The nitrogen doesn't leach; it gets consume by bacteria on the grass. When cut grass is left out to weather in the rain, the nitrogen is consumed by the bacteria leaving most of the brown cellulose behind. So then it would be considered a "brown."

When grass clippings are piled up and emit that ammonia smell that is Nitrogen escaping to the atmosphere. Grass clippings put into a compost pile and covered with adequate amounts of carbonaceous material will "trap" that Nitrogen and the bacteria will use it to digest that carbon.

Depending on how the grass clippings have been dried could affect the amount of Nitrogen they have so the brown color may not really reflect the C:N ratio of those clippings. Just as Alfalfa hay that has been sitting around awhile may turn brown and that does not indicate a loss of protein that can be as true of aged grass clippings..

If, while the clippings were laying about and emitted a strong ammonia odor they most likely do have a high C:N ratio and are now carbons rather than nitrogen's.

Keep in mind that some "browns", manure, feather meal, blood meal, are high Nitrogen sources, while most all greens are also.

kimmq is kimmsr

Someone posted awhile back that fresh grass clippings dried in the sun have been tested and there is something like 15-25% loss of N in that process. So they become weaker greens.

If we're talking about old dead grass like the 'thatch' you can rake out of the lawn, it might be a little different, but I don't know.

Thatch in a lawn and grass clippings are not the same things. Perhaps this from Penn State might be of some help. http://plantscience.psu.edu/research/centers/turf/extension/factsheets/thatch

kimmq is kimmsr

I thought that thatch is a buildup of grass clippings which has not yet decomposed; but will in time.

It can have shallow roots and dead grass plants in it, not just clippings. My point was that if it has been sitting there for quite some time, its N level might be even lower than clippings cut a few days ago and dried in the sun.

For gumby, from the article linked above.

" Thatch is a loose, intermingled organic layer of dead and living shoots, stems, and roots that develops between the zone of green vegetation and the soil surface. Thatch build up begins when turf produces organic debris faster than it can be broken down. Those parts of grass plants that are the most resistant to decay — stem nodes, crowns, fibers of vascular tissues, and roots — make up the bulk of thatch. Although you'll find some leaf clippings in the thatch layer, they usually don't contribute to thatch build up because soil microorganisms easily break them down. "

kimmq is kimmsr

Thanks everyone.

*Believe It or NOT* - Cutting grass (no doubt) does accelerate lawn thatch buildup.

5. - *Horticulture. a tightly bound layer of
dead grass, including leaves, stems, and roots, that builds up on the
soil surface at the base of the living grass of a lawn. *

http://dictionary.reference.com/browse/thatch