I can point to quite a few lawns that use that fertilizer that would dispute your info. These yards that use the 9-23-30 look a heck of a lot better then the ones getting the 4 step plan. And the fertilizer will burn the grass if the soil is dry and the conditions are very hot. I usually apply it when rain is coming but if it is cool and the soil has good moisture there won't be any burning.......
2-1-2 is too much N unless you like to mow your lawn 2 times a week. Commercial fertilizer programs are high in N because they want to show immediate results and above the ground shows up faster. Meanwhile root development at the levels applied by the Scotts program does not happen like it does when a higher rate of P and K are applied, although it takes a little longer for it to show up in the yard, but your mowing frequency does not increase. It also develops drought tolerance.
Might start at 43 degrees but doesn't really start taking off till the grass gets to 50 and above......
ON the last part we agree.
The bad part of all these recommendations is that you can google lawn fertilizer and you can find links to support any fertilizer program out there no matter how scatter brained the program is. The research based on what I think should be applied is based on being in the agronomy business for 15 yrs and using the information I provide based on what I have done in the past.
20 years of growing grass, a minor in agronomy, and my turfgrass degree from ISU tells me that is WAAAAAY too much phosphorus. Turfgrass has a large root system that can utilize phosphorus in the soil much better than a lot of plants due to its fibrous nature. The phosphorus is also not harvested and removed unless you collect clippings. It is mostly returned to the soil when you mow.The big difference between crops and turf, is when you harvest a crop, you harvest the phosphorus which isn't the case with turf. Putting down that much phosphorus is a waste. It will tie up the Fe, as well as other micronutrients that are essential for plant growth especially in a high pH soil. Fe is the foundation of the chlorophyll molecule and is essential to energy production. Long term tie up of Fe will in turn lead to a weaker plant. While phosphorus is THE component of energy storage, more P does not equal more roots. And yes, Ag grade fertilzers will burn the turf if not watered in. You need to apply just before a rain or water them in and get them off the plant tissue. That is what i said.
If you want to build roots with little growth then use a nitrate fertilzer when soil temps are 43-50 degrees. That is when you build roots. Fertilizing at that time will produced stored energy (roots) without top growth as the turf plant is not producing top growth. KNO3 13.5-0-45 (my favorite but it is very hot) or Calcium nitrate this time of the year are great products. Spring and late fall are when you build roots and produce lateral growth. Then use light N and Fe applications through the summer for color as well as K 990-0-50)applicaions for stress. DAP is a poor reecommendation this time of the year(depending where you live) as ammonium isn't readily available to the turf plant and has to be microbially broken down before the plant can use it. And like I said, the best way to build roots is with nitrogen in early spring and late fall.
I agreee 100% about 4 step programs. They are worthless.
ALL fertility should be done based off a soil test. I recommend a 2-1-2 ratio because N and K are relatively mobile so that type of fertilizer will not create any issues in the soil but will provide for photosynthesis(energy production) and stress. Therefore, it is a safe recommendation without knowing the soil type or its fertillity levels. What you have recommended could have long term negative affects on soil fertility based on what kind of soil it is. Sandy soil will not be affected but a clay soil will see major issues. Heck a 2-1-4 ratio is what I consider ideal but you will rarely find that in a commercial fertilzer. Your growth rate can be manipulated with your fertility rates pretty easily. lb of N early in the spring(soil temps at 43+) and then .25 ll N/month throughout the season for color. Then a lb of N later in the fall. Throw in .5-1lb of K per month throughout the season.
BTW- Phosphorus is not in a lot of commercial grade fertilizers because you don't need it and it has gotten expensive. That is also a big reason you are seeing phosphorus restrictions. Phosphorus is immobile in the soil but if you put it down on the quantities you suggest, it may leach prior attaching to the soil colloid. I am sure we will begin to see phosphorus deficiencies years down the road but most homeowners have over applied for years so initially it won't be an issue.
In the end, unless a homeowner is collecting clippings(harvesting phosphorus), amount of phosphorus fertilzer needed is extremely low. The turf plant is very efficient in its phosphorus use
