Final report for GS19-209
Thousands of tons of spent coffee grounds (SCG) are sent to landfills each year, and with the recent growth in cold-brew coffee production this is expected to increase. Waste utilization is a key component to sustainable agriculture and creating a circular economy. The use of SCG in agriculture can improve soil properties and plant growth by increasing organic matter and nutrients. Increasing sustainable practices in the horticulture industry has been an ongoing dilemma for many years. Sphagnum peat moss is the main ingredient of commercial potting mixes and when harvested releases large amounts of CO2 into the atmosphere. A number of organic wastes such as composted bark have been tested, and somewhat adopted by some growers as a substitute for peat-based potting media. There are a number of possible uses for SCG due to their valuable physical, chemical, and biological qualities. Our research investigated the use of non-composted and composted SCG (CSCG) as a source of ammonium and nitrate when added to soil. We also studied the effect of SCG on germination, growth and carotenoid concentration when amended to a potting mix.
Our research demonstrates:
1. Composted SCG can act as a biostimulant for seed germination (spinach, radish, pea, eggplant, basil) when used as a partial peat replacement. Future research should include a variety of different plant species and an investigation of the mechanisms responsible for the biostimulant effect on germination.
2. Composted SCG can be used as a partial replacement for peat-based media with no effect on biomass, but should be used at species-specific rates.
3. SCG may serve as a long-term fertilizer due to the time it takes to mineralize. They may increase the nutrient and water-holding capacity of soil, which can improve plant growth over a shorter time period.
4. Carotenoid concentrations showed no clear trends and further research is needed for conclusive results.
- Develop research-based data to establish composted spent coffee grounds as a viable peat substitute by assessing the range in physiochemical properties of different proportions of composted SCG (CSCG) and peat-based media mixtures and leachate from the mixture creating more sustainable and cost-effective practices.
- Improve the competitiveness of basil and eggplant by enhancing their nutritional properties without increasing economic inputs by evaluating the effect of composted and non-composted SCG on their growth and carotenoid concentration.
- Characterize the nitrogen mineralization dynamics of composted and non-composted SCG compared to other commonly used fertilizers
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Non-composted, static pile composted and/or in-vessel composted spent coffee grounds were tested for phytotoxicity using germination and growth experiments. Germination and growth experiments were carried out at the Texas A&M Department of Horticultural Sciences, Horticulture Teaching Research and Education (Hort. T.R.E.C.) greenhouse facility. The spent coffee grounds used throughout this study came from a cold brew coffee company based in San Antonio, TX. Pro-Mix general-purpose potting mix was the peat-based media used in these experiments. Potting mixture treatments were made on a volume/volume basis and mixed by hand. Treatments included 10%, 25%, 50%, 75% and 90% SCG and potting mix in order to cover the full spectrum of the effect on the plant at high and low levels of SCG. The first eggplant experiment also included SCG and sand at the same ratios as above. These treatments were not repeated due to the difficulty and poor results of using sand in nursery pots.
Spent Coffee Ground Preparation and Compost
The spent coffee grounds used throughout this study came from a cold brew coffee company based in San Antonio, TX. The SCG were delivered by dump truck loads to the Scotts Miracle-Gro Turf Science Center at Texas A&M University. They were dumped in a pile in an area at the turf center designated for large quantities of soil components.
Non-Composted SCG: The non-composted SCG used in these experiments were collected from the pile of SCG within a 24-hour period of delivery and dried in a 62 °C oven for 72 hours. The SCG were removed from the oven, cooled, and stored indoors in a plastic container. A sample was sent to Texas A&M AgriLife Extension Soil, Water and Forage Testing Laboratory for chemical analysis.
Static-Pile Composted SCG: The static-pile composted SCG used in these experiments were taken from the pile of SCG about nine months after composting began. Temperatures ranged from 38-60 °C depending on where in the pile the temperature was measured. Approximately 0.34 m3 of this nine-month composted SCG were taken from the pile and air dried for 48 hrs. After drying they were sieved to 2 mm, and stored indoors in a plastic container.
In-Vessel Composted SCG: May 21, 2020 a new batch of spent coffee grounds were delivered to the Scotts Miracle Gro Turf Center. A small amount was taken to air dry in the greenhouses at the Hort. T. R. E. C. After they were dry, they were stored indoors in a plastic container. On August 17, 2020 SCG were taken from the pile and transported to the Poultry Science Center at Texas A&M University to put in their Ecodrum® in-vessel composter. At this time temperatures of the pile of SCG ranged from 50-60°C which is considered thermophilic composting. Four 200 kg barrels of SCG were added initially, then a barrel every other day for approximately 21 days (September 7, 2020).
After 21 days a sample was taken from the composter and due to the lack of moisture water was added. Any SCG that had exited the composter were added back in but no new SCG were added. At this point, temperatures had reduced to a mesophilic stage of composting (>40°C). Turning was reduced to biweekly and temperatures continued to stay within mesophilic range, this continued for approximately 90 days. The composted SCG were removed from the composter and stored in plastic barrels indoors. Samples were sent to the Texas A&M AgriLife Extension Soil, Water and Forage Testing Laboratory for chemical analysis. To verify the compost maturity a Solvita CO2 and NH3+ co-variate test will be used.
Each mixture was spread evenly into seedling trays (25 cm wide by 51 cm long, and 6.4 cm deep) with forty seeds per tray. Each tray was replicated three times. Seeds tested included Pisum sativum ‘Wando’ bush peas, Spinacia oleracea hybrid #7 spinach, and Raphanus sativus, Cherry Belle radish. Percent germination was calculated.
Solanum melongena ‘Patio Baby’ were planted into seed plug trays (2 cm by 4 cm cell size), one seed per plug, filled with seedling potting mix (Pro-Mix general purpose seedling mix). Eggplants were transplanted into 20 cm nursery pots after the first set of true leaves were fully developed. Each treatment had five replicates given a high fertilizer rate (15-5-25 at 0.4 g/L) and five replicates given a low fertilizer rate (15-5-25 at 0.1 g/L). Plants were watered daily using a dosatron set at a dilution rate of 1:100 The sand and potting mix treatments were sperate experiments, assigned to different benches with pots arranged in a Completely Randomized Design. Data collected on a weekly basis included: height, number of flowers and fruits. Nine weeks after transplanting the eggplants were harvested and fresh weight was recorded as well as fruit number, fruit weight, and fruit length. Eggplants were left on greenhouse benches to dry until a constant weight was achieved, and dry weight was recorded. This experiment was repeated but did not include the sand treatments because the sand did very bad in the pots. It also only included a high fertilizer rate because there were no differences between the high and low fertilizer treatments.
Ocimum basilicum ‘Rutgers obsession’ seeds were started in 3.8 cm rockwool cubes and transplanted according to the methods described above. Treatments included potting mix and static-pile composted SCG, and potting mix and non-composted SCG with ratios the same as previously stated. A high fertilizer rate (15-5-25 at 0.4 g/L) was applied to all treatments, with five replicates per treatment and in a completely randomized design. Data collected on a weekly basis included: height, number of flowers and branches. Eight weeks after transplanting the basil was harvested and fresh weight was recorded. Basil plants were left on greenhouse benches to dry until a constant weight was achieved, and dry weight was recorded.
After the plants were harvested eggplant fruits and basil leaves were placed in zip-loc baggies and stored in a deep freezer. Samples were freeze dried and mailed to UW Madison Department of Nutritional Science for analyses. Chemical analysis of eggplant fruit and basil leaves using HPLC and LC-MS were used to identify carotenoids (carotenes [beta-carotene, alpha-carotene], xanthophylls [lutein]). Data will be compared to published nutritional value data for the same crops. A total of 80 samples were analyzed, 25 basil leaf samples and 55 eggplant fruits. Basil samples will be from 0%, 10%, and 25% non-composted and static-pile composted SCG treatments with five replicates from each treatment. Eggplant fruit samples will consist of 0%, 10%, 25%, 50%, 75% and 90% non-composted and static-pile composted SCG treatments with five replicates from each treatment.
Supplies (per sample)
- 3 large test tubes/lids
- 3 15 mL screw top
- 3 HPLC vials / caps
- 6 disposable pipets/ bulbs
- *Start water bath and set sample(s) out to thaw
- Fill ice bucket and put in DI H2O to cool and internal standard to keep cool
- Label large test tubes with sample numbers
- Label disposable test tubes
- Prepare/label vials
- Weigh first tube à zero scale
- Measure 03g – 0.035g / 0.15g – 0.155g of first sample into tube
- Repeat with rest of tubes/samples
- Record each weight
- Label sample bag as analyzed and return to freezer
- Get 5mL pipet, set to 3 mL
- Add 6 mL (3 mL x 2) of EtOH + BHT in each tube
- Cap each tube (don’t screw too tight, or may crack in hot water bath)
- Vortex each tube ~30 seconds
- Put in water bath for 5 min
- When 5 minutes is up, remove tubes from bath to rack
- Add 500 uL KOH with 1 mL pipet set to 0.5
- Vortex each tube again ~30 sec
- Add tubes back to hot water bath for 5 min
- When 5 min are up, vortex each tube and return back to bath for 5 more min
- When last 5 min are up, remove each tube from water bath and put into ice bucket
- Add 3 mL DI water (1 mL pipet x 3)
- Add 500 uL / 200 uL B-apo internal std
- Vortex each tube ~15 seconds
- Add 4 mL Hexanes (5 mL pipet set to 4 mL) to each tube
- Vortex ~30 sec and centrifuge ~ 2 min
- Take small tubes and pipets to hood
- Pipet off top layer of sample into corresponding 15 mL tubes USING DIFFERENT PIPET FOR EACH SAMPLE
- Add 3 mL hexanes to each tube
- Vortex and centrifuge
- Repeat top layer extraction for each sample
- Add final 3 mL of hexanes to each tube
- Vortex and centrifuge
- Repeat top layer extraction for each sample
- **After all extraction steps, should have 10 mL of collected hexanes (4 mL, 3 mL, 3 mL)
- Put under nitrogen to dry
- Once samples are dry, add 600 uL / 200 uL of 50:50 MeOH:DCE
- Vortex and centrifuge
- With remaining pipets, pipet samples into corresponding vials as well as a vial with B-apo
- Take to HPLC or refrigerate- inject 10 uL / 20 uL
Modified from previously published method: Howe, J. A., and S. A. Tanumihardjo. 2006. Evaluation of analytical methods for carotenoid extraction from biofortified maize (zea mays sp.). J. Agric. Food Chem. 54:7992–7997.
Mineralization Rate of SCG
A 70-day and 100-day laboratory incubation study was conducted at Texas A&M University in Fall 2019 and Spring 2021, respectively. The treatments included non-composted SCG (2.2-0.9-0.5), composted SCG [73-day (2.2-0.9-0.5), 100-day (3.9-0.1-0.7)], Milorganite (5-2-0), and Urea (46-0-0), and the control was soil with nothing added to it. Each treatment was mixed into 50 g of Booneville fine-sandy loam soil at a rate of 9.8 g N m2 for comparison. The soil was brought to field capacity (60% w/w) and a 9.8 g N m2 rate of each treatment was added to 50 g of dry-weight soil. Treatments were thoroughly mixed in 50 ml polypropylene beakers. Each beaker was placed inside a Mason jar with 5 ml of water in the bottom to create a microcosm. A CO2 trap which consisted of a 50 ml polypropylene centrifuge tube, with no lid, filled with 20 ml of 1.0 M sodium hydroxide was also placed in each Mason jar. The jars were immediately sealed and placed in an incubator held at 25 °C in a completely randomized design with three replicates per treatment. Aerobic conditions were maintained by opening the jars every 7 days. The CO2 (sodium hydroxide) trap was sampled every 10-days by adding barium chloride and back titrating with hydrochloric acid (HCl). The amount of HCl used in the titration was recorded and used to monitor CO2 release throughout the incubation. The CO2 flux was used as an index for net mineralizable nitrogen. Ammonium (NH4+), and nitrate (NO3-) were extracted from destructive samples every 10-days by inductively coupled plasma spectrometry (ICP) following Keeney and Nelson (1982).
One-way ANOVA followed by a Tukey’s HSD post hoc test for multiple comparisons among means was used to detect differences in germination, growth, and phytochemical concentrations among the different treatments.
Germination rates were calculated for sugar snap peas, spinach, radish, eggplant, and basil. A biostimulant effect was seen in all plant species tested. Peas had a decrease in days to germination at 50% composted SCG. Spinach had a decrease in days to germination, and a significantly greater germination rate than all other treatments and the control, at 75% composted SCG. Radish also showed a decrease in days to germination at 75% composted SCG. Our study demonstrates that composted SCG can be used as a biostimulant and partial peat replacement for these particular species. Future research should include a variety of different plant species and an investigation of the mechanisms responsible for the biostimulant effect on germination. Eggplant and basil germination results will be updated soon.
The addition of static-pile composted SCG resulted in decreased time to germination for peas and spinach. At a rate of 75 % static-pile composted SCG with media (sand and potting mix) showed the highest germination rate for spinach. The first four days of germination were the highest for peas in all treatments, and for spinach in 75% SCG. The germination experiments in 2019 and 2020 showed similar results. Chrysargyris et al. 2019 tested germination of brassica seeds in mixtures of peat and SCG of 2.5, 5, and 10%. They found cabbage germination was stimulated at 2.5% SCG and cauliflower at up to 5%. At 10% SCG the percent germination decreased but mean emergence time increased. They concluded that up to 5% SCG could be used as a bio-stimulant and or partial peat replacement for brassica seedlings. These results are similar to what were found in our experiments although the percentage of SCG we used was much higher. This could be due to the fact that our SCG were composted and the plant species tested. It would be interesting to test brassica species in composted SCG. Release of toxic substances particularly from non-composted SCG have been attributed to inhibited germination and growth in some plants (seed germination alfalfa (Medicago sativa), clovers (Trifolium repens and T. pretense); growth Chinese mustard (Brassica juncea), komatsuna (Brassica campestris), Italian ryegrass (Lolium multiflorum), inch plant (Tradescantia albiflora), geranium, and asparagus fern.
We investigated the effect of different rates of composted and non-composted SCG on the above-ground biomass of Solanum melongena, ‘Patio baby’ eggplant, and Ocium basilicum, Sweet Basil. The goal was to identify opportunities to utilize SCG as a partial replacement for peat-based potting mixtures. The treatments included 10, 25, 50, 75, and 90% composted or non-composted SCG mixed with Pro-Mix peat-based media. Compared to the control, there was no significant difference in eggplant biomass when up to 50% composted SCG were added to the Pro-Mix. Additionally, at 10% composted SCG eggplant biomass was significantly greater than the control. Non-composted SCG significantly reduced eggplant growth and stunted development in all treatments. Therefore, we do not recommend non-composted SCG at any rate as a partial peat replacement for eggplant production. Basil showed no differences in biomass within or among treatments of 10% and 25% composted and non-composted SCG. The control and 10% non-composted SCG were not significantly different but biomass in 10% composted SCG was significantly lower. Basil died before the experiment ended in all non-composted SCG treatments ≥50%. Our results indicate that composted SCG can be used as a partial replacement for peat-based media with no effect on biomass, but should be used at species-specific rates. Differences between composted and non-composted SCG could be due to phytotoxicity, which is removed after composting. Calcium deficiency could cause tip death.
After day 41 at a high fertilizer rate differences in eggplant height between potting mix and static-pile composted SCG treatments and control diminish, possibly due to inorganic N mineralization of the static-pile composted SCG. At a low fertilizer rate, height compared to high fertilizer treatment is comparable, possibly due to the addition of the static-pile composted SCG. In sand at high fertilizer rate, after day 45 treatments with higher ratios of static-pile composted SCG have greater average height. Possibly due to a combination of inorganic N mineralization, lower bulk density and increased pore space. In sand at a low fertilizer rate, after day 41 static-pile composted SCG contribute inorganic N and improve soil physical properties, shown in greater average height of treatments over control.
Our results were inconclusive and therefore we were not able to make any conclusions based on the data we collected. Future research would include measuring total antioxidants which would be more accurate and less dependent on environmental conditions. The carotenoid levels of eggplants and basil are expected to be positively correlated up to as much as 50% of composted SCG and 5% of non-composted SCG. Phytochemical concentrations are known to differ between varieties which could be a factor in comparing the ‘patio baby’ to published data on carotenoid and anthocyanin content of other eggplant varieties. In cabbage and cauliflower phytochemicals increased in up to 5% SCG but decreased with higher amounts of SCG, although broccoli showed no difference from the control in any treatments (Chrysargyris et al., 2019b). The SCG used in our experiments were composted and were able to be used at higher percentages in eggplant without decreased growth.
Mineralization Rate of SCG
Despite their relatively favorable N content (2.3%N) and C:N ratio (20:1), SCG appear slow to mineralize. Net immobilization of N was seen during the initial 42 days, with net mineralization of N occurring later on. No significant differences were seen between fresh and composted SCG for any of the parameters tested. The high levels of CO2 respiration observed with SCG demonstrates higher amounts of microbial activity are required for the breakdown of SCG, relative to other fertilizers. Given that N mineralization appears slow, the positive benefits previously seen following sand amendment suggest microbial or physical factors may be responsible.
Educational & Outreach Activities
Presented initial research to Colin County Master Gardeners Association.
Presentations and Published Abstracts
In 2020, four presentations on our spent coffee grounds research were given. Initial research was presented to the Collin County Master Gardeners Association CollinCo.SCGpres.2020ALB. Collaboration with a post-doc and PhD student at the Energy Institute at Texas A&M resulted in two presentations: 1. Circular economy systems engineering for food supply chains: A case study on the coffee supply chain. International Conference on Sustainable Development ICSD 2020_CE Systems Engineering_Styliana; 2. Circular economy systems engineering: A case study on the coffee supply chain. American Institute of Chemical Engineering Abstract_Chemical Engineering_Stefanos_Styliana2020. A poster on the mineralization rate and CO2 release of spent coffee grounds, and their potential use as a slow-release fertilizer was presented at the Agronomy Society of America International Annual Meeting Amanda-Incubation Experiment_ASA poster2020Final.
In 2021, a poster was presented at Student Research Week, at Texas A&M. This included undergraduate students, who applied through the Aggie Research Program, to assist with certain aspects of our spent coffee grounds project in order to gain research experience. The title of this poster was "The Effect of Spent Coffee Grounds on Germination and Growth of Container Grown Specialty Crops."Germination in media_SRWposterSpring 2021
In August 2021, a poster was presented at the American Society of Horticultural Sciences annual meeting in Denver titled "Spent Coffee Grounds Have a Biostimulant Effect on Germination of Spinach, Peas, and Radish."ASHS2021-Birnbaum-Final
In November 2021, a poster was presented at the Agronomy Society of America annual meeting in Utah. This poster expands on the use of spent coffee grounds as a slow-release fertilizer. It verifies the results of a previous experiment and provides additional data by extending the time span of the experiment. Amanda-Incubation poster2021-Final
In February 2022, a poster was presented at the Southern Region American Society of Horticultural Sciences annual meeting in New Orleans, LA. This poster details the results of composted versus non-composted growth experiment using eggplant and basil. SouthernRegionASHS 2022-Birnbaum-Final
Mentored undergraduate students participating in the Aggie Research Program. Students applied to participate in our research project to gain research experience. In the Fall of 2020 I mentored six students, and in the Spring of 2021, I mentored seven students. The students assisted with maintaining experiments and data collection. Two students participated in Student Research Week and presented a poster on the research they helped with.
Gave a presentation to the Colin County Master Gardeners Association and had lunch with them. A number of people were very interested in my research and we exchanged emails. They expressed interest in seeing my final results.
Through our research experiences we have found promising applications for spent coffee grounds such as a biostimulant for seed germination, a substitute for peat based potting mix, a slow release fertilizer, and increased levels of some carotenoids. We have also learned that some plant species have a positive response, and some have a negative response to the application of spent coffee grounds. Additionally, we saw that spent coffee grounds are highly compostable using different methods and can be used as the primary, or even only, feed stock for composting. All of this knowledge will contribute to sustainability by providing a use for a waste product, spent coffee grounds, and creating a circular economy. By using them as a substitute for peat moss, germination media, additive to increase certain carotenoids, compost feedstock, and slow release fertilizer, large quantities will be taken out of the waste stream and replace other materials that would have to be harvested from the environment.
During the course of this project we have learned that there is increasing interest in sustainable agriculture by people from many different backgrounds. Farmers, gardeners, educators and those interested in circular economy have all shown interest and support for researching the use of spent coffee grounds in agriculture and horticulture. We have become more aware of the potential for many different groups adopting the use of spent coffee grounds in a variety of real world applications.