Re: How does fertilizer help plant growth?

Hallo Melissa,
Using nutrients are very much like adding a little extra food to the 
plants.  Plants need a number of things to grow. They need water from the 
soil, energy from the sun, carbon dioxide from the air and they need 
nutrients.  Very often one or more of these resources are limiting so that 
the plant can not grow as big as it would otherwise. Often the most 
limiting resources are water or nutrients. This can be helped by irrigation 
in the case of water or by fertilisers in cases were nutrients are deficit. 
Nutrients are building blocks in the plant. For example nitrogen, which is 
most abundant in the plant except for carbon, is an important element in 
proteins, as is sulphur. Magnesium is needed in the chlorophyll so that the 
plants can gain energy from sunlight. These elements can be given to the 
plants by fertilising the soil. Nitrogen, phosphorous and potassium are 
generally given in the largest amounts. Sulphur, magnesium, copper, zinc 
and so on are given much sparse and are called micronutrients. Carbon is 
not a nutrient in the same way, as the roots do not take it up. It is 
assimilated in needed quantities from the air as carbon dioxide.