Carbon, hydrogen, and oxygen are the three most abundant elements in plants, comprising 95% of their dry weight. They are key components of organic compounds and provide structure to plants. Carbon and hydrogen are absorbed from air and water, while oxygen is partly taken from air and water. Nitrogen is also important, typically comprising 1-5% of dry weight in plants. Nitrogen can be taken up by plants as nitrate or ammonium ions and is required for photosynthesis, growth, and metabolism. The document discusses the various forms and sources of nitrogen in soil as well as gains and losses of nitrogen in soil systems.

1. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning
Essential Elements: Forms, Occurance,
Functions and Deficiency Symptoms
Krishna Aryal
Asst. Professor (Soil Science)
Krish.aryal2014@gmail.com
1

2. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 2
Forms and functions of carbon, hydrogen, oxygen in plants
• C, H & O are obtained by plants from air & water.
• C & H absorbed in combined form, O partly taken from molecular form.
• These 3 elements for all life form about 95% of the dry weight of plants.

3. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 3
Functions
• They are major constituents of all organic chemical compounds of which
the plant is made & they are concerned with different metabolic reactions vital
for plant growth & development.
• They provide structure & give shape to plants.
• Required for photosynthesis.
• They play key role in providing energy required for growth and metabolism
of the plant.
• The bulk of energy required for the plant metabolism is derived from
oxidative breakdown of carbohydrates, fats, & proteins during cellular
respiration.

4. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 4
Nitrogen
• N is foremost important element which limits crop prod.
• Plants normally contain between 1-5% N by dry weight (1.5% Shoot DM)
• Nitrogen may be taken up by plants as either an anion NO3- (nitrate) or a
cation NH4+ (ammonium)
• Plant preferences for nitrate or ammonium are species-specific & are
usually related to the natural environment of the species, with plants
adapted to bogs, marshes, cold, or acid conditions often preferring
ammonium-N, & most other dryland species preferring nitrate-N.)
• In moist, warm & well-aerated soils, NO3- form is dominant.

5. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 5
N presence in soil
• Surface soil contain 0.02 to 0.25%.; OM contains 5% N.
• NO3-, NO2- & NH4+ forms available for plant nutrition
• Minerals humus complex also accounts for much additional N of soils.
• Appreciable amount of NH4+-N may be fixed in sub soil & rocks

6. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 6
Gains of nitrogen
• Layer silicate clays, rocks and
minerals
• Mineralization of organic matter.
• Fixation
i. Physical N fixation
ii. Chemical N fixation/industrial
fixation
iii. Biological N fixation
a) Symbiotic N fixation
b) Non symbiotic/asymbiotic
N fixation
N Fluxes in soil
Losses of nitrogen
• Leaching
• Volatilization
• NH4
+ fixation by crystal lattice
• Surface runoff
• Denitrification
• Crop removal, microbial removal
• Soil erosion and runoff

7. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 7

8. Institute of Agriculture and Animal Science (IAAS)
Prithu Technical College
Deukhuri, Dang
SSC-121 Assignment Planning 8