Two important values measured by a soil analysis are “soil pH” and the “available plant nutrients.” Soil pH is a measured value which represents the level of acidity or alkalinity of a soil. Different types of plants have various pH ranges at which plant nutrients are available. The soil analysis identifies pH problems and provides recommendations for correcting them as well as recommendations on types and amounts of fertilizer to apply to optimize plant growth.
Recommendations (Table 3) for lawns are provided in pounds per 1000 square feet. Before calculating the recommended amount of fertilizer, measure the lawn’s total area. If your lawn is 50 ft. x 100 ft. then the total area equals 50 ft. x 100 ft. = 5000 sq. ft.
If the recommendation is to apply 2 lb. of N per 1000 sq. ft., then you will need a total of 10 lb. of N to obtain coverage of your 5000 sq. ft. lawn 2 lb. x 5000 sq. ft. /1000 sq. ft. = 10 lb. total
Now the question is where to obtain 10 lb. of N. At the local garden center you find a 60 lb. bag of 34-0-0 "lawn fertilizer.” The sequence of the three numbers separated by hyphens is the guaranteed analysis and is always given in the specific order of percent nitrogen, percent phosphate, (P205) and percent potash (k20) in the bag.
(% Nutrient / 100) x total lbs. of fertilizer = lbs. of nutrient in the bag (34% N/100) x 60 lbs. = 20.4 lbs. of N in the bag.
You’ve already determined that you need 10 lbs of N to fertilize your 5000 sq. ft. lawn and the 60 lb. bag contains 20.4 lbs. of N. You will need 29 lbs. of fertilizer, or about half of the 60 lb. bag (60 lb. bag / 20.4 lbs. N per bag) x 10 lbs. N = 29.4 lbs fertilizer.
If you want to apply fertilizers at a rate of 2 lbs. per 1000 sq. ft. and you have a 60 lb. bag of fertilizer with a grade of 34-0-0, then 60 lb. x 34/2 lb. x 1000 sq. ft. = 10200 sq. ft. total coverage. Remember: