There is a basic formula for the amount of fertiliser needed per acre of grass. One important things to remember about a lawn is that dense, healthy grass "provides the best weed control," according to Texas A&M System Aggie Horticulture.
Weakened lawns are susceptible to invasion by opportunistic weeds. Fertilising a lawn plays a part in weed control by giving grass nutrients it needs to grow. Fighting weeds begins with making sure that mowing, fertilising and watering are "done in a manner and time that will favour the grass rather than the weeds," according to Texas A&M.
Many fertiliser formulas contain a combination of nutrients in certain ratios. However, the most important nutrient is nitrogen, according to the University of Illinois Extension. Fertilizer for grass comes in a variety of forms. There are both organic and synthetic fertilisers in liquid or dry (granular) form. In addition, fertilisers are available with the nitrogen in a controlled-release or a fast-release form.
The suggested amount of nitrogen for 1,000 square feet of grass is 0.454kg. Since an acre of lawn is 43,560 square feet, divide that by 1,000, according to the University of Illinois. That equals 43.56, then multiply that by the number of lbs. of fertiliser needed per 1,000 feet, which, in this case is 0.454kg. That means you need 19.8kg. of nitrogen per acre of grass.