Well-aged cow manure is one of the best organic fertilizers you can apply to lawn turf. It is high in nitrogen and many other trace nutrients but releases its benefits slowly over time so burn and stress on the grass are not an issue. Lay down aged cow manure as a top dressing over recently mowed grass. Use bagged commercial aged manure or buy from a reputable bulk dealer. Manure can be used to top dress grass once or twice a year, with the first application in the early spring and the second in the early fall. Watering the manure well when applying will kick-start the fertilizing process.
Buy enough aged manure to cover the square footage of your lawn with a depth of at least 1/2 inch to 1 1/2 inches of manure. Lawns with less even surfaces can take the higher end of the range, while younger lawns or more level lawn surfaces will be fine with the lower end.
Spread the aged manure over the entire surface of the recently mowed lawn with a shovel or drop spreader. Lay down as even a layer as possible to minimize the amount of raking and walking over the surface you will have to do later. Start at the perimeter and work your way over the surface in slightly overlapping rows to ensure even coverage.
Water deeply the applied manure to settle it into the thatch and to begin to release its nutrients into the soil. Use a hose with an adjustable spray nozzle to lay the water on without disturbing or displacing the manure. Do a second light watering a few days later to further settle the manure, and resume your regular weekly watering regimen thereafter.