to be a fairly accurate estimate of soil
fertility. The CEC of various soil types and humus is shown in Table 1; note that the
more clay and humus a soil has, the greater its ability to store nutrients. Thus, it is
valuable to enrich clay soils with organic matter such as that found in the Bradfield
natural fertilizer products to enhance their nutrient-holding ability.
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3. Ions, Nutrition and all that
“Scary” Chemistry (Continued from next page)
Table 1. Cation Exchange Capacity of Soil Types
Soil Texture
Sands
Sandy loams
Loams, silt loams
Clay loams
Peat
Clays
Humus
CEC
1–5
5 – 10
5 – 15
15 – 30
10 - 30
over 30
100 – 300
Now, remember that while a soil may be able to hold a lot of nutrients, those nutrients
must be available to the plant to be useful. A soil may have a great capacity to store
nutrients but may be depleted of available nutrients from many years of growing
plants with little or no supplemental fertilization or organic matter recycling. Under
these circumstances, the negatively charged sites on the soil colloids that normally
bind nutrient cations such as calcium, magnesium and potassium, will become filled
with positively charged hydrogen ions. This meets the need of the negative site to
bind with a positively charged ion, but it does nothing for the plant. Indeed, as
hydrogen ions pile up, the soil’s pH drops, becoming more acidic, which is a sign of
nutrient-poor soil. “Liming” a soil to increase its pH is really a matter of replacing
hydrogen ions with needed nutrients. The material used for liming should be
designed to replace those nutrients specifically missing, so having soil thoroughly
tested for elemental composition is important for proper restoration. Enhancing a soil
with natural fertilizers such as the Bradfield products, which directly provide nutrients
as well as organic matter that supports microbial growth and provides colloidal
binding sites, can help to prevent excessive soil acidity in the first place. Proper
fertilization with an organic matter- containing fertilizer will help to maintain the
physical characteristics of soil that are so necessary for optimal soil fertility and
superior plant health.
REFERENCES
Zimmer, Gary. 2006. Soil Basics: How It Works. Acres U.S.A.
MicroSoil: Cation Exchange Capacity. www.microsoil.com/CEC.htm
Cation-Exchange Capacity. Tree Fruit Soil and Nutrition. Washington State University.
soils.tfrec.wsu.edu/webnutritiongood/soilprops/04CEC.htm
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4. Who are these Microbes, and what
are they doing in my Soil? (Continued on next page)
Strong, healthy soil is critical to anyone who has planted anything for any reason. Without
it, your chances for success are pretty poor. But what makes one soil support abundant,
vigorous plant life while another seems to produce only sickly plants and weeds?
Let’s start with soil structure, which has an important impact on transport of nutrients
from soil to plants. There are three main types of soils. Sandy soils are composed of
large, loose particles that drain easily. Sandy soils will never compact, but they are
also poor repositories for water and nutrients. Unless sufficiently amended and
maintained, sandy soils will support only the hardiest of plant life.
At the other end of the spectrum are clay soils. Clay soils are composed of very small
particles that are sticky when wet. They have a lot of valuable surface area for
adherence of nutrients and retain water very well, but they compact very easily and
may be lacking in the air spaces that allow movement of water and nutrients, thus
limiting their availability to the plant.
In between sandy and clay soils lie the loamy soils. These soils are actually a
combination of sand, clay and organic matter. They resist compaction but retain
enough water and nutrients to support plant life when well-managed. The good news
is that both clay and sandy soils can be made more like loamy soils with the proper
care and amendments.
All plants require 16 essential elements, and many require a few more. They get
carbon, hydrogen and oxygen from the air and water, the availability of which is
directly related to the structure of the soil they are growing in. Loamy soils with good
aggregate structure and adequate porosity allow plenty of air and water to reach plant
roots. But no soil, regardless of structure, will support vigorous plant life and deliver
enough of the other 13 or 14 essential elements unless it is teeming with the billions
of microbes that are necessary for maintaining soil health and supporting vegetative
growth. Just what do soil microbes do? The list is impressive:
•
•
•
•
•
•
•
•
Increase availability of phosphorus, potassium and other nutrients
Deliver nitrogen
Break down organic residues
Increase soil aeration
Improve water penetration and retention
Increase naturally occurring organic acids that stimulate root growth
Improve delivery of multiple nutrients to plant roots
Inhibit pathogens
How do microbes do all this? Soil microbes exist in the “rhyzosphere”, the area of soil
surrounding the roots of plants. They exist in a symbiotic relationship with the plant
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4. Who are these Microbes, and what
are they doing in my Soil (Continued from next page)
roots; microbes deliver nutrients plants need and either directly destroy pathogens or
produce compounds that are antagonistic to pathogenic organisms, and plants provide
microbes with amino acids and carbohydrate products of photosynthesis. Obviously,
the healthier and more extensive the root system of the plant, the deeper and richer
will be the rhyzosphere, and vice versa. Many microbes also derive carbon from
organic matter that is broken down by bacteria, so the combination of abundant
organic matter and a healthy bacterial population is essential to supporting a rich and
vibrant rhyzosphere. Indeed, the microbe population in the top six inches of one acre
of healthy soil has a metabolic equivalent of 10,000 humans, and each gram of soil
may contain 10,000 different species of microorganisms!
Many classes of microbes exist to service the soil and plant life. Bacteria serve to
decompose organic matter, leaving in their wake a sticky, mucus-like substance that
acts as a glue to hold the soil together in aggregates that provide soil structure with
multiple spaces for movement of air and water. Some bacteria also consume many
pathogens that might otherwise be able to attack plants or other beneficial microbes.
Rhizobial bacteria infect the root nodules of legumes and participate in nitrogen-fixing
by these plants.
Fungi are responsible for delivery of a significant amount of the nitrogen that is taken
up by plants. While much free solute nitrogen is absorbed directly from the soil water
solution, fungi are responsible for delivery of fully one-third of the nitrogen plants
need. They do this by linking soil nitrogen to carbon, moving the combined N-C
molecule to the root surface, and then, just before delivery, the carbon is released and
only the nitrogen is presented to the plant. Other fungi, specifically mycorrhizal fungi,
are critical for phosphorus uptake and also aid in improving availability of potassium.
These fungi send tiny root-like stru c t u res called “hyphae” into the soil and can bring
p h o s p h o rus to a plant root from four inches away (which is miles in terms of soil
nutrient provision!). Mycorrhizae also produce a substance called “glomalin”, which
improves soil stru c t u re and may form as much as 30% of the organic matter in the soil.
Beneficial nematodes (tiny roundworms) keep pathogenic root-eating nematodes
under control. They also consume other nematodes and bacteria, thus releasing
nitrogen and phosphorus into the soil, where fungi can make them available to plants.
Some nematodes eat pathogenic fungi, thus helping to maintain a healthy balance of
microbial life.
One-celled protozoa in the soil serve as soil police squads, preying on bacteria and fungi to
keep these populations under control. As with any system made of multiple components, if
one portion of the population gets out of control, the system fails to function as it should.
The presence of ciliate protozoa, which feed on anaerobic bacteria, indicates that oxygen is
in limited supply and some soil aeration is needed.
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4. Who are these Microbes, and what
are they doing in my Soil (Continued from next page)
Arthropods are a class of assorted creatures ranging from the microscopic to beings as large
as ants, beetles and centipedes. Their general function is to break up debris and aerate the
soil with their foraging. Arthropods will not be present if there is nothing to forage.
Earthworms, though not really microbes, are great contributors to soil richness with
their nutrient-dense castings and the aeration provided by their burrowing, and their
presence is a good indication that the soil is healthy and abundant in nutrients and
multiple forms of microbial life.
Clearly, a soil that is barren of organic matter and microbial activity will have very
limited ability to support any kind of plant life. Chemical fertilizers will only be
available to plants in the form that is readily soluble in water; much will be wasted
and will run off because there are no microbes to transport nutrients. Root systems
will be shallow, the rhyzosphere will be thin, and soil structure will suffer. Application
of large amounts of chemical fertilizers, as well as herbicides and fungicides, in an
effort to feed weakening plants may even decimate what little microbial life exists,
resulting in an even more sterile, barren soil. Use of organic fertilizers and
amendments such as Bradfield Organics products to build soil structure and support
microbial life is critical to the optimal growth of vigorous, healthy plants!
REFERENCES
Bago, B., P. E. Pfeffer, and Y . Shachar-Hill. 2000. Carbon metabolism and transport in
arbuscular mycorrhizas . Plant Physiol. 124:949-957.
Booker, Karen. 2000. Fertilizers and Soil Amendments: It’s Tricky Business. Erosion
Control Feature Article, September/October. www.forester.net/ec_0009_fertilizer.html
Drinkwater, L. E., P. Wagner, and M. Sarrantonio. 1998. Legume-based cropping
systems have reduced carbon and nitrogen losses. Nature. Vol. 396, Nov. 19.
Ellis, J. R. 1995. Mycorrhiza – An essential part of most plant root systems. Better
Crops 79(1):10-11.
Marschner, Horst. 1995. Mineral Nutrition of Higher Plants. (2nd ed.)
Wright, S. F. 2003. The importance of soil microorganisms in aggregate stability. Proc.
North Central Extension-Industry Soil Fertility Conference. 19:93-98.
www.agro-K.com/organics/soil_health.htm
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