kimberlyvilla
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Growing Strawberry Cultivars Organically and Conventionally in a Vertical Urban Hydroponics System
Kimberly Villanueva1, Dr. Sam Wortman2, Michael Douglass2
1Research Apprentice Program Participant, 2Department of Crop Sciences: College of Agricultural, Consumer, and Environmental Sciences, University of Illinois Urbana-Champaign
July 31, 2015
Abstract
Urban farmers in Illinois have a strong interest in hydroponically growing and selling organic strawberries to their local community. Therefore, a need exists for information on the most successful cultivars and the use of organic fertilizers. This study sought to investigate those two key items by keeping four strawberry cultivars in a high-tunnel hydroponics system in Illinois. Their yield data and chlorophyll readings were taken frequently in order to assess health and progress. After examining this data, it was found that it is more practical to use conventional fertilizer rather than organic on crops growing in a hydroponics system because it produces a higher average yield weight. It was also noted that of the four cultivars, Seascape and Albion performed the best.
Introduction
Hydroponics is one of several evolving urban farming methods that has accumulated a significant amount of interest among local urban farmers who wish to take advantage of this innovation for their own crop production and marketing. Hydroponics is an alternative growing method that substitutes soil with media containing the necessary nutrients for growth. Urban hydroponics, as an extension of urban agriculture, creates the opportunity for increased food security and equality, as well as the erasure of food deserts in and around cities (Wagstaff and Wortman, 2015). Urban hydroponics has also generated so much interest among urban farmers because of the income opportunities it presents and the ability to integrate vertical farming into hydroponics, which allows for less space and water usage (Schnitzler, 2013). Much of the urban farming community’s interest in urban hydroponic crop production also extends to the practicality of using organic fertilizers and nutrients on crops being grown in the aforementioned system. However, many of these urban farmers lack the most vital information needed before one can begin to successfully utilize organic hydroponic crop production, including the highest yield producing cultivars, the cultivars that yield the most marketable fruit, ideal climate, temperature, and other various growing conditions, all of which are factors that differ based on the chosen crop. There have not been many studies that address the challenges, benefits, opportunities, and the various existing complications that go along with growing food in urban communities (Wagstaff and Wortman, 2015).
The research conducted in this study aims to address the needs of urban farmers in Illinois who take an interest in producing and bringing to market organic strawberries grown in a hydroponic, high-tunnel microclimate. The first objective of this study was to determine the most successful strawberry cultivars grown in hydroponic conditions based on the largest marketable yield, resistance to disease and pests, and overall endurance. It was hypothesized that, because of the many unknown factors going into this study, the results of successfulness of each cultivar would each be significantly different from one another. It was unknown how each cultivar would behave in an Illinois climate, how each cultivar would behave under hydroponic conditions, and how they would all hold up to pests and disease. Therefore, the only reasonable assumption that could be made was that the results for each variety would not be same. The second objective of this study was to decide the overall practicality of using organic fertilizer versus conventional fertilizer on strawberry crops grown in a hydroponics system. The determination would be based on the overall success of the organically treated cultivars compared to that of the conventionally treated cultivars. In most hydroponics systems, whether they are being used for research, profit, or recreation, conventional fertilizer is used more often than not because organic fertilizers often contain substances that are somewhat poisonous to plants and cause poor yields and plant growth (Shinohara et al., 2011). For this objective, it was hypothesized that the plants treated with conventional fertilizer would perform better than those treated with the organic fertilizers, again because of the existence of unknown factors.
Literature Review
Growing Strawberry Cultivars in a Hydroponics System
There have been several studies conducted in the recent past concerning strawberry growth in hydroponics systems under various conditions. One study in particular included strawberry varieties being grown in hydroponic conditions with the purpose of reducing the negative effects of alkalinity by varying the ammonium (NH4+) to nitrate (NOз-) ratios and the concentrations of bicarbonate (Roosta, 2014). High alkalinity causes low chlorophyll levels and raises pH levels, in nutrient solutions. Plants usually fare better when nitrate is their primary source of nitrogen, instead of ammonium nitrate (N2H4O3). If ammonium makes up too much of the nitrogen solution in a hydroponics system, low yields and stunted plant growth are often some of the consequences (Shinohara et al., 2011). In this study, it was found that when strawberry plants were subjected to the application of only nitrate or only ammonium when there was a high concentration of bicarbonate (HCO₃−), they faced growth suppression and subsequent death. The yield amount and general growth of the plants were shown to have increased when there was an almost equal mix of ammonium and nitrate, with a concentration of all bicarbonate was present. The average leaf area was at its lowest when there were high levels of both bicarbonate and ammonium (Roosta, 2014). This study provides a look at what can create a volatile nutrient solution and ideal nitrogen sources for crops growing under hydroponic conditions.
Comparison of Strawberry Cultivars
In a study conducted in the fall and winter of 2014 by Rodrigues et al., the growth of four different strawberry cultivars grown in a closed hydroponics system with coconut coir were compared. Albion, one of the cultivars used in this study as well, was one of the analyzed varieties. It was noted that Albion had its peak growth period in its 17th of 38 weeks of growth. In this study, the cultivars were grown in two different types of hydroponic systems: gutters and grow bags. The Albion cultivar yielded the least amount of fruit in both the gutter system and the growbags because it did not adapt well to the climate of the Ibiapaba region of Brazil. However, this did not mean it was the least successful cultivar of the four. In the gutter bag system, the Albion cultivar produced the second highest fruit weight of the four cultivars at 11.4g. In grow bags, it also produced the second highest fruit weight at 10.81g, despite its low yield count in both gutters and grow bags. Its average combined fruit weight came to 11.1g, again the second highest of the four cultivars.
The cultivar Chandler, also used in this study, was the focus of a study that was conducted in 2010 by Daniel Rowley in Utah. This study experimented with advancing the early growing season of Chandler strawberries through the usage of high tunnels. For this specific purpose especially, planting on what is considered the most optimal date was crucial. Optimal planting date was another factor the study sought to determine. In this study, Chandler strawberry plants were grown both in a vertical system and directly into the ground. By the end of the study, it was observed that for two planting seasons in a row the strawberry plants that were put directly into the ground performed better in terms generating a monetary profit. They did not require the same upkeep and maintenance costs that high tunnels did, which made direct planting the more practical option.
Usage of High Tunnels
On the west coast of the United States, high tunnels are utilized on a large scale for the protection of small fruit plants, so they can be shipped across seas while sustaining limited damage. This large scale production is possible because California has ideal growing temperatures for strawberry production (Rowley, 2010). In the Midwest region, hydroponic production of small fruit is conducted mostly on a small, grower-to-consumer basis. In areas such as the Midwest where the climate limits the utilization of small fruit hydroponics to a small scale, the main objective is to advance the growing season of the fruit (Demchak, 2013). High tunnels have been used on many occasions to prolong the growing/harvest season for small flowers, vegetables, strawberries, and other small fruits because the temperature inside the tunnel can be easily controlled (Rowley, 2010). Extending the growing season for farmers attempting the produce strawberries in the Rocky Mountain region of the United States allows these farmers the chance to make more profit using the higher out of season prices, which can often be more than double the regular in season pricing. It is particularly difficult to produce strawberries in the Rocky Mountain region of the United States because its general climate does not match up well with the ideal growing temperatures for strawberries (Rowley, 2010).
In a study mentioned previously that was conducted in 2010 by Daniel Rowley, in which Chandler strawberries were grown in high-tunnels in Utah, it was found that strawberries growing in a vertical system in this type of climate are highly vulnerable to cold or winter damage. Even though the use of the high tunnels did manage to advance the growing season of the strawberry plants by 5 weeks, the profit from the higher yield did not make up for the income lost to repair and maintenance costs for the vertical hydroponics systems. This study honed in on the strengths and benefits of vertical growing systems, while also defining its limits in terms of climate, region, and endurance. Because this study was conducted in the Rocky Mountain region, it leaves behind some unanswered questions. For example, how practical are high tunnels when utilized in the Midwest?
Organic Fertilizer vs Conventional Fertilizer
When used on plants growing under hydroponic conditions, organic fertilizer can be detrimental to plant growth and fruit yield because hydroponic solutions generally do not have the right number of microorganisms present to combat the negative materials (Shinohara, 2011). Garland et al. conducted a study in 1993 that investigated the possibility of using hydroponics to grow soybeans, wheat, and potato seedlings in space, using recycled inedible crop residue. The ideal growing system had to be useful on long term space missions, meaning they had to be completely self sustainable for as long as several years. This could be possible if the organic and inorganic nutrients and material from crop residue were recycled time and time again inside the hydroponics system. For this to happen, Garland et al. had to compare different nutrient recycling systems to determine which was the most efficient. The results of this study showed that recycling the organic and inorganic nutrients is easily accomplished through water extraction. However, there was evidence of stunted plant growth due to a buildup of organic material. From this, it can be concluded that applying organic material directly onto a crop, at least in the case of one growing in a hydroponics system, is harmful to its health.
Methods and Materials
Strawberry Cultivars and Bottom Pot Crops
The four strawberry cultivars used in this study were Albion, Chandler, Seascape, and San Andreas and were all obtained, regardless of variety, from Indiana Berry, a company based in Plymouth, Indiana. The strawberry plants were held in a high-tunnel, vertical hydroponic system on a University farm which was purchased from Verti-Gro, a company which operates out of Summerfield, Florida. Inside the high-tunnel were sixty towers, which were divided evenly into five repetitions. One tower included four levels that contained four plants each, all of which were strawberry plants of a single variety. Each tower, and all of the plants in it, received one treatment. At the base of each tower was one bottom pot that contained two of the same type of crop. The four different crops planted in the bottom pots of each vertical tower were borage, lettuce, celery, and cabbage, all of which were purchased from a local Menards. Each tower had its treatment/fertilizer pumped directly to it via a pipe system that ran across the high-tunnel. Bottom pot crops received the same treatment that the strawberry plants in the same tower as them received after the remaining liquid fertilizer dripped down to bottom pot from the top level each day.
Fertility Treatments
One synthetic fertilizer and two organic fertilizers were used to treat the strawberry varieties in this study. A combination of conventional synthetic fertilizer (CONV, Verti-Gro 6-12-28) and calcium nitrate (CaNOз) was pumped once daily through the pipe system to strawberry plants that were not being treated organically. These plants’ pots were made up of 50% coconut coir and 50% Perlite. This combination supplied the strawberry plants with all of their required nutrients. A combination of liquid organic fertilizer (L-ORG, Verti-Gro 6-0-16), molasses, fish emulsion, and Pro-Min were applied to strawberry plants that were being treated organically and whose pots were made up of 50% coconut coir and 50% Perlite. Molasses and 6-0-16 were pumped to these plants once daily through the pipe system. Fish emulsion was applied once a week by hand and Pro-Min was applied once every two weeks, also by hand. The last fertilizer used was charged media organic fertilizer (C-ORG). Plants undergoing this treatment received all of the components of L-ORG in the same amounts and at the same time. However, these plants’ pots were made up of 30% coconut coir, 50% Perlite, and 20% vermicompost, which was the charged media. All of the treatments listed above were purchased from Verti-Gro.
Collecting Yield and Chlorophyll Data
Strawberries were routinely harvested every two to three days, dependent on observed growth. After the fruit was separated between marketable and unmarketable, it was counted and weighed (g). Bottom pot plants were also harvested and weighed (g) until they stopped producing vegetables. Once a month, chlorophyll readings were taken on every strawberry plant and every bottom pot plant using a handheld atLEAF+ chlorophyll meter. In addition to chlorophyll readings, the bottom pot plants also had their height measured (cm). Chlorophyll readings were taken to assess alkalinity levels and were seen as another factor to determine the overall health of each plant. Time taken out to harvest and take chlorophyll readings was also used to conduct general pruning of the strawberry plants. Weeds were pulled, runners were trimmed, and diseased leaves were removed to prevent the spread of any kind of disease. Other general upkeep included mixing and refilling fertilizer buckets when they ran out, which was usually every two weeks. This provided the opportunity to check pH levels of solutions and make sure, if they were not at 5.5, to adjust them using acetic acid.
Statistical Analysis
Data that included marketable and unmarketable yield count and yield weight underwent an analysis of variance (ANOVA). It was used to identify any significant interactions between and among the fertilizers and cultivars.
Results
After running an analysis of variance, it was seen that throughout all aspects of the data related to unmarketable and marketable yield count or weight there were strong differences between cultivar results and strong differences between treatment results. However, interactions among the cultivars and the treatments were not significant.
All data that is related to the overall harvest yield is represented in the following figures on a “per tower” basis. Comparisons of both unmarketable and marketable average yield count gathered from the four strawberry cultivars are displayed in Figure 1. This figure indicates that the average marketable counts between the cultivars Albion and Chandler were not significantly different from eachother. This is also true for the average marketable counts of Chandler and Seascape. For average unmarketable yield counts, the figure shows that Chandler and San Andreas were not different, Chandler and Seascape were not different, and finally, San Andreas and Seascape average unmarketable counts were not different.
Figure 1. A comparison of each cultivar’s average marketable and unmarketable yield count
Data that compares the average unmarketable and marketable yield weights per tower of the four strawberry cultivars is included in Figure 2. The data presented in this figure indicates that the average marketable yield weight of the cultivar Albion was not significantly different from that of the cultivar Seascape. Also, Albion’s average unmarketable yield weight was not different from Chandler’s. This was true for Chander and San Andreas, and Seascape and San Andreas as well.
Figure 2. A comparison of each cultivar’s average marketable and unmarketable yield weight
Figure 3, like Figure 1, compares average marketable and unmarketable yield count. However, instead of cultivars, it depicts a comparison of the treatments’ growth effects on yield count. It is shown in the figure that CONV fertilizer behaved differently from L-ORG and C-ORG. It is also shown that the two organic fertilizers, L-ORG and C-ORG, were not different from eachother. It is true for average unmarketable yield count as well that L-ORG and C-ORG were not different from eachother. There is also no difference to be shown between CONV and L-ORG in the case of average unmarketable yield count, which is the only time this occurs throughout the data.
Figure 3. A comparison of each treatment’s produced average marketable and unmarketable yield count
A comparison of the treatments’ effects on average marketable and unmarketable yield weights is shown in Figure 4. The chart shows that in the cases of marketable and unmarketable yield weights, CONV was different than the two organic treatments, but the organic treatments were not different from each other.
Figure 4. A comparison of each treatment’s produced average marketable and unmarketable yield weight
Discussion
Based on average marketable yield weight, Albion on the Seascape were the two most successful cultivars of the study. Albion also had the lowest average unmarketable yield count and the lowest unmarketable yield weight. Either Albion or Seascape can be used with equal predicted success in a vertical hydroponics system under the specific conditions present in this study, because their marketable weight results were not significantly different from each other. This is consistent with the study conducted by Rodrigues et al. in 2014, in which Albion yield the second highest average yield weight. Similar to the study described in this paper, Albion was also being compared to the three other strawberry cultivars in a hydroponics system, although it was not vertical. While San Andreas had the lowest average marketable yield weight, it had the second highest average unmarketable yield weight, below Seascape. San Andreas also had the lowest average marketable yield count. Overall, this would make San Andreas the least successful cultivar of the study, presumably because it could not adapt to the growing conditions as well as the other three cultivars.
In all cases except for average unmarketable count, CONV was different from the two organic fertilizers, but L-ORG and C-ORG were not different from each other. When it came to average unmarketable count, the results of the two organic fertilizers, again, were not dissimilar, but neither were the results between L-ORG and CONV. Throughout the study, both yield count and weight results were consistently higher than those of L-ORG and C-ORG, which can be seen in Figure 3 and Figure 4. This supports the study’s hypothesis, which stated that CONV would perform better than the two organic fertilizers. If organic fertilizer was to be used for growing strawberries hydroponically, it could be assumed that either of them would perform near equally, because of their multiple data similarities.
Conclusion
Urban farmers are often looking for information on hydroponic growing methods that will allow them to bring in-demand fruits to market. After completing this study, it was found that CONV is more practical for crops growing in a hydroponics system because it produces a consistently larger yield weight than one would receive when using an organic fertilizer. Also, based on average marketable yield weight, Albion and Seascape were the best performing cultivars of the four present in this study. San Andreas was noted as the least successful cultivar of this study, after considering it had the lowest marketable yield weight, lowest marketable yield count, and highest unmarketable yield weight. Though time did not allow for this, it would have been valuable to analyze the data on a per tunnel basis. The work done also raises the question of whether or not hydroponics for small fruit has the capacity to be utilized on a large scale in the Midwest. Hydroponics are a valuable emerging tool for urban farmers, and create the possibilities for community growth and new income opportunities.
Acknowledgements
Recognition goes to mentor Dr. Sam Wortman and research team leader Michael Douglass for sharing their time, research, and expertise with me. Thank you to the graduate students of the Plant Sciences Lab, Ashley Holmes, Theodore Doellman, Alejandro Zavala, and all others for being kind at all times and enthusiastic about their fields of study. Finally, thank you to the Rap II program and program director Jesse Thompson for giving me the opportunity to gain experience in a lab and academic setting and allowing me to have an unforgettable experience.
References
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Rodrigues de Miranda, Fabio; Barros da Silva, Valsérgio; Ribeiro dos Santos, Francisco Sérgio; Guimarães Rossetti, Adroaldo; Bruce da Silva, Christiana de Fatima. "Production of strawberry cultivars in closed hydroponic systems and coconut fibre substrate". Revista Ciência Agronômica 4 (2014): 833-841.
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Wagstaff, Ross K., Wortman, Sam E. "Crop Physiological Response across the Chicago Metropolitan Region: Developing Recommendations for Urban and Peri-urban Farmers in the North Central US." Renewable Agriculture and Food Systems Renew. Agric. Food Syst. 30.01 (2013): 8-14. Web.
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Shinohara, Makoto, Chihiro Aoyama, Kazuki Fujiwara, Atsunori Watanabe, Hiromi Ohmori, Yoichi Uehara, and Masao Takano. "Microbial Mineralization of Organic Nitrogen into Nitrate to Allow the Use of Organic Fertilizer in Hydroponics." Soil Science and Plant Nutrition. 57.2 (2011): 190-203. Web. 21 July 2015.
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