Question
I appreciate the quick follow-up!
The PH is 7.8. Will this level prohibit my St.Augustine from taking up/utilizing the nitrogen? I do not remove the clippings when I mow and I have supplemented the grass with a fine compost as well. Additionally, I get virtually no green up when I put liquid Ironite on the grass. Are there certain nutrients that will cause my nitrogen to be leeched from the soil or prohbit the grass from fully utilizing it?

Thanks again,

D. J.
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Followup To

Question -
Rockport/Corpus Christi TX

I think I have a problem with the nitrogen uptake of my grass. I put Ironite and similar products and the result is nil if any change in color from yellow to green. Is there something I can do to help release the nitrogen in my soil? We have mostly sand here and the fertilizer goes right through past the roots very quickly. I have a sprinkler system that is fed by a shallow well so kt gets plenty of water. My neighbor, who could care less about his yard, has no problem with the yellowing. Is it my well or do I need to put something down to help mt grass take up the nitrogen? Also, is there a "bad" nitrogen source?

Thanks.

D. J.

Answer -
Fertilizer nutrients are leached fast in sandy soils. Using a slow release fertilizer or an organic alternative will help eliviate this problem.

The yellowing could also be due to too fast draining soil and the grass not getting enough water because it drains too quickly. This would particularily be a problem in summer.

Improving the soil by core aerating and incorporation of compost at the same time may help.

Nitrogen is taken up continously and by using slow release fertilizer and amending soil (w/compost) so there are more surfaces for the nutrients to attach themselves to (at molecular level) will help.

Finally, I recommend that you have a soil test done to test pH. Make sure it is between 5.5 and 7.5.


Answer
Soil pH of 7.8 is high, but not excessively.
Nutrients can be tied up chemically in the soil if the soil pH is very high. However, I doubt this is your problem.

We are slowly working ourselves through the list of possible problems.


Have you dethatched ? St. Augustine especially will develop a thick layer of matted dead roots, stems and runners between the grass and the roots in the soil. This layer of intermingled dead roots, stems and runners will create a barrier which nutrients can not penetrate and where water will have difficulty reaching the roots.

The lack of fertilizer and water deficiency can result in a yellowing lawn, even if you do fertilize and water regularily. It looks as if the lawn gets enough water and fertilizer, but in reality it never gets to the roots.

The remedy is to dethatch the turf. The dethatcher will rip out this thatch layer.

You can check for thatch by cutting a core of soil approximately 6" deep and look carefully at the section between the green (or in your case yellow) grass blades and the roots. The layer is brownish (may resemble soil) and have a "felt" like quality to it. This is not soil but partially decomposed roots, stems, and runners.

Thatch layers thicker than 1/2" is a concern and can cause the problems you mention.

See pictures of thatch here:

(notice how the thatch layer is a bit lighter in color - usually - and have a different texture than soil. Sometimes thatch can be difficult to see, but carefully examining the core can reveal it. You can not detect thatch in a lawn while looking at it, or walking on it. Only by careful examination of a core can you determine if it is there, and the width).

http://www.oldhouseweb.com/gardening/garden/visuals/thatch01.jpg

http://versicolor.ca/lawns/img/ThatchDPlg.jpg

http://www.nutrite.com/images/FeutreEpais.gif

http://www.urbanext.uiuc.edu/lawntalk/images/pics/15.jpg

Thatch is very common in an aggressively spreading grass like St. Augustine especially if well managed (fertilized, watered, mowed frequently, etc).

Therefore, check for thatch. If present in widths larger than 1/2", rent a dethatching machine and run it over the lawn in several directions. The damage to the lawn may be substantial, but it should recover soon after.

After dethatching, fertilize the lawn and water regularily (infrequently but deeply such as twice per week for 45 minutes on sandy soil. 3 times per week in very hot months).

By the way, your lawn grass (St. Augustine) should be fertilized from late spring through early fall (not late fall as with cool season grass).

-> Test for thatch and let me know what you find.


There is usually no problem with absorbtion of fertilizer nutrients in soil even with pH of 7.8.. at least I don't think this is the problem.

-- Kenneth