So you put the grass clippings in your compost, then you put the compost on your lawn; so in your case the clippings are getting returned to your lawn in the form of compost.

If you were bagging the clippings and not putting them back in the lawn as compost, then you might see a difference.... provided you didn't use supplemental fertilizers.

Mulching grass clippings is essentially composting in place... eventually they decay, feed the soil, just like the compost. Its just a bit less labor, dumping the bag of clippings and spreading the compost is not necessary.

And compost made from a variety of materials probably is better for the lawn, than simple grass clippings alone.

I think you're ignoring a lot of variables. Are both mowers set to mow at the same height? Are the blades of each equally sharp? Are they both turning at the same RPM?

The areas around the fences, near the house, etc may well be getting less water, or losing water to the other plants in the area. Often, in areas near houses, curbs, sidewalks, edging, etc, the soil heats up faster and water is lost to evaporation.

Something that's less likely to be a problem where you are but that can really stress the lawn where I am is the effect of concrete on the pH of the soil. It may be having an effect for you, too. If you're liming the entire lawn periodically, the areas near the house and sidewalks may have a pH that is too high, making it difficult for the grass to use various nutrients (especially iron).

There is also the point that using mulching mowers means that you don't have to deal with bagging and hauling to the compost. So, for us lazy people, that alone is worth it :)

I agree that not all conditions may be equal in the two areas. Can you continue the experiment? Do NOT mulch near the house, but remove the clippings for one season or more, making no other changes to your routine, and then compare results again.

The only real way to know why you are seeing what you are seeing is to have a good, reliable soil test done for each area. Contact your local office of the University of Massachssets USDA Cooperative Extension Service to find out about how to do this.

Here is a link that might be useful: UMASS CES

Chris, I'd love to experiment a little more, but it might be difficult. The thing is, I can't get the tractor in the tight spaces that the push (mulching) mower can get to. So I pretty much have to mulch the trim.

Bpgreen, I don't know the turning RPM of either of the mowers, but I can tell you they ARE set to the same height (I mow the grass fairly high at 3"), and the blades are all reasonably sharp.

I believe there's something going on with nitrogen cycling. I think all of us on this forum would agree that fresh grass clippings are a "green" and dried grass clippings are a "brown," right? (a side question which I know has come up on this forum over the years is what happens to the nitrogen as grass clippings dry out? I'm not sure I've ever seen a complete explanation. Although one would assume that most of the nitrogen available in grass clippings is in the form of proteins, it seems a little dubious to assume that bacteria are digesting these proteins and releasing nitrogen because it happens so fast. Futhermore, grass clippings can dry out in a matter of hours on hot pavement, where the strong ultraviolet light from the sun probably deters most bacterial action. So where does the nitrogen go? Perhaps the plant cells themselves are triggered to convert some of that protein back to volatile ammonia - similar to how corn goes to starch after it's picked or dry beans pack on protein.)

Anyway, for whatever reason, fresh grass clippings are a green and dried grass clippings are a brown. As mulched grass clippings sit on the lawn, the nitrogen is lost to the atmosphere. There is now a net loss of nitrogen to the "ecosystem" of your lawn. Each time you mow your lawn, you lose more nitrogen from the system, eventually necessitating the use of some form of fertilizer to replace it.

In comparison, composting the grass clippings seems to this casual observer to be more conservative with regard to nitrogen. My guess is that bacteria in the compost pile quickly start chowing down on the grass proteins before the clippings dry out and the nitrogen soon ends up as biomass, which is much more stable than ammonia (or for that matter nitrates/nitrites).

Granted, compost is made from lots of different ingredients, so putting finished compost on the lawn gives the grass plants a shot in the arm with lots of different goodies in it. So of course the lawn always responds well to compost. That much is not surprising.

I guess now every time I use the mulcher, I will have visions in my head of all those tiny little severed grass blades sitting on the lawn drying out and losing nitrogen to the atmosphere. (The cruel irony to the story is that my mulching mower is on its last legs. I think the main bearing is broken. I'll be lucky to get a few more cuts out of it. Someone was giving away an old reel mower, so I scarfed that up. It needs a little work, but I've always wanted a reel mower. Hopefully I can get it rehabilitated before the mulcher bites the dust!)

-Diggity

Diggity, You do what I do with two mowers, except I do it the opposite with the clippings. I pick up the grass clippings around the house using the smaller mower; this because, even if I use the mulching blades and stuff, I still get a house full of grass clippings as everybody tracks them indoors. With the mulching blade, they are really short clippings, and with the regular blade, they are longer, but having to sweep and vacuum them up is all pretty much the same.

Then, out on the far horizons of the lawn, I use a riding mower that just shoots the stuff out the side leaving the place looking like a hay meadow after mowing, with lines of heaped up dead grass, but it sounds a lot better if I call it "direct composting".

The kids cavort out there as well, but having a 20' wide band of clipping free grass around the house works as a huge door mat, and the clippings from out there get wiped off feet as they come into the house.

I notice the grass does better closer in where I pick the clippings up. I attribute this to all the coffee grounds I heave out the doors, and the flower beds that are fed compost often and leach out onto the lawn, and the better rain moisture from runoff from the roof, and so on. The grass out where I leave the clippings doesn't look all that great and gets more disease issues.

I am looking into replacing my riding mower, which gave up the ghost a month ago, with one that picks up clippings. And, with that added amount of compostable stuff, I will have plenty to put back.

A major benefit of mulching is that it eliminates a source of garbage that does not need to be in the waste stream, headed for a landfill.

Whether they actually improve your lawn by any serious amount is perhaps marketing, but your observation is not a good experiment designed to test that fact. There are too many uncontrolled factors to consider. For example, perhaps the edge of your lawn gets different amounts of water, fertilizer, or sun. Perhaps the bugs like it more around the edges. Compaction from the tractor might be an issue for your soil type. Maybe the trees/bushes in your flower beds suck extra water from the ground, starving the lawn in that area.

So, I'm sorry, but there are not really any significant conclusions to be drawn from your limited observations about mulching.

John

True, John - 'tis better to use a mulching mower than to throw it on the landfill. No argument here. I always laugh when I see people hauling grass clippings (and for that matter leaves) out to the curb. These are the same people who complain that their gardens don't grow well.

So yes, before passing judgment on mulching mowers, it pays to consider what you're comparing them against. I think, though, that the absolute best solution is to bag the clippings, compost them with with other stuff, then return the finished compost to the lawn. Anyway, that's my story and I'm stickin' to it. ;-)

-Diggity

You wrote:
"...What do you folks think? Am I on to something, or have I been sniffing too much fresh grass? ;-)..."

Perhaps you are not smelling enough fresh grass...:-)

If you bag your grass then dump it in a pile. Then come back several hours later...the pile will be warm, perhaps even hot.

The odor of freshly cut grass will be changing to an pungent ammonia based smell. I only got a B in HS chemistry...but I'd bet there is some N being worked on in that grass pile. Anhydrous ammonia is the #1 farm nitrogen fertilizer in this part of the country.

I think you could make a case for some nitrogen being returned to your lawn through mulching.

I mulch my grass most of the time, with the exception of once a month adding some bagged grass to my compost pile to heat things up. It seems like every time I add grass to the pile...my nose tells me to add more shredded paper to the mix to sweeten the smell.

My Craftsman mower mulches the cut grass into fine bits and I endeavor cut the lawn only when it is dry...so tracking in cut grass into the house is rare.

And lastly, Iowa out-lawed lawn waste in landfills in 1989 so the only legal way to handle cut grass here ... is to recycle it.

I don't believe that green grass clippings are a green and brown grass clippings are a brown. As you say, where does the nitrogen go? Not to mention, hay is brown grass clippings, and cows can live on it. One might as well say that coffee grounds and bread are browns, too, because they're brown :-).

If you pile up some fresh green grass clippings and come back a short time later you will notice an ammonia like odor from that pile, and that is Nitrogen escaping to the atmosphere. That is where the Nitrogen in grass clippings go if they are not properly handled.
If you recycle your grass clippings in place, mulch mow, you will be providing that soil with 1/2 the nutrient requirements of the turf, over the year and if nothing else is added, if those clippings are not supplemented with other nutrients, as indicated by a good, reliable soil test, the grass growing in the area can still fail to grow strong and healthy because it is not getting enough nutrients to keep it healthy.
Hay is a kind of grass that is a high protein diet. Simply because some hay looks to be brown in color does not mean it is a "brown", properly cured hay should be a light green color unless it is exposed to sunlight which can bleach the color out.

Right - the ammonia smell demonstrates that nitrogen is lost to the atmosphere. Thus, each time you cut your grass, you are removing nitrogen from the ecosystem of your lawn. This is why lawns require a periodic boost of fertilizer (or compost or coffee grounds or urine or whatever), to replace that which is lost.

So does it make sense to mulch it and leave it in place, knowing that most of the N will be gone in 24 hours, or to put it in the compost pile where at least some of it will eventually become finished compost?

Kim, I'm curious - where does the 1/2 figure come from? Is that a guesstimate or has someone actually studied this in depth and provided that number?

I hope you all realize I'm not trying to ruffle any feathers here. I was being a bit facetious in referring to the lovable mulcing mower as "bunk." If you have a mulcher and love it, then that's great. I have a genuine interest in nutrient cycling in the environment, so the question is not a trivial or pedantic one to me. (and admittedly, I don't mind taking a pot shot at the corporate marketers once in a while. If they're over-hyping a product, they've got it coming). I also realize that not everyone is going to ditch their mulcher and start a compost pile (except perhaps for those of us who have one already). It's more a question of in a perfect world, what is the highest and best use of grass clippings? I submit that from a nitrogen mass-balance perspective, it's better to compost them and return the finished compost to the lawn than it is to mulch them.

Thanks for all your replies.

-Diggity

I've never noticed an ammonia smell coming from a freshly mown, mulch-mowed lawn :-).

The big issue, from a grass clipping point of view re nitrogen retention, is to dry out quickly with no bacterial decompositon, meaning the nitrogen is still holding hands, so to speak, with all those other carbon molecules and sundry trace elements that form plant protein. These bits of dried grass then work their way down towards the roots and soil, where in due course they get snarfed by detritus eating things like worms. If they, the grass clippings, stay sodden, they rot, releasing the ammonia. This is why they mow hay when the weather is forecast to stay dry. This is also why, in all those old corny movies, the young fiancee grabs ahold of the farmer-tanned heroic figure and gushes about the sweet smell of freshly mown hay, no ammonia reek there. OTOH, should she get a whiff of ammonia, her Ma comes up on the buggy and tells her to hop in, with some line about "He's not your kind".

Here, where the riding mower is not a mulching mower and leaves long clippings, its dry enough that they won't rot. It takes, usually, 2x over the dry stuff to turn it to powder so it works its way down to the happy worms.

I have noticed an ammonia smell when I cut the grass... but I had three dogs at the time and I don't think the smell was coming from the grass. ;-)

I know what you mean, Alfie - a freshly cut lawn doesn't smell like ammonia per se. But what exactly is that fresh cut grass smell that we all know and love?

What compounds are responsible for that smell, and are they high in nitrogen?

What exactly happens to a blade of grass after it is cut, as it turns from green to brown?

I've searched the web trying to find a clue, but so far have come up with diddly squat. If anybody knows, I'd sure appreciate it if you'd enlighten me, because the deeper we get into this thread, the more and more curious I become. :-)

Thanks!
-Diggity

What an interesting thread! Our lawn has been a great source of compost and mulch for everything other than the lawn (we bag it) and even if you get that nasty ammonia smell, plants grow like the jolly green giant! It certainly amends the soil well too, we have clay. Great discussion.

That 1/2 the needed nutrients has come from Michigan State, Ohio State, Iowa State, Cornell, Purdue, University of Wisconsin, Guelph University, Rutgers, and many other of the Cooperative Extension Service publications.
If you mulch mow your grass clippings into your turf and smell the ammonia after that you are waiting much too long to mow and cutting too much off your grass. The only time you would smell that ammonia odor is if the freshly cut clippings were piled up.

Did any of those publications explain what happens to the other half?

I've never smelled ammonia after cutting the grass, either with the mulcher or regular mower. So if the missing nitrogen is escaping into the atmosphere, it must be doing so in the form of some other compound besides ammonia. Either that, or it *IS* escaping as ammonia and the human nose just isn't sensitive enough to smell it at low concentrations. I have no idea what the human threshold of detection is for ammonia.

Thanks,
-Diggity

Just one teeny problem with your 'theory'. You have not run a controlled experiment and you have not accounted for the fact that the conditions under which the grass is growing vary tremendously between that which is mowed one way and that which is mowed a different way.

In other words you have 2 possibly unrelated variables in each test plot that have not been accounted for.

You have: Wide open space lawn
Up against obstructions lawn
lawn mowed with garden tractor
lawn mowed with mulching mower

And those are just the obvious ones. There's also varying soil conditions, irrigation, sun, pest populations, traffic patterns, fertilizer applications, soil compaction from house construction ...

You have at least 4 variables. But your 'theory' only accounts for 2 of them.

Right up front let me say that I have over 20 years experience managing lawns under a variety of conditions and mowing regimes. I can say with a high degree of certainty that there are a number of things that are associated with each of your 4 variables that affect lawn growth. House foundations and fence post footings, for instance, are made of concrete, which affects lawn growth negatively. Flower border edges affect lawn growth too, either positively or negatively, depending on what you do to your flower border. And garden tractors are much heavier than a push mower and so in my experience they compact the soil and reduce lawn growth, especially where you make turns.

Here's my experience with mulching mowers. I operated a garden maintenance business for some years with a conventional push mower before switching to a mulching mower. The difference in lawn health was dramatic. All my customers noticed the positive change within weeks of the switch. Lawns greened up, even with reduced irrigation and fertilizing, and grew more evenly over the course of the season rather than running rampant and then collapsing. And it's way less labor than bagging and dumping and composting and sifting and spreading the clippings. Just puree them and drop them right back on the lawn in one step! And in all these years of using mulching mowers I have never had enough volatilization of the nitrogen to smell the ammonia. You get that when you pile up the clippings so they rot. I had a few clients who wanted the clippings bagged so they could mulch their trees with the clippings - that's where I smelled ammonia, never from the mulched lawn itself.

If your push mower is leaving severed grass blades on the surface of the lawn, then you are not using a mulching mower, or you're cutting off too much at a time, or the mulching system is not working properly. Reel mowers are not mulching mowers. You need a special blade, and baffles on the shroud, for it to be a mulching mower, and if the blade is too dull or the baffles are matted with grass then it won't mulch properly. A properly functioning mulching mower, used properly, will not leave visible residue on the lawn. The 'clippings' are pureed and dropped onto the soil surface, where they release their water content and nitrogen (grass blades are ~90% water). I've never had a problem with volatilization from a mulched lawn.

You need to do a better job controlling your variables before you can say you've got a theory! all you've got right now is a field observation that has not been sufficiently investigated to even qualify as a hypothesis.

My plant pathology proff in college was a big time composting nut. His rule of thumb was, if it was green when it was cut from the plant, then it's still a green even after it dries. Therefore grass clippings, even dried, are greens for composting. Similarly leaves from pruning are greens, even after drying, but leaves that fall off in autumn are browns.

You don't have to like mulching mowers, but you can't say you have proof they don't work.

Geez, some people... No need to get peevish, Reg. Did you read what I'm trying to say or just skim the thread and start flaming?

If you'd really like to mince words, then I must concede, you are correct. This explanation of the difference between a theory and a hypothesis courtesy of m-w.com: HYPOTHESIS implies insufficient evidence to provide more than a tentative explanation . THEORY implies a greater range of evidence and greater likelihood of truth .

My original post was somewhere on the intersection of an observation, a hypothesis and a question.

Whatever...

Anyway, I'm well aware of the factors you mention that affect lawn growth. I too have been around the block for quite a while and have observed lawn growth and various other aspects of agriculture and botany under many different conditions. These factors, however, do not account for what I observe right outside my own back door. I'm also well aware that a reel mower is not a mulching mower. I don't believe I ever said that it is.

If you swear that switching to a mulching mower improved the condition of your customers lawns, then great. Thank you for that data point. Color me genuinely curious about this whole mulching mower thing. I'm more interested, however, in what you did with the clippings BEFORE you switched to the mulching mower? Did you compost them? If so, what did you do with the compost? Did you spread it back on your customers' lawns?

-Diggity

Man, I cannot imagine bagging clippings, composting them, and trundling a wheelbarrow around spreading compost one shovelful at a time over the whole lawn.

Whew. I'm getting tired just thinking about it.

I have no controls, just this datapoint: I mulch mow, plus I feed with cottonseed meal or CGM twice per year, and I mulch in as many leaves as the lawn can take in the fall. I do fling UCG one basket at a time (2+ per day) in the area around my back door (haven't seen marked improvement from this). I spot treat weeds and crab grass all summer.

My lawn has improved quite a bit in the five or so years I've been doing this, markedly more than in the previous five years, during which I aerated, Scott'sd, and removed autumn leaves. My lawn is much thicker and healthier with way less crabgrass now.

So I like my mulching mower. Probably mostly because I am lazy.

diggity- is there also a difference in the quality of the lawn where either of your lawn mowers occasionally puke out clumps of grass clippings? Certainly it can be hypothesized that those areas are getting an increased intake of nitrogen, vs the rest of your lawn where the mower is functioning properly. I think you'd need also to study the full range of even the potential variables that come with your two mowers...

Check the manual on the time of day that is best for mowing, because if you mow right after it rains, it is more likely that you will get these puked clumps, thus throwing yet another variable even into THAT variable.

Oh, and does your mower come with a cup-holder? Because there would also be the factor of how much beer beverage is spilled onto the lawn, and where it spills, thus skewing any results of your soil analysis if you did not keep accurate records on what actually makes up your better or worse spots.

And who's walking on this lawn? Are the 'small mower' spaces subject to foot traffic, and how big are their feet, how much do they weigh...is the soil being compacted proportionately in all spots, or do your kids use a different path?

I dunno...this might very well involve YEARS of study before you have any accurate data to even propose a theory.

Another factor to consider: is the compost you put on the lawn ONLY made from those grass clippings removed from the lawn? Or was there other stuff in the compost? You really can't compare grass that was fed just recycled grass with grass that was fed recycled everything.

The mulched area was recycling only what it originally had in it - with a cycle like that, you lose a little nutrients each time around and the only input would be from whatever clover or other nitrogen fixers would be there. The area with compost was getting not only what was available from the grass, but also from your kitchen scraps and whatever else was in there. You're constantly adding to the system.

You're right, it probably would take years to get to the bottom of it. There really are a lot of factors that go into how a lawn grows. And the amount of beer the lawn receives can be estimated by the number of swerves in the pattern of the cut. The more beer I spill, the straighter I drive!

Kidding, kidding! :-)

Demeter, no, the clippings are definitely NOT the only thing that goes into the compost, and that fact would certainly make any kind of mass balance computation quite a bit more difficult.

Here's the thing - I have quite a bit of trim work, and it's varied... some of it is along a fence, some is along a stone wall, some is along plastic edging, some is around the kids swingset and the picnic table, some is around trees, some is just adjacent to the weeds and bushes at the edge of the property. It's all different terrain, but I would think that after 4 years of following the same paths week after week with the mulching trim mower, that a pattern would start to emerge. It has not.

Here's the other thing (and then I'll be quiet!): What exactly happens to grass clippings as they turn from a green to a brown? It was suggested by one poster above that nothing happens to them; they were a green when they were cut and are still a green even after they dry out. This is contrary to every other compost resource I've seen, which always list fresh grass clippings as a green and dried clippings as a brown. It's also contrary to my own experience, which is that fresh clippings heat up a pile very quickly (presumably because of the high N content), whereas dried clippings do not produce the same effect. If indeed they do lose N as they dry, how is that N lost? Through bacterial action? Off-gassing of ammonia? Off-gassing of some other volatile N containing chemicals (possibly whatever chemicals are responsible for that "fresh cut grass smell?)?

-Diggity

Hmmm..."off gassing"..."fresh cut grass smell"...
Interesting observation...most gaseous emissions (especially if you're still drinking that beer) are considerably less 'fresh' smelling...

My understanding of the green vs brown of clippings is that they may lose a small amount of nitrogen as they dry due to off gassing, but they're still a green (perhaps not as strong a green as before). My understanding is that the green vs brown is a function of whether it was living or dead when it was cut (so leaves that fall from a tree are brown, but leaves on a branch that comes down in a windstorm are green, even after they dry).

I think the reason the fresh clippings heat the pile faster is that they also have a fair amount of water, so they begin composting almost immediately.

I don't think I've seen references that list dried clippings as a brown. I did a little searching just now and all references to grass clippings that I found treated them as a green, including a couple of sites that recommended drying them before using them (to prevent clumping).

Do you have any links that list dried clippings as a brown? I'm not doubting that you've seen that. I just haven't had any luck finding anything that lists dried clippings as a brown.

If you have a 15 year old son who "helps" you mow the lawn, sometimes you can find fairly advanced compost right there in the grass catching bag, still on the mower, in the garage. There is a distinct whiffyness.

But why, I asked myself rhetorically, is grass any different than hay, vis a vis nitrogen retention? What about alfalfa? Do that too lose nitrogen when cut? What about nitrogen loss when you pellet the stuff? So gently peruse the linked article, which concludes that chopping up alfalfa makes it easier to dry and gives a better product. Enjoyable reading, and it helps if you know, before hand, that 810% really is 8 to 10%.

There is no other half. What those recycled grass clippings (mulched) provide is enough nutrients for 1/2 what your turf grass needs to grow strong and healthy each year. It would be like you eating 1,000 calories per day when you needed to consume 2,000 calories to stay healthy. You need to get the rest of what your turf grass needs from some other place, compost, fertilizer, a good quality organic lawn food, but some outside source.

We haven't put compost on the lawn, or indeed done anything else to it except mulch mow, weed whack, and pull up dandelions, for seven years now, and the lawn does not look like it's suffering from malnutrition. It's not a golf course, of course -- for one thing, we have clover -- but it looks perfectly healthy, unless there's a drought.

Interesting article, David - thanks! I was actually thinking about possible differences between grass and hay too. One thing that sticks in my mind is that even after it is dried and pelletized, alfalfa is still green. I wonder if ordinary lawn grass would still be green after the same processes? I don't know for sure, but I kinda doubt it.

Of course the color "green" does not necessarily equal "green" in the context of a compost ingredient. Or does it? Chlorophyll does contain some nitrogen atoms (chlorophyll a is C55H72O5N4Mg). So maybe the question should be - what happens to chlorophyll after the grass is cut?

bpgreen, I posted below one link that describes fresh clippings as a green and dried as a brown. I'm sure I could find more, as I know I've heard this numerous times before. In fact, I *think* some people may have even proffered the same rule of thumb right here on this very forum.

-Diggity

I think I'm still a bit confused. While I accept that dead leaves are a brown, at what point did the C ratio become higher than the N? That's the part that confuses me...where did the high content of C come from to make it a brown v. the green that it was initially?

My issue is: If a dried "green" leaf is still a green, then the loss of N as it dries is not significant enough to cause the C/N ratio to become opposite. So what difference does it make if it dries ON the tree or OFF? Is there another process going on that causes the leaves to become carbon-infused?

I think you're on to something here, mmqchdygg, because every 3rd grade botany class tells us that in the fall, a tree takes sugar and stores it underground it the roots. C12H22O11 is table sugar, not tree sugar, but still, not a whole lot of nitrogen there, and when I research on the trusty internet, I find that even Maple syrup, which is concentrated tree sugar, doesn't have any measurable amount of protein, at least the Canadian stuff.

So it must be the nitrogen in the chlorophyll, C55H72O5N4Mg, that makes a green leaf a "green" although is sure isn't much, compared to, say, alfalfa.

So looking around a bit, there a lot of learned people who worry about the chlorophyll break down, and get doctorates in the subject. Phyto-Organic chemists study the role of diminishing sunlight, plain old Organic Chemists study plain old organic leaf chemistry, Sociologists study the role of the breakdown of the family tree, and so on.

You know what I think? I think that the mulching you do has improved the general health of the entire soil. Its not like microorganisms know the boundry between the mulcher mover and the other stuff. The health in "this" area of the lawn extends to "that" area of the lawn.

As they say on the TV show boards, Thats my fanwank on the subject

Mmqchdygg, I have the same question you do. Where did the N go?

David's article offers a clue:

"RCCR is a novel ferredoxin-dependent reductase that shows some sequence homology to ferredoxin-dependent bilin reductases."

Kidding, kidding! I'm being cheeky again - I have absolutely no idea what that means. :-)

But seriously, it's an interesting article, and it does list some of the chlorophyll catabolites. You can see if you look at the molecular structure of those compounds that there is indeed nitrogen present. Are these catabolites (or at least the one that is the final product) gasses? If so, we've just figured out where the nitrogen goes.

-Diggity

Diggity--Thanks for the link. I'm still not sure it means what you're interpreting it to mean. They list "dried brown grass clippings" as a brown. English is sometimes somewhat imprecise, and this is an example. Dried brown grass clippings can have two meanings. Clippings of dried brown grass, or grass clippings that are dried and brown. I think they mean the former.

The questions of where the N goes when the greens dry out and why alfalfa that has been dried is still a green but grass when dried out is a brown both assume that removing the water from the grass clippings somehow removes the nitrogen. I don't think that is the case. Everything I've read on the subject says that if it dries out on the plant, it's a brown, but if it's green when it is on the plant and dries out afterward, it's still a green.

What happens to the N when you dry grass? Nothing. Where does it go? Nowhere.

Actually, bpgreen, that's not what I mean. I DON'T think that removing the water from the clippings somehow removes the nitrogen. Water is water, nitrogen is nitrogen, and whatever organic molecules may or may not be escaping are whatever they are too.

The clippings may be drying out at the same time they are losing nitrogen, but the two processes are not necessarily connected. I just wish we knew what (if anything) is escaping to the atmosphere and is it a nitrogen-containing compound?

Do we have any botanists or organic chemists lurking on this thread? If so, please chime in and put this thing to bed for us!

-Diggity

"I just wish we knew what (if anything) is escaping to the atmosphere and is it a nitrogen-containing compound?"

Water is escaping to the atmosphere. It's not a nitrogen containing compound. Perhaps a small amount of nitrogen is escaping, but not much.

I just realized that I have an example from personal experience that can demonstrate this.

Last year, in preparation for overseeding, I mowed the lawn really short. I don't have a bagger, so I just left the grass on the lawn. The next day, after the clippings were dried out, I raked them up. I piled some directly on the garden and bagged some up until I had room in the compost bin (didn't happen until spring). At that point, I dumped a bag of grass clippings followed by some water, followed by a bag of leaves, then some water, then some mixing. Repeated the proce3ss until the bin was almost completely full. Within a couple of days, it was over 140 degrees F and reached 152 at one point.

I forgot all about this until just a few minutes ago. Since there were only two ingredients (leaves and grass clippings), and since leaves are high carbon, the N for the hot composting process had to be coming from the dried grass clippings. Drying them removed the water and kept them from rotting and stinking in the bags, adding water and leaves started the composting process.

Would it be heretical to suggest that a green leaf really isn't a green, but a masquerading brown? Or that there are green leaves, and then there are really green leaves?

To further complicate things, in my previous life I once upon a time studied (way too much, in retrospect) the use of chicken manure as potential animal feed, the point being that the modern chicken diet, combined with a modern chicken sitting in either a cage or a deep litter system, is going to poop out a high protein poop, which can be recombined with a high calorie source and fed to other animals, who then, theoretically, will use this protein. The trick here is to dry it quickly or the protein decomposes, and off goes the nitrogen, volatile ammonia-wise. Rapidly drying the manure meant the nitrogen stayed around longer.

Most of the dried chicken manure produced is used as a rumen nitrogen source, and protein quality isn't that much of an issue. However we did find that protein un-efficient chicken feed formulation led to a significant amount of viable protein in the manure, but had to be consumed by the secondary animal within a very short period of time or it decomposed.

Green Brown issue.
To some extent in many composting related situations the exact meanings of these two words can be a bit confusing.
Also the exact ratios of each needed for composting doesn't need to be that exact. If some one is calling dried grass clippings a brown, it is probably because they will help cover other compost items that may be wet and smelly. In which case they should probably be calling the ingredients wet and dry instead of green and brown.

Your lawn needs about 2 pounds of Nitrogen per 1,000 square feet each year for optimal growth. The grass clippings could provide about 1 pound of Nitrogen per 1,000 square feet if they are mulch mowed back into the turf, ie. 1/2 the needed nutrients.
Trees do not just store "sugars" in the fall. Once the tree leafs out in the spring soil nutrients flow from the roots to the leaves where, through photosynthesis, these nutrients are converted into other necessary nutrients that are sent back to the roots for storage for next years growth, as well as todays. So while that 3rd grade botany class description is not totally wrong it is greatly simplified. Nitrogen does not disappear but it is used by plants to manufacture other nutrients and is converted to other materails. Nitrogen is, along with many other nutrients, part of the cell walls that make up the plant, or the person or animal.