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Article

The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields

by
Kristina S. Walker
1,* and
Katy E. Chapman
2
1
Department of Agriculture and Natural Resources, University of Minnesota Crookston, Crookston, MN 56716, USA
2
Department of Math, Science, and Technology, University of Minnesota Crookston, Crookston, MN 56716, USA
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(8), 869; https://doi.org/10.3390/horticulturae10080869
Submission received: 29 June 2024 / Revised: 31 July 2024 / Accepted: 15 August 2024 / Published: 17 August 2024
(This article belongs to the Special Issue Sustainable Strategies and Practices for Soil Fertility Management)
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Abstract

:
Greenhouse gas (GHG) emissions are known to contribute to global climate change. A two-year field study on Kentucky bluegrass (Poa pratensis L.) evaluated cultivation practices and fertilizer use on GHGs. The presence of urea and hollow-tine aerification resulted in the highest soil carbon dioxide (CO2) emissions. No significant differences between soil methane (CH4) flux were observed based on fertilizer; however, in 2014 the verticutting cultivation treatment fluxed significantly more soil CH4 than the uncultivated control. Results showed no significant differences in soil nitrous oxide (N2O) in 2013; however, in 2014, both fertilizer and cultivation practices showed significant differences between treatments, with the urea and the hollow-tine treatments fluxing significantly more soil N2O. The hollow-tined plots produced the greenest turf in 2013, followed by the uncultivated control and the verticutted treatment. In 2014, both the hollow-tine and the uncultivated control produced the greenest turf, followed by the verticutted treatment. The hollow-tined and uncultivated control treatments had significantly higher turfgrass quality than the verticutted treatment. The verticutted urea treatment was above acceptable levels (>6.0) for turfgrass quality following all cultivation events. The results show cultivation practices can be identified that reduce GHG emissions while maintaining turfgrass quality and color.

1. Introduction

Agricultural activities related to crop and livestock production contribute to greenhouse gas (GHG) emissions. In 2021, GHG emissions from agriculture accounted for 10% of total United States (US) emissions, an increase of 7% since 1990. Although carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) occur naturally in the atmosphere, anthropogenic activities have changed their concentrations, thus increasing the potential for global warming. Greenhouse gases emitted during management practices of agricultural soils account for just over half of the GHG emissions from the agricultural sector [1].
In the US, land coverage by turfgrass is estimated at 13 to 20 million ha (irrigated and nonirrigated), covering nearly 2% of the US [2]. Greenhouse gas emissions from turfgrass have been scrutinized since it is a crop produced for non-consumption, and there is a perception that turfgrass managers implement management practices, such as nitrogen (N) fertilization and irrigation, in excessive amounts [3]. This is especially true for turfgrass areas that are intensively managed for sports (golf, football, soccer, etc.) and recreational purposes. Turfgrass managers within the green industry are known for being environmental stewards and are asking for turfgrass management strategies to mitigate the effects of climate change due to increased GHG concentrations [4].
To date, GHG research on turfgrass has been primarily conducted on golf courses. Nutrient cycling on golf courses can sequester GHG through the accumulation of soil organic carbon [5,6,7,8,9]. Cultural management practices can offset sequestration by mitigating GHG emissions directly and indirectly [10]. Fertilization [11,12], irrigation [13], clipping management [14], and other turfgrass management practices have both the potential to contribute to emissions and sequester greenhouse gases, leading to uncertainties in the net contribution of turfgrass ecosystems to climate change [15]. However, most of the N fertilization studies (rates and types) have been conducted solely on N2O. Nitrous oxide is produced by biological processes that occur in soil and by a variety of anthropogenic activities. The application of synthetic and organic fertilizers, livestock manure, and the retention of N-fixing plant residues were the largest contributors to US N2O emissions in 2021, accounting for 75% of the total agricultural N2O emissions [1]. Turfgrass studies ranged in N fertilizer rate (0 to 300 kg N ha−1 yr−1) and type (fast and slow release), where N2O emissions ranged from 0.5 to 3.36 kg N2O-N ha−1 yr−1. This represented 5% of the N applied being lost as N2O at the high end of this range [13,16,17,18,19,20]. While five percent is not a high percentage, considering the global warming potential of N2O (265 times that of CO2), the impact of these emissions on global warming merits further investigation [1]. Of the three GHGs, CH4 has been studied the least in turfgrass systems. Riches et al. [21] found that CH4 emissions were generally negligible except when there were brief periods of heavy rainfall on waterlogged soils. Methane fluxes seem to be highly variable due to differing turfgrass species and management practices [14]. More GHG research needs to include CH4 to develop a comprehensive management plan to decrease all GHG emissions in turfgrass systems.
In sports turf management, aesthetics and player safety are extremely important [22]. However, sports fields are extremely difficult to manage due to concentrated traffic on a regular basis. This intensity of use leads to thinning of the turf canopy, decreasing turfgrass quality, and increasing soil compaction [23]. Root function decreases under compaction due to the lack of oxygen needed for respiration and the buildup of toxic gases such as CO2 and CH4, which impact climate change. Cultivation techniques are used to loosen the soil and reduce compaction, to reduce thatch, or to groom the surface. These techniques range in plant benefits and the level of surface disturbance, where the most beneficial for soil management are the most disruptive to the playing surface. Cultivation techniques in turf include aerification, verticutting, spiking, slicing, and water/air injection. The two most commonly used cultivation techniques by turfgrass managers are aerification (hollow-tine) and verticutting. Hollow-tine aerification is where hollow tines are inserted into the soil and soil cores or plugs are removed, leaving a hole or cavity in the turf canopy and soil. This method of cultivation relieves soil compaction and increases water, fertilizer, and oxygen penetration into plant roots [24]. Verticutting, or vertical mowing, is the slicing of the turfgrass canopy with a series of vertically mounted blades rotating on a shaft. The shaft can be raised or lowered to vary the depth (cut shallowly or more deeply) into the turf canopy. Verticutting is implemented when the thatch layer exceeds 0.64 to 1.27 cm [24]. When verticutting is used to control thatch, the depth of the blades is typically adjusted to reach the bottom of the thatch layer.
Cultivation has been shown in row crop agriculture to increase GHG emissions depending on the degree of soil disturbance. Differences in CO2 losses are related to the degree to which the soil was disturbed in conventional tillage systems (moldboard plow > disk harrow > chisel plow > no-till) [25,26]. It has also been shown that traditional soil tillage (e.g., disk, plow) of grass pastures with high soil organic carbon led to root decomposition and a subsequent release of CO2 into the air [27]. Tillage practices that promote deep O2 penetration into the soil profile increase soil carbon losses [26].
Additionally, other studies have shown increased CO2 [28], CH4 [29], and N2O [28,29] losses following tillage events. In turf, the influence of various cultivation practices on GHG fluxes is unknown [11]. For agricultural soil management of row crops, tillage practices are implemented prior to planting and/or after harvest. For cool-season sports fields, aerification is recommended twice per year, once in May and once in September [23]. At a minimum, verticutting is recommended in the spring and early fall [24]. The surface disturbance caused by cultivation methods in turf is much lower than the surface disturbance generated by conventional tillage methods in agriculture. However, turfgrass systems are disturbed more frequently to maintain plant and soil health.
Therefore, the influence of various cultivation practices in turfgrass systems needs to be evaluated to determine the impact they have on contributing to GHG emissions (CO2, CH4, N2O). Greenhouse gases in the atmosphere have been increasing, leading to changes in our global climate. The GHGs being examined in the current study are significant contributors to the global warming being experienced today. All sectors of society must take steps to reduce or eliminate emissions of greenhouse gases. The turfgrass industry represents a relatively large land area that has the potential to help mitigate GHG emissions and is therefore worthy of consideration as we look for solutions to combat global climate change. A two-year field study was conducted on a Kentucky bluegrass (Poa pratensis L.) athletic field to evaluate cultivation practices (hollow-tine aerification, verticutting, and an uncultivated control) and fertilizer use (221 kg N ha−1 yr−1 using urea and 0 kg N ha−1 yr−1) on GHG emissions. This research aimed to contribute to the body of scientific knowledge around the impacts of cultivation and N fertilizer on the soil flux of three important greenhouse gases while also providing turfgrass managers with best management practices to maintain turfgrass systems with the color and quality expected in turfgrass systems.

2. Materials and Methods

This two-year (i.e., two growing seasons) field project began in May 2013 and continued through October 2014. It was located at the University of Minnesota Crookston football practice facility on Kentucky bluegrass turf and on Gunclub silty clay loam soil (fine-silty, mixed, superactive, frigid, Aeric Calciaquoll). Soil testing (15 soil cores taken to a 10.2 cm depth) prior to the start of the study indicated a pH of 8, 74 kg ha−1 P, 648 kg ha−1 K, and 56 g kg−1 organic matter (AgVise, Harwood, ND, USA). The research area was set up as a split-plot design with three cultivation regimes and two fertilizer treatments. The plot size was 12.2 m × 1.8 m for the cultivation regimes and 1.5 m × 1.8 m for the fertilizer treatments. Both cultivation and fertilizer treatments were replicated four times.
For this project, cultivation regimes included hollow-tine aerification (HT), verticutting (VC), and an uncultivated control (CT). Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. For hollow-tine aerification, soil cores (1 cm diameter, 18 cm deep) were removed, and aerification holes were left unfilled using a tractor-drawn Verti-Drain with a tine spacing of 6.4 cm. Soil cores were left on the surface and mowed, which allowed the soil to resettle. The Bluebird verticutter was set on the lowest setting, approximately 5 cm deep, to cut into the soil (blade spacing was 1.6 cm). Debris was not removed from the plots, which allowed decomposition to occur on the plots. For the uncultivated control, no cultivation techniques were applied during the study period. There was one fertilizer treatment of granular urea (221 kg N ha−1 yr−1) containing 46% N and an unfertilized control (no fertilizer was applied during the study period, 0 kg N ha−1 yr−1). Plots were fertilized (by hand) from May through October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot. Monthly fertilizer applications were applied the first week of each month throughout the growing season (May–October). Cultivation and fertilizer treatments were implemented prior to field measurements being taken. Data collection started on June 1, 2013, and ended on May 20, 2014. Total rainfall (mm) and mean air temperatures (C) were recorded during the growing season (May–October) of 2013–2014 (Figure 1). Weather data were collected by a local weather station located at the Northwest Regional Outreach Center (Crookston, MN, USA), which was located across the road from the research plots.
Research plots were mowed at 5 cm throughout the growing season (May–October). In the absence of significant rainfall, irrigation was supplementally applied each week (no more than 0.38 cm) to promote growth and maintain the soil at or near field capacity. The research area did not receive any additional fertilization or cultivation practices during this two-year study.

2.1. Environmental Conditions

Temperature (soil and air) and soil moisture were recorded weekly synchronously with GHG collection during the growing season using an HM digital TM-1 industrial grade digital thermometer and a Dynamax TH300 TDR (Houston, TX, USA) soil moisture probe, which takes the average soil moisture in the top 60 mm of soil.

2.2. Greenhouse Gas Analysis

Gas samples were taken weekly during the growing season (May–October) following the protocols of the United States Department of Agriculture-Agriculture Research Service Greenhouse Gas Reduction through the Agricultural Carbon Enhancement Network [30,31]. Briefly, a polyvinyl chloride pipe (0.152 m diameter × 0.114 m height) was tamped into the ground until it was flush with the soil surface following cultivation. The bases remained in the soil until cultivation treatments were reapplied and then immediately replaced. Gas samples were taken by tamping a vented-close gas chamber covered in reflective tape (no light penetration) over the base in the ground for the sampling period. Gas samples were taken at chamber closure and 20 and 40 min post-chamber closure. The samples were placed into gas-tight vials using a 10 mL syringe.
These samples were analyzed using a gas chromatograph to determine the concentration of CO2, CH4, and N2O in each sample. The gas chromatograph used was a Varian 350 equipped with a thermal conductivity detector for CH4, an electron capture detector for N2O, and a flame ionization detector for CO2. Concentrations were determined by interpolation using gas standards obtained from Scott Specialty Gases (Air Liquide, Paris, France). Standard curves were used if they had an r2 value of 0.99 or greater. The concentrations of the samples collected were then used to determine a change in concentration (flux rate) during the 40-minute sampling period using linear regression.

2.3. Turfgrass Color and Quality

Turfgrass appearance was evaluated by quantifying canopy greenness and using visual turfgrass quality ratings. Turfgrass greenness was determined weekly using a chlorophyll meter that measured the normalized difference vegetation index (NDVI) of the turfgrass stand (FieldScout CM 1000 NDVI from Spectrum Technologies, Inc., Aurora, IL, USA). Three measurements were taken from approximately 90 cm above the turfgrass canopy using a diagonal grid pattern, which measured the back, center, and front of each plot. The three measurements were averaged to produce a single plot rating and are reported as NDVI (−1 to 1). Turfgrass color data were not available from June to mid-July 2013 due to technical issues with the equipment. Turfgrass quality was visually rated (per plot) weekly throughout the growing season using a 1 to 9 scale, where 1 = completely brown dead turf, 6 = minimally acceptable turf, and 9 = optimum uniformity, density, and greenness [32]. Before the start of the study, turfgrass color was 0.75 and turfgrass quality was 7.0 for the research area. Although a number of studies have correlated NDVI and turfgrass visual quality [33,34,35,36,37,38], Leinauer et al. [39] found it valuable to include both visual turfgrass quality and turfgrass color (NDVI scale) to characterize the aesthetic appeal of turfgrass accurately.

2.4. Statistical Analysis

Greenhouse gas data and turfgrass data were analyzed via analysis of variance (ANOVA) and regression analysis (REG) utilizing the split-plot design procedures in SAS [40]. Cultivation was modeled as the whole plot, and fertilizer was modeled as the subplot. We modeled the main effects (Cultivation and Fertilizer) as well as the interaction (Cultivation × Fertilizer) in the analysis. The assumptions of the model were checked, and transformations were applied to the data as needed to meet the assumptions of the model. The carbon dioxide data were transformed with a square root transformation, and the methane data were transformed with a natural log. No transformation was necessary for the nitrous oxide or turfgrass data. All graphs and data tables presented in the paper represent untransformed data, but statistical conclusions are based on the transformed data. Mean separation tests were done using the Fisher’s Protect least significant difference (LSD) and a significance level of α = 0.05, which was established a priori.

3. Results and Discussion

3.1. CO2 Emissions

Results show significant differences between soil CO2 emissions based on fertilizer and cultivation practice during both years of the study, with the interaction between fertilizer and cultivation not being significant (Table 1). Across both growing seasons, the treatments fertilized with urea consistently fluxed more soil CO2 than the unfertilized control (Figure 2, Table 1). This is likely a result of urea providing a flux of soluble nitrogen into the soil, stimulating microorganisms to grow and incorporate carbon into their bodies. When more microorganisms are present, they will respire more, resulting in more CO2 being released. As these organisms complete their life cycle, the carbon incorporated into their bodies decomposes, which may result in higher CO2 emissions. These results are not surprising, as numerous studies have shown that nitrogen fertilizers increase rhizosphere respiration [41,42].
Across both growing seasons, the verticutting cultivation treatment consistently resulted in the lowest soil CO2 flux, with the hollow-tine flux significantly higher in 2013 (Figure 3, Table 1) and both the hollow-tine and the uncultivated control flux significantly higher in 2014 (Figure 3, Table 1). Both hollow-tine and verticutting cultivation are implemented to increase water movement into the soil profile and have been shown to reduce the offsite transport of nutrients and pesticides associated with overland flow or runoff [43,44]. The primary purpose of hollow-tine cultivation is to combat soil compaction and thatch development [24]. Furthermore, McCarty [24] indicates hollow-tine cultivation releases gases (CO2, CH4) and minimizes the development of a “black layer” in the soil while also stimulating environmental conditions that promote healthy soil microbial activity, which helps reduce thatch and organic matter accumulation. Given that textbooks [24,45] cite releasing CO2 from the soil as a benefit of hollow-tine cultivation, it is not surprising that the hollow-tine cultivation treatment increased gaseous losses of soil CO2. One purpose of verticutting is to rip out the thatch from the surface to stimulate new growth. Verticutting disturbs the soil surface less deeply and with closer spacing than hollow-tine cultivation; thus, it is not surprising that verticutting results in less soil CO2 flux. However, it is interesting that verticutting resulted in lower CO2 emissions than the uncultivated control in one of two years, suggesting the importance of removing thatch layers not only for improved turfgrass health but also to reduce mineralization of organic matter and other biomaterials on the soil surface. This study observed a significant increase in soil moisture associated with hollow-tine cultivation in 2013 (Table 2), but no significant differences in soil moisture content were observed between cultivation practices in 2014. This is supported by the regression analysis, which showed both soil temperature [parameter estimate 11.48 (2013), 23.50 (2014), p < 0.0001] and soil moisture [parameter estimate 4.45 (2013), 3.26 (2014), p < 0.05] are significant predictors of soil CO2 flux. The magnitude of the parameter estimates indicates that soil temperature is a more influential predictor of soil CO2 flux; thus, they are both important predictors of soil CO2 flux.
The surface debris (dead grass leaves) caused by verticutting was not removed from the plots but was allowed to settle back into the grass/soil profile. This introduction of air to the debris likely slowed the natural decomposition processes as the biomaterials had less access to soil moisture at the surface. It is possible that some of the debris dried and blew away, in which case it would decompose elsewhere. However, it is also likely that the verticutting broke up the debris into smaller pieces that settled back into the profile. The decreased flux of CO2 observed in verticutting could also be a result of the introduction of oxygen into the soil profile where the verticutting made slits into the soil, which would potentially slow the decomposition of surface debris. The mechanism by which verticutting resulted in lower CO2 emissions warrants further study.

3.2. CH4 Emissions

Results showed no significant differences in CH4 emissions between fertilizer treatments across both years of the study (Table 1). In 2013, there were also no significant differences between the cultivation practices (Table 1); however, in 2014, significant differences between the cultivation practices were observed (Table 1). In 2014, verticutting yielded significantly more CH4 emissions than did the uncultivated control. During this growing season, 4 dates showed significant treatment differences, with verticutting yielding the highest fluxes in 3 of those 4 dates. Of these 3 events, one showed large differences between the treatments and occurred 4 days after the second of two significant (>5 cm) rainfall events. It is likely that these large rainfall events shifted the microbial community and resulted in the large CH4 flux we observed on 23 June 2014. Given that verticutting does not penetrate deeply into the soil [24], this is likely a result of water being retained in the upper part of the soil, although our data did not show significant differences in soil moisture content in 2014 (likely because sampling did not occur immediately following rainfall events). In 2013, neither soil temperature nor soil moisture were significant predictors of soil CH4 flux, which is unsurprising since there were no significant soil CH4 fluxes. However, in 2014, both soil temperature (parameter estimate 0.00192, p < 0.05) and soil moisture (parameter estimate 0.00154, p < 0.01) were significant predictors of the soil CH4 emission observed, thus the differences observed in the verticutting treatment are likely due to differences in soil moisture among the cultivation treatments.

3.3. N2O Emissions

Results showed no significant differences in N2O emissions based on fertilizer or cultivation practice in 2013 (Table 1); however, in 2014, both fertilizer and cultivation practices showed significant differences between treatments (Table 1). In 2013, despite the absence of a significant difference between fertilizer treatments across the growing season, there were 2 dates on which significant differences between fertilizer treatments occurred (Figure 4), and in both cases, the urea treatment fluxed more soil N2O than the unfertilized control. This same trend continued into 2014, with urea treatments fluxing more soil N2O than the unfertilized control across the season and on 16 of 24 sampling dates (Figure 4b), hence across the season. Significant differences between cultivation practices were not observed in 2014 (Table 2), which was wetter than in 2013. The wet conditions, in combination with the release of soluble nitrogen from the urea applications, are the likely cause of the increased flux of soil N2O observed in 2014 [5,12,13,16]. Given the role of soil moisture in accelerating denitrification [46,47,48], this result is not surprising and is consistent with what others have found [13,17]. The regression analysis did not reveal soil temperature and soil moisture as significant predictors in 2013; however, in 2014, both soil temperature (parameter estimate 0.00096, p < 0.0001) and soil moisture (parameter estimate 0.00090, p < 0.0001) were significant predictors of soil N2O flux, supporting the idea that some of the soil N2O flux observed in this study was due to differences in soil moisture between the cultivation treatments.
Although a few dates in 2013 showed significant differences between cultivation treatments, no consistent trend emerged (Table 1). In 2014, cultivation practice had a significant impact on soil N2O emissions, with the hollow-tine treatment fluxing significantly more soil N2O than both the verticutting and the uncultivated control (Table 1). This trend was observed on 6 of the 7 sampling dates, showing significant differences between cultivation practices throughout the 2014 growing season (Figure 5). This is consistent with what we understand about the nitrogen cycle in that the hollow-tine cultivation treatment creates preferential water pathways into the soil profile, resulting in very wet spots near the holes created by the hollow-tines [24,49]. Although there were no significant differences in soil moisture content, 2014 experienced twice as much rainfall (nwroc.umn.edu/weather, accessed on 28 June 2022) during the growing season (Table 2), which likely resulted in more wet spots associated with the aerification holes. As discussed above, the first limiting factor in denitrification is the absence of oxygen; thus, as the soil experiences a higher moisture content, the potential for denitrification is higher [46,47,48].

3.4. Turfgrass Color and Quality

For turfgrass color, cultivation practice, and N fertilizer treatment were significant (p < 0.0001) for 2013 and 2014 (Table 3). Cultivation and fertilizer treatment interactions (p < 0.05) only occurred twice in July and October of 2013 (Figure 6a). However, in 2014, cultivation and fertilizer interactions occurred 79% of the time (Figure 6b). The fertilized plots that were aerified using hollow-tines produced the greenest turf in 2013 (Figure 6a), followed by the fertilized uncultivated control and the verticutted plots (p < 0.001). Whereas in 2014 (Figure 6b), both the fertilized hollow-tine and the fertilized uncultivated control produced the greenest turf, followed by the fertilized verticutted plots (p < 0.01). The use of urea greatly improved turfgrass color for all cultivated (hollow-tined and verticutted) and uncultivated fertilized plots in 2013 (Figure 6a) and 2014 (Figure 6b). The plots that were hollow-tined and fertilized had the highest turfgrass color values in 2013 (p < 0.001). In 2014, all fertilized plots (hollow-tined, verticutted, and uncultivated control) produced the greenest turf (p < 0.001).
Following cultivation events in May (2014) and September (2013 & 2014), urea fertilizer helped the turfgrass recover faster and produced a greener turfgrass stand throughout the growing season (Figure 6). The fertilized verticutted plots had lower canopy greenness following cultivation (September 2013) than the other fertilized plots (hollow-tined and un-cultivated control). Turfgrass color for the verticutted plots with urea fell below 0.6 on the canopy greenness NDVI scale following cultivation in September 2013. However, the verticutted plots with urea only took one week to recover to an NDVI reading above 0.6 in turfgrass color after cultivation (no data for May 2013). In May 2014, the fertilized hollow-tined and uncultivated control plots were greener than the fertilized verticutted plots. In September 2014, the fertilized hollow-tined plots alone were greener than the fertilized verticutted plots. Following cultivation in May and September, the fertilized verticutted plots had NDVI readings of 0.77 and 0.86, respectively. Both of which are above 0.6 on the NDVI scale for turfgrass color. The unfertilized verticutted treatment was acceptable for turfgrass quality (=6.0) following all cultivation events. The unfertilized verticutted treatment fell below 0.6 NDVI for turfgrass color following cultivation but so did the unfertilized hollow-tine treatment 50% of the time.
For turfgrass quality, cultivation practice and N fertilizer treatment were significant (p < 0.0001) for 2013 and 2014 (Table 3). An interaction (Figure 6c,d) between cultivation and fertilizer (p < 0.05) occurred only 5 times in 2013 (2 dates in July and September; 1 date in October) whereas in 2014 an interaction occurred for 54% of the sampling dates (except for 3 dates in May and August; 2 dates in September; 1 date in June, July, and October). For cultivation, the hollow-tined and uncultivated control plots had significantly (p < 0.001) higher turfgrass quality than the verticutted plots over the study period. Urea increased (p < 0.001) turfgrass quality for all fertilized plots (hollow-tined, verticutted, and uncultivated control) in 2013 and 2014 (Figure 6). Following cultivation in June 2013, the fertilized uncultivated control had the highest turfgrass quality, followed by the fertilized hollow-tine and the fertilized verticutted treatments. Whereas following the September 2013 and May 2014 cultivations, all the fertilized cultivated treatments (uncultivated, hollow-tined, verticutted) were statistically the same. In September 2014, the fertilized hollow-tined and fertilized uncultivated control had higher turfgrass quality ratings than the fertilized verticutted treatment. All the turfgrass quality ratings for the fertilized and cultivated treatments were above 7.0. Turfgrass quality for the unfertilized verticutted plots had the lowest ratings throughout the study period, ≤6.0, for 60% of the sampling dates.
Following cultivation events, turfgrass color (May 2014) and quality (2013–2014) were affected due to surface disturbance for all plots (Figure 6). However, plots that were treated prior to and after cultivation with fertilizer (urea) recovered. The verticutted plots had the lowest turfgrass color and quality immediately following cultivation (May 2014 and September 2013–2014). When the verticutting depth is set to the lowest setting, thatch, roots, rhizomes, stolons, and leaves are mechanically ripped out and can cause extensive surface damage [24]. This type of surface damage or stress can result in lower turfgrass color and quality values [35,36]. However, it is important to note that for the verticutted urea treatment, the turfgrass quality values were above acceptable levels (>6.0) following all cultivation events during the study period [32]. Hollow-tine aerification can also be disruptive to the surface as tines are injected into the soil and soil cores are removed [24]. This is especially true for golf courses putting greens where the mowing height is low (≤0.32 cm for Creeping bentgrass greens). However, athletic fields are mowed at a higher height (3.8–7.6 cm for Kentucky bluegrass athletic fields) and can therefore hide the aerification holes and any mechanical damage beneath their canopy [23]. Turfgrass color and quality support this, with values being higher for the hollow-tined plots.
It is recommended that golf course putting greens are aerified twice a year in Spring and Fall (same as study plots). Cultivation recommendations for athletic fields are twice a year (May and September), and lawns are generally aerified once a year in the spring for Kentucky bluegrass. However, for athletic fields under severe traffic stress, cultivation is recommended more often during the season to reduce soil compaction. As our results show, aerifying turfgrass using hollow-tine cultivation twice per year led to increased GHG emissions. When turfgrass managers need to cultivate more often on athletic fields, other cultivation techniques that limit GHG emissions should be implemented.

4. Conclusions

In this study, CO2 flux contributed to 99% of the global warming potential even when considering the flux of N2O and CH4. As a result, urea contributed significantly more to the global warming potential than the unfertilized control. Hollow-tine aerification contributed significantly more to the global warming potential than verticutting. Thus, to reduce global warming potential turfgrass managers should implement minimal soil disturbance techniques like verticutting when cultivating. Even though hollow-tine aerification had significantly higher turfgrass quality ratings (8.0, with 6.0 being acceptable), the magnitude of the differences was not high. To reduce GHGs, verticutting could be added to an existing management plan when turfgrass managers want to implement more cultivation strategies while maintaining acceptable turfgrass color and quality. The fertilized verticutting cultivation had favorable turfgrass quality (>7.0, with 6.0 being acceptable) and therefore would be a preferable choice for turfgrass managers when selecting environmentally friendly cultivation practices to reduce global climate change impacts.

Author Contributions

Conceptualization, K.E.C. and K.S.W.; methodology, K.E.C. and K.S.W.; resources, K.E.C. and K.S.W.; writing—original draft preparation, K.E.C. and K.S.W.; writing—review and editing, K.E.C. and K.S.W.; visualization, K.E.C. and K.S.W.; supervision, K.E.C. and K.S.W.; project administration, K.E.C. and K.S.W.; funding acquisition, K.E.C. and K.S.W. All authors have read and agreed to the published version of the manuscript.

Funding

Funding for this project was provided by the Minnesota Turf and Grounds Foundation and by the University of Minnesota Crookston.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Acknowledgments

This work could not have been completed without the hours of work by many undergraduate research students: Amber Koep, Wade Wallace, Andrea Ramponi, Gylatso Gurung, DeAndra Navratil, Constantin Adelakoun, Melissa Carlson, Nathan Harthoom, and Michael Laurich.

Conflicts of Interest

The mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the University of Minnesota.

References

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Horticulturae 10 00869 g001
Figure 1. Total rainfall (mm) and mean air temperatures (C) were recorded during the growing season (May–October) of 2013–2014. Weather data were collected by a local weather station located at the Northwest Regional Outreach Center (Crookston, MN, USA).
Figure 1. Total rainfall (mm) and mean air temperatures (C) were recorded during the growing season (May–October) of 2013–2014. Weather data were collected by a local weather station located at the Northwest Regional Outreach Center (Crookston, MN, USA).
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Figure 2. Carbon dioxide (CO2) emissions for each of the fertilizers (Unfertilized Control, Urea) in 2013 (a) and 2014 (b). Note: The y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
Figure 2. Carbon dioxide (CO2) emissions for each of the fertilizers (Unfertilized Control, Urea) in 2013 (a) and 2014 (b). Note: The y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
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Figure 3. Carbon dioxide (CO2) emissions by cultivation practice in 2013 (a) and 2014 (b). CT = uncultivated control; HT = hollow-tine cultivation; VC = verticutting cultivation. Notes: a HT > VC; b CT = HT > VC; c HT > CT; d CT > VC; e VC > CT = HT; f VC > HT; g CT > HT = VC; i HT > CT = VC; letters do not represent LSD notations; the y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
Figure 3. Carbon dioxide (CO2) emissions by cultivation practice in 2013 (a) and 2014 (b). CT = uncultivated control; HT = hollow-tine cultivation; VC = verticutting cultivation. Notes: a HT > VC; b CT = HT > VC; c HT > CT; d CT > VC; e VC > CT = HT; f VC > HT; g CT > HT = VC; i HT > CT = VC; letters do not represent LSD notations; the y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
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Figure 4. Nitrous oxide (N2O) emissions by fertilizer (Unfertilized Control, Urea) in 2013 (a) and 2014 (b). Note: The y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
Figure 4. Nitrous oxide (N2O) emissions by fertilizer (Unfertilized Control, Urea) in 2013 (a) and 2014 (b). Note: The y-axis scale is different by year to highlight differences between treatments. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
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Figure 5. 2014 Nitrous oxide (N2O) emissions by cultivation practice. CT = uncultivated control; HT = hollow tine cultivation; VC = verticutting cultivation. Notes: a HT > VC; c HT > CT; e VC > CT = HT; i HT > CT = VC; j VC > CT; letters do not represent LSD notations. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
Figure 5. 2014 Nitrous oxide (N2O) emissions by cultivation practice. CT = uncultivated control; HT = hollow tine cultivation; VC = verticutting cultivation. Notes: a HT > VC; c HT > CT; e VC > CT = HT; i HT > CT = VC; j VC > CT; letters do not represent LSD notations. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot.
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Figure 6. The effects of cultivation (HT = Hollow-tined, CT = Uncultivated Control, and VC = Verticutting) and fertilizer [(Urea or Control (Unfertilized)] on turfgrass color (NDVI −1 to 1) in 2013 (a) and 2014 (b) and turfgrass quality (1–9 visual scale; where 1 = completely brown dead turf, 6 = minimally acceptable turf, and 9 = optimum uniformity, density, and greenness) in 2013 (c) and 2014 (d). Data points on the graphs represent means by date. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot. Data were not available from June to mid-July 2013 (a) due to technical issues with the equipment.
Figure 6. The effects of cultivation (HT = Hollow-tined, CT = Uncultivated Control, and VC = Verticutting) and fertilizer [(Urea or Control (Unfertilized)] on turfgrass color (NDVI −1 to 1) in 2013 (a) and 2014 (b) and turfgrass quality (1–9 visual scale; where 1 = completely brown dead turf, 6 = minimally acceptable turf, and 9 = optimum uniformity, density, and greenness) in 2013 (c) and 2014 (d). Data points on the graphs represent means by date. * Means are significantly different at the 0.05 level according to LSD. Cultivation occurred on 31 May and 12 September, 2013, and on 20 May and 5 September, 2014. Plots were fertilized the first week of every month from May to October with an annual N rate of 221 kg N ha−1 yr−1. For May, September, and October, a rate of 49 kg N ha−1 was applied to each plot. For June, July, and August, 24.5 kg N ha−1 was applied to each plot. Data were not available from June to mid-July 2013 (a) due to technical issues with the equipment.
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Table 1. Mean and median soil CO2, N2O, CH4 flux by year, cultivation practice, and fertilizer treatment.
Table 1. Mean and median soil CO2, N2O, CH4 flux by year, cultivation practice, and fertilizer treatment.
CO2N2OCH4
YearTreatmentMeanMedianMeanMedianMeanMedian
g CO2-C m−2 h−1µg N2O-N m−2 h−1µg CH4-C m−2 h−1
2013
Cultivation
CT0.27 ab0.213.631.64−3.24−3.53
HT0.28 a0.263.052.89−3.38−2.52
VC0.24 b0.217.991.277.92−0.864
Fertilizer
Urea0.29 A0.268.132.920.201−1.30
UC0.24 B0.191.651.260.864−2.59
ANOVA
Source of Variationdf df df
  Cultivation2*2NS2NS
  Fertilizer1***1NS1NS
  Cultivation × Fertilizer2NS2NS2NS
2014
Cultivation
HT0.44 a0.3532.5 a14.310.8 ab0.30
VC0.33 b0.2820.5 b8.9520.1 a2.90
CT0.41 a0.3614.6 b8.42.66 b−1.94
Fertilizer
Urea0.44 A0.3939.6 A21.89.36−1.58
UC0.35 B0.297.41 B4.7413.01.22
ANOVA
Source of Variationdf df df
  Cultivation2***2**2*
  Fertilizer1***1***1NS
  Cultivation × Fertilizer2NS2NS2NS
CT = uncultivated control; HT = hollow tine cultivation; VC = verticutting cultivation; Urea = urea fertilizer, (221 kg N ha−1 yr−1); UC = unfertilized control, (0 kg N ha−1 yr−1). Within columns, means followed by a different letter are significantly different according to LSD (0.05). Capital letters represent statistical differences between fertilizer treatments; lowercase letters represent statistical differences between cultivation treatments. No letter means nonsignificant. * Significant at the 0.05 probability level; ** Significant at the 0.01 probability level; *** Significant at the 0.001 probability level; NS, nonsignificant.
Table 2. Mean and median soil moisture (%) by year, cultivation practice, and fertilizer treatment.
Table 2. Mean and median soil moisture (%) by year, cultivation practice, and fertilizer treatment.
YearTreatmentMeanMedian
2013
Cultivation
HT13.6 a12.8
VC12.2 b10.5
CT11.9 b10.4
Fertilizer
Urea13.110.7
UC12.111.8
ANOVA
Source of Variationdf
  Cultivation2*
  Fertilizer1NS
  Cultivation × Fertilizer2NS
2014
Cultivation
HT19.617.6
VC20.217.8
CT19.617.3
Fertilizer
Urea18.7 B18.9
UC20.7 A20.7
ANOVA
Source of Variationdf
  Cultivation2NS
  Fertilizer1*
  Cultivation × Fertilizer2NS
CT = uncultivated control; HT = hollow tine cultivation; VC = verticutting cultivation; Urea = urea fertilizer, (221 kg N ha−1 yr−1); UC = unfertilized control, (0 kg N ha−1 yr−1). Within columns, means followed by a different letter are significantly different according to LSD (0.05). Capital letters represent statistical differences between fertilizer treatments; lowercase letters represent statistical differences between cultivation treatments. No letter means nonsignificant. * Significant at the 0.05 probability level; NS, nonsignificant.
Table 3. The effects of cultivation and N fertilizer treatment on mean annual turfgrass color and turfgrass quality.
Table 3. The effects of cultivation and N fertilizer treatment on mean annual turfgrass color and turfgrass quality.
TreatmentTurfgrass ColorTurfgrass Quality
2013201420132014
NDVIVisual Rating (1–9 Scale)
Cultivation
HT0.75 A0.82 A7.5 A7.4 A
VC0.64 C0.76 B7.0 B7.0 B
CT0.70 B0.82 B7.4 A7.3 A
Fertilizer
Urea0.75 a0.86 a8.0 a7.9 a
UC0.64 b0.74 b6.6 b6.6 b
ANOVA
Source of Variation
Cultivation ************
Fertilizer ************
Cultivation × FertilizerNS********
Turfgrass color, the Normalized Difference Vegetation Index (NDVI) measurements can range from −1 to 1, with higher values indicating greater plant health. Turfgrass quality is a visual rating of 1–9; where 1 = completely brown dead turf, 6 = minimally acceptable turf, and 9 = optimum uniformity, density, and greenness. HT = hollow-tine cultivation; VC = verticutting cultivation CT = uncultivated control; Urea = urea fertilizer, (221 kg N ha−1 yr−1); UC = unfertilized control, (0 kg N ha−1 yr−1). Within columns, means followed by a different letter are significantly different according to LSD (0.05). Capital letters represent statistical differences between fertilizer treatments; lowercase letters represent statistical differences between cultivation treatments. No letter means nonsignificant. ** Significant at the 0.01 probability level; *** Significant at the 0.001 probability level; NS, nonsignificant.
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Walker, K.S.; Chapman, K.E. The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields. Horticulturae 2024, 10, 869. https://doi.org/10.3390/horticulturae10080869

AMA Style

Walker KS, Chapman KE. The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields. Horticulturae. 2024; 10(8):869. https://doi.org/10.3390/horticulturae10080869

Chicago/Turabian Style

Walker, Kristina S., and Katy E. Chapman. 2024. "The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields" Horticulturae 10, no. 8: 869. https://doi.org/10.3390/horticulturae10080869

APA Style

Walker, K. S., & Chapman, K. E. (2024). The Effects of Cultivation Practices and Fertilizer Use on the Mitigation of Greenhouse Gas Emissions from Kentucky Bluegrass Athletic Fields. Horticulturae, 10(8), 869. https://doi.org/10.3390/horticulturae10080869

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