Looking for clarifications. You say most lawns are high in P and K based on farmers bringing in their soil...black coal top soil. That may be true for them, however, I am not so sure that is true in new developements over the last 20 years. Most developers grade and sell the good black top soil and only leave clay, then lay sod on top of the clay which does make having a nice yard more difficult in the hot months. I have even been putting on gypsum to try and break down the clay and to chemically arerate.
Are you saying that clay is high in P and K as well as top soil?
I was referring bringing in soil tests of their lawns. For the most part most established lawns don't need any P and K if you leave the clippings on the lawn. Most established lawns from acerages and older parts of towns will never need P and K.
Most clay I've been around from developments is very poor stuff and the P and K levels are all over the place. Fertility levels with clay are the least of the concerns as the soil structure of it is so poor that it is the main limiting factor. Clay can be very high in K due to all the exchange sites in the soil, but it is all about how much of that the plant can access. Clay can also be very high in P but the pH can be so high that the P is tied up as well.
I would send in some samples of different spots of the lawn to see what your fertility levels are as well as your pH and CEC. My guess is that your lawn will be a very high pH and CEC (i.e. a very tight soil that is not good for new plant growth).
IMO your best bet right now is a combination of anything you can physically do to improve soil structure as well as the use of amendments like gypsum. We have been seeing some great response in using humic acid products on clay soils in grass crops (corn, wheat, and oats) so that may be another option for you too. Another product that helps lawns in clay environments is Ammonium Sulfate, it gives N and sulfur plus it is acidic so it can give you a temporary response in fertility availability.
Either way good luck with your lawn, I don't envy anyone who has to deal with new development lawns.
I know I am bumping a 2 month old thread. A few weeks ago I had about 7 tons of black dirt hauled in to make the lady a few raised garden beds. Then about 4 days ago a weed started to grow, after reading this thread and a couple classes at ISU I knew what the weed was. I dug below the soil and this is what was hidden.
The tip of the pencil is the part that sends the plant above ground.
Good thing to kill yellow nutsedge as soon as possible, it does take over.
I cannot kill that nutsedge. Weed b gone does nothing. I picked it all, spent 2 hrs one day doing it. It all just came back... looks horrible. Got a different bottle of some weed killer, but it says you cannot use it until daytime temps are below 90, so I guess I finally can try it.
Last edited by brianhos; 08-29-2010 at 01:55 PM.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety. - Benjamin Franklin 1775
I agree on the fertilizer. The best mix of fertilizer I have found is half potash (0-0-60) and have DAP (18-46-0) which gives you a 9-23-30. Set that a little lower then you would apply the Scott's(or pick your brand) and do that a couple times a year and you'll be golden. Go to a Coop and ask for that mix. A heck of a lot cheaper and a heck of a lot better product.
First number is the Nitrogen which affects the growth of the grass on top of the ground. I want a nice looking lawn but don't want to mow all the damn time.
The second two numbers are the phosphorous and potassium. They affect the growth of grass below the soil. They stimulate root growth and develop drought tolerance in your grass this time of year. They give the grass a good greenish blue color but don't send the grass into a growing frenzy.
I know the phosphorous is limited in lawn fertilizers to minimize runoff, but if you don't overapply the stuff, you don't have to worry about runoff.
You absolutely do not need that much P for turf. P is immobile once in the soil and is generally returned with clippings (unless you harvest). You would be better off going with MAP but you probably wouldn't need to apply P for five years.. If you apply two aps per year then you just applied enough P to last you for about 5 years. Too much P will end up tying up a lot of micronutrients in the soil and will lead to issues down the road. If it isn't tied up in the soil then it washes away and the soil can only handle so much P.
The primary reason P is limited in lawn fert because you just don't need to apply as much as you do N or K because P is immobile in the soil whereas N and K leach much easier. The turf plant has a very fibrous root system so once it is mature it can pull that P from the soil.
Yes, states have been banning P from lawn fertilizer to reduce runoff but that is not the primary reason. they ban it because it is over applied and that is why it leaches.
Heck, you would be better off getting som13-0-43 PNO3 (potassium nitrate) or using 21-0-0 and 0-0-50.
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