According the University of Illinois Extension, the amount of nitrogen a lawn needs is the most important part to watch when fertilizing. Too much or too little nitrogen can cause serious damage to a lawn. In general, lawns need about 1 pound of nitrogen for every 1,000 square feet of space.
Remember, though, though most fertilizer is not pure nitrogen. For example, Scotts Lawn Prop Super Turf Builder fertilizer is designated as 30-2-3 fertilizer, meaning that it has 30 parts nitrogen for two parts phosphorous for three parts potassium. Figuring out the nitrogen content requires basic math. Divide 100 (the percent of nitrogen you want) by the nitrogen number on the package (in this case, 30). The answer, three and one-third, is the number of pounds of the product you need for every 1,000 square feet of land you have.
A half acre of land measures 21,780 square feet. Divide that by the 1,000 square feet you used to calculate your fertilizer needs, and you get 21.78. Multiple the 3 1/3 pounds of fertilizer you need for every 1,000 square feet by that number to determine that you need to apply 65.34 pounds of Scotts Lawn Pro Super Turf Builder fertilizer to your half acre of land. If the designation of nitrogen changes, so will this calculation, so read your chosen type of fertilizer carefully.
Depending on the type of Scotts you choose, application methods may change. Scotts can be applied to either wet or dry lawns, but the lawn should always be watered immediately following fertilization, so the fertilizer immediately sinks into the soil. Some Scotts products (including the one mentioned above) can be applied during any time of year, while others are designed specifically for spring, summer or fall application. Scotts granular fertilizer generally distributes through a seed spreader, though the company does produce some liquid products.