How much nitrogen can be applied at one time?
This is in reference to test #E555LF. My lawn area is roughly 5,000 sq ft. Since the soil test I have applied a fertilizer 26-0-3 (13.35 lb). I'm also wanting to apply another one only a few weeks later that is 26-0-2 (16.68 lb). I'm having a hard time figuring out how much nitrogen I can put down without burning it. The rest of the plan is as follows. At the end of the month another one that is 28-0-6 (13.88 lb), 8 weeks later one that is 32-0-4 (12.5 lb), and 8 weeks after than one that is 32-0-12 (12.5 lb). Please advise, thank you.
Oakland County Michigan
The maximum amount of actual nitrogen (that means 100% pure; none exist) that you can apply at one time is one pound. It depends on the percentage of nitrogen. As an example, you could apply 2 lb. of 46-0-0 or 5 lb. of 21-0-0.
Your fertilizer bags will have application recommendations on them. Follow their directions. You want to separate your applications by about six weeks. Nitrogen is a double-edged sword; it provides green top growth but over-application can easily kill thee plants. It is a soluble salt and has the ability to attract water in the soil much more successfully the roots can. Basically the grass desiccates from lack of water. Moral of that story: do not over apply.
The time not to fertilize is July and the first two weeks of August. This is when we usually have the highest temperatures and the least amount of natural rainfall. The high temperatures cause the grass to go semi-dormant and fertilizer does not need to be applied to partially conscious grass. It will do nothing. Your irrigation system keeps the grass alive but cannot make it grow because of your cool season grasses and hot weather.
Most people begin fertilizing in mid May and discontinue in early October. If fertilizer is applied too early in the year, the grass is not growing because of the cold soil temperatures. If you are fertilizing too late in the year, the grass could be growing lushly, get covered with snow and the lawn ends up with snow mold in the early spring. It's not fatal, just annoying.
Mow to a finished cut height o 3 to 3 1/2 inches.
With this little list of guidelines, check your application times and amounts.
But also consider that you could chose one nitrogen/potassium fertilizer instead of several but supplement with 0-0-60 which is a potassium fertilizer only.