Benefits of using lawn fertilizers containing slow release nitrogen

Slow release fertilizers can help to reduce mowing frequency and improve lawn quality.

It can be confusing to sort out what kind of fertilizer to choose for a lawn; there are so many choices available. The nutrients needed in the largest quantities by turfgrass are nitrogen (N), phosphorus (P) and potassium (K). Michigan State University Extension recommends to start by taking a soil test to determine the nutrient s needed by your lawn. The P and K requirements can vary considerably due to soil type and texture. Nitrogen is not routinely tested because it is very mobile in the soil. Instead, N needs for turfgrass are estimated based on the lawn use and maintenance level. Low maintenance lawns need 1-2 pounds of N per year, medium maintenance lawns need 3 pounds of N per year, and high maintenance lawns such as golf courses or athletic fields with sprinkler irrigation need 4-6 pounds of N per year. Regardless, no more than 1 pound of N per 1,000 square feet of lawn should be applied at one time.

A bag of a complete fertilizer contains N, P and K – listed in that order – as percentages by weight of the total bag contents (guaranteed analysis). For example, a 50-pound bag of 10-10-10 fertilizer is 10 percent N, 10 percent P and 10 percent K. Those percentages equate to 5 pounds actual N, 5 pounds actual P, and 5 pounds actual K. The remaining 35 pounds are carriers and fillers – additives to make the product easier to spread and apply evenly. In January 2012, a Michigan law restricting phosphorus use on turfgrass was enacted. For home lawns, fertilizer containing phosphorus may only be applied:

  1. For new sodded or seeded lawns.
  2. When a soil test indicates that phosphorus is needed.
  3. When it is part of an organic manure, compost or sewage sludge product (i.e., Milorganite).

A soil test will tell you whether or not phosphorus is needed for your lawn.

As mentioned, nitrogen is mobile in the soil. It can also be volatile. Although fertilizers with slow-release nitrogen are more expensive than quick-release synthetic fertilizers, the benefits include low risk of burning the turf; more even, sustained grass growth (less mowing); and less leaching into ground and surface water. IBDU, methylene urea, sulfur-coated urea and polymer-coated urea are all forms of slowly soluble nitrogen. IBDU has low water solubility and is not affected by the activity of soil microbes, making it ideal for use on cool-season turfgrass. Sulfur-coated urea breaks down as water enters pores in the sulfur coating, causing the urea to slowly dissolve. Polymer-coated fertilizers release nitrogen as the plastic coating slowly dissolves. Urea-form fertilizers depend on long chain polymers to slow the release of nitrogen. You are more likely to find these types of slow-release fertilizers in products listed for professional use than in typical home lawn fertilizers.

Methylene urea and natural organic products such as activated sewage sludge (Milorganite) and processed turkey manure (Sustane) are dependent on soil temperature and biological activity for conversion to usable forms of nitrogen. Other organic products include composts, seed meals and poultry and other manures. These products release nitrogen slowly to very slowly. They tend to have a low guaranteed analysis (Milorganite is 6-2-0, Sustane is 4-6-4) and are expensive per unit of nitrogen. However, they do offer low burn and leaching potential. The natural organic products such as Milorganite and Sustane are readily available. They do contain phosphorus, which your lawn may not need; check your soil test results to determine whether or not these are appropriate choices.

Look for turf fertilizers that have at least a portion, 25 percent or more, of their nitrogen in the form of slow release N. Your lawn will benefit from lower risk of fertilizer burn, and the growth will be more even. The environment will benefit from lower risk of fertilizer moving into ground and surface water, and you will benefit from having a beautiful lawn that needs to be mowed and fertilized less often.

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