A fertilizer is any natural or synthetic substance added to soil to supply essential nutrients that promote plant growth. Fertilizers compensate for nutrient deficiencies in soil and are critical for modern agriculture to sustain crop yields.
Plants require 16 essential elements for healthy growth, classified as:
Category Nutrients Primary Macronutrients Nitrogen (N), Phosphorus (P), Potassium (K) Secondary Nutrients Calcium (Ca), Magnesium (Mg), Sulfur (S) Micronutrients Fe, Mn, Zn, Cu, B, Mo, Cl
The three primary macronutrients are collectively referred to as NPK nutrients and form the basis of most commercial fertilizers.
These supply nitrogen (N) , which is essential for:
Synthesis of proteins , nucleic acids , and chlorophyll
Promoting rapid vegetative growth and green foliage
Deficiency causes chlorosis (yellowing of leaves) and stunted growth
a) Urea [ N H 2 C O N H 2 ]
Most widely used nitrogenous fertilizer
Contains ~46% nitrogen — the highest of any solid nitrogenous fertilizer
Industrial synthesis:
2 N H 3 + C O 2 high P, T N H 2 C O O N H 4 dehydration N H 2 C O N H 2 + H 2 O
Step 1: Liquid ammonia reacts with C O 2 ammonium carbamate ( N H 2 C O O N H 4 )
Step 2: Ammonium carbamate is dehydrated to yield urea
b) Ammonium Sulfate [( N H 4 ) 2 S O 4 ]
Contains ~21% nitrogen
Physiologically acidic — suitable for alkaline soils as it helps lower soil pHWhen plants absorb N H 4 + S O 4 2 −
c) Ammonium Nitrate [ N H 4 N O 3 ]
Contains ~34% nitrogen
Provides both ammonium and nitrate forms of nitrogen
Fast-acting but hygroscopic (absorbs moisture)
d) Calcium Ammonium Nitrate (CAN)
A mixture of ammonium nitrate and calcium carbonate
Less acidifying than pure ammonium nitrate
Phosphorus (P) is essential for:
Root development and energy transfer (ATP synthesis)Flowering, fruiting, and seed formation
Deficiency causes purple discoloration of leaves and poor root growth
a) Single Super Phosphate (SSP)
Prepared by reacting phosphate rock [ C a 3 ( P O 4 ) 2 ] concentrated sulfuric acid :
C a 3 ( P O 4 ) 2 + 2 H 2 S O 4 → C a ( H 2 P O 4 ) 2 + 2 C a S O 4
Contains ~16–20% P 2 O 5
Also supplies calcium and sulfur as secondary nutrients
b) Triple Super Phosphate (TSP)
Prepared by reacting phosphate rock with phosphoric acid ( H 3 P O 4 ) C a 3 ( P O 4 ) 2 + 4 H 3 P O 4 → 3 C a ( H 2 P O 4 ) 2
Main constituent: Calcium dihydrogen phosphate [ C a ( H 2 P O 4 ) 2 ]
Contains ~44–48% P 2 O 5
Does not contain sulfate (unlike SSP)
c) Diammonium Phosphate (DAP) [( N H 4 ) 2 H P O 4 ]
A complete fertilizer supplying both N and P
Contains ~18% N and ~46% P 2 O 5
Most widely used phosphatic fertilizer globally
Prepared by reacting ammonia with phosphoric acid:
2 N H 3 + H 3 P O 4 → ( N H 4 ) 2 H P O 4
Potassium (K) is essential for:
Enzyme activation and regulation of stomatal openingWater regulation within plant cells (osmoregulation)Improving disease resistance and overall plant vigor
Deficiency causes scorching of leaf edges (leaf scorch)
a) Potassium Chloride (Muriate of Potash, MOP) [ K C l ]
Most common potassium fertilizer
Contains ~60% K 2 O
b) Potassium Sulfate (Sulfate of Potash, SOP) [ K 2 S O 4 ]
Preferred for chloride-sensitive crops
Also supplies sulfur
c) Potassium Nitrate [ K N O 3 ]
Supplies both K and N
Used in fertigation (fertilizer + irrigation)
Effect Description Soil acidification Ammonium-based fertilizers lower soil pH over time Nutrient leaching Excess nitrates leach into groundwater causing pollution Eutrophication Runoff of N and P into water bodies causes algal blooms Soil salinity Excessive fertilizer use increases soil salt concentration Organic matter depletion Over-reliance on synthetic fertilizers reduces soil microbial activity
Fertilizer Type Key Nutrient % Nutrient Urea Nitrogenous N ~46% N Ammonium Sulfate Nitrogenous N ~21% N SSP Phosphatic P ~16–20% P 2 O 5 TSP Phosphatic P ~44–48% P 2 O 5 DAP N + P N, P 18% N, 46% P 2 O 5 KCl (MOP) Potassic K ~60% K 2 O