Progress report for FNE24-085
Project Information
Levo International, Inc. (Levo) is a 501(c)3 nonprofit with the main objective to provide food security solutions for families. Hydroponic agriculture is the main mechanism we use to promote this objective. Hydroponics is the growth of plants in a water-based nutrient solution, without the use of soil. We both run local hydroponic farms and support local growers to start their own small-scale farms. Hydroponics is a sustainable form of agriculture which can be used on nonarable land and enables efficient use of water and fertilizer in a closed loop. High start-up costs and complexity of operation render hydroponics inaccessible for many. Our research focuses on developing and deploying hydroponic systems that are simpler and less expensive
to build and operate.
It is standard practice in hydroponic production to either regularly replace the nutrient solution or to frequently complete expensive analysis of the ion content of the nutrient solution and inject individual nutrient salts accordingly. In a recently published research project, we produced greens and fruiting crops in our hydroponic systems without replacement of the nutrient solution. This approach enables us to conserve water and
fertilizer. This proposed project will enable us to pilot the implementation of this more sustainable and efficient approach.
Through the proposed research we will gain directly applicable data about how we can adjust nutrient additions for different crops, how yields change without replacement of the nutrient solution and the risk of disease pressure if the nutrient solution is not replaced.
Our first objective (Obj. 1) is to determine the concentration of macronutrients over time in nutrient solutions which are, or are not, replaced. We hypothesize that macronutrients decrease in a consistent pattern over time and that measurements of electrical conductivity (E.C.) and total dissolved solids (TDS), which provide an estimate of the total concentration of ions in the solution, can be used to estimate when nutrients should be added.
Our second objective (Obj. 2) is to test the hypothesis that reuse of nutrient solution decreases the inputs of fertilizer and water sufficiently that it justifies decreased yields. To test this hypothesis, we will conduct yield trials at three different Levo farm locations in which nutrient solutions are
replaced every 3 weeks, or they are not replaced for the duration of a crop.
Our third objective (Obj. 3) is to record the incidence of disease in systems described in objective two. We hypothesize that due to the rapid multiplication and spread of root rot causal agents such as Pythium, recycling of the nutrient solution will not lead to greater risk of
disease.
Hunger may be at its worst levels in over a quarter century, with over 20 million people living in food deserts (1). Urban agriculture is one important component of creating access to healthier food choices for many suffering from food insecurity, but obstacles of urban agriculture are substantial.
Significant literature indicates that environment plays a role in dietary behaviors and health outcomes (2). Several challenges are associated with urban agriculture including soil contaminants, water availability, and changes in climate and atmospheric conditions. Utilizing hydroponic farming methods can address these challenges. Hydroponics is the growth of plants in a water-based nutrient solution, without the use of soil. Hydroponics is a sustainable form of agriculture because it does not require arable land and enables the efficient use of resources such as water and fertilizer in a closed loop system. One of the biggest challenges with hydroponics is that it is not very accessible for many due to high start-up costs and complexity of operation. Levo’s simplified DFT hydroponics overcomes the inaccessibility challenge allowing hyper-local placement of growing operations not practical utilizing traditional agricultural methods.
Levo International was founded to address food insecurity through agricultural innovation. As part of fulfilling this objective, the organization installs urban micro-farms and trains neighborhood residents to operate them. Some research suggests that hyper-local proximity to fresh vegetables has an impact on consumption of vegetables. Indications are that increasing fresh vegetable availability within 100m of a residence correlates to greater vegetable intake (2).
The key to the hyper-local farming strategy is that accessibility must be defined in terms of cost, geography, and operation. Levo utilizes simplified hydroponic methods as the principal driver of participation. By developing and deploying hydroponic systems that are simpler and less expensive to build and operate, we increase accessibility and retain the sustainable benefits of hydroponic production.
It is standard practice in hydroponic production to either regularly replace the nutrient solution or to frequently complete analysis of the ion content of the nutrient solution and make adjustments accordingly (3). This is because plants unevenly consume ions from the nutrient solution over time, leading to imbalances in available nutrients which can have deleterious effects on plant health. Nutrient solution replacement costs a great deal in wasted water and fertilizer and constant ion measurement and adjustment is prohibitively expensive. In a recent research project, we produced both greens and fruiting crops on par with field production without replacing the nutrient solution (4). To accomplish this, we used a lower than standard salt concentration and added nutrient ions slowly over time. In order to fully implement this more sustainable approach and recommend it to growers, we need to know how yield is affected compared to systems in which the nutrient solution is regularly changed.
Changes compared to systems in which nutrient solution replacements or constant adjustments are made. This proposed project would enable us to implement a more sustainable production approach where we avoid replacing the nutrient solution. Proposed work would include tracking ion concentrations over time with current fertilizer additions. Then, we will adjust fertilizer additions per crop time according to nutrient needs. We will track yields of multiple crops under replacement or no replacement regimes of their nutrient solution. We also will record data on disease incidence to determine whether maintaining a single nutrient solution rather than replacing it leads to a higher risk of plant disease. If successful, this project will enable us to widely adopt a more sustainable approach to water and fertilizer usage.
1. Morris, Alanna A., et al. "Relation of living in a “food desert” to recurrent hospitalizations in patients with heart failure." The American journal of cardiology 123.2 (2019): 291-296.
2. Bodor, J. Nicholas, et al. "Neighbourhood fruit and vegetable availability and consumption: the role of small food stores in an urban environment." Public health nutrition 11.4 (2008): 413-420.
3. Resh, Howard M. Hydroponic food production: a definitive guidebook for the advanced home gardener and the commercial hydroponic grower. CRC press, 2022.
4. Vega, Isabella, et al. "Intermittent circulation of simplified deep flow technique hydroponic system increases yield efficiency and allows application of systems without electricity in Haiti." Agriculture & Food Security 12.1 (2023): 18.
Cooperators
- - Technical Advisor
- - Technical Advisor
Research
Nathaniel Heiden (NH), Max Alphonse (MA) and the research technician (RT) will have weekly project meetings to discuss data and any issues that need troubleshooting. NH will maintain regular communication with Jason White (JW) and Leigh Whittinghill (LW) via email and bi-monthly meetings. NH, MA, RT, JW and LW will meet quarterly to discuss experiments and data analysis for the proposed research project and to set goals.
The experimental unit for the proposed research will be the Levo Victory Garden (VG) system, described in Vega et al. (2023). This system is widely used by Levo’s growing operation. This system is a deep flow technique system which enables intermittent circulation of a system in an A-frame layout and uses a standpipe to maintain the level of nutrient solution level. Nutrient solution is recycled from a reservoir tank up to the top pipe of the system constantly or four times per day for 15 minutes.
Seeds will be germinated in 1 inch2 rockwool blocks and after their emergence will be fertilized with half-strength fertilizer consisting of 2g/gallon of Jack’s (J.R. Peters) 5-12-26 NPK fertilizer and 1.2g/gallon of 15-0-0 NPK calcium nitrate. Upon the emergence of initial true leaves, seedlings will be transferred to 3 inch2 net pots in trays and perlite will be added to stabilize seedlings. Seedlings will continue to be watered with half-strength fertilizer until they have a minimum of four true leaves and their roots protrude from the bottom of the net pots marking them as ready for transfer into VG systems. This occurs at approximately three weeks for Black Seeded Simpson lettuce (BSS; Burpee) and 4 weeks for tomatoes and bell peppers.
Systems will be run with either a recycling or replacement protocol. Under both protocols, VG systems will start with a mixture of 27 gallons of water, 107g of Jack’s (J.R. Peters) 5-12-26 NPK fertilizer and 66g of 15-0-0 NPK calcium nitrate. For the recycling protocol, a half-strength fertilizer addition of 53.5g of Jack’s 5-12-26 NPK fertilizer and 33g of 15-0-0 NPK calcium nitrate will be made every 3 weeks. For the replacement protocol, every 3 weeks the nutrient solution will be fully replaced with fresh tap water and initial fertilizer concentrations. BSS can be grown in only three weeks in VG systems (Vega et al. 2023), so they will not be subjected to the replacement or recycling protocols.
For Obj. 1, we will conduct research at an experimental site at Lockwood Farm at the Connecticut Agricultural Experiment Station (CAES) and at Levo’s farm locations. Measurement will be taken of E.C. and TDS values on a weekly basis with VIVOSUN E.C./TDS and pH meters, respectively. The key macronutrients: nitrate, phosphate, potassium, calcium, magnesium and sulfur will be measured regularly with a Howard Hanna nutrient photometer and the corresponding test kits. Data will be recorded in excel and we will test for correlation between E.C. or TDS values and the listed macronutrients using linear regression and multivariate modeling. This experiment will be repeated over multiple replicates. BSS and bell peppers will be grown at CAES and bell peppers and tomatoes will be used as experimental crops at Levo locations. 4 VG systems for each crop will be used as replicates.
For Obj. 2, we will conduct research at three different Levo farm locations. Bell peppers and tomatoes will be grown under recycling or replacement protocols. A minimum of 4 systems per treatment (recycling and replacement protocols) per location will be used and placed in alternating arrangement. E.C., TDS and pH readings will be taken weekly in experimental systems with VIVOSUN E.C./TDS and pH meters, respectively. Data will be deposited weekly into excel. Harvests will be conducted as fruit ripens for both recycling and replacement protocol systems for each crop type. The date of harvest and the system from which fruit is harvested will be recorded. Final harvest data for recycling and replacement protocol systems will be compared. The time to harvest for systems under recycling and replacement protocols will also be compared, as a shorter time to harvest results in less risk for harvest loss due to inclement weather or plant pests and disease.
For Obj. 3, incidence of root rot and wilting diseases will be recorded. Daily walkthroughs will be conducted of experiment sites to scout for signs of wilting. Every week roots will be observed, by pulling net pots from the VG systems and occurrence of browning and soft roots, characteristic of root rot will be recorded. The experimental technician will wear gloves and clean them with 70% ethanol between systems to prevent transfer of pathogens between systems. If root rot symptoms are observed, daily observation will take place of disease progression. After harvest, or if an outbreak occurs, pictures will be taken of the root mass of affected plants and ImageJ will be used to quantify the percentage of roots which are affected by browning.
We made some adjustments to the initially proposed methods. We were not able to carry out a full season of experiments in 2024. This was largely due to administrative delays, logistical challenges, as well as land access. For example, our contract was not completed until May 10th, instead of the planned March 1st. We had a disease issue in some seedlings due to the extreme heat we experienced during the summer of 2024 in Connecticut. Due in part to this heat, we used constant circulation in the preliminary experiment we ran rather than intermittent circulation in an effort to decrease water temperatures. We plan to use intermittent circulation as initially proposed for the 2025 experiments. We were unable to use the Bloom Hill Farm location as long as expected as we were unable to renew our lease for the Fall 2024 season. However, we have three available locations starting in spring 2025 and will be able to conduct additional replicates throughout the 2025 season including lettuce, bell peppers, and tomatoes. Therefore, the methods have been changed to include experiments to be conducted over the 2025 season at multiple locations with additional replicates rather than during 2024 and 2025. We also have gained the opportunity to use inductively coupled plasma - optical emission spectroscopy (ICP-OES) in collaboration with the Connecticut Agricultural Experiment Station Analytical Chemistry Laboratory to analyze the concentrations of phosphorus, potassium, calcium, magnesium, and sulfur. ICP-OES increases the accuracy and precision of our data compared to the nutrient photometer test. This analysis will also allow us to analyze samples for their concentration of micronutrients such as boron, zinc, and iron. We used the originally proposed photometer test for nitrate, as the ICP-OES could not provide information about the concentration of this compound. We also will request to change one of the project leaders from Isabella Vega (IV) to Max Alphonse (MA).
In the first partial year of this project, we were able to make substantial progress on objective 1, which was to determine the concentration of macronutrients over time in nutrient solutions which are, or are not, replaced. In our above protocol, we had decided on a three week period to add fertilizer, however we wanted to carry out an initial preliminary experiment to see if the nutrient levels of our fertilizer were within recommended ranges. The 2013 edition of the book Hydroponic Food Production by Howard M. Resh lists the concentrations of macronutrients in published fertilizers. These include a range of recommended concentrations in parts per million (ppm) for calcium (98-500 ppm), magnesium (22-484 ppm), potassium (65-593 ppm), nitrate (47 - 246 ppm), phosphorus (4 - 448 ppm; mostly 30-60 ppm), and sulfur (26 - 640 ppm). We hypothesized that nutrients remain within these accepted ranges when fertilizer is added to systems producing peppers every three weeks. To test this, we analyzed the nutrient solution of bell pepper plants grown in four systems at Bloom Hill Farm during June - September 2024. We found that nitrate, phosphorus, calcium, magnesium, and sulfur levels remained within the suggested ranges at all timepoints (Figure 1). The one exception was that potassium levels dropped to undetectable levels at the end of the experiment (Figure 1). We hypothesize that increased potassium uptake during pepper fruiting may explain this phenomenon. This provides us useful insight, as additions of potassium during pepper fruit formation could improve yields.
We expected that a fertilizer addition was necessary every three weeks due to decreases in EC. However, this analysis demonstrated that concentrations of key macronutrients remained in the acceptable ranges even at the timepoint when additional fertilizer was added. The exception to this may be at the end of the growth period for fruiting crops as nutrient uptake increases. This result has led us to understand that we may be able to delay fertilizer additions longer than three weeks in some cases without negative effects. This data also has informed us that we may be able to increase pepper yields if we add supplemental potassium during fruiting.
We also used this dataset to challenge our assumption that electrical conductivity (EC) and individual macronutrient concentrations are directly correlated. We tested this by completing linear regressions between nutrient concentrations and EC values on the same day (Figure 2). Surprisingly, we found that there was no correlation between EC values and the concentration of any of our tested macronutrients (Table 1). As macronutrient levels did not drop substantially, we were unable to establish a relationship between EC and individual nutrients. This led us to realize that we need to carry out a longer trial period without nutrient replacement to be able to establish the relationship between EC and the individual nutrients in our system. Therefore, we have adjusted our experimental plan to include an experiment where the EC is allowed to drop to the same level as the source water without replacement.
Table 1. No correlation of electrical conductivity and individual macronutrient concentrations on the same day according to linear regression. Linear regressions were carried out in R version 4.3.1.
| EC versus | Adjusted R2 | p-value |
| Nitrate | 0.0821 | 0.189 |
| Phosphorus | -0.0843 | 0.712 |
| Potassium | -0.0992 | 0.934 |
| Calcium | -0.0384 | 0.459 |
| Magnesium | -0.0998 | 0.963 |
| Sulfur | -0.0061 | 0.357 |
We found that macronutrients remained within desired levels during pepper production when nutrients were added every three weeks, with the exception of potassium. Low potassium levels may limit pepper production with our protocol. This will inform our production immediately, as we know that this three week approach is effective for peppers and that we should add supplemental potassium during fruit formation. We were unable to find a predictive relationship between EC and the concentration of individual nutrients. We will carry out additional replication and allow longer time periods between fertilizer addition to determine whether there is a useful relationship between EC and individual nutrients. If there is not, we will not use EC as a proxy for nutrient concentration, and instead periodically test nutrient levels.
Education & Outreach Activities and Participation Summary
Participation Summary:
We will present our data at the upcoming 2025 Connecticut Agricultural Experiment Station Plant Science Day. We also have an ongoing hydroponic training program in collaboration with the Hispanic Health Council and we will teach new protocols based on the results from this project in the upcoming two years. We began to teach protocols including the option of intermittent circulation to a class including 18 participants in 2024.