I'm just going to give you the basics on fertilization.
This is a big money maker and not hard work at all. In the beginning I would suggest sticking to granule fertilizers instead of liquid.
To find out what works best for your area, again I suggest talking to your local wholesale supplier. They can tell you what works and what other lawn care companies are buying. Some suppliers even have special mixes they will suggest to you for your area, the types of grass you are working on and the time of year.
Fertilizers contain nutrients that plants and grass need to grow.
A typical fertilizer contains:
N (nitrogen)
P (phosphorus)
K (potassium), in that order. (See below)
Below are the three numbers in a fertilizer analysis. A 5-10-15 fertilizer, for example, contains 5% nitrogen, 10% phosphorus, and 15%
Nitrogen: The first number that you see on a bag of fertilizer, it's primarily responsible for plant growth and color.
Nitrogen what makes the grass greener, so to speak. Adding nitrogen to plants has the most visible effect on plants. Too little of it causes yellowish leaves and weak roots. Too much nitrogen can make a plant over-succulent, turgid, and soft because of thinner cell walls. This makes it susceptible to cold, drought, disease, and pests. Plants lose nitrogen to competition by weeds, use by microorganisms, leaching, and volatilizing. Nitrogen comes in organic, synthetic, and "synthetic organic" formulas. It's the cheapest plant nutrient and buying combined fertilizers by the amount of nitrogen in them permits tailoring soil enrichment to specific plant needs. It also means a better price for the customer and a better profit for you.
Be sure and get slow release nitrogen.
Phosphorus
(P)-the middle number on the bag and an important part of DNA, RNA, and some enzymes-assists the plant's energy system and respiration, and plants can store it for later use. It shows up naturally in some soil minerals, and inorganic and organic compounds.
Potassium
(K)-the last number on the bag and the third major plant nutrient- It doesn't
become part of the plant but regulates the plant's life processes. Potassium is
a catalyst for water intake, transpiration, and enzyme actions. Plants need it
to form and transfer starches, sugars, and oils. Potassium increases plant vigor
and disease resistance. Most soils contain potassium but it is usually
unavailable and is best added before planting and regularly after that. Adding
too much potassium, however, can cause a magnesium deficiency, especially in
sandy soils.
Below
is an example of a couple types of fertilizer and how you may use them.
15-0-15
This is a General-purpose landscape fertilizer for shrubs, small trees, lawns, flowers, and groundcovers. Select one with 7.5% slow-release nitrogen.
15-5-15
This would be for new plantings, where the available, phosphorus may help establishment. Also for short-term plantings such as flowering annuals or for when a soil test indicates a need for phosphorus. Select one with 7.5% slow-release nitrogen.
*Keep in mind, too much Nitrogen will burn up a lawn. Even in granule form.