SOILS
Agriculture 2
ESSENTIAL NUTRIENTS
Lesson 1
ESSENTIAL ELEMENT CLASSIFICATION
Can be classified as mineral or non-mineral nutrients
Non-Mineral Nutrients: Obtained from the atmosphere and water.
 Carbon (C), Hydrogen (H) and Oxygen (O)
Mineral Nutrients: Classified as Macronutrients or micronutrients.
 Macronutrients: Needed in relatively large amounts.
 Primary Macronutrients: Nitrogen (N), Phosphorous (P) and Potassium (K)
 Secondary Macronutrients: Calcium (Ca), Sulfur (S) and Magnesium (Mg)
 Micronutrients: Needed in small amounts. Although they are only needed in small amounts they are
just as essential to plant health as are macronutrients.
 Boron (B), Chlorine (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni)
and Zinc (Zn)
Plants absorb most of their essential elements from water in the soil.
MASTER 1.5: SOURCES
OF ESSENTIAL
ELEMENTS
THE NITROGEN CYCLE
Although the atmosphere is about 78% Nitrogen (N), plants cannot make use of
Nitrogen Gas (N2).
 Instead, plants need to obtain their nitrogen by taking up cation ammonium (NH4+) or the anion
nitrate (NO3-) in the soil.
 These are generated by the breakdown of organic material in the soil or through nitrogen fixation
 Some crop plants (legumes such as peas, beans, peanuts and soybeans) live with nitrogen-fixing
bacteria that live in their roots and convert Nitrogen Gas (N2) into a form plants can use.
Nitrogen Cycle: Describes the processes by which nitrogen moves between its various
chemical forms. Biological or physical processes can cause these chemical conversions
Four processes are essential to the nitrogen cycle.
FOUR PROCESSES
1. Nitrogen Fixation: Refers to the process by which atmospheric nitrogen (N2) is
converted to nitrogen-containing compounds that are usable by plants. Nitrogen
fixation can be accomplished through the action of lightning or bacteria in the soil.
2. Ammonification: Refers to the process by which bacteria and fungi convert
decomposed nitrogen-containing compounds into ammonium ions (NH4+)
3. Nitrification: Refers to the process by which bacteria convert ammonium ions into
nitrite (NO2-). Other bacteria convert nitrite and nitrate (NO3-). This is important
because nitrites can reach levels that are toxic to plants.
4. Denitrification: Refers to the process by which bacteria convert nitrates back to N2.
SUMMARIZE THE NITROGEN CYCLE
Plants cannot use the nitrogen in the air that is so plentiful.
When plants and animals die and decompose they add nitrogen to the soil.
Bacteria in the soil convert the nitrogen into compounds that plants can use.
Plants take in these nitrogen-containing compounds through their roots and use them
to grow.
Animals eat the plants, use the nitrogen and return it to the soil when they die and
decompose.
TEST YOUR KNOWLEDGE
1. Bacteria are responsible for fixing most of the nitrogen used by plants. Some
nitrogen also is fixed by lighting and industrial processes but these are much smaller
amounts.
2. The symbiotic bacteria in legumes fix additional nitrogen for plants to use, farmers
can be less concerned with replenishing the soil using nitrogen-containing fertilizers.
WHERE DO ESSENTIAL ELEMENTS COME FROM?
Essential elements found in the soil come from:
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Natural ones, such as the erosion of rocks
The action of lightning
The decomposition of plant and animal material
Human-associated activities, such as runoff from fertilizers used by farmers and the public as well as
from waste that humans produce
 Emissions from industry and automobiles
PROPERTIES OF SOILS
Lesson 2
NUTRIENTS FOR LIFE WEBSITE
https://www.nutrientsforlife.org/