Functions of main nutrients in the plants : - 

1. Nitrogen: - 

Due to this nutrient, the plant grows many leaves, the growth is vigorous and fast. More shoots grow and it ensures increase in the yield. The photosynthesis increases. The protein content in the grains as well as leafy and fruit vegetables increases and quality of the agricultural product improves. The fresh, shiny green color of the crop depends on the chlorophyll content in the plant. The amount of chlorophyll depends on the nitrogen supply to the plant. 

2. Phosphorus: -

Phosphorus has significant role in bio-chemical processes in the plant. Due to these nutrients, mainly growth of the roots becomes fast and vigorous, and the capability of the plants to absorb water and other nutrients increases. This stimulates production of carbohydrates, fats, and protein. These nutrients help to increase oil content in the oil seeds and protein contents in cereals, pulses. Due to nitrogen, mainly vegetative growth of the plant is stimulated. Phosphorus increases reproduction activities. So, the crop enters flowering stage early and becomes mature early. 

3. Sulphur: -

This nutrient is very essential for crops for preparing protein, fats, and chlorophyll. In pulses and oilseed crops, the amount of proteins and oils respectively increases due to this nutrient. Sulphur is helpful to produce Sulphur containing amino acids in the plants (e.g. methionine, cysteine, and growth regulators (e.g. thiamine, biotin). Due to this, there is more nitrogen fixation. Absorption is almost as much as phosphate; the quality of agricultural product improves. So, after nitrogen, phosphorus, and potash, now a days Sulphur is mentioned as the fourth main nutrient.