LANSING, Mich. – On Jan. 1, 2012, phosphorus fertilizer applications to turfgrass in Michigan were regulated according to Act 451 of 1994, Part 85 Fertilizers. Basically, the amendments to the Fertilizer Act restricted phosphorus fertilizer applications to turfgrass unless a soil test indicated need or for new establishment. However, there were provisions that phosphorus fertilizer could be applied at 0.25 pounds phosphorus per 1,000 sq. ft. if the source was a "finished sewage sludge, organic manure or a manipulated manure." This provision resulted in many questions and some confusion about which natural fertilizers fell within this category.

On Nov. 5, 2013, Governor Snyder signed Public Act 151, reports Kevin Frank, Michigan State University Extension. This Act made revisions to Act 451 and in particular to phosphorus applications to turfgrass. The key addition was that the term "natural fertilizer" was introduced into the language. According to MSU Extension, natural fertilizer is defined as a substance composed only of natural organic, natural inorganic or both types of fertilizer materials and natural fillers.

Public Act 151 has immediate effect, meaning today a person may apply biosolids, a natural fertilizer, or manipulated manure to turf at a rate of not more than 0.25 pounds phosphorus per 1,000 square feet per application. The addition of the term natural fertilizer certainly expands the number of fertilizers containing phosphorus fertilizer that can be applied.

The key for the turf manager is to understand that the rate restriction of 0.25 lbs. phosphorus per 1,000 sq. ft. per application is still in effect for these fertilizers, so correct product calculations, calibration and application is critical to ensure applications don’t exceed the 0.25 pounds phosphorus per rate.