Biochar is a pyrolytic product generated by heating biomass in the absence of oxygen such as during bioenergy production. Biochar can be made from various feedstocks and research into its potential use in agricultural systems has examined its effects on plant growth, trace gas emissions, and N loss. However, since a paucity of work has examined biochar use in horticultural container production systems, we investigated how biochar additions to growth media impacted trace gas efflux (CO2, CH4, and N2O), plant growth, and N loss via leachate in two separate experiments: a peat-based greenhouse study using viola (Viola cornuta L. ‘Sorbet® XP Deep Orange’) and a pinebark-based outdoor study using daylily (Hemerocallis x ‘EveryDaylily Cream PBR’ L.). Biochar had little effect on viola growth, but growth inhibition was noted for daylily. Both studies clearly showed that N in leachate was reduced by biochar additions, with higher biochar rates having greater effects on reducing N loss. Reductions in N loss with biochar suggest improved N use efficiencies in agricultural systems. Biochar use also decreased N2O and CO2 fluxes in daylily, which suggests that biochar could help mitigate global climate change. Our results suggest that future studies should focus on testing lower rates of biochar in terms of growth and environmental impacts. The complexities of N management highlight the importance of developing biochar practices that increase N retention for the benefit of both agriculture and the environment.

Species used in this study: viola (Viola cornuta L. ‘Sorbet® XP Deep Orange’); daylily (Hemerocallis x ‘EveryDaylily Cream PBR’ L.).

Ornamental plant producers may be incentivized to alter production practices to reduce greenhouse gas (GHG) emissions in response to oncoming legislation, potential tax incentives or consumer demand. Two studies investigated biochar as a substrate amendment to mitigate GHG emissions from the production of one annual [viola (Viola cornuta L. ‘Sorbet® XP Deep Orange’)] and one perennial [daylily (Hemerocallis x ‘EveryDaylily Cream PBR’ L.)] crop. Viola growth was evaluated over 42 days in five treatments [80:20 peatmoss:perlite (PMP) amended with 0, 5, 10, 20, or 30% biochar by volume]. Treatments included (1) 100% PMP, (2) 95:5 PMP:biochar, (3) 90:10 PMP:biochar, (4) 80:20 PMP:biochar, and (5) 70:30 PMP:biochar. At study termination, no differences were observed for viola top dry weight or total plant N across treatments. Emissions of N2O were significantly less for the 30% biochar treatment at one sampling date; no differences occurred for total emissions of CO2, N2O or CH4. Daylily was evaluated over 74 days in four treatments (6:1 pinebark (PB):sand control, or PB mixed with 10, 20 or 30% biochar by volume). Treatments included (1) 6:1 PB:sand, (2) 90:10 PB:biochar, (3) 80:20 PB:biochar, and (4) 70:30 PB:biochar. In general, daylily top dry weight, root dry weight, and total plant N was less for all biochar treatments compared to the control. Most notably, results early in the study indicated that the O biochar control treatment had higher N2O emissions than those with any level of biochar. Total emissions of N2O and CO2 declined with increasing amounts of biochar. Results from both studies suggested N in leachate was reduced by biochar use. Given the growth inhibition of daylily with higher biochar levels, future work will focus on evaluating lower biochar rates and differing incorporation strategies on growth and GHG emissions.

Since the onset of the industrial revolution, atmospheric concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have increased significantly (Dlugokencky et al. 2005, IPCC 2007, Prinn et al. 2000). These trace gases are the primary greenhouse gases (GHG) thought to be driving factors in global climate change (Dlugokencky et al. 2005, Florides and Christodoulides 2008). Energy production is the largest contributor to GHG emissions in the U.S, followed by agriculture (Johnson et al. 2007). Agriculture accounts for approximately one-fifth of the annual increase in emissions of these trace gases; when one considers land use changes (e.g., land clearing, biomass burning, soil degradation), the overall radiative forcing from agriculture production accounts for approximately a third of the anthropogenic greenhouse effect (Cole et al. 1997). Thus, development of mitigation strategies to reducing trace gas emissions from the agricultural sector is crucial to lessen impacts of climate change.

Altering agriculture production practices to mitigate trace gas emissions has been widely investigated (Cole et al. 1997, Kroeze and Mosier 2000, Lal 2004, Paustian et al. 2000, Smith et al. 2007). Most of the work on reducing trace gas emissions has focused on row crops, forests, and animal production systems. Little emphasis has been placed on contributions from specialty crop systems such as horticulture even though it is a multi-billion-dollar industry impacting rural, suburban, and urban environments (Hall et al. 2018). For example, 7,300 nursery crop producers (top 17 states) occupied approximately one-half million acres (USDA 2007). In Alabama, this industry (nursery, greenhouse, and floriculture) is estimated at $629.2 million annually and supports ∼8,000 jobs (ACES 2013). Given the magnitude of the green industry and its contribution to national, state and local economies, it is important to understand how industry management practices can be altered to mitigate climate change.

Increased interest in bioenergy has resulted in enhanced availability of biochar, a pyrolytic byproduct generated during bioenergy production from various feedstocks. Research into potential uses of biochar in agricultural systems has examined its effects on growth, yield, soil carbon sequestration, and movement of nutrients within and out of these systems, including as trace gases (Laird 2008, Clough and Condron 2010, Agegnehu et al. 2017, Ding et al. 2017, Nguyen et al. 2017). While less is known about the effects of biochar in horticultural container production systems, it represents a mechanism for increasing C sequestration and for mitigating trace gas emissions from growth substrates used in these systems by adding a highly recalcitrant form of carbon into the landscape at planting.

Some work has evaluated plant responses in growth media amended with biochar. Álvarez et al. (2018) reported that adding biochar (up to 12%) and vermicompost (up to 30%) to peat moss enhanced petunia (Petunia x hybrida hort. Ex E. Vilm.) and Pelargonium [Pelargonium peltatum (L.) L’Hér] plant size and flower production when compared with peat moss alone. In another study of Pelargonium [P. zonale (L.) L’Hér] response to peat replacement with biochar, Conversa et al. (2015) reported that plant growth was enhanced by biochar concentrations up to 30% when used with fertilization; however, greater rates of biochar replacement negatively impacted growth. Tomato (Lycopersicum esculentum Mill.) and pepper (Capsicum annuum L.) plant growth and development were also shown to be significantly enhanced by biochar addition (1-5%) to a commercial media containing coconut fiber and tuff (Graber et al. 2010). They attributed these positive responses from biochar to shifts towards beneficial plant growth promoting rhizobacteria or fungi and/or low doses of biochar chemicals stimulating plant growth.

Other studies have evaluated the effects of biochar additions to growth media on nutrient leaching. An examination of a standard PP (85:15 v:v) growth medium amended with 0-10% biochar suggested that biochar addition could be effective in moderating extreme fluctuations of nitrate levels in container substrates over time (Altland and Locke 2012). These same researchers also reported that biochar type influenced macronutrient retention and leaching, with each macronutrient responding differently and each biochar type having a different impact (Altland and Locke 2013). Bradley et al. (2015) found that increasing levels of biochar (0-5%) decreased cumulative levels of total N (21-59%), nitrate (17-46%), and ammonia (46-90%) in leachate, but increased cumulative leaching of total P. Nemati et al. (2014) also showed decreased nutrient leaching (11%) from adding biochar (30%) to a peat moss growth media compared with peat moss alone; additions of biochar also increased cation-exchange capacity and pH. In a study examining runoff from a greenroof study, Beck et al. (2011) reported that that adding biochar (7%) to a peat-based growth media (ProMix) increased water retention and significantly decreased total N, total P, nitrate, phosphate, and organic C in discharge. These findings suggest that biochar addition could improve downstream water quality by reducing N, P, and organic C losses, decreasing turbidity and discharge quantity.

In addition to potential reductions in nutrient loss through leaching, biochar use could be included in mitigation strategies to minimize trace gas emissions associated with current management practices. Wu et al. (2019) reported that incorporation of a biochar amendment in the presence of vermicompost significantly decreased (14.1-18.6%) cumulative N2O emissions and that the lowest emissions of both NH3 and N2O were achieved using biochar in combination with a low dose of vermicompost. Reduced N2O emissions (up to ∼60%) with additions of biochar were also reported by Kammann et al. (2012), who found that biochar improved the greenhouse gas (GHG) to crop yield ratio under field-relevant conditions, which is important for growers concerned with climate change.

Recent efforts at our laboratory have begun to investigate contributions of the Southeastern horticulture container industry to climate change (Marble et al. 2011, Prior et al. 2011), as well as opportunities to reduce these contributions (by decreasing GHG emissions and/or increasing C sequestration) through management. These systems primarily use a soilless PB-based potting growth substrate (Marble et al. 2011, 2016). Previous work has examined effects of container size (Marble et al. 2012a), fertilizer placement (Marble et al. 2012b) and/or irrigation (Murphy et al. 2018) on growth and GHG emissions. This work has utilized a number of varying plant types, e.g., woody or herbaceous, perennial or annuals, and sun or shade tolerant (Murphy et al. 2019). More recent work has begun to examine how use of alternative growth media (as opposed to PB or peat-based substrates) might impact growth and GHG emissions from ornamental plants (Murphy et al. 2021).

Given the potential of biochar to reduce GHG emissions and to enhance soil C sequestration, it was logical for our work to progress into examining biochar incorporation in nursery containers. While some research has examined the effects of biochar additions to peat-based growth media, no work to our knowledge has investigated biochar use in PB-based container systems. The primary objective of this research was to determine how different levels of biochar additions to growth media impact trace gas efflux (CO2, CH4, and N2O) in two separate experiments: a peat-based greenhouse study and a PB-based outdoor study. In addition, this work examined impacts of biochar additions on plant growth and loss of nitrogen via leachate.

Two separate biochar studies were conducted. In the first study, the Paterson Greenhouse Complex (Auburn University, AL) was utilized with viola (Viola cornuta L. ‘Sorbet® XP Deep Orange’) as the test crop. On August 31, 2018, liners [3 plugs from a 200-cell flat per pot] were transplanted into 1.33 L (1.41 qt) pots (06.00 AZ TW; Dillen Products, Middlefield, OH). Containers were filled with a peat:perlite (80:20) media. Treatments were established by adding biochar (Premium Biochar; Mother Earth®, Vancouver, WA) to the standard greenhouse growth medium [80:20 (v:v) fine professional sphagnum peatmoss: coarse horticultural perlite (PM:P) blend] to create five treatments: 1-) 0% biochar (100% 80:20 PM:P); 2-) 5% biochar (remaining 95% is 80:20 PM:P blend); 3-) 10% biochar (remaining 90% is 80:20 PM:P blend); 4-) 20% biochar (remaining 80% is 80:20 PM:P blend); and 5-) 30% biochar (remaining 70% is 80:20 PM:P blend). All substrate treatments were amended on a per cubic yard basis at mixing with: 2.3 kg (5 lb) dolomitic limestone, 0.9 kg (2 lb) of 8:2.2:10 N:P:K (8-5-12 N:P2O5:K2O) starter nutrient charge (GreenCare Fertilizers, Kankakee, IL), and 0.45 kg (1 lb) AquaGro-G granular wetting agent (The Scotts Co., Marysville, OH).

The study used 12 replicates for each treatment; all containers were placed on greenhouse benches in a randomized complete block design. Containers were hand-watered as needed (generally, every 2-3 days). Containers were fertigated (150 ppm N 20-10-20 fertilizer; GreenCare Fertilizers, Kankakee, IL) four times over the course of the study [days after planting (DAP) 13, 17, 31, and 39].

Pour-thru leachates were collected from unused substrate mixtures at study initiation (1 DAP) using the Virginia Tech Pour-Thru technique to determine substrate pH and EC (Altland 2021, Wright 1986). Leachates were collected at three additional dates (13, 31, and 41 DAP). Given the protocol for conducting pour-thru leachates, which requires substrates to be saturated to their maximum water-holding capacity and then waiting 60 minutes to allow substrates to reach equilibrium, four separate reps were used to collect leachates at each collection date.

After leachate collection, samples were centrifuged, vacuum filtered through a 0.45 µm membrane, acidified with concentrated HCl, and then stored at 4 C (39 F) until analysis. Filtered samples were analyzed for inorganic N using the Lachat QuickChem 8500 Series 2 Flow Injection Analysis System (Hach, Loveland, CO). This method of determining N used colorimetric procedures like those described by Kovar and Pierzynski (2009).

Trace gas efflux from containerized plants in this first experiment were sampled in situ four times across the final 10 days of the study (DAP 32, 35, 39, and 42) using the static closed chamber method (Hutchinson and Mosier 1981, Hutchinson and Livingston 1993). Based on criteria described in the GRACEnet protocol (Baker et al. 2003, Parkin and Kaspar 2006), we constructed custom-made gas efflux chambers designed to accommodate nursery containers. These chambers consisted of a polyvinyl chloride (PVC) cylinder base [25.4 cm (10 in) inside diameter by 38.4 cm (15.1 in) tall] that was sealed at the base. During gas efflux measurement, the containerized plant was placed inside the base cylinder; a vented efflux chamber [25.4 cm (10 in) diameter x 11.4 cm (4.5 in) height] was then placed on top of the base cylinder. The top efflux chambers were also constructed of PVC, covered with reflective tape, and contained a center sampling port. Following chamber closure, samples for CO2, CH4, and N2O were taken at 0-, 20-, and 40-minute intervals. At each interval, the center sampling port was pierced with a polypropylene syringe and a 10 mL (0.6 in3) gas sample extracted; samples were then transferred by injection into evacuated glass vials [6 mL (0.4 in3)] fitted with butyl rubber stoppers (Parkin and Kaspar 2006) for analysis via gas chromatography.

A gas chromatograph (Shimadzu GC-2014, Columbia, MD) was used to analyze gas samples. This gas chromatograph was equipped with three detectors: a thermal conductivity detector for CO2, an electrical conductivity detector for N2O, and a flame ionization detector for CH4. Gas standards (Air Liquide America Specialty Gases LLC, Plumsteadville, PA) were used to develop standard curves from which gas sample concentrations were determined. Gas efflux was calculated from the rate of change in trace gas concentration in the chamber headspace during the time interval when the chambers were closed (Parkin and Venterea 2010); data were expressed as mg CO2-C, mg CH4-C, and mg N2O-N per day. Cumulative efflux estimates of each trace gas were calculated from efflux at each sampling date integrated over time using a basic numerical integration technique (i.e., trapezoidal rule).

At study termination, all plants were harvested. Shoots were cut at the soil line and roots were separated from the growing medium using the sieve method (Bohm 1979). Shoots and roots were dried for approximately 72 hours at 55 C (130 F) in a forced-air oven and weighed. Roots and shoots were then ground separately to pass through a 0.2 mm (0.08 in) mesh sieve and C and N determined using a LECO 600-CHN analyzer (St. Joseph, MI).

The second experiment was conducted at the soil bin facilities of the USDA-ARS National Soil Dynamics Laboratory, Auburn, Alabama and utilized daylily (Hemerocallis x ‘EveryDaylily Cream PBR’ L.) as the test species. As previously described by Prior et al. (2003), the bin used for the experiment was 6 m wide x 76 m long and was modified for container studies by installation of a geomembrane liner (20 mil) and gravel drain system to ensure a good working surface and drainage for container studies.

This study used 2.5 L (#1 trade gal) nursery containers filled with a PB:sand (6:1 v:v) media as a control (0% biochar). Biochar treatments consisted of containers filled with PB:biochar at 10, 20, or 30% biochar; specific treatments included (1) 6:1 PB:sand, (2) 90:10 PB:biochar, (3) 80:20 PB:biochar, and (4) 70:30 PB:biochar. The biochar used in this study was granulated coconut char (GC 8 X 30S; General Carbon Corp., Patterson, NJ). The growth media was amended with 6.9 g (0.015 lb) lime and 27 g (0.059 lb) fertilizer (16-5-10 Osmocote – 12-month release with micronutrients) per container. Rooted cuttings of daylily were potted into treatments on May 18, 2020. The study was conducted as a randomized complete block design of the four biochar treatments with six blocks.

To collect 100% of the leachate from containers, the 3 L containers were retrofitted with a collar constructed from another 3 L container. Each collar was made from the upper ∼10 cm (∼4 in) of the other container. This 10 cm was cut off, turned upside down, and slid onto an intact 3 L container from the bottom such that the collar was flush with the bottom of the intact container. The collar and the intact container were secured using silicone to insure a watertight seal. This retrofitted container was then snuggly placed over a 15.2 cm (6 in) standard nursery pot (drain holes sealed with silicone) to act as a leachate collection vessel. These retrofitted container/collection vessels were placed into modified standard wooden pallets to hold them in an upright and stable fashion.

Leachate was collected (from irrigation and rainfall events) and held in 3.8 L (1 gal) jugs. At the end of each week, total leachate volume was determined using graduated cylinders and a 50 ml subsample was collected for leachate N analyses. Leachate N was analyzed using the methods described for the first study above. From the volume and N analyses data we calculated N concentration, N content, and total N lost in leachate.

Trace gases were sampled weekly on the same 13 dates on which leachate was collected. Trace gases were measured using the same custom-made gas efflux chambers described for the first study. The methodologies used to collect, analyze, and manipulate the trace gas data in the viola study were used in this daylily experiment. Further, daylily plants were harvested, processed, and analyzed at study termination in the same manner described for the viola plants in the first study.

For both studies, data analyses were conducted using the Mixed Models Procedure (Proc Mixed) of the Statistical Analysis System (Littell et al., 1996). Means separations were performed using the LSMeans statement under Proc Mixed. In both studies, a significance level of (p ≤ 0.05) was established a priori.

Biomass (viola greenhouse study)

There was no effect of biochar on viola top dry weight (Table 1). However, in the highest biochar level (30%), viola had significantly greater root dry weight compared to all other treatments. Given that shoots dominated dry weight, total dry weight also did not different among biochar treatments. The overall total dry weight averaged 2.62 g per plant.

Table 1

Violaz biomass data [topy, rootx, and totalw dry weights (DW)], root:shoot ratiov (R:S), total Nu, and carbon:nitrogen ratiot (C:N) for the biochar treatment levels.

Violaz biomass data [topy, rootx, and totalw dry weights (DW)], root:shoot ratiov (R:S), total Nu, and carbon:nitrogen ratiot (C:N) for the biochar treatment levels.
Violaz biomass data [topy, rootx, and totalw dry weights (DW)], root:shoot ratiov (R:S), total Nu, and carbon:nitrogen ratiot (C:N) for the biochar treatment levels.

As seen with root dry weight, root-to-shoot ratio (R:S) was greatest at the highest biochar level (30%) and was significantly higher than all other treatments. Although total plant N was not affected by biochar level, the carbon-to-nitrogen ratio (C:N) was impacted by biochar treatments. The C:N was highest at 30% biochar and was significantly higher than all treatments except for 5% biochar (Table 1).

Trace gas efflux (viola greenhouse study)

There were no significant differences among biochar levels for viola daily trace gas efflux (CO2, CH4, and N2O) at any of the four measurement dates (Fig. 1). However, on DAP 39 there was a trend (p=0.096) for N2O to be lowest at highest level of biochar (Fig. 1). The average daily efflux across the sampling periods was 46.75 mg CO2-C·d−1, 0.0064 mg CH4-C·d−1, and 0.0056 mg N2O-N·d−1 and were not significantly affected by biochar level (Table 2). Cumulative efflux of all three trace gasses were also not significantly affected by biochar level and averaged 462.06 g CO2-C, 0.0630 g CH4-C, and 0.0599 g N2O-N (Table 2).

Fig. 1

Daily trace efflux (CO2, CH4, and N2O) at five levels of biochar (0, 5, 10, 20, and 30%) for the viola greenhouse study.

Fig. 1

Daily trace efflux (CO2, CH4, and N2O) at five levels of biochar (0, 5, 10, 20, and 30%) for the viola greenhouse study.

Close modal
Table 2

Violaz average daily and cumulative trace gas efflux for the biochar treatment levels.

Violaz average daily and cumulative trace gas efflux for the biochar treatment levels.
Violaz average daily and cumulative trace gas efflux for the biochar treatment levels.

Leachate nitrogen (viola greenhouse study)

In general, NO3 concentration in leachate was numerically lowest at the higher biochar levels (20 and 30%) and numerically highest at lower biochar levels (5 and 10%) for the first three sampling dates (Table 3). A similar response pattern was observed for NH4 concentration; thus, this overall pattern held true for total N concentration. Biochar-driven differences in both N species and total N became negligible at the last leachate sample date. When averaged across sampling dates, total N was significantly lower at 30% biochar than treatments with 0, 5, and 10% biochar(Table 3) Average leachate N for the 30% biochar treatment was numerically lower than that of 20% biochar, but statistically similar. In general, higher levels of biochar released less N from containers via leachate.

Table 3

Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the violax greenhouse study by sample date (DAP = days after planting) for the biochar treatment levels.

Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the violax greenhouse study by sample date (DAP = days after planting) for the biochar treatment levels.
Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the violax greenhouse study by sample date (DAP = days after planting) for the biochar treatment levels.

Biomass (daylily outdoor study)

Compared to the control (0 biochar), all biochar levels decreased top dry weight (Table 4). In general, top dry weight decreased with increasing biochar added to growth media. Root dry weight also showed decreases with biochar compared to the control; however, there were no significant differences among biochar addition rates (i.e., 10, 20, and 30%). Given that root dry weights were larger than top dry weights, total dry weight followed the same pattern seen with roots. As expected, R:S showed a reverse pattern, in which plants grown with 30% biochar had significantly greater R:S than all other treatments. Plant crowns (the small white cores located between the leaves and the roots) and flowers showed a general pattern of decreasing numbers at higher biochar levels (Table 4).

Table 4

Daylilyz crown and flower numbersy, biomass data [topx, rootw, and totalv dry weights (DW)], root:shoot ratiou (R:S), total Nt, and carbon:nitrogen ratios (C:N) for the biochar treatment levels.

Daylilyz crown and flower numbersy, biomass data [topx, rootw, and totalv dry weights (DW)], root:shoot ratiou (R:S), total Nt, and carbon:nitrogen ratios (C:N) for the biochar treatment levels.
Daylilyz crown and flower numbersy, biomass data [topx, rootw, and totalv dry weights (DW)], root:shoot ratiou (R:S), total Nt, and carbon:nitrogen ratios (C:N) for the biochar treatment levels.

Total plant N content was significantly greater in controls (0 biochar) compared to all levels of added biochar (i.e., 10, 20, and 30%). In general, plant C:N increased as more biochar was added to the containers (Table 4).

Trace gas efflux (daylily outdoor study)

In general, CO2 efflux tended to decline with increasing biochar rates, but this decline was often not statistically significant, except for a few dates (Fig. 2). On DAP 1, CO2 efflux was higher (p=0.005) for the control (0 biochar) than for all levels of added biochar (10, 20, and 30%). On DAP 5, CO2 efflux was greater (p=0.040) at 10% biochar compared with 0 biochar or 30% added biochar. On DAP 12, CO2 efflux was greater (p=0.023) with 0 biochar and 10% added biochar than at 30% added biochar. On DAP 75, there was a trend (p=0.059) for the control (0 biochar) to have higher CO2 efflux than 20 and 30% added biochar. It was expected that CO2 flux would decrease as biochar percentages increased, which was the general pattern observed. This was expected for two reasons: 1-) more biochar = less organic substrate to be degraded by microbes leading to less CO2 flux; and 2-) biochar, particularly at the highest rate, reduced plant growth; smaller plants would be expected to respire less. It should also be noted that trace gas efflux data tend to be highly variable and don’t always follow the expected pattern.

Fig. 2

Daily trace efflux (CO2, CH4, and N2O) at four levels of biochar (0, 10, 20, and 30%) for the daylily outdoor study.

Fig. 2

Daily trace efflux (CO2, CH4, and N2O) at four levels of biochar (0, 10, 20, and 30%) for the daylily outdoor study.

Close modal

Daily CH4 efflux was not significantly affected by biochar rates and all rates resulted in containers being very small net sinks or sources of CH4 (Fig. 2). On DAP 68 and 75, trends (p=0.089 and p=0.102, respectively), were noted for 30% added biochar to have higher efflux than most other biochar rates. It is possible that at this highest tested rate of biochar, soil remained wet longer leading to greater anaerobic respiration and greater CH4 flux.

Early in the study, N2O efflux showed significant differences among biochar levels (Fig. 2). On DAP 3, the 0 biochar control had higher N2O efflux (p<0.001) than all levels of added biochar. On DAP 12 the control also showed higher N2O efflux (p<0.001) than all biochar additions; on this date 20% added biochar had higher N2O efflux than 10 and 30% biochar. On DAP 19, 0 and 20% biochar had higher N2O efflux (p=0.001) than 10 and 30% added biochar. On DAP 26, 10% added biochar had higher N2O efflux (p=.0001) compared to 0 and 30% biochar; further, 20% biochar had higher N2O efflux than the 0 biochar control. On DAP 33, the control (0 biochar) had lower N2O efflux (p=0.004) than all levels of added biochar. On all other dates, N20 efflux was not affected by biochar rate. As with the CO2 data, it was expected that - if biochar is binding N (as the leachate data suggest) - N2O flux should decrease as percentages of biochar increases. While this general pattern was observed in some of the data, the high variability in trace gas data, noted in the discussion of the CO2 results, impacted results for N2O flux as well.

The average daily CO2 efflux across sampling periods declined with increasing amount of biochar (Table 5). Average daily CH4 effluxes were low and showed no differences among biochar treatments. Average daily N2O efflux was highest for the control (0 biochar) and lowest at the highest biochar level (30%), with the other treatments falling between these extremes. Cumulative efflux of the three trace gases followed patterns like those seen for average daily efflux for each trace gas (Table 5).

Table 5

Daylilyz average daily and cumulative trace gas efflux for the biochar treatment levels.

Daylilyz average daily and cumulative trace gas efflux for the biochar treatment levels.
Daylilyz average daily and cumulative trace gas efflux for the biochar treatment levels.

Leachate nitrogen (daylily outdoor study)

In general, daily leachate NO3, NH4, and total N concentrations tended to decrease as biochar level increased (Table 6). The control (0 biochar) tended to have the highest leachate N concentrations and it was usually higher than all biochar added treatments. The highest biochar treatment (30%) usually had the lowest leachate N concentrations, but differences among the three biochar levels varied across sampling dates and with N type. Average leachate N concentrations also tended to decrease as biochar level increased (Table 6).

Table 6

Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.

Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.
Leachatez N concentrationY (NO3, NH4, and Total N in mg·L−1) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.

Leachate N content tended to follow the same general pattern as leachate N concentrations although fewer significant differences among the three levels of added biochar were noted (Table 7). Further, effects of biochar rate on leachate NO3 content became non-significant toward the end of the study, while NH4 and total N content in treatments with 30% biochar remained significantly lower than the other treatments throughout the study period. Again, average leachate N contents tended to decrease with increasing amount of biochar. Cumulative leachate N losses (NO3, NH4, and total N) were all highest with no added biochar (control) and tended to decline as biochar level increased with the lowest N content being at the highest biochar rate (30%; Table 8).

Table 7

Leachatez N contentY (NO3, NH4, and Total N in mg) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.

Leachatez N contentY (NO3, NH4, and Total N in mg) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.
Leachatez N contentY (NO3, NH4, and Total N in mg) for the daylilyx outdoor study by sample date (DAP = days after planting) for the biochar treatment levels.
Table 8

Cumulative leachatez N contenty (NO3, NH4, and Total N in mg) for the daylilyx outdoor study for the biochar treatment levels.

Cumulative leachatez N contenty (NO3, NH4, and Total N in mg) for the daylilyx outdoor study for the biochar treatment levels.
Cumulative leachatez N contenty (NO3, NH4, and Total N in mg) for the daylilyx outdoor study for the biochar treatment levels.

Biochar amendment to agricultural systems could potentially be a means of improving plant performance and soil conditions (Agegnehu et al. 2017). In our viola greenhouse study, biochar additions did not positively affect aboveground and total plant dry weights. However, root dry weight was observed to be significantly increased at the highest biochar addition level (30%). This may have been a result of nitrogen being tied up by biochar and unavailable to the plant, thereby leading to a proliferation of roots searching for nitrogen. Supporting this contention, we noted that top N concentration (data not shown) was lowest at this highest level of biochar despite having the largest root biomass. Plants grown with 30% biochar also had higher total C:N (as seen in Table 1), which was noted with top and root C:N values as well (data not shown).

Biochar amendment did not significantly impact trace gas efflux from viola at any of the four measurement dates. Average daily and cumulative efflux values were also not affected by biochar addition. However, we did note a trend for biochar to reduce N2O emissions on one date. It is important to note that technical problems prevented earlier assessments of trace gas efflux during the first month of the experiment. Thus, it is possible that we missed a biochar effect which might have occurred earlier in the growth cycle. To date, little work has examined effects of biochar on trace gas emissions in containerized systems. Kammann et al. (2012) reported reduced N2O emissions with biochar, but no significant effect on CH4 emissions. Wu et al. (2019) also found that incorporation of biochar (combined with vermicompost) reduced N2O emissions.

As opposed to trace gas findings, biochar addition did impact N leaching from viola in the greenhouse study. Higher levels of biochar reduced leachate NO3 and NH4 concentrations showing that biochar use resulted in less N loss from containers via leachate. Similarly, Beck et al (2011) showed that adding biochar (up to 7%) reduced N and P discharge from greenroof trays. Others have reported that biochar additions to a peat- and perlite-based media reduced nutrient leaching and those different types of biochar reacted differently for different nutrients (Altland and Locke 2012, 2013).

Unlike viola, biochar additions led to reductions in daylily dry weights. This was reflected in both top and root dry weight; plant crown and flower numbers also showed a pattern of decrease with higher biochar levels. In general, plant growth was lowest at the highest biochar level (30%). In terms of plant N, total content was reduced by biochar addition and was reflected by shifts in plant C:N. Conversa et al. (2015) reported no negative effects of biochar addition on plant growth if these additions did not exceed 30%. Graber et al. (2010) found that biochar enhanced development and productivity of pepper and tomato plants, but only tested biochar levels of 1-5%. Álvarez et al. (2018) noted that biochar additions to a peat/vermicompost growth media up to 12% (maximum tested) improved plant size and flower production compared to peat alone. In another containerized study, Kammann et al. (2012) reported that biochar addition to a soil/compost media significantly increased plant biomass compared to a soil control. Dumroese et al. (2011) reported that mixing peat growth media with biochar/wood flour pellets up to 25% demonstrated good properties for plant growth (e.g., hydraulic conductivity, water availability), but addition levels of 50% or higher would not be beneficial to plants. Collectively, the literature indicates that there may be a maximum level of biochar addition that can improve plant growth. This level may vary depending on plant species, growth media, and the makeup of the biochar. Specifically, biochars are diverse materials that have different properties depending on the original feedstock properties, pyrolysis conditions (e.g., temperature, processing, grinding, final particle size, etc.), and storage or other postproduction processes (Spokas et al. 2011), which can affect plant growth through a variety of mechanisms (e.g., pH, CEC, nutrient retention and availability, etc.). Thus, the use of different biochars might help explain some of the different responses noted between the viola and daylily studies.

Unlike the viola greenhouse study, biochar additions in the daylily outdoor study did have significant effects on lowering CO2 and N2O efflux with higher volumetric additions of biochar. The low, nonsignificant CH4 emissions noted here and in the viola study were not surprising since we have observed a similar response pattern in previous container studies (Marble et al. 2012a, b, Murphy et al. 2018, 2019, 2021). Methane emissions are generally small in non-saturated soils (Robertson et al. 2000); given that containerized media are often well drained, they do not have the anaerobic conditions needed for CH4 production and do not significantly contribute to total trace gas emissions from container-grown nursery crops.

Generally, adding biochar to the PB media reduced CO2 efflux, which tended to decline with increasing biochar rates. This effect for biochar to reduce CO2 emissions tended to be more apparent towards the beginning, rather than the end, of the daylily study. Similarly, N2O efflux was reduced by biochar in the first half of the study. Average daily and cumulative efflux values of these three trace gases followed patterns similar to those seen for daily efflux noted above. These findings support the contention that biochar use can reduce N2O emissions (Kammann et al. 2012, Wu et al. 2019) and further show that reduced CO2 efflux is another advantage of using biochar as a tool to reduce overall GHG emissions from contain production systems, which could help mitigate climate change.

As seen in the viola study, daily leachate NO3, NH4, and total N concentrations showed a pattern of decreasing with increasing levels of biochar. It was clear that the control with no biochar addition had the highest leachate N concentrations, and the highest biochar treatment (30%) usually had the lowest N levels. Likewise, this was reflected in the leachate N content values over the course of the study such that cumulative leachate N losses (NO3, NH4, and total N) were all highest with no added biochar (control) and showed a pattern of decline as biochar level increased. Nitrogen lost via surface water runoff can contribute to eutrophication issues in the landscape. Further, excess NO3 leaching to groundwater can have negative health effects for humans and livestock (Carpenter et al., 1998). The leachate content data clearly show that use of biochar reduced N loss and indicates that biochar can be used as a tool to mitigate N losses to the environment.

In conclusion, we found that biochar additions to a peat-based media had little effect on overall viola growth but growth inhibition in the PB-based media was noted for daylily. Given this was the first work with biochar use in a PB-based container system, we tested high biochar rates to identify a range of response for both growth and N losses from this system. Based on these results, future studies will focus on testing lower rates of biochar and impacts on growth and environmental responses. Further, since biochar is a highly variable product (based on feedstock material and pyrolysis methods), more extensive research is required to maximize environmental and agricultural benefits of using biochar in nursery production systems.

Results from both studies clearly showed that N in leachate was reduced by biochar additions, with higher biochar rates having greater effects on reducing N loss. In addition, decreased N2O and CO2 fluxes with increasing biochar rates was noted in the daylily study. Collectively, decreases in these trace gases could be beneficial in helping mitigate global climate change. Further, reductions in N loss from biochar use are significant since worldwide estimates of agricultural N use efficiency are low (∼30-50%) with the excess being lost to gaseous efflux, leaching, and/or runoff. Difficulties in N management highlight the importance of adopting practices that increase N retention (such as biochar additions) for the benefit of both agriculture and the environment.

Agegnehu,
G.,
Srivastava
A.K.,
and
Bird
M.I.
2017
.
The role of biochar and biochar-compost in improving soil quality and crop performance: A review
.
Appl. Soil Ecol
.
119
:
156
170
. .
Alabama Cooperative Extension System (ACES)
.
2013
.
Economic impacts of Alabama’s agricultural, forestry and related industries. Combined ANR-2012, ANR-2013, ANR-2014, ANR-2015, ANR-2016, ANR-2017, and ANR-2018
.
Alabama Cooperative Extension System, Auburn University, AL. https://www.madeinalabama.com/assets/2013/01/ECON-IMPACTS-AG.pdf. Accessed September 8, 2022
.
Álvarez,
J.M.,
Pasian
C.,
Lal
R.,
López
R.,
Díaz
M.J.,
and
Fernández
M.
2018
.
Morpho-physiological plant quality when biochar and vermicompost are used as growing media replacement in urban horticulture
.
Urban For. And Urban Green
.
34
:
175
180
. .
Altland,
J.E.
2021
.
The pour-through procedure for monitoring container substrate chemical properties: A review
.
Horticulturae
7
:
536
. .
Altland,
J.E.
and
Locke
J.C.
2012
.
Biochar affects macronutrient leaching from a soilless substrate
.
HortScience
47
:
1136
1140
. .
Altland,
J.E.
and
Locke
J.C.
2013
.
Effect of biochar type on macronutrient retention and release from soilless substrate
.
HortScience
48
:
1397
1402
. .
Baker
J.,
Doyle
G.,
McCarthy
G.,
Mosier
A.,
Parkin
T.,
Reicosky
D.,
Smith
J.,
and
Venterea
R.
2003
.
GRACEnet chamber-based trace gas flux measurement protocol
.
Trace Gas Protocol Development Committee
,
March 14
, p.
1
18
.
Beck,
D.A.,
Johnson
G.R.,
and
Spolek
G.A.
2011
.
Amending greenroof soil with biochar to affect runoff water quantity and quality
.
Environ. Pollut
.
159
:
2111
2118
. .
Bohm,
W.
1979
.
Methods of Studying Root Systems
,
188
p.
New York, NY
:
Spring-Verlag
.
Bradley,
A.,
Larson
R.A.,
and
Runge
T.
2015
.
Effect of wood biochar in manure-applied sand columns on leachate quality
.
J. Environ. Qual
.
44
:
1720
1728
. .
Carpenter,
S.R.,
Caraco
N.F.,
Correll
D.L.,
Howarth
R.W.,
Sharpley
A.N.,
and
Smith
V.H.
1998
.
Nonpoint pollution of surface waters with phosphorus and nitrogen
.
Ecol. Appl
.
8
:
559
568
. .
Clough,
T.J.
and
Condron
L.M.
2010
.
Biochar and the nitrogen cycle: Introduction
.
J. Environ. Qual
.
39
:
1218
1223
. .
Cole,
C.V.,
Duxbury
J.,
Freney
J.,
Heinemeyer
O.,
Minami
K.,
Mosier
A.,
Paustian
K.,
Rosenburg
N.,
Sampson
N.,
Sauerbeck
D.,
and
Zhao
Q.
1997
.
Global estimates of potential mitigation of greenhouse gas emissions by agriculture
.
Nutr. Cycl. Agroecosyst
.
49
:
221
228
.
Conversa,
G.,
Bonasia
A.,
Lazzizera
C.,
and
Elia
A.
2015
.
Influence of biochar, mycorrhizal inoculation, and fertilizer rate on growth and flowering of Pelargonium (Pelargonium zonale L.) plants
.
Front. Plant Sci
.
6
:
429
. .
Ding,
Y.,
Liu
Y.,
Liu
S.,
Huang
X.,
Li
Z.,
Tan
X.,
Zeng
G.,
and
Zhou
L.
2017
.
Potential benefits of biochar in agricultural soils: A review
.
Pedosphere
27
:
645
661
. .
Dlugokencky,
E.J.,
Myers
R.C.,
Lang
P.M.,
Masarie
K.A.,
Crotwell
A.M.,
Thoning
K.W.,
Hall
B.D.,
Elkins
J.W.,
and
Steele
L.P.
2005
.
Conversion of NOAA atmospheric dry air CH4 mole fractions to a gravimetrically prepared standard scale
.
J. Geophys. Res
.
110
:
18306
.
Dumroese,
R.K.,
Heiskanen
J.,
Englund
K.,
and
Terbahauta
A.
2011
.
Pelleted biochar: chemical and physical properties show potential use as a substrate in container nurseries
.
Biomass and Bioenergy
35
:
2018
2027
. .
Florides,
G.A.
and
Christodoulides
P.
2008
.
Global warming and carbon dioxide through sciences
.
J. Environ. Int
.
35
:
390
401
.
Graber,
E.R.,
Meller Harel
Y.,
Kolton
M.,
Cytryn
E.,
Silber
A.,
David
D.R.,
Tsechansky
L.,
Borenshtein
M.,
and
Ylad
Y.
2010
.
Biochar impact on development and productivity of pepper and tomato grown in fertigated soilless media
.
Plant Soil
337
:
481
496
. .
Hall,
C.R.,
Hodges
A.W.,
Khachatryan
H.,
and
Palma
M.A.
2018
.
Economic contributions of the green industry in the United States in 2018
.
J. Environ. Hort
.
38
:
73
79
.
Hutchinson,
G.L.
and
Mosier
A.R.
1981
.
Improved soil cover method for field measurements of nitrous oxide fluxes
.
Soil Sci. Soc. Am. J
.
45
:
311
316
. .
Hutchinson,
G.L.
and
Livingston
G.P.
1993
.
Use of chamber systems to measure trace gas fluxes
. p.
63
78
In:
Harper
L.A.,
Moiser
A.R.,
Duxbury
J.M.,
Rolston
D.E.
(eds.).
Agricultural Ecosystem Effects on Trace Gas and Global Climate Change
.
ASA Spec. Publ. 55 ASA
,
Madison WI
.
IPCC
.
2007
.
Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
, p.
987
In:
Parry
M.L.,
Canziani
O.F.,
Palutikof
J.P.,
van der Linden
P.J.
and
Hanson
C.E.
(eds.).
Cambridge University Press
,
Cambridge, UK
.
Johnson,
J.M.,
Franzleubbers
A.J.,
Weyers
S.L.,
and
Reicosky
D.C.
2007
.
Agriculture opportunities to mitigate greenhouse gas emissions
.
Environ. Pollut
.
150
:
107
124
.
Kammann,
C.,
Ratering
S.,
Eckhard
C.,
and
Müller
C.
2012
.
Biochar and hydrochar effects on greenhouse gas (carbon dioxide, nitrous oxide, and methane) fluxes from soils
.
J. Environ. Qual
.
41
:
1052
1066
. .
Kovar,
J.L.
and
Pierzynski
G.M.
2009
.
Methods of Phosphorus Analysis for Soils, Sediments, Residuals, and Waters; Southern Cooperative Series Bull. 408
;
Virginia Tech University
:
Blacksburg, VA, USA
. .
Kroeze,
C.
and
Mosier
A.R.
2000
.
New estimates for emissions of nitrous oxide
. p.
45
64
In
van Ham
J.E.A.
(Ed.).
Non-CO2 Greenhouse Gases: Scientific Understanding, Control and Implementation
.
Kluwer Academic Publishers
,
Netherlands
.
Laird,
D.A.
2008
.
The charcoal vision: a win-win-win scenario for simultaneously producing bioenergy, permanently sequestering carbon, while improving soil and water quality
.
Agron. J
.
100
:
178
181
.
Lal,
R.
2004
.
Soil carbon sequestration to mitigate climate change
.
Geoderma
123
:
1
22
.
Littell,
R.C.,
Milliken
G.A.,
Stroup
W.W.,
and
Wolfinger
R.D.
1996
.
SAS System for Mixed Models
.
SAS Institute, Inc.
,
Cary, NC
.
Marble,
S.C.,
Prior
S.A.,
Runion
G.B.,
Torbert
H.A.,
Gilliam
C.H.,
and
Fain
G.B.
2011
.
The importance of determining carbon sequestration and greenhouse gas mitigation potential in ornamental horticulture
.
HortScience
46
:
240
244
.
Marble,
S.C.,
Prior
S.A.,
Runion
G.B.,
Torbert
H.A.,
Gilliam
C.H.,
Fain
G.B.,
Sibley
J.L.,
and
Knight
P.R.
2012a
.
Determining trace gas efflux from container production of woody nursery crops
.
J. Environ. Hort
.
30
:
118
124
. .
Marble,
S.C.,
Prior
S.A.,
Runion
G.B.,
Torbert
H.A.,
Gilliam
C.H.,
Fain
G.B.,
Sibley
J.L.,
and
Knight
P.R.
2012b
.
Effects of fertilizer placement on trace gas emissions from nursery container production
.
HortScience
47
:
1056
1062
. .
Marble,
S.C.,
Prior
S.A.,
Runion
G.B.,
Torbert
H.A.,
Gilliam
C.H.,
Fain
G.B.,
Sibley
J.L.,
and
Knight
P.R.
2016
.
Species and media effects on soil carbon dynamics in the landscape
.
Scientific Reports
.
6
:
25210
. .
Murphy,
A-M.,
Runion
G.B.,
Prior
S.A.,
Torbert
H.A.,
Sibley
J.L.,
and
Gilliam
C.H.
2018
.
Greenhouse gas emissions from an ornamental crop as impacted by two best management practices: Irrigation delivery and fertilizer placement
.
J. Environ. Hort
.
36
:
58
65
. .
Murphy,
A-M.,
Runion
G.B.,
Prior
S.A.,
Torbert
H.A.,
Sibley
J.L.,
Fain
G.B.,
and
Pickens
J.M.
2019
.
Effects of fertilizer placement on greenhouse gas emissions from a sun and shade grown ornamental crop
.
J. Environ. Hort
.
37
:
74
80
. .
Murphy,
A-M.,
Runion
G.B.,
Prior
S.A.,
Torbert
H.A.,
Sibley
J.L.,
Fain
G.B.,
and
Pickens
J.M.
2021
.
Effects of growth substrate on greenhouse gas emissions from three annual species
.
J. Environ. Hort
.
39
:
53
61
. .
Nemati,
M.R.,
Simard
F.,
Fortin
J-P.,
and
Beaudoin
J.
2014
.
Potential use of biochar in growing media
.
Vadose Zone J
.
14
(6)
:
1
8
. .
Nguyen,
T.T.N.,
Xu
C-Y.,
Tahmasbian
I.,
Che
R.,
Xu
Z.,
Zhou
X.,
Wallace
H.M.,
and
Bai
S.H.
2017
.
Effects of biochar on soil available inorganic nitrogen: A review and meta-analysis
.
Geoderma
288
:
79
96
. .
Parkin,
T.B.
and
Venterea
R.T.
2010
.
Sampling Protocols. Chapter 3. Chamber-based trace gas flux measurements
, p.
3-1-3 to 39
In:
Follet
R.F.
(ed.).
Sampling Protocols
. .
Parkin,
T.B.
and
Kaspar
T.C.
2006
.
Nitrous oxide emissions from corn-soybean systems in the Midwest
.
J. Environ. Qual
.
35
:
1496
1506
. .
Paustian,
K.,
Six
J.,
Elliot
E.T.,
and
Hunt
H.W.
2000
.
Management options for reducing carbon dioxide emissions from agricultural soils
.
Biogeochem. J
.
48
:
147
163
.
Prinn,
R.G.,
Weiss
R.F.,
Fraser
P.J.,
Simmonds
P.G.,
Cunnold
D.M.,
Alyea
F.N.,
O’Doherty
S.,
Salameh
P.,
Miller
B.R.,
Huang
J.,
Wang
R.H.J.,
Hartley
D.E.,
Harth
C.,
Steele
L.P.,
Sturrock
G.,
Midgely
P.M.,
and
McCulloch
A.
2000
.
A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE
.
J. Geophys. Res
.
105
:
17751
17792
.
Prior,
S.A.,
Rogers
H.H.,
Mullins
G.L.,
and
Runion
G.B.
2003
.
The effects of elevated atmospheric CO2 and soil P placement on cotton root deployment
.
Plant Soil
255
:
179
187
. .
Prior,
S.A.,
Runion
G.B.,
Marble
S.C.,
Rogers
H.H.,
Gilliam
C.H.,
and
Torbert
H.A.
2011
.
A review of elevated atmospheric CO2 effects on plant growth and water relations: Implications for horticulture
.
HortScience
46
:
158
162
. .
Robertson,
G.P.,
Paul
E.A.,
and
Harwood
R.R.
2000
.
Greenhouse gases in intensive agriculture: Contributions of individual gases to the radiative forcing of the atmosphere
.
Science
289
:
1922
1925
.
Smith,
K.A.,
McTaggart
I.P.,
and
Tsuruta
H.
2007
.
Emissions of N2O and NO associated with nitrogen fertilization in intensive agriculture and the potential for mitigation
.
Soil Use Manag
.
13
:
296
304
.
Spokas,
K.A.,
Cantrell
K.B.,
Novak
J.M.,
Archer
D.W.,
Ippolito
J.A.,
Collins
H.P.,
Boateng
A.A.,
Lima
I.M.,
Lamb
M.C.,
McAloon
A.J.,
Lentz and
R.D.,
Nichols
K.A.
2012
.
Biochar: a synthesis of its agronomic impact beyond carbon sequestration
.
J Environ Qual
.
41
:
973
89
. .
USDA
.
2007
.
U.S. Nursery crops 2006 summary
.
Publ. No. Sp Cr 6-3
.
U.S. Department of Agriculture, National Agriculture Statistics Service
.
Wright,
R.D.
1986
.
The pour-through nutrient extraction procedure
.
HortScience
21
:
227
229
.
Wu,
D.,
Feng
Y.,
Xue
L.,
Liu
M.,
Yang
B.,
Hu
F.,
and
Yang
L.
2019
.
Biochar combined with vermicompost increases crop production while reducing ammonia and nitrous oxide emissions from a paddy soil
.
Pedosphere
.
29
:
82
94
. .

Author notes

1

The authors thank Robert Icenogle and Barry Dorman, USDA-ARS National Soil Dynamics Laboratory, for technical support. Financial support for this research was provided by the USDA-ARS Floriculture Nursery Research Initiative, Project No. 0500-00059-001-00D. The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the USDA-ARS or U.S. Environmental Protection Agency. Any mention of trade names, products, or services does not imply an endorsement by the U.S. Government or the EPA. The EPA does not endorse any commercial products, services, or enterprises.