a. Chemical fertilizer/Inorganic fertilizer: Inorganic fertilizer may be defined as the synthetic material which are manufactured in factories and added to the soil in order to provide one or more of the essential plant nutrients.

e.g. Urea, triple super phosphate, muriate of potash etc.

b. Organic fertilizer/Organic manure: Manure may be defined as the organic material of plant and animal origin under varying stages of decomposition which are added to the soil in order to increase the soil organic matter status, improve the soil health as well as to increase the nutrient status of the soil.

e.g. Compost, farmyard manure (FYM), green manure (GM) etc. Improvement of soil health includes improvement of physical, chemical and biological properties/characteristics of soil.

c. Biofertilizer/Microbial fertilizer/Microbial inoculant/ Inoculum: `Bio’ means life or living. Fertilizers involving microorganism are known as biofertilizers or, fertilizers that are made of microorganism are known as biofertilizers. Biofertilizers may be defined as the preparations containing live or latent cells of different strains of N2-fixing, P-solubilizing and cellulytic microorganisms used for application to soil, seed and composting areas in order to increase such microorganisms or to increase the availability of nutrients in a suitable form to be taken up by plants.

e.g. Rhizobium biofertilizer, Azotobacter biofertilizer, blue green algae (BGA), Azolla etc.

a. Solid fertilizer:Urea, TSP, MP, FYM, Compost etc.

b. Liquid fertilizer:Liquid ammonia, animal urine, sewage, nutrient solution etc.

c. Gaseous fertilizer: NH₃, CO₂ etc.

a. Quickly/readily soluble: Solubilize very quickly in soil solution and nutrients become available within a few (maximum 7 days) days after application.

e.g. urea, oil cakes etc. Because of high solubilization these fertilizers persists for very short duration in soil after application.

b. Slowly soluble:Solubilize very slowly in soil solution and nutrients become and remain available to the plants for a long time after application.

e.g. urea super granule (USG), sulphur coated urea (SCU) etc. Because of low solubilization these fertilizers persists for a long duration in soil after application. So, they are also known as controlled release fertilizer.

a. Acidic fertilizer:Increases soil acidity (lowers soil pH) after application.

e.g. urea (equivalent acidity 80), ammonium nitrate (equivalent acidity 93), ammonium sulphate (equivalent acidity 110), ammonium chloride (equivalent acidity 124) etc.

b. Basic fertilizer:Increases soil alkalinity (increases soil pH) after application. e.g. sodium nitrate (equivalent basicity 29 ), calcium nitrate (equivalent basicity 21) etc.