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When leaves turn into litter

Discussion in 'Organic Lawn Care' started by Gerry Miller, Nov 18, 2007.

  1. Gerry Miller

    Gerry Miller LawnSite Senior Member
    Messages: 504

    Turfgrass deciduous leaf-litter experiments

    Beginning in 1990, three studies have been conducted at Michigan State University's Hancock Turfgrass Research Center to examine the feasibility of mulching tree leaves into existing turfgrass canopies. The first study examined different deciduous leaf rates (50 and 100 pounds of dry leaves per 1,000 sq. ft.) and the timing of nitrogen fertility applications. The objectives were to determine if there were any negative effects of mulching tree leaves into the existing canopy with a lawn mower and if the nitrogen fertility would enhance leaf-litter decomposition. The study ended in 1996, concluding that there were no negative effects of mulching the leaves into the turf at the rates applied and that the nitrogen treatments did not aid in the degradation of the leaf litter.

    The second study was initiated in October 1991 to examine the effects of mulching different leaf types (oak and maple) at the rate of 100 pounds of dry leaves per 1,000 sq. ft. into Midnight Kentucky bluegrass turf using a rotary push mower. The study was concluded in the fall of 1998. Objectives were to determine if different leaf types would have an effect on soil pH or turfgrass quality. Turfgrass quality increased on plots that had maple leave treatments due to the fact that less broadleaf weed growth was observed in those plots. No differences were observed regarding soil pH for the duration of the field experiment. Soil cores taken in the fall of 1998 concluded that there was an increase in the amount of organic matter in plots that had oak and maple leaves mulched into them compared to the check plot. Tissue analyses of clippings collected in October of 1998 also revealed that grass plants grown in plots having leaves mulched into them also had greater percentages of carbon and nitrogen. However, the carbon nitrogen (C/N) ratio was not affected.

    These studies led to the conclusion that there were more benefits than negatives for turf managers and homeowners who mulch tree leaves into existing sites. The question then became, "Could there be an expanded roll for turfgrass in the leaf-litter collection process?" As previously cited, decreasing landfill space led many states to dispose of leaf litter in farm fields. Truckloads of leaves were taken to farms and tilled into the soil. However, it was found that this activity had the potential to increase the C/N ratio above 30/1, which immobilizes the nitrogen (makes it unavailable to the plant). It was also determined that, while within EPA standards, some loading of heavy metals was taking place due to the collection process of leaf litter. On several occasions, leaf samples that were analyzed revealed high concentrations of lead as a result of urban soil that contained high levels of the heavy metal. To minimize this, it is suggested that municipalities strive to eliminate picking up urban soil during the collection process to cut down on the lead contamination of the leaf-litter. However, since many municipalities direct homeowners to rake the leaves to the curbside, where they are picked — up with a vacuum, it stands to reason that debris and petroleum products that rest in the gutter are also sucked-up with the leaves.

    With these facts in mind, the third leaf-mulching study was initiated in October of 1995. The objective was to determine if low-maintenance turfgrass sites could take heavy loads of deciduous leaves and maintain their usefulness. The study consisted of mulching a mix of deciduous leaves into an existing sunny mixed-turf area (Kentucky bluegrass, perennial rye, and fine fescue). Excessive leaf rates of 150, 300 and 450 pounds per 1,000 sq. ft. (approximately 6-, 12- and 18-inch layers) were mulched in with the aid of a mulching mower. Two mower deck heights (1.5 and 3 inches) were included in the study to determine if deck height had a significant impact on the degradation of the leaf litter. The area was mowed at 2.5 inches for the remainder of the year. Furthermore, because the plots represented low-input turfgrass areas, they never received fertilization for the three years in which the experiment ran.

    Mulching at such excessive rates resulted in visible leaf liter still being present in the spring. As anticipated, as the rate of leaves mulched increased, the percentage of visible leaf litter increased. However, at the higher mower-deck leaf-mulching height of 3 inches, there was reduced visibility of leaf litter the following spring. This is most apparent at the dry leaf rate of 300 pounds per 1,000 sq. ft. It is noteworthy that all visible leaf litter soon dissipated as the grass growth increased in the spring, and these plots also tended to green-up quicker.

    Because the plots represented turfgrass areas of low input, it follows that the areas receiving leaf litter for mulching would be home lawns, municipal parks, low-maintenance ball fields and golf course roughs. This means that the areas would potentially be utilized for numerous outdoor activities that would result in persons coming into contact with the turf. With that in mind, plots were tested for surface hardness in 1998. Results indicated that all three rates of leaf mulching provided a softer surface the following summer providing a cushion that would be more forgiving for persons engaging in physical activity in the area.

    As previously mentioned, the C/N ratio was a potential problem when applying leaf litter to agricultural fields. Samples were obtained from the turfgrass plots to analyze the C/N ratio in September of 1999. No differences were anticipated regarding the C/N ratio because no apparent color differences were recorded on the plots, which would indicate that the plots required nitrogen fertilization in comparison with the check plots. Results of the sampling indicated that, as the amount of leaf-litter increased, the percentage of carbon and nitrogen increased in the soil thatch layer. However, the increases were such that the C/N ratio did not significantly increase and was maintained well below the 30/1 ratio.

    Mulching is fine, for now

    While the practice of disposing of deciduous leaf-litter to agricultural land has merit, it is not feasible to dispose of all leaves in this manner. Rotary mowers cut leaves into small pieces, allowing them to fall into and beneath the turfgrass canopy instead of resting upon it. This process results in increased surface area, which in turn makes it easier for insects and microbes to consume.

    Undoubtedly, the use of blowers for placement and rotary mowers for mulchers is adequate. Research clearly indicates that the practice of mulching leaf litter into existing turfgrass canopies provides benefits for the soil and the turfgrass plant. Also, turfgrass can take up to three times the legal load limit that agricultural fields can have applied. However, it is apparent that technology could improve (or devolve, in this case) to give the turfgrass manager a specialized machine for this annual chore.

    It is also time that municipalities (and possibly homeowners) follow the lead of golf course superintendents and ground managers by mulching leaf litter into existing turfgrass sites with rotary-mowers. With a little education, literally millions of dollars could be saved annually in the United States.

    Thomas A. Nikolai is the turfgrass academic specialist at Michigan State University (East Lansing, Mich.).

    For the entire article:

  2. ICT Bill

    ICT Bill LawnSite Platinum Member
    Messages: 4,115

    I guess what we need to remember is that this cycle of leaves falling and being consumed by the plant and soil biology has been going on for 100's of millions of years before we figured out how to make fertilizer.
    When managed properly this cycle can be enhanced and provide 75 to 90% of the nutrient needs to the turf.
    The beatiful part is that these types of inputs do not leech and stay in the soil for a long time providing nutrients for years.

    Nice find Gerry
  3. cantoo

    cantoo LawnSite Silver Member
    Messages: 2,910

    I've been saying for years that I was going to build an efficient leaf shreader. Start with my Walker with GHS remove the bin and install a 10 hp chipper in it's place behind the seat. The Walker would shoot the leaves into the chipper that would grind them up real small and spread them back on the lawn. We get leaves 12" deep so it would be pretty thick in spots but using a backpack blower you could spread them around to the thin areas.
  4. Daner

    Daner LawnSite Bronze Member
    Messages: 1,307

    I always try to leave the leaves on the lawn and use the mulching ZTRs To chop them up...sometimes running over them 4 times...as long as there not too deep.

    Its better to leave them right on the lawn, Instead of bagging and then composting....Its all part of a Organic Lawn Care Program.
  5. PHS

    PHS LawnSite Senior Member
    Messages: 724


    Thanks for the info. I've never lived in an area where I would get the amount of leaf litter described on those articles but I've been mulching up leaves like that on lawns for years and have never seen any problems. Sometimes I've had customers question me about my blowing the leaves onto the lawn and then mowing but I always just told them it added organic matter to the soil which is a good thing and I've never seen a prob but if it starts to cause a problem I'll stop. It never did so I never stopped. Now I have some scientific evidence to back it up :).
  6. Marcos

    Marcos LawnSite Gold Member
    Messages: 3,720

    Nice info Gerry.

    I believe leaves are put here on Earth 1st for enjoying, 2nd for the kid's leaf collections, and when we get tired of them they're made to be mulched!

    ....but what I'm really looking toward is the day when it becomes 'mainstream' in this country for large and small landowners AND green industry professionals to take all of their clean biosolids to private /municipal composting 'stations' instead of dumping in landfills, on their property, or otherwise dumping illegally.

    I know there are fledgling operations like this happening now, but certainly not enough to gather the momentum of the idea yet nationally.

    My gut guess is that once the technology improves to the degree that the amount of energy created per ton of waste is increased, the recycling of green industry biosolids will become more competitive. At some point (maybe even with an Uncle Sam subsidy or two to start), I see Joe the mower and Sam the blower getting paid a nominal sum for dumping their clean loads.
  7. fred333

    fred333 LawnSite Member
    Messages: 17

    Those are some crazy amounts. I know we have some properties that give us some headaches when the fall comes around, but nothing like that.

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