FARMLAND AND URBAN
Turfgrass Producers International
1855-A Hicks Road, Rolling Meadows, Illinois
TPI would like to acknowledge Dr. R.W. Sheard, Professor, University of Guelph, Guelph, Ontario and Dr. C. Richard Skogley, Professor of Agronomy, The University of Rhode Island, Kingston, Rhode Island for their original scientific research in this subject area and for their technical review of this document prior to its formal release.
Additional acknowledgement should be made and thank you given for the technical review and editing completed on this document by Dr. Eliot C. Roberts, Executive Director, The Lawn Institute, Pleasant Hill, Tennessee. This paper was compiled and edited by Douglas H. Fender, CAE, Executive Director of the Turfgrass Producers International, Rolling Meadows, Illinois.
FARMLAND AND URBAN SOIL CONSERVATION
CULTIVATED TURFGRASS SOD
The effects that commercial turfgrass sod production may have on farmland are often questioned by land owners, land-use regulators, environmentalists, consumers and others. Specifically, concern is expressed for how long sod can be harvested from a given field before all of the topsoil is exhausted. Some people have considered entry into the turfgrass sod business in the hope they could receive special tax advantages by claiming depletion of soil as a natural resource.
Casual examination of a piece of harvested sod shows the upper surface to be composed of a closely-knit leafy top, while the lower portion appears to be composed of farmland soil. Although the thickness of the leafy portion and the root segment may vary considerably, most often there is a 1 to 2 inch leafy portion, attached, to a root layer that would measure 1/4 to 1/2 inch.
Does Harvested Sod Deplete Soil Resources?
The immediate impression is that while it takes many centuries for topsoil to develop, removal of soil with each harvest of sod will quickly diminish or destroy the productivity of the land. Land owners may choose not to lease their land to turfgrass sod producers. Land-use regulators may want to define sod production as a form of strip mining. Environmentalists may decry the waste of a precious natural resource. Consumers may simply raise the question from a point of curiosity.
The facts do not substantiate these concerns. Many soil scientists, and even the United States Internal Revenue Service have carefully examined this question and have unanimously agreed that commercial turfgrass sod production will not deplete top soil. Cultivated turfgrass sod production has been shown to have a positive influence as it regenerates soil in its production process and prevents erosion in the urban construction environment.
There are many positive findings that show turfgrass sod production actually improves farmland by adding organic material and nutrients, and that it opens the soil to accept greater amounts of moisture, while it reduces water and wind erosion of the soil. Open row crops such as corn and cotton, using even the best conservation techniques; have been shown to lose greater amounts of topsoil through erosion soil than sod production.
To better comprehend the manner in which turfgrass sod production contributes to the quality and even quantity of the soil, the grass plant's physiology and the processes used in sod production should be examined, especially in comparison to other potential crop alternatives and their relative soil loss potential.
Grass Plant Characteristics
Whether initiated from seed, sprigs or stolons, turfgrass plants exhibit almost identical growth characteristics and patterns. "Grass roots are continually developing, dying off, decomposing and redeveloping. Every individual plant of Kentucky bluegrass produces about three feet of leaf growth under favorable growing conditions each year. The average lawn produces clippings at the rate of 233 pounds per 1,000 square feet a year. By leaving clippings on the lawn and allowing them to decay in place, the equivalent of three applications of lawn fertilizer is made. This process builds up humus, keeps soils microbiologically active and over time, improves soils physically and chemically. Microorganisms in the soil feed on grass roots. Worldwide grassland soils are best in terms of productivity. Grass improves the soil by stimulating biological life in it and by creating a more favorable soil structure for plant growth [1. Hamm 1964] (2-A).
"Turfgrass roots penetrate into the soil and hold particles so that they are not lost by wind and water erosion. Fine fibrous roots make up an extensive, branched system that is characteristic of the grass plant. Up to 90% of the weight of the grass plant is in roots [3. Brown 1979]. Grass binds the soil more effectively than any other plant. One single grass plant grown under ideal conditions has a tremendous root system - 387 miles of roots. Howard Dittmer at the University of New Mexico estimated that a Kentucky bluegrass plant could have 2,000 root branches [4. Owen 1980].
Roots also loosen the soil and add organic matter, both of which increase soil permeability so there is less water runoff. The denser the cover, the more efficient the turf is in preventing erosion [5. Watschke 1987] and grass plants remove soil particles from silty water. Studies show healthy lawns absorb rainfall six times more efficiently than a wheat field and four times better than a hay field [6. Anonymous N, 1987] (2-B). A considerable volume of evidence has been accumulated which demonstrates that grass increases the organic matter content of the soil
[9. Troughton, 1957].
"Sixty-two percent of the total root system of bluegrass occurs in the upper 10 cm of soil. When expressed on a weight basis, including the thatch layer, the weight of root increases sharply toward the upper portion of the
0-10 cm layer, the zone with the highest root concentration being the very proportion that is removed in the sod harvesting operation. Furthermore as the surface is removed during sod harvesting, an equivalent depth of soil material, or more, is intermixed during the following plowing and tillage operation. The intermixing of material from depth, lower in organic matter, will have a diluting effect on the organic matter generated by the grass root system. Even though dilution may be occurring following the sod harvest, the overall-sod farming operation maintains or increases the organic matter level of the soil [10-A].
University of Rhode Island Research
Dr. C.R. Skogley at the University of Rhode Island has noted in his research report, "Soil Loss and Organic Matter Return in Sod Production," "Soil erosion from sod production should be minimal. During the long period from seed germination and early field establishment until the field is cultivated for the next crop little wind or water erosion will occur. Even after the sod crop is harvested there is essentially no erosion potential until the field is tilled in preparation for the next crop. (Editor's Note: warm-season sod production techniques do not require tillage between harvests, thus the soil is left virtually undisturbed for several years.)
"Previous research has clearly demonstrated the advantages of handling and rooting sod that is thinly cut. Thus, there is triple benefit (less soil loss and quicker rooting, plus reduced trucking costs of a lighter weight product) for the producer by taking as little soil as possible when harvesting. In recent years the development of farming equipment specific to the sod (and turf) industry has made it possible to prepare extremely smooth seedbeds and to harvest the crop with great precision. These developments provide the opportunity to harvest sod with less soil removal." (7-A).
Dr. Skogley also reported, "When sod is harvested most of the grass root system is left in the soil. To determine the quantity of this organic matter return a study was run. One-inch diameter soil cores were taken to a six-inch depth at random locations on adjacent sod and potato fields. The same soil type existed in both locations. Potatoes had been grown continuously for many years on both fields but one field had been converted to sod production. Two sod crops had been grown on this field over a five-year period and the soil samples were taken just after the second harvest.
"The soil samples were divided into six one-inch samples from the soil surface to a six-inch depth. Organic matter content was determined on the samples using the combustion method." (7-B)
Compared to the potato field, Dr. Skogley found the sod field to contain an average difference of 1.9% more organic matter in the sod field. He noted, "Assuming that a six-inch depth of soil on an acre weighs 1,000 tons, then this 1.9% increase in organic matter would represent a 19 ton per acre return to the soil." He concluded that based on the sod field's five years of production, it could be assumed that the sod operation had added the equivalent of nearly four tons of organic matter to the soil each year (7-C).
Skogley also noted, "In addition to organic matter contribution from root systems, from 10 to 20 percent of each sod crop in the form of sod strips and scrap sod may be returned to the soil to further subtract from measured acreage soil losses." (7-D)
Further, Dr. Skogley has found that a thickness of root layer removed, with soil attached, in harvesting sod to be in the range of 0.36 inches to 0.21 inches, depending upon the age and the type of harvesting equipment being utilized.
University of Guelph Research
In studies conducted at the University of Guelph, Ontario, Dr. R.W. Sheard and Mr. M. Van Patter reported, "Grass plants add organic matter to the soil by the decay of old roots and shoots while living and following harvesting by the plowing-in of the root remains."
The Guelph report also noted, "Thatch may be mistaken in part for mineral soil by those unfamiliar with the sod industry resulting in overestimation of soil removal." [10 A&B]
Further, Dr. Sheard has reported that the depth of soil removed in sod harvesting, as measured in the laboratory, averaged 9.4 mm (0.37 inches) for eight different sites studied.
Comparison of Research Results
In discussing the variations found between the two research methods, Dr. Sheard commented, "The average depth of topsoil removal of 9.4 mm is higher than the 5.3 to 9.1 mm of soil removal reported by Hesseltine and Skogley (7. 1978). They estimated the depth by removing the soil from the root mass by washing and using an estimated density of 1.2 gm/cm3, a density much below that found in this study. Whereas incomplete removal of soil by washing would tend to lower the depth of soil removed, a lower than actual density would increase the depth, canceling some or all of the error due to incomplete removal of soil. Beard (11. 1973) suggests a cutting depth adjustment for the harvester of 12.7 to 20.3 mm which would include the thatch layer and should not be interpreted as soil removal. Other published data on mineral soils are not available, however, in a study on a muck soil in Michigan, Rieke et al. (12. 1968) reported soil removal by sod-farming to be only slightly more than lost through natural subsidence under a row crop of onions. Excessive soil removal is detrimental to establishment. Hodges (13. 1958) illustrated that the thinner the layer of sod harvested the more rapidly it roots when laid, but it is more subject to drought and burning until the new root system develops (10-D)."
Sod Production Specifications in California
Perhaps the clearest illustration of the sod harvesting operation and its significance in reduction of soil removal is presented by Steve Cockerham in, "Turfgrass Sod Production." He reports, "Soil preparation is the first cultural practice in sod production and one of the most important. The quality of the work at this stage often determines whether or not a field will be profitable.
"To understand why preparation is so vital, just visualize how a sod harvester works. A sod cutter or harvester lifts the turf using a reciprocating blade that slices through the soil just under the grass. The blade is about 1/4 inch thick, 3 inches from front to back and 18 inches wide. The working head of the machine rides on a roller, allowing the blade to follow most of the contours of the land. As the unit moves forward, the roller and blade will bridge little hills, valleys and holes that are narrower than the width of the blade.
"The roller on the cutting head acts as a gauge, allowing the blade to cut at a uniform depth. Surface irregularities left by soil preparation operations cause the cutting head to move erratically, preventing the blade from uniformly cutting the sod.
"One low spot a few inches wide will cause a hole in the sod pad, and the entire pad will be thrown away. If the sod is harvested as square-yard pads (9 square feet), one rejected pad in 60 linear feet of harvest will constitute a 10 percent loss (8)."
Thus, sod harvesting requires an even, smooth surface so that marketable sod is cut and soil loss kept to a minimum.
Universal Soil Loss
The loss of soil is not an event restricted to farm operations, although that is the most commonly identified source. It has been estimated that 2.5 million acres of arable cropland are lost each year to highways, urbanization and other special uses (15). Additionally, 153,000 acres are disturbed each year by strip mining activities (16).
Water's erosive effects are seen as the "dominant form of soil loss in the United States, delivering approximately 4 billion tons/ year of sediment to waterways in the 48 contiguous states (17). It has been conservatively estimated that wind accounts for about 1 billion tons of soil erosion each year. When this estimate is added to the 4 billion tons of soil washed annually from the land, gross soil erosion in the United States is about 5 billion tons annually. The annual gross transfer of 5 billion tons of soil to streams and elsewhere is the equivalent of about 7 inches of soil from about 5 million acres (18).
Soil is not only lost from farm fields, but also through the land development processes whenever soil is disturbed and exposed to water and wind erosion. In many instances, the displaced soil is channeled into sewer systems which may become silt-filled, thereby reducing their intended use capacity and overburdening a system.
There can be no argument that erosion of a nation's top soil reserves is a critical problem; however, care must be taken to comprehend the full scope and magnitude of the problem and possible solutions before lunging into an answer that may only contribute further to the problem rather than finding an actual solution. While turfgrass sod production will in fact relocate some small amount of soil from the area where the sod was grown to an area where the sod is transplanted, the transplanted sod will provide an immediate erosion control device on the new site, while not significantly harming the original growing location. When properly grown and utilized, cultivated turfgrass sod can in fact become a major component in reducing soil erosion and storm system or waterway siltation.
Wischmeier and Smith (19. 1965) developed the "Universal Soil Loss Equation" that can be used to calculate the loss of soil through water erosion. The equation: A =RKLSCP, where A = the predicted average soil loss in tons per acre per year, R = rainfall factor, K = soil-erodibility factor, L = slope-length factor, S = slope-gradient factor, C = cropping management factor and P = erosion control practice factor. By use of this equation, generally acceptable predictions and actual calculations can be achieved for any site.
Through the use of the "Universal Soil Loss Equation," and other means, a number of studies have been undertaken to examine the amount of soil and water losses related to various cropping activates, with very strong evidence being presented regarding the performance of grasses.
Grasses have been repeatedly shown to be greater conservers of both soil and water when compared to other cropping activities. "Soil Conservation" reports the following:
|A. on Marshall silt loam, with a 9 percent slope -
(% of rainfall)
|ROTATION (corn/oats clover)
|(20-A) see footnotes
|B. on Kirvin fine sandy loam, with 8.75 percent slope-
|(20-B) see footnotes
|C. on Cecil sandy clay loam, with 10 percent slope-
|(20-C) see footnotes
|D. on Muskingum silt loam, with 12 percent slope-
|(20-D) see footnotes
Erosion losses caused by water can be exceptionally high, particularly dependent upon soil type, slope, rainfall quantities, etc. The following table has been reproduced from "Soil Conservation" (Table 84):
|| Tons of Soil
|Uncultivated, weeds puffed
|Cultivated through summer
|Same, w/deeper plowing
|Wheat every year
|Corn, wheat, clover
|Corn every year
|(20-E) see footnotes
Sod Soil Depletion and the IRS
In September 1979, the U.S. Internal Revenue Service issued Revenue Ruling 79-267 which held, "Because the amount of naturally occurring soil extracted with each harvesting of sod cannot be established, a deduction for cost depletion of the soil is not allowable." While brief in its approach, a lengthy debate, spanning several years, had previously taken place.
The facts as presented in Rev. Rul 79-267 by the I.R.S. independently provides sufficient information to eliminate fears of a sod producer significantly depleting the soil. The I.R.S. found, "The taxpayer is engaged in the business of producing and selling nursery grown turfgrass sod that it harvests from Kentucky bluegrass grown on its sandyloam soil. When the turfgrass sod is harvested, the taxpayer adjusts the harvesting machine to cut 1/2 to 3/4 inch below the surface. The physical composition of the subsurface portion of the sod consists of rhizomes and grass roots naturally matted together so that the harvested strip of sod remains conveniently intact for handling and transplanting. In the process of lifting the strips of sod, soil normally clings to the matted roots and rhizomes and is thus carried from the premises to the transplanting site. Such clinging soil is composed chiefly of organic material or humus, and a small quantity of mineral materials such as sand and clay.
""Taxpayer harvests each crop of sod two years after sowing the turfgrass seed. During the 2-year period, the turfgrass is cared for and mowed regularly by the taxpayer to maintain its quality and uniformity. Following each second crop (every fifth year), the taxpayer grows an annual leguminous cover crop and plows it under before seeding the site again to turfgrass. Periodically, the taxpayer adds fertilizer and lime to the soil in order to maintain proper nutritional levels.
"The soil that is removed with each harvesting of sod is partially replenished through the decomposition of grass roots that remain in the soil and through the addition of the fertilizer and lime to the soil. In addition, the decomposition of the leguminous cover crop grown and plowed under after every second sod harvest serves as an additional source of organic material for the soil. Some of the mineral nutrients that are absorbed from the soil by the growing turfgrass are returned to the soil when the turfgrass is mowed. As a result of these farming techniques, there is no measurable reduction in the volume of soil present.
"Some of the naturally occurring soil upon which the taxpayer began cultivation is probably removed with each sod harvest. However, because the soil is constantly being replenished, the amount of the naturally occurring soil that is removed cannot be established. When examining the soil that clings to the roots and rhizomes of the turfgrass, the naturally occurring soil cannot be distinguished from soil attributable to the fertilizer, lime and organic material added by the taxpayer. The soil created by the taxpayer's cultural methods is not subject to the depletion allowance (14)."
Unquestionably, care and concern must be taken to ensure the best and safest use of all natural resources, particularly productive farmland. The ability of wind and water to move soil particles has been well established and even with the best of conservation practices significant soil losses will take place in the production of many crops, especially open-row varieties such as cotton, corn, vegetables, etc.
Based upon the best scientific evidence now available, land owners, land-use regulators, environmentalists, consumers and others should be encouraged to take full advantage of the many benefits provided by cultivated turfgrass sod. It is a product that enhances the farmland upon which it is grown and it provides a wide array of immediate and long-term, direct and indirect environmental and aesthetic benefits.
As Dr. Skogley noted in his summary, "measurements have been made which clearly show that sod farming is not a soil depleting enterprise when compared to other, accepted, routine agricultural enterprises. The studies have indicated that the age of the stand and harvesting method can very significantly influence soil losses. Data obtained also reaffirmed that soils are improved through grass production as a result of incorporation of large amounts of organic matter.
"Sod production need not be detrimental to our land resources. In addition, if this high value crop can be grown to keep land in agricultural production, adjacent to our large urban population, it is of great benefit." (7-F)
Soil Removal With Sod Research Methodology
Both the University of Rhode Island and University of Guelph studies attempted to quantify the amount of farmland soil removed as part of the sod harvesting operation. While their methodology was different, the results were quite similar.
From the Guelph report, Dr. Sheard reports, "The major objective of this study was to establish the depth of mineral topsoil removed during the (sod) harvesting operation. Six sod rolls were removed directly from the harvester while at the same time duplicate bulk density cores were removed from the uncut area adjacent to where each sod had been cut. The six rolls were chosen in such a manner as to be representative of the general topography in the harvesting location.
"Six plugs were removed from each sod roll by a 10.16 cm diam. "cup changer", as employed on golf greens. The thickness of the thatch and of the soil removed for each of the six sod plugs from each roll of sod was visually measured in millimeters, individually bagged and transported to the laboratory.
"The sod plugs and bulk density cores were immediately weighted upon arrival at the lab. The wet weight of a roll of sod (lb/yd2) was calculated from the weight of the plugs. The duplicate bulk density cores were dried at 1050 C for 48 hours, reweighed, and the bulk density of the soil for each roll of sod was calculated.
"The organic material (top, thatch and roots) in each plug was removed by burning in a two-step procedure. In the first step each plug was heated over a gas burner for 1.5 hours to remove the top growth and some of the thatch. The plug was then heated at 425" C for 1.5 hours in a muffle furnace during which the remainder of the thatch and root fibers were removed. The remaining mineral soil was then weighed. Heating for longer periods of time did not result in further weight loss.
"The depth (mm) of mineral soil removed was calculated from the weight of the soil following burning and the bulk density. The data for each site (farm) was subjected to analysis of variance using a completely randomized design @ and a probability level of P = .05 for calculating the standard error of the mean for a roll of sod.
"The depth of soil removed, as measured in the laboratory averaged 9.4 nun (0-37 inches) for the eight sites." (10-C)
Dr. Skogley, in his Rhode Island study reports the following methodology and results: "In this study sod pieces were taken randomly during commercial harvesting. The pieces were cut into squares the width of the sod pieces, being careful not to remove soil. Sod samples were taken from several locations during routine harvesting. The pieces were oven dried for several days at a temperature of 120" F and then weighed. Soil was then carefully washed from tile root system. The sod pieces were again oven dried and reweighed. The difference in weight between the first and second weighing was considered to be the weight of soil removed. (7-E)."
Utilizing this methodology, Dr. Skogley found that a thickness of soil layer removed to be in a range of .36 inches to .21 inches, depending upon the age of the sod and type of harvesting equipment being utilized.
LITERATURE CITED AND REFERENCES
1. Hamm, R.L. and L. Nanson. 1964. An Ecological Approach to Conservation. Burgess Publ. Co., Minneapolis, MN. Pages 169-173, 181-182.
2. Roberts, E.C. and Roberts B.C. 1989. Lawn and Sports Turf Benefits. Better Lawn and Turf Institute. Pleasant Hill, TN. (A. Page 15) (B. Page 16)
3. Brown, Lauren. 1979. (Grasses: An Identification Guide). Houghton Mifflin Co., Boston, MA. Page 6.
4. Owen, O.S. 1980. National Resource Conservation: An Ecological Approach (3rd Ed). McMillian Publishing Co., Inc. New York. Page 231.
5. Watschke, T., G. Hamilton and S. Harrison. 1988. "Run-off as Effected by Establishment Method." New York State Turfgrass Association Bulletin 132. Spring 1988. Page 1286.
6. Anonymous. N1987. "Facts and Figures for Defending Lawns." Grounds Maintenance. November: 31-34, 72-74.
7. Skogley, C.R. and B.B. Hesseltine. 1978. "Soil Loss and Organic Matter Return in Sod Production." University of Rhode Island, Kingston, RI. (A. Page 4), (B. Pages 7-8), (C. Page 7), (D. Page 7), (E. Page 5), (F. Pages 7-8).
8. Cockerham, S.T. 1988. Turfgrass Sod Production. Division of Agriculture and Natural Resources, University of California, Oakland, CA. Pages 28-29.
9. Troughton, A. 1957. "The Underground Organs of Herbage Grasses." Bul. 44. Commonwealth Agricultural Bureau.
10. Sheard, R.W. and M. Van Patter. 1978. "Soil Modification During Nursery Sod Production." Department of Land Resource Science, Ontario Agricultural College, University of Guelph, Ontario. (A. Pages 50-51), (B. Page 17), (C. Pages 14-15), (D. Page 19).
11. Beard, J.B. 1973. Turfgrass: Science and Culture. Prentice Hall, Inc., New Jersey.
12. Rieke, P.E., J.B. Beard, and R.E. Lucas. 1968. "Grass Sod Production on Organic Soils In Michigan." Proc. 3rd International Peat Congress. Pages 350-354.
13. Hodges, T.K. 1958. "Cutting Sod For Rhizome Values." Proc. 1958, Midwestern Regional Turf Conference. Pages 40-42.
14. United States Internal Revenue Service. 1979. Revenue Ruling 79-267. 26 CFR 11.611-1: Allowance for deduction for depletion.
15. "Agriculture and the Environment," Economic Research Service No. 481. Department of Agriculture, Washington, DC, July 1971.
16. "Surface Mining and Our Environment," U.S. Department of the Interior, No. 7967-0-278-800. Government Printing Office, Washington, DC. 1967.
17. Committee on Interior and Insular Affairs to Accompany HR 11500. "Surface Mining Control and Reclamation Act of 1974," HR 93-1072. U.S. House of Representatives, Washington DC May 30, 1974.
18. Pimentel, D., and E.C. Terhune, et. al. 1976. "Land Degradation: Effects on Food and Energy Resources., Science. October 8, 1976. Volume 194, Page 150.
19. Wischmeier, W.H. and D.D. Smith. 1965. Predicting rainfall-erosion losses from cropland east of the Rocky Mountains. USDA Agr. Handbook 282. Washington, DC.
20. Bennett, H.H. 1939. Soil Conservation. McGraw-Hill, Inc. New York. (A. Page 138), (B. Page 142), (C.
Page 145), (D. Page 147), (E. Page 191).
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TURFGRASS PRODUCERS INTERNATIONAL
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