The
Use of Recycling Mowers in Grasscycling
M. Ali Harivandi, W. Bill
Hagan, and Clyde L. Elmore
Area
Environmental Horticulture Advisor and Research Associate, respectively;
Cooperative Extension, San Francisco Bay Area. Extension Weed Scientist,
University of California, Davis.
Turfgrass
Culture
Public
interest in recycling (mulching) mowers has increased considerably in the past
few years. Conventional rotary mowers typically are used with a bag attachment
to catch turfgrass clippings. Clippings are often removed, despite the fact
that their removal is time consuming and results in nutrient loss, because they
can be unsightly and are feared to contribute to disease and thatch buildup.
Nevertheless, the passage of AB 939 in California and increased yard waste and
grass clippings dumping fees in many other states have prompted several mowing
equipment manufacturers to renew recycling mower production. These mowers have
an enclosed housing wherein clippings are chopped to fine debris before
discharge beneath the mower. By reducing the size of clippings left behind, a
recycling mower facilitates their disappearance into the turf canopy and their
speedy decomposition, thereby addressing concerns about both appearance and
thatch.
Grasscycling
saves time, labor, and fertilizer. The following study focused on the effect of
recycled clippings on weed invasion, turf quality and thatch accumulation. It
also measured biomass and nitrogen removed using a non‑recycling (bag)
mower.
To
compare the effects of recycling and non‑recycling mowing, a two‑year
study was initiated in May, 1992, at the University of California Bay Area
Research and Extension Center, Santa Clara, CA, on a 2‑ year‑old
turf mixture of Kentucky bluegrass (Poa
pratensis), and perennial ryegrass (Lolium
perenne). Treatments were arranged in a randomized complete block design
with split‑plots and 4 replications. Half of each replication was
overseeded with three "weeds": rough bluegrass (Poa trivialis), in November, 1992; hairy crabgrass (Digitaria sanguinalis), in February and
April, 1993; and dandelion (Taraxacum
offrcinale), in June, 1992. Plots were mowed weekly at 2 inches with either
a recycling or bag mower. The plots were evaluated in May, 1993 and April, 1994
for type, number, and percentage weed cover. Mowers used were Toro 21 inch SF
Recycler, Model No. 20107 and Toro 21 inch SF 4-in-1 Rear Bagger, Model No.
26622. Sample size for clipping measurements was 26.25 ft2 within
each plot. Total clipping weight (fresh and oven dried) removed with the bag
mower was recorded biweekly and doubled for monthly totals. Total nitrogen
removed through the clippings was measured by laboratory analysis. Average
overall turf quality ratings which include density, texture and color, were
trade quarterly using a scale of 1‑9, with 9 being best. Thatch
accumulation was measured yearly from 3 non‑compressed core samples taken
from each plot with a golf green cup
cutter. Ammonium sulfate (21-0-0) was applied quarterly at the rate of 1
lb N/1,000 ft2. Plots were irrigated as needed to prevent stress.
Results
and Discussion
Biomass
(clippings) production for 1992‑94 remained relatively constant from
April to July, increased during August and September and dropped during October
and November. Small quantities of biomass were produced from December through
February. Average biomass produced was 12,995 lbs/acre/year fresh and 4,206
lbs/acre/year oven‑dried (Table 1). Nitrogen removal with the clippings
followed the pattern of biomass production and was highest during high biomass
production. Average total nitrogen removed with the clippings was 139
lbs/acre/year (Table 1). Although a clear benefit of grasscycling is nitrogen
return to the turf stand, not all the nitrogen returned from grasscycling
becomes available to plants. Based on research information from throughout the
country, it appears that turf stands on which grasscycling is practiced require
20‑30% less nitrogen then where clippings are removed. Extrapolating from
this information, a recycling mower should be able to reduce nitrogen
application approximately 25% from levels required when a bag mower is used.
Rough
bluegrass and dandelion took hold when overseeded on the established stand of
Kentucky bluegrass and perennial rye (Table 2). Although hairy crabgrass was
overseeded twice, in February and April of 1993, this weed did not become
established in the plots during the term of this study. Tables 2 and 3
summarize data related to rough bluegrass and dandelion overseeding. Weed presence
increased as the study progressed (Table 2). Turf quality did not differ for
weed overseeded plots (6.6) compared to non overseeded plots (6.9) in 1993.
However, in 1994 turf quality was inferior (5.9) in weed overseeded plots
compared to weed free (7.6) plots (Table 2). Mower type had no effect on weed
establishment in 1993 or 1994 (Table 3). Turf quality was superior (7.5) when a
recycling mower was used in 1993, but this superiority was lost by 1994 (Table
3). This may suggest that the, extra nitrogen from clippings enhanced turf
quality in .993, before weeds were established, but enhanced weed growth once
they took hold.
Effect
of weed overseeding and mower type on overall turf quality and thatch
development is presented in Table 4. Each treatment (weed overseed and mower
type) significantly affected quality (Table 4). Quality was best for all
treatments in 1993 compared to the same treatments in 1994 (6.1), best when no
weed overseeding was compared with an overseeded plot with the same mowing
treatment (6.2), and best for the recycling mower in all treatments (5.9).
Density was better in 1994 (7.0) than in 1993 (6.8) for all treatments. Texture
was not affected by any of the treatments. Turf color was superior where weeds
were not overseeded (6.7) and when a recycling mower was used (6.4) but on
overseeded plots the recycling mower produced better color than the bag mower.
Thatch was thicker in 1994 (0.2 inches) than in 1993 (0.024 inches) for all
treatments and was thicker where a recycling mower was used (0.18 inch) than
were a non‑recycling mower was used (0.004 inch). Even though these
differences in thatch depth were statistically significant (Table 4), their
magnitude was too small to concern a turf manager.
As
anticipated, significant biomass (12,995 lbs/acre/ year) and nitrogen (139
lbs/acre/year) were removed with a non‑recycling (bag) mower. A recycling
mower enhanced turf quality and color; however, texture and density were not
affected by mower type.
It
appears from these studies that the advantages (additional nitrogen, higher
turf quality, and reduction of green waste) of mowing a turf stand of mixed
bluegrass‑ryegrass with a recycling mower far outweigh the few
disadvantages (i.e., slightly higher thatch development). This study did not
indicate a significant interaction between grasscycling and weed invasion.
However, further studies, with more invasive and prolific seed producing weeds
(e.g. annual bluegrass) would be useful.
Acknowledgments:
The authors
wish to thank the following for the generous financial support that made this
study possible: The Toro Company; Northern California Turf and Landscape
Council; and Golf Course Superintendents Association of Northern California.
|
Table
1. Average removed fresh and dry turfgrass clipping weight and nitrogen
content when mowed with a non-recycling mower (1992-1994). |
|||||||||||||
|
Fresh |
Jan |
Feb |
Mar |
Apr |
May |
June |
July |
Aug |
Sept |
Oct |
Nov |
Dec |
Annual |
|
|
Lb/acre |
||||||||||||
|
Clippings |
72.1
|
105.0 |
977.7
|
1288.5 |
1415.8
|
1359.7
|
1130.0 |
1662.5 |
2162.9
|
1477.2 |
1174.5 |
170.9 |
12,995.5 |
|
Oven
Dry Clippings |
36.5
|
48.0 |
308.9
|
424.7 |
455.9
|
479.0
|
445.2
|
571.6 |
643.8
|
420.3 |
307.2 |
62.3 |
4,206.5 |
|
Total
Nitrogen Within Clippings |
0.9
|
1.7 |
9.8
|
13.3 |
13.3
|
13.3
|
13.3
|
17.8 |
25.8
|
16.0 |
11.5 |
1.7 |
138.9 |
|
Table
2. Kentucky bluegrass-perennial ryegrass turf quality and weed invasion when
overseeded with rough bluegrass and dandelion (1992-1994)Z. |
|||
|
|
|||
|
|
Rough
bluegrass |
Dandelion |
Turfx |
|
Treatment |
(°/
cover) |
(number
plants/plot) |
Quality |
|
May
1993 |
|
|
|
|
Weed
Overseed |
5.0
aY |
21.4
a |
6.6
a |
|
No
Overseed |
1.4
b |
2.3
b |
6.9
a |
|
April
1994 |
|
|
|
|
Weed
Overseed |
45.6
a |
31.3
a |
5.9
a |
|
No
Overseed |
4.3
b |
5.06 |
7.6
b |
|
z
Established Kentucky bluegrass-perennial ryegrass plots were overseeded with
rough bluegrass in November 1992, and dandelion in June 1992. |
|||
|
YMean
values followed by similar letters are not statistically significantly
different. |
|||
|
X
Turf quality visual ratings based on a scale of 1-9, with 9 being best. |
|||
|
Table
3. Effects of mower type (recycling and non-recycling) on turfgrass quality
and weed establishment (1992-1994). |
|||
|
Treatment |
Rough
bluegrass |
Dandelion |
Turfy |
|
|
(%
cover) |
(number
plants/plot) |
Quality |
|
May
1993 |
|
|
|
|
Non-recycling
Mower |
3.3
aZ |
15.0
a |
6.0
a |
|
Recycling
Mower |
3.1
a |
8.6
a |
7.5
6 |
|
April
1994 |
|
|
|
|
Non-recycling
Mower |
28.4
a |
21.4
a |
6.6
a |
|
Recycling
Mower |
21.6
a |
14.9
6 |
6.9
6 |
|
zMean
values followed by similar letters are not statistically significantly
different. |
|||
|
yTurf
quality visual ratings based on a scale of 1-9, with 9 being best. |
|||
|
Table
4. Effects of year, weed overseeding and mower type on turf quality and
thatch development. |
|||||
|
Overall
Turf Qualityz |
|||||
|
Treatment |
Turf
Quality |
Density |
Texture |
Color |
Thatch
(inch) |
|
1993 |
6.1
ay |
6.8
a |
6.5
a |
6.3
a |
0.024
a |
|
1994 |
5.5b |
7.06 |
6.5
a |
6.2
a |
0.200b |
|
Weed
Overseed |
5.5
a |
6.9
a |
6.5
a |
5.7
a |
0.136
a |
|
No
Overseed |
6.2
b |
6.9
a |
6.6
a |
6.7
6 |
0.088
a |
|
Non-recycling
Mower |
5.7
a |
6.9
a |
6.6
a |
6.1
a |
0.040
a |
|
Recycling
Mower |
5.9
b |
6.9
a |
6.5
a |
6.4
6 |
0.184
b |
|
Z
Average visual ratings for 1992-94. Ratings are based on a scale of 1-9, with
9 being best quality, most dense, finest texture and darkest color. |
|
|
|
Y
Mean values followed b similar letters are not statistically significantly
different. |
Grasscycling
in California
M. Ali Harivandl, Victor A.
Gibeaultz, and Trevor O'Shaughnessy
Mowing
is the primary cultural practice in sound turfgrass management. It is also the
most stressful of all maintenance activities; even under ideal conditions, 1 /3
of the turfgrass plant's aboveground portion is removed once a week for the
life of the turf stand. Historically, much basic and applied research has
focused on how to mow so that turfgrass will recover quickly and healthy from
this drastic removal of photosynthetically active tissue.
In
the past, the practice of clipping removal from the site after mowing has been
standard. Among the reasons for this practice have been: aesthetically a more
pleasing (manicured) lawn, and minimizing thatch buildup, disease carryover and
weed invasion. Recently, however, turf and landscape professionals, as well as
homeowners in California and many other states face mounting pressure to reduce
the volume of landscape waste sent to municipal landfills.
Each
year Californians generate in excess of 40 million tons of municipal solid
waste. As our population grows and landfills become scarce, the solid waste
problem becomes more critical. Although voluntary waste recycling has been in
place in many California communities for years, waste reduction became
mandatory for California municipalities with the passage of AB 939,
California's Integrated Waste Management Act. This statute mandates that each
city and county in the state reduce the amount of waste it sends to the
landfills by 25% by 1995 and 50% by the year, 2000, with 1990 as the base year.
Concurrent with the passage of AB 939, the newly created California Integrated
Waste Management Board (CIWMB), began implementing a comprehensive set of
guidelines addressing California's solid waste reduction mandates.
It
is estimated that 20% of waste going to landfills is yard (green) waste.
Composting is one successful method of dealing with such waste; other ways to
reduce green waste generation must also be explored and grasscycling, the
contemporary term for the old practice of returning lawn clippings to the lawn
after mowing, could be the most sensible method in many cases. If widely
adopted, grasscycling has the potential to reduce California's current urban
solid waste production by 5‑10%.
Grasscycling
is Environmentally Sound
Grasscycling
can be practical on most stands of grass, the few exceptions being close‑cut
sports fields such as golf putting greens, bowling, tennis and croquet courts,
or where an exceptionally uniform turf is required, such as a major league
sports field or sod farms. Grasscycling is simple, easy and environmentally
sound. Also:
Grasscycling
and Maintenance Activities
Grasscycling
can be practiced on any healthy turfgrass stand as long as proper turf
management guidelines are followed. Many people, both novice and professional,
treat their lawns like a "crop" encouraging (unnecessary) extra
growth by overwatering and over-fertilizing. The "crop" (grass
clippings) is bagged and transported to a landfill. Proper mowing, watering,
and fertilizing moderates turf growth while still producing a healthy, green
lawn.
Mowing
Frequent
mowing is required for successful grasscycling. Turfgrass should be mowed when
dry with a sharp bladed mower. The "1/3 rule" should be followed:
turfgrasses should be mowed often enough so that no more than 1/3 of the length
of the grass blade is cut in any one mowing. When grass is mowed frequently,
short clippings will fall through the canopy and will not cover the lawn
surface. In most cases once-a-week mowing is frequent enough for successful
grasscycling. However, in colder months of the year when turf grows slowly, the
period between mowing can be extended. Turfgrasses mowing height requirements
differ among species. The following
table lists California turfgrasses and their respective proper mowing heights.
|
Grass
Type |
Mower
Setting |
Mow
when grass reaches this height (inches) |
|
Bentgrass |
½-1 |
¾-1
½ |
|
Bermudagrass
(common) |
1
– 1 ½ |
1
½ -2 ¼ |
|
Bermudagrass
(hybrid) |
½
- 1 |
¾
- 1 ½ |
|
Kentucky
Bluegrass |
1
½ - 1 ½ |
2
¼ - 3 ¾ |
|
Kikuyugrass |
1
–1½ |
1
½ - 2 ¼ |
|
Perennial
Ryegrass |
1
½ - 2 ½ |
2
¼ - 3 ¾ |
|
Tall
Fescue |
1
½ - 3 |
2
¼ - 4 ½ |
|
St.
Augustine |
1
– 2 |
1
½ - 3 |
|
Zoysia |
½
- 1 ½ |
¾
- 2 ¼ |
Grasscycling
is possible with any type of mower, although the most effective type of mowers
for grasscycling are known as mulching mowers or recycling mowers. These mowers
cut grass blades into very small pieces and force them into the turf canopy to
mulch the soil. Within the past few years, nearly all lawn mower manufacturers
have introduced new lines of recycling mowers to the market, satisfying any
lawn maintenance needed. Grasscycling is also possible with "bag"
mowers, if the collection bag is removed to allow clippings to drop on the
lawn. If a bag mower does not have a safety flap when the collection bag is
removed, a local dealer may be able to provide a retrofit kit.
Irrigation
Turfgrasses
vary in their need for water. Although,
each site's evapotranspirational (ET) rate determines a given
turfgrass's water needs, most turfgrasses need about 1 inch of water every 5-7
days during the growing season and much less during the colder winter months.
Deep, infrequent watering produces a deep extensive root system which enables
turfgrasses to resist disease and use stresses. Lawns watered too frequently
tend to develop shallow root systems which may make them more susceptible to
disease, and environmental and use stresses. Turfgrass stands which are
irrigated with more water than necessary (over-watering), in addition to being
wasteful, also grows faster and require more frequent mowing for proper
grasscycling.
As
a general rule, lawns should not be mowed when grass blades are wet; i.e.,
shortly after irrigation, or early morning when dew is still present on turf
blades. is difficult to mow effectively
under these conditions.
Fertilization
Proper
fertilization is essential in maintaining a healthy turfgrass stand.
Over-fertilization weakens turfgrass plants by causing excessive and succulent
top growth. Excessive shoot (stems and leaves)
growth requires more frequent mowing for successful grasscycling, and
thus should be avoided. For moderate, even growth, use a combination of fast
acting fertilizers (ammonium nitrate, ammonium sulfate, or urea) and slow
release nitrogen, such as sulfur-coated urea, urea formaldehyde, IBDU, or
organic fertilizers. Avoid applying large quantities of fast acting
fertilizers; these fertilizers produce very fast growth for short periods.
Regardless of grass type and specific fertility needs, generally it is better
for the lawn and for grasscycling, to apply smaller quantities of fertilizer
more frequently rather than larger amounts less frequently. Grasscycling can
reduce the amount of fertilizer needed by 15-25% since grass clippings return
nitrogen to the soil.
Thatch
is composed primarily of roots, stems, rhizomes, crowns and stolons; plant
parts that contain large amounts of lignin (wood) and decompose slowly. Grass clippings, on the other hand, are
largely leaves composed of 80-85% water with only small amounts of lignin, and
they therefore decompose rapidly.
Research projects in different areas of the United States have shown
non or very small additional thatch
development from grasscycling. Although
to date research in California has shown some thatch buildup due to
grasscycling, the benefits received from grasscycling appears to far outweigh
the potential disadvantages of a slightly higher rate of thatch development.
Some
turfgrasses, such as bermudagrass, Kentucky bluegrass and kikuyugrass, are
naturally more thatch-prone than others, and should be regularly detached even
if grasscycling is not employed.
A
small amount of thatch (approximately ½ inch) is actually beneficial to a lawn,
providing insulation to roots and serving as a mulch to prevent excess water
evaporation and soil compaction. It may
also create a cushioning effect for lawn play.
Disease
Management
Most
turfgrass diseases occur in improperly irrigated and fertilized stands or under
poor soil conditions. Much research has been conducted on grasscycling
throughout the country but no relationship, positive or negative, between
grasscycling and the spread of turfgrass disease, has been established. It
appears that if a desirable environment for turfgrass disease exists,
infestation will occur with or without grass clippings.
Weed
Management
Concern
over an increase in weed populations due to grasscycling is common. However,
the limited data available on this issue do not support the popular belief that
grasscycling encourages weed invasion. Although further research is needed to
establish more precise guidelines in this regard, it can be argued that weed
invasion is a problem on lawns regardless of whether grasscycling is practiced:
i.e., weeds are opportunists and will invade any turfgrass stand unable to
out-compete them. Therefore, if a lawn is healthier due to the more desirable
environment created by proper grasscycling, it may overcome weeds, even if
additional weed seeds remain on the lawn.
Conclusions
If
a turfgrass stand is properly irrigated, fertilized and mowed, grasscycling can
actually produce a healthier lawn. It is important to mow a grasscycled lawn
frequently to produce small clippings that will decompose quickly. If a turf
stand is not mowed frequently and clippings are left on the lawn, the result is
a "hay-like" look some consider unsightly.
Fortunately,
most golf courses and parks have successfully practiced grasscycling for years,
providing encouragement for hesitant homeowners and managers of small sites. On
the other hand, grasscycling is not appropriate in every situation. Prolonged
wet weather, mechanical breakdown of mowers, or the necessity of infrequent
mowings are situations where grass clippings should probably be bagged, since
an excessive volume of clippings will be generated.
If
clippings are removed from a lawn, it may not always be necessary to discard
them in landfills. Grass clippings contain large amounts of both nitrogen and
water and are excellent additions to both large-scale, commercial and small,
backyard composting programs. Unless herbicides have been applied recently to a
stand of grass, its clippings can also be used as mulch to provide weed control
and prevent moisture loss around flower beds, trees, and shrubs.
Turfgrasses
1) protect our soils from erosion and our surface waters from sediment
deposition; 2) cool our environment through transpiration; 3) protect our
surface water and ground water by absorbing chemicals in their thatch layer and
root system; 4) increase infiltration of water movement into the soil and out
of the storm system; and 5) enhance property values and recreational surfaces.
Grasscycling is an environmentally sound approach to maintaining this great
resource.