The role of turfgrasses in C and N cycling in the southeastern U.S. has not been well documented. The objectives of this research were to determine the characterization of chemical quality, clipping decomposition rates, and C and N release from warm- and cool-season turfgrasses. The study was conducted for 46 weeks in 2012 in Auburn, AL. Four warm season turfgrasses were used included (bermudagrass [ Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy], centipedegrass ( Eremochloa ophiuroides (Munro) Hack), St. Augustinegrass ( Stenotaphrum secundatum (Walter) Kuntze), zoysiagrass ( Zoysia japonica Steud.), and one cool season turfgrass (tall fescue ( Festuca arundinacea Schreb)). Litter was placed into nylon bags at an oven dry rate of 3.6 Mg?ha?1. Litter bags were retrieved after 0, 1, 2, 4, 8, 16, 24, 32, and 46 weeks, and analyzed for total C and N. A double exponential decay model was used to describe mass, C, and N loss. Results indicated that tall fescue decomposition occurred rapidly compared to warm season turfgrasses. Litter mass loss measured after 46 weeks was determined to be 61.7%, 73.7%, 72.2%, 86.8%, and 45.4% in bermudagrass, centipedegrass, St. Augustinegrass, tall fescue, and zoysiagrass respectively. Zoysiagrass litter had a higher lignin concentration, while tall fescue had the lowest lignin. Over 46 weeks’ release of C was in the order: zoysiagrass > bermudagrass = centipedegrass = St. Augustinegrass > tall fescue, and release of N was in the order zoysiagrass > centipedegrass > bermudagrass = St. Augustinegrass > tall fescue. Our study concluded that, zosiagrass is a better choice for home lawns.
Understanding litter decomposition process in a given ecosystem is vital due to its effect on greenhouse gas concentration and biogeochemical cycling in terrestrial ecosystems. During decomposition, significant amounts of greenhouse gases, including CO2, CH4, and N2O, are released [
Organic matter with higher C:N or lignin:N ratios decomposes slower, a function of lower N mineralization rates and increased N immobilization in microbial biomass [
Litter decomposition pattern of any material can be divided into two phases: an early and a later stage which are regulated by fractions different chemical of the material. The early phase is regulated by the labile fraction including sugars, starch, soluble and unprotected cellulose and hemicelluloses [
There is limited research which examines decomposition rate of C and N dynamics in the long-term, non-tilled conditions in which warm and cool season’s turfgrasses are grown. There is a need to evaluate C and N dynamics in warm and cool season’s turfgrasses in the southeast United States. The objectives of this research were to determine the characterization of chemical quality, clipping decomposition rates, and C and N release from warm- and cool-season turfgrasses. That will solidify our understanding of different turfgrasses dynamics under current environment. In addition, it will reduce the emission of greenhouse gases through altering current turfgrass management by lowering fertilizer application rates and timing. A recent study summarized net C sequestration in home lawn turfgrasses across the U.S. included some warm- season turfgrasses, a large-scale survey from 16 sites across the U.S. [
A field decomposition study was initiated in May 17, 2012 and conducted for 46 weeks (wk) at the Auburn University Turfgrass Research Unit (32.58˚N, 85.50˚W), Auburn, AL, USA, on a Marvyn loamy sand soil (fine-loamy, kaolinitic, thermic Typic Kanhapludult). The mean annual air and soil temperatures were 17˚C and 19˚C, respectively and the mean annual precipitation was 1233 mm (2011-2014, AWIS, 2014). Experiments were installed in 5 existing areas of common southeaster turfgrasses (4 warm season and 1 cool season): bermudagrass [Cynodon dactylon (L.) Pres. × Cynodon transvaalensis Burtt. Davy cv “Tifway”], Centipedegrass (Eremochloa ophiuroides Munro Hack cv “common”), St. Augustinegrass (Stenotaphrum secundatum Walter Kuntze cv “Floratam”), and zoysiagrass (Zoysia japonica Steud.) cv “Meyer”, and cool season- tall fescue (Festuca arundinacea Schreb) cv “Rebel Exeda” were the selected species and cultivars. All of the turfgrass stands had been established for at least 5 years, and none were older than 7 years. All plots areas were no more than 300 m from each other. Swards were managed as lawn grasses, with the following mowing heights for each: bermudagrass and zoysiagrass (5.0 cm), tall fescue and St. Augustinegrass (7.6 cm) and centipedegrass (6.4 cm). Plots were mown either with a walk behind homeowner-type reel mower (Tru-Cut Mowers, Inc., 141 East 157th Street, Gardena, CA 90248) (bermudagrass and zoysiagrass) or with a homeowner riding rotary mower (Husqvarna Professional Products, Inc. Charlotte, NC 28269) (all other grasses), respectively. All plots were mown three days a week with clippings returned. Supplemental irrigation was provided in the absence of rainfall so that irrigation + precipitation equaled 2.5 cm∙wk−1. An on-site weather station was used to determine daily precipitation.
A litter bag decomposition method, often used in forestry, was employed for this study [
Soil moisture and temperature were measured on a weekly basis using an auxiliary sensor (Onset Computer Corporation, 470 MacArthur Blvd., Bourne, MA 02532). The sensor was placed at a 5.0 cm depth in the soil, with soil moisture and temperature recorded at 5 minute intervals. Three sensors were placed in the bermudagrass plot area and results averaged for use for all grasses. Spot checks throughout the study period revealed that soil moisture and temperature was not substantially affected (over the entire study period) by grass species.
The four replicate bags from each grass species were retrieved from the field at 0, 1, 2, 4, 8, 16, 24, 32, and 46 wk. Retrieved bags were emptied into plastic containers and oven-dried at 55˚C for 72 h and weighed for dry-matter determination. Litter was ground to pass a 1 mm-sieve and analyzed for total C and N using LECO TruSpec CN analyzer (Leco Corp, St. Joseph, MI). All data were converted to an ash-free dry weight basis by ashing 1 g of sample in a muffle furnace at 450˚C for 16 hours [
Initial values of lignin concentration in leaf litter were assessed by the acid-detergent digestion technique [
A double, four-parameter exponential decay model (Equation (1)) [
where Y = remaining mass (normalized %),
A = the labile portion,
C = the recalcitrant portion,
b and d are the labile and the recalcitrant constants, respectively, and
x = time in weeks.
Means, standard errors, and statistical variations of treatments were determined using mixed models procedures [
The initial fiber composition of harvested clippings had significant variation among the five turfgrass species (
The litter exhibiting higher initial lignin content had slower decomposition rates. For example, decomposition of Quercus dealbata (6% lignin) litter had slower decomposition than Quercus fenestrata (4% lignin) [
In all cases, the decay models were significant (P < 0.0001) with reasonably high adjusted R2 values (
Grasses | Initial contents (g∙kg−1) | Released contents (%) | |||||
---|---|---|---|---|---|---|---|
NDF | ADF | ADL | Carbon | Nitrogen | Carbon | Nitrogen | |
Bermuda | 849.60a | 347.61b | 49.00b | 396a | 23.0b | 63.3c | 53.6b |
Centipede | 731.66d | 356.37b | 39.43c | 421a | 14.5c | 66.2c | 37.3c |
St. Augustine | 800.85c | 424.65a | 48.80b | 340b | 14.7c | 82.1b | 85.8a |
Tall fescue | 629.34e | 296.17c | 31.33c | 412a | 40.0a | 87.9a | 87.7a |
Zoysia | 824.54b | 371.19d | 59.61a | 429a | 14.6c | 45.1d | 31.5c |
Means in the same column with the same letter are not significantly different at α ≤ 0.05; NDF = Natural Detergent Fiber contains hemicellulose + cellulose + lignin (approximately total cell wall), ADF = Acid Detergent Fiber comprise cellulose + lignin, and ADL = Acid Detergent Lignin.
Turfgrass | Equation | P > F† | Syx‡ | |
---|---|---|---|---|
Mass | ||||
Bermudagrass | Y = 56.22e−0.08x + 44.33e−0.003x | <0.0001 | 0.99 | 1.14 |
Centipedegrass | Y = 89.54e−0.05x + 13.75e−8.28E−19x | <0.0001 | 0.97 | 5.24 |
St. Augustinegrass | Y = 19.43e−0.09x + 80.02e−0.02x | <0.0001 | 0.96 | 4.69 |
Tall Fescue | Y = 91.25e−0.11x + 9.47e−8.12E−19x | <0.0001 | 0.96 | 4.69 |
Zoysiagrass | Y = 16.87e−0.12x + 84.14e−0.01x | <0.0001 | 0.96 | 4.69 |
Carbon | ||||
Bermudagrass | Y = 47.61e−0.11x +52.13e−0.01x | <0.0001 | 0.99 | 2.46 |
Centipedegrass | Y = 87.82e−0.04x + 13.72e−4.93E−18x | <0.0001 | 0.98 | 3.14 |
St. Augustinegrass | Y = 87.67e−0.04x + 5.21e−9.92E−18x | <0.0001 | 0.96 | 4.69 |
Tall Fescue | Y = 89.91e−0.11x + 9.32e−1.08E−17x | <0.0001 | 0.97 | 6.04 |
Zoysiagrass | Y = 11.17e−0.28x + 90.14e−0.01x | <0.0001 | 0.98 | 2.06 |
Nitrogen | ||||
Bermudagrass | Y = 30.15e−0.28x +69.82e−0.01x | <0.0001 | 0.98 | 2.97 |
Centipedegrass | Y = 8.64e−0.89x + 91.36e−0.01x | <0.0001 | 0.97 | 2.54 |
St. Augustinegrass | Y = 28.58e−0.56x + 72.31e−0.02x | 0.0002 | 0.95 | 4.70 |
Tall Fescue | Y = 72.26e−0.21x + 22.68e−0.01x | 0.0001 | 0.96 | 5.71 |
Zoysiagrass | Y = 20.49e−0.16x + 79.94e−3.62E−19x | 0.0290 | 0.69 | 4.95 |
†Significance of fit. ‡Standard error of the estimate.
centipedegrass, St. Augustinegrass, and tall fescue, respectively. However, zoysiagrass had very slow decomposition, with only 25% loss from an initial equivalent of 360 g∙m−2 to 270 g∙m−2. Similar results were observed by [
The labile decay constant of zoysiagrass residue value (0.12) was 2.6 times greater than that of centipede grass (0.05) but closer to that of tall fescue (0.10). The effects of grass species on decay of recalcitrant portions were more distinct. The recalcitrant decay constant of zoysiagrass (0.0096) was greater than that of centipedegrass (8.28 × 10−19) or tall fescue (8.12 × 10−19). Rapid decay of turfgrass tissues are typically related to warmer soil temperatures (
Labile portions of warm-season turfgrass litter increased from 16.9% to 89.5%, and recalcitrant portions decreased from 84.1% to 13.8% under zoysiagrass and centipedegrass, respectively (
All C data were expressed on a normalized basis (percent remaining) (
R2 values (
The time to decompose the turfgrass clipping varied with species. At 24 weeks, tall fescue C had declined by 85.2%, while zoysiagrass decreased by 25.7%. These differences may be caused by the chemical fiber structure such as NDF in the clippings. After 46 weeks, there were significant differences in C among turfgrass clippings with exception of bermudagrass and centipedegrass.
Carbon concentrations were negatively correlated with sampling time in bermudagrass (r = 0.88**) and St. Augustinegrass (r = 0.72*), however, correlation was positive for centipedegrass (r = 0.85**), tall fescue (r = 0.91***), and zoysiagrass (r = 0.75*) (
Nitrogen data fit to double exponential decay models on a normalized basis. Adjusted R2 value for that model was high, with the exception of that calculated for zoysiagrass (0.69). This was likely due to the small amount of N and fast release of labile N for zoysiagrass. Initial N concentrations in turfgrasses were low, with a N concentration of 14.5 g∙N∙kg−1 in centipedegrass, compared to 14.7 and 14.6 g∙kg−1 in St. Augustinegrass and zoysiagrass, respectively. Tall fescue had a higher N concentration (40 g∙kg−1,
The labile decay constant of centipedegrass (0.88;
Week | Bermuda grass | Centipede grass | Tall fescue | St. Augustine grass | Zoysia grass |
---|---|---|---|---|---|
0 | 18.6 ± 0.7 | 28.7 ± 1.0 | 10.3 ± 0.1 | 22.4 ± 1.3 | 29.3 ± 0.7 |
1 | 19.4 ± 0.3 | 29.1 ± 0.8 | 11.6 ± 0.3 | 22.2 ± 2.5 | 28.3 ± 0.5 |
2 | 19.9 ± 0.4 | 30.5 ± 1.3 | 12.4 ± 0.2 | 23.2 ± 0.9 | 30.5 ± 0.6 |
4 | 20.6 ± 0.5 | 28.7 ± 1.4 | 14.0 ± 0.4 | 24.7 ± 1.0 | 28.6 ± 1.1 |
8 | 19.4 ± 0.3 | 26.5 ± 0.5 | 12.8 ± 0.5 | 18.3 ± 5.5 | 28.3 ± 0.6 |
16 | 16.1 ± 0.9 | 22.1 ± 0.5 | 8.9 ± 0.1 | 21.7 ± 1.7 | 26.8 ± 0.5 |
24 | 15.1 ± 0.4 | 17.8 ± 0.7 | 9.4 ± 0.4 | 16.4 ± 0.8 | 26.1 ± 1.1 |
32 | 14.7 ± 0.2 | 15.5 ± 0.4 | 8.8 ± 0.4 | 14.7 ± 0.3 | 23.6 ± 0.4 |
46 | 14.3 ± 0.5 | 15.0 ± 0.2 | 9.6 ± 0.6 | 13.4 ± 0.3 | 20.5 ± 0.3 |
The labile portion of tall fescue was 72%, and the recalcitrant portion was 23% (
After 46 weeks, statistical analysis shows significant differences in the remaining and released N concentration among turfgrasses. For example, zoysiagrass represented the lowest value of released N with a value of 31.5% of total N compared to 87.7% of released N from tall fescue (
Although the biomass of all grasses are decreasing over time, the N concentration is increasing (
Previous studies reported similar results under different ecosystems, included five exotic plant species such as Acacia auriculiformis, Cassia siamea, Casuarina equisetifolia, Eucalyptus hybrid and Grevillea pteridifolia growing on coal mine spoil [
The nature of warm-season turfgrass decomposition is different than that of cool-sea- son turfgrass [
allowing for slower initial decay [
During the first 4 weeks the C:N ratio increased for all turfgrass species but does not limit the activity of decomposer organisms (C:N ratio < 30:1, [
Warm season turfgrasses had higher lignin:N ratio contents than tall fescue. Initial lignin:N ratios were: 0.33, 0.27, 0.99, 0.40 and 0.08 for bermudagrass, centipedegrass, St. Augustinegrass, zoysiagrass, and tall fescue, respectively. Lignin:N ratios of warm season turfgrasses are comparable with that measured for sub-tropical forest ecosystem litter [
Our research demonstrates important aspects of warm and cool season turfgrass decomposition, mainly that tall fescue is comprised mostly of a quickly decaying labile fraction. Labile and recalcitrant decomposable C and N are important for short- and long-term effects on available N concentration in soil. Modeling warm- and cool- season turfgrass decomposition may enable turfgrass researchers and professionals to more accurately choose the best grass for home owners. Our study concluded that, zoysiagrass may be a better choice for lower N fertilization requirements and higher C accumulation in soils followed by bermudagrass, centipedgrass, St. Augustinegrass, and tall fescue. In addition, our study clearly shows that the decomposition of different turfgrass clippings presents rapidly released N within the thatch layer of turfgrass. Thus, a portion of that N will be available to that turfgrass during growing season. Then, N fertilization should be reduced when clippings are returned to turfgrass lawns. Moreover, differences in clipping C released under our study can be assumed that a portion of remaining C in the thatch layer could be important factor in soil C sequestration under southeastern U.S. turfgrass species and reduce climate change effect on turfed lawns [
Hamido, S.A., Guertal, E.A. and Wood, C.W. (2016) Seasonal Variation of Carbon and Nitrogen Emissions from Turfgrass. American Journal of Climate Change, 5, 448-463. http://dx.doi.org/10.4236/ajcc.2016.54033