Soil Nutrients and pH
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pH is a measure of the acidity or alkalinity of the soil. The pH scale runs from 0 to 14. A reading of 7.0
represents a neutral pH, neither acid nor alkaline - the pH of pure water. A pH below 7 is acid, the lower
the number, the stronger the acidity. Numbers above 7 are alkaline. When gardeners talk about soil
being "sweet" or "sour," they're referring to this property. Sour means acidic (think lemons - a very acidic
fruit.) Sweetening the soil means making it closer to neutral.
Soil pH is affected by factors like soil composition and rainfall. Soil in the desert Southwest and areas with
large limestone deposits tends to be alkaline. Here in the Northwest, west of the Cascades, rain and
organic matter make our soils acidic, typically in the 5.0 - 6.0 range.
Soil pH is an important factor in soil fertility because it affects how available nutrients are for plants. Even
if nutrients are present in sufficient amounts, a soil that is too acidic or alkaline can bind them up and
prevent them from being absorbed and utilized by plants. Your plants literally starve while surrounded by
unattainable plenty. Different nutrients are most available at different pH levels, which means that plants
with differing nutrient requirements will thrive in soils of differing pH. Most plants prefer a neutral to slightly
acidic pH, but there are quite a few exceptions. Potatoes, blueberries, rhododendrons, and azaleas, for
example, like a strongly acid soil.
If your soil isn't in the preferred range of the crops you want to plant in it, you can amend it to alter the pH.
This isn't an instant fix; it takes time for the additives to break down and be incorporated into the soil. To
sweeten an acidic soil, apply lime. Dolomite lime or agricultural limestone both work. Hydrated lime acts
much more quickly, but it is caustic and may harm plants if not used carefully. Wood ashes also act to
raise soil pH.
To make the soil more acidic, or neutralize an alkaline soil, use soil sulfur, or amend the soil with peat
moss, evergreen needles, or cottonseed meal. Aluminum sulfate is a quick-acting acidifying agent that's
often used on hydrangeas to turn their blossoms blue.
represents a neutral pH, neither acid nor alkaline - the pH of pure water. A pH below 7 is acid, the lower
the number, the stronger the acidity. Numbers above 7 are alkaline. When gardeners talk about soil
being "sweet" or "sour," they're referring to this property. Sour means acidic (think lemons - a very acidic
fruit.) Sweetening the soil means making it closer to neutral.
Soil pH is affected by factors like soil composition and rainfall. Soil in the desert Southwest and areas with
large limestone deposits tends to be alkaline. Here in the Northwest, west of the Cascades, rain and
organic matter make our soils acidic, typically in the 5.0 - 6.0 range.
Soil pH is an important factor in soil fertility because it affects how available nutrients are for plants. Even
if nutrients are present in sufficient amounts, a soil that is too acidic or alkaline can bind them up and
prevent them from being absorbed and utilized by plants. Your plants literally starve while surrounded by
unattainable plenty. Different nutrients are most available at different pH levels, which means that plants
with differing nutrient requirements will thrive in soils of differing pH. Most plants prefer a neutral to slightly
acidic pH, but there are quite a few exceptions. Potatoes, blueberries, rhododendrons, and azaleas, for
example, like a strongly acid soil.
If your soil isn't in the preferred range of the crops you want to plant in it, you can amend it to alter the pH.
This isn't an instant fix; it takes time for the additives to break down and be incorporated into the soil. To
sweeten an acidic soil, apply lime. Dolomite lime or agricultural limestone both work. Hydrated lime acts
much more quickly, but it is caustic and may harm plants if not used carefully. Wood ashes also act to
raise soil pH.
To make the soil more acidic, or neutralize an alkaline soil, use soil sulfur, or amend the soil with peat
moss, evergreen needles, or cottonseed meal. Aluminum sulfate is a quick-acting acidifying agent that's
often used on hydrangeas to turn their blossoms blue.
One of the most important factors in soil fertility is the amount of essential plant nutrients it contains.
Nutrients are divided into two categories, macronutrients and micronutrients. Macronutrients are
needed in large amounts, and can be easily depleted from the soil. Three macronutrients, carbon,
oxygen, and hydrogen, are obtained from the air and water. The remaining macronutrients must come
from the soil. These are divided into primary nutrients - nitrogen, phosphorous, and potassium - and
secondary nutrients - calcium, magnesium, and sulfur.
Micronutrients, also known as trace elements, are needed in minute amounts, but many are
indispensable for the life and health of plants. All of them must be supplied by the soil.
Nitrogen, phosphorous, and potassium are the major nutrients contained in most synthetic fertilizers.
Some also contain some or all of the secondary nutrients and essential trace elements. Fertilizers made
of organic materials usually contain some of these also, even if they aren't explicitly listed on the label. If
you have a reasonably good and well-maintained soil that's high in organic material, chances are that
most of the micronutrients are already present in adequate amounts.
One other factor that needs to be considered in soil fertility is its acidity or alkalinity, known as pH.
It's a good idea to periodically test your soil for nutrient content. Simple test kits for pH, Nitrogen,
Phosphorous, and Potassium levels are readily available for purchase. Testing services for other
nutrients are often available from laboratories.
Nutrients are divided into two categories, macronutrients and micronutrients. Macronutrients are
needed in large amounts, and can be easily depleted from the soil. Three macronutrients, carbon,
oxygen, and hydrogen, are obtained from the air and water. The remaining macronutrients must come
from the soil. These are divided into primary nutrients - nitrogen, phosphorous, and potassium - and
secondary nutrients - calcium, magnesium, and sulfur.
Micronutrients, also known as trace elements, are needed in minute amounts, but many are
indispensable for the life and health of plants. All of them must be supplied by the soil.
Nitrogen, phosphorous, and potassium are the major nutrients contained in most synthetic fertilizers.
Some also contain some or all of the secondary nutrients and essential trace elements. Fertilizers made
of organic materials usually contain some of these also, even if they aren't explicitly listed on the label. If
you have a reasonably good and well-maintained soil that's high in organic material, chances are that
most of the micronutrients are already present in adequate amounts.
One other factor that needs to be considered in soil fertility is its acidity or alkalinity, known as pH.
It's a good idea to periodically test your soil for nutrient content. Simple test kits for pH, Nitrogen,
Phosphorous, and Potassium levels are readily available for purchase. Testing services for other
nutrients are often available from laboratories.
Soil pH
Nitrogen
Phosphorous
Potassium
Iron
Calcium
Nitrogen is a building block of all proteins, and thus a vitally important macronutrient. It's necessary for
the growth of leaves and foliage and the formation of chlorophyll. A plant deficient in nitrogen appears
stunted and sickly yellow in color. Nitrogen is used rapidly by growing plants, and easily leached out of
the soil, so this is one of the most common nutrient deficiencies. You'll probably need to regularly
replenish the supply of nitrogen in your lawn and garden soil.
While the earth's atmosphere is 78% nitrogen, plants are unable to absorb it from the air. It must first be
converted to compounds which can be used by plants. In nature, this is done by nitrogen-fixing
bacteria. Plants of the legume family - peas, beans, alfalfa, and clover - have nodules in their roots that
house colonies of these bacteria, giving them access to a continuous supply of usable nitrogen.
Manure, blood meal, cottonseed meal, grass clippings, alfalfa, corn gluten meal, and fish meal or
emulsion are all sources of nitrogen for the garden or compost pile.
the growth of leaves and foliage and the formation of chlorophyll. A plant deficient in nitrogen appears
stunted and sickly yellow in color. Nitrogen is used rapidly by growing plants, and easily leached out of
the soil, so this is one of the most common nutrient deficiencies. You'll probably need to regularly
replenish the supply of nitrogen in your lawn and garden soil.
While the earth's atmosphere is 78% nitrogen, plants are unable to absorb it from the air. It must first be
converted to compounds which can be used by plants. In nature, this is done by nitrogen-fixing
bacteria. Plants of the legume family - peas, beans, alfalfa, and clover - have nodules in their roots that
house colonies of these bacteria, giving them access to a continuous supply of usable nitrogen.
Manure, blood meal, cottonseed meal, grass clippings, alfalfa, corn gluten meal, and fish meal or
emulsion are all sources of nitrogen for the garden or compost pile.
Phosphorous is important for development of robust root systems. It is also a component of ATP
(adenosine triphosphate) molecules, in which solar energy is stored as chemical energy in the process
of photosynthesis.
Phosphorous is found in many minerals, and is much more stable in the soil than nitrogen, so
deficiencies are less common. A plant suffering from lack of phosphorous may be stunted and show
purplish coloration in leaves and stems.
Besides synthetic fertilizers, phosphorous is found in bone meal and rock phosphate.
(adenosine triphosphate) molecules, in which solar energy is stored as chemical energy in the process
of photosynthesis.
Phosphorous is found in many minerals, and is much more stable in the soil than nitrogen, so
deficiencies are less common. A plant suffering from lack of phosphorous may be stunted and show
purplish coloration in leaves and stems.
Besides synthetic fertilizers, phosphorous is found in bone meal and rock phosphate.
Potassium promotes disease resistance and controls root growth. It aids in the production of sugars
and starches. It also regulates the opening and closing of stomata, the tiny pores through which plants
take in gases from the air. Since stomata also regulate water loss, potassium helps increase drought
resistance.
Signs of a potassium deficiency include older leaves yellowing and dying, and irregular fruit production.
Potassium supplements for the garden include muriate of potash, wood ashes, kelp meal and extracts,
and greensand, a mineral from ancient seabeds.
and starches. It also regulates the opening and closing of stomata, the tiny pores through which plants
take in gases from the air. Since stomata also regulate water loss, potassium helps increase drought
resistance.
Signs of a potassium deficiency include older leaves yellowing and dying, and irregular fruit production.
Potassium supplements for the garden include muriate of potash, wood ashes, kelp meal and extracts,
and greensand, a mineral from ancient seabeds.
Magnesium
Calcium is an important component of plants' cell walls. It provides structure and elasticity to plant cells
and helps them to resist stress and disease. Calcium is also involved in the growing tips of new growth
in both roots and foliage.
Calcium deficiency may show in new leaves being deformed. The weakening of cell walls associated
with calcium deficiency is responsible for the condition of blossom end rot in tomatoes and peppers, in
which the blossom end of the fruit darkens and rots.
The most common supplemental source of calcium is lime, either dolomite or limestone. Crushed egg
shells may also be added to garden soil or the compost pile as a source of calcium.
and helps them to resist stress and disease. Calcium is also involved in the growing tips of new growth
in both roots and foliage.
Calcium deficiency may show in new leaves being deformed. The weakening of cell walls associated
with calcium deficiency is responsible for the condition of blossom end rot in tomatoes and peppers, in
which the blossom end of the fruit darkens and rots.
The most common supplemental source of calcium is lime, either dolomite or limestone. Crushed egg
shells may also be added to garden soil or the compost pile as a source of calcium.
Sulfur
Magnesium is a component of the chlorophyll molecule. It also plays an essential role in metabolizing
carbohydrates, and in transporting nutrients to different parts of the plant.
Magnesium deficiency often appears as interveinal chlorosis on the leaves - yellow areas between dark
green veins.
Magnesium is present in dolomite lime. Epsom salts (magnesium sulfate) are another commonly used
source of this nutrient.
carbohydrates, and in transporting nutrients to different parts of the plant.
Magnesium deficiency often appears as interveinal chlorosis on the leaves - yellow areas between dark
green veins.
Magnesium is present in dolomite lime. Epsom salts (magnesium sulfate) are another commonly used
source of this nutrient.
Sulfur is essential for the production of amino acids and chlorophyll. It also aids in making efficient use
of nitrogen.
Sulfur deficiency causes stunted growth, delayed maturity, and yellowing. It is sometimes mistaken for
nitrogen deficiency.
Sulfur is present in organic matter and gypsum. Many fertilizers used to provide other nutrients also
contain sulfur, such as ammonium sulfate (used to supply nitrogen) and magnesium sulfate. Of course,
elemental sulfur, often used as a fungicide and a soil acidifying agent, also provides sulfur as a nutrient.
of nitrogen.
Sulfur deficiency causes stunted growth, delayed maturity, and yellowing. It is sometimes mistaken for
nitrogen deficiency.
Sulfur is present in organic matter and gypsum. Many fertilizers used to provide other nutrients also
contain sulfur, such as ammonium sulfate (used to supply nitrogen) and magnesium sulfate. Of course,
elemental sulfur, often used as a fungicide and a soil acidifying agent, also provides sulfur as a nutrient.