Introduction
Materials and Methods
1. Plant material and growing conditions
2. Treatments
3. Irrigation and drainage management
4. Measurement of plant growth parameters
5. Statistical analysis
Results and Discussion
1. Drainage water and water retention capacity
2. Plant growth parameters
Conclusions
Introduction
Chinese cabbage (Brassica rapa) is the most edible vegetable in South Korea, consumed throughout the year (Kim et al., 2013). It is a rich source of calcium, α- and β- carotenoids, free amino acids, proline, and glucosinolates (Shawon et al., 2020). In South Korea, 91% production of chinese cabbage is gained from open-field cultivation (KOSIS, 2024). However, due to climate change and the same crop grown over a long period in the same place, soil-borne diseases are a trouble for growers in open fields. Even with good nutritional status or providing sufficient fertilizer in the soil, a satisfactory yield and quality are absent because of infected soil. In that case, the hydroponic system in a controlled environment-operated greenhouse has a unique opportunity to protect crop cultivation from soil-borne pathogens and ensure year-round production (Chinta et al., 2015). It is an advantageous method for growing plants without soil as a growing medium. Nutrient flow (only water flow) or horticultural substrates are used to replace soil for crop cultivation in hydroponic systems. However, considering size and weight matter chinese cabbage is difficult to grow in a nutrient-flow system. For this reason, solid substrate material is useful for chinese cabbage in hydroponic systems.
Furthermore, the reuse of substrate materials is a beneficial point of the hydroponic system. One such growth media organic product coir dust is a leading substrate in the horticulture industry. Coir substrate is commonly used two to three times for horticultural crop production including leafy plant lettuce (Vargas et al., 2021). Its advantages include pathogen-free, water-holding capacity and good drainage. Peat moss is also a familiar substrate because of its porosity and natural suppression ability to fungal-borne diseases (Larcher and Scariot, 2009). Perlite is another option, it brings down the risk of damping off, fits the optimum balance between water and air in the root zone of a plant and enhances its root growth (Asaduzzaman et al., 2013). Coir or peat moss can serve either alone growing medium or as an ingredient in a mix. However, the mixture of different materials raises concern about the ratios' ability to create a high-quality substrate for optimum plant growth. It depends on the combination of the substrate’s physical conditions such as porosity, air permeability, hardness for root growth and moisture retention capacity.
Tipburn is considered a serious threat to chinese cabbage due to reduced quality and yield in recent years (Zhang et al., 2022b). Notably, calcium application as a fertilizer in growing medium, helps to reduce different disease accumulation including tipburn in plants. It is an essential macronutrient for plants that plays a major role in cell membranes and cell wall development (Dodd et al., 2010). Additionally, plant nutrition management in substrate cultivation requires attention to control the proper pH and EC of substrate in the hydroponic system. In that case, drainage water is a good indicator. The drainage quality represents the chemical reaction between substrate components and nutrient solution. For this reason, drainage inspection is helpful for growers to have proper nutrient management in hydroponic system.
Many studies are relevant to chinese cabbage by researchers considering different factors such as coir substrate, calcium deficiency, and hydroponic system (Maboko et al., 2019; Su et al., 2016). Contrarily, to the best of our knowledge, the effects of calcium mixed-reused substrate medium using a hydroponic system for chinese cabbage cultivation have not been broadly studied in Korea and other parts of the world. Therefore, this study investigates the effect of reuse coir substrate and substrate ratios on drainage quality and growth performance of chinese cabbage in hydroponic systems. As well focused on using calcium to prevent the occurrence of tipburn, which affects growth and quality of chinese cabbage.
Materials and Methods
1. Plant material and growing conditions
This study was conducted in a venlo type smart farm house at Kangwon National University, Chuncheon, Korea during January 2024 to March 2024. The seeds of chinese cabbage cv. Bulam Plus (FarmHannong, Korea) are sown in a plug tray (128 holes) containing growing media (Seoul Bio Co., Ltd., Korea). After germination, at 11th January one month old healthy and uniform-sized plants (height around 11.5 cm and number of leaves around 13) were transplanted into pots (28 cm × 30 cm) filled with growing medium and treatments started on January 11. Coir dust (reused), peat moss and perlite were used in different ratios as a growing medium. We considered coir for second-time use after completing one crop cycle (in fall cultivation). The greenhouse environment (Figs. 1A, B) was measured using a complex environment control program (Ridder Synopta, Ridder Harderwijk, Netherlands). When the night temperature fell below 10℃, the heater was turned on to maintain the temperature for cabbage growth. During the treatment period, the average temperature of smart farm house was 15.2℃, where in January, February and March it was 13.6℃, 15.4℃, and 16.6℃ respectively (Fig. 1A).
2. Treatments
There were six different treatments. Firstly, three different compositions of growing mediums (coir dust: peat moss: perlite ratios were 10:0:0, 7:2:1, 5:3:2). Peat moss and perlite were used after washing. Secondly, each composition was divided into two groups based on the mixing (200 g/m2) of two types of calcium sources gypsum (CaSO4) and quicklime (CaO). Gypsum and quicklime treatment are marked as G and Q respectively. In addition, these six treatments also indicated by G10:0:0, G7:2:1, G5:3:2, Q10:0:0, Q7:2:1 and Q5:3:2. In every treatment, 3 g/L of boric acid (H3BO3) was added.
3. Irrigation and drainage management
During the experiment period, it was ensured that same amount of irrigation provided in all treatments and at a time. For irrigation, only two types of nutrient solutions were used. Where one is N-P-K = 17-6-18, commercial fertilizer (Yaraterra crystallon blue, Yara Korea, Korea) and another one especially for cruciferae leaf vegetables where N, P, K, Ca, and Mg were 13, 3, 7, 5, and 2 me·L-1 (Choi et al., 2005). Everyday irrigation was applied based on plant’s requirement, but each day used only one type of nutrient solution and the following day used another type. Furthermore, the total amount of irrigation was measured, it was minimum 200 ml but not similar during the treatment period due to the plant’s development phase (Fig. 1C). The total supplied amount of irrigation was 4.14 L/plant at the first four weeks. Whereas, for the next three weeks it was 8.31 L/plant, and for the final three weeks it was12.55 L/plant. The amount of drainage was measured every day at 1 hour after the irrigation. EC and pH of drainage were also measured with a multipurpose water quality meter (HI9813-6, Hanna Instruments Inc., Romania). The pH and EC of irrigation water (nutrient solution) was maintained 6.2 ± 0.3 and 1.5 ± 0.1 respectively. Before transplanting plants, we also measured substrate’s EC and pH and it was 6.2 ± 0.2 and 1.8 ± 0.2 respectively.
4. Measurement of plant growth parameters
Plant height and leaf width (from the largest leaf of the plants) were measured by a ruler. The number of leaves was counted visually. Chlorophyll content was measured also from the largest leaf of cabbage using a chlorophyll content meter (SPAD-502 Plus, Minolta Inc., Japan), and brix was measured using a brix meter Pal-1 (Atago Co., Ltd., Japan). At 10 weeks after treatment, plants were uprooted and separated from the root. Plant width and stem length were measured by a ruler too. Fresh weight and dry weight were measured using an electronic scale (HS5301V, Hansung instruments Co., Ltd., Korea). Later, dry weight was gained after oven-drying (convection oven, SANYO Inc., Osaka, Japan) at 60℃ for 48 h.
5. Statistical analysis
The experiment was conducted in a completely randomized design with 15 single plants replicates per treatment. Effect of treatments were analyzed using the IBM SPSS for Windows, version 24 (IBM Corp., Armonk, NY, USA). Significant variation (P ≤ 0.05) were examined through analysis of variance (ANOVA) followed by Duncan’s Multiple Range Test (DMRT).
Results and Discussion
1. Drainage water and water retention capacity
During the treatment period, the same amount of irrigation was provided in all treatments. However, due to the growth response of plants, the amount and quality (pH and EC) of drainage water varied in different treatments. From two to four weeks of treatment, the drainage rate steadily decreased in all treatments (Figs. 2A, 2B and 2C). Furthermore, between weeks 4 and 6 it remained similar. At 9 weeks after treatment, the drainage rate of all treatments was one-third compared to their drainage rate at the initial stage. In addition, at 9 weeks after treatment, the drainage rate was less than 20% in all treatments. Plant growth and size are the reasons for low drainage rate at the 10 weeks after treatment compared to initial stage. Because at the initial stage, plant’s water demand and water uptake capacity were lower, even although the daily supplied amount of irrigation was 200 ml and resulted maximum proportion of irrigated nutrient solution become drainage. But utilization of irrigated water was increased with the age of plants with their morphological development. For this reason, drainage rate was higher at initial stage than later (Figs. 2A, 2B and 2C).
From Fig. 2, observed that the EC level of drainage water was sharply decreased in every treatment from week 3 to week 5. In addition, compared to their initial stage (EC 4.0) it was decreased 50% or more in all treatments at week 9. The drainage EC was higher at initial stage may be due to combined effect of EC of substrates and irrigation water (nutrient solution) at initial stage and low amount of nutrients uptake by plants. It may be also relevant to irrigation amount and drainage rate (Fig. 1C). Where from 5 weeks after treatment, the irrigation amount was sharply increased and drainage rate (Figs. 2A, 2B, and 2C) was similar or fluctuated at low range. This phenomenon of irrigation amount and drainage rate is also correlated to the growth stages of plants. Choi et al. (2022) also showed that drainage EC of hydroponically grown strawberry plants was gradually decreased in different drainage treatments at 4 weeks after. In addition, from 5 weeks after treatment, Drainage EC was higher in gypsum-treated plants compared to those grown in quicklime treatments (Figs. 2D, 2E and 2F). However, drainage pH was higher in quicklime-treated plants compared to those grown in gypsum treatments (Figs. 2G, 2H and 2I). It happened due to the chemical structure of gypsum and quicklime. The hydrated form of calcium hydroxide (CaO) is called quicklime. when quicklime was added to the soil, due to the quicklime hydration and its dissociation reaction hydrated lime formed resulted in increased soil pH to make it alkaline (Bessaim et al., 2018). On the other hand, gypsum is composed of calcium and sulfate with the chemical formula CaSO4·2H2O. When it is added in soil, provides both sulfate and calcium in the soil system (Abdalla et al., 2010). As well as, it provides into both anion and cation (Ca2+) and sulfate (SO42−) for further reaction (Rashmi et al., 2018). For this reason, after leaching irrigation water through the gypsum-treated substrates, these drainage pH levels were lower compared to the quicklime-treated substrates (Figs. 2G, 2H and 2I).
During the treatment period, the drainage pH level was almost constant (variation range around 0.2) in G10:0:0, G7:2:1 and Q10:0:0treatments (Figs. 2G and 2H). Furthermore, that period's pH level fluctuated in G5:3:2, G7:2:1 and Q5:3:2 treatments. Jun et al. (2011) also showed that pH level of drainage water has fluctuated in a little range during 15 weeks of nutrient-strength treatment in the strawberry plant.
Fig. 2
Drainage rate (A, B, and C), drainage EC (D, E and F) and drainage pH (G, H and I) in different treatments. G and Q indicate gypsum and quicklime respectively. 10:0:0, 7:2:1, 5:3:2 indicate reused coir dust: peat moss: and perlite ratios in the growing medium. Lines in the graph represent the standard deviation of the mean (n = 10).
The total amount of drainage and total drainage rate was round 30% significantly higher in G7:2:1 treated plants than others (Fig. 3A). These are the results of cumulative effect on everyday drainage. Water retention volume was lowest (18.6 L/plant) in G7:2:1 treated plants (Fig. 3C). It was around 10% lower than other treatments. Water retention volume greatly depends on the plant’s growth and development. Maybe, growth and tipburn association are the reasons of comparatively less water retention volume G7:2:1 treated plants (Table 1 and Fig. 3C).
Table 1.
Effects of calcium sources and substrate ratios on growth characteristics of chinese cabbage. Q and G indicate quicklime and gypsum respectively. 10:0:0, 7:2:1, 5:3:2 indicate reused coir dust: peat moss: and perlite ratios in the growing medium.
|
Calcium source (A) |
Substrate ratios (B) | Plant growth characteristics | ||||||||||
|
Plant height (cm) |
Leaf weight (cm) |
Leaf number (ea) |
SPAD (value) |
Cabbage width (cm) |
Stem length (cm) |
Soluble solid (°Brix) |
Fresh weight (g·plant-1) |
Dry weight (g·plant-1) |
Dry rate (%) |
Tipburn (score) | ||
| Q | 10:0:0 | 37.9 yaz | 20.4 a | 67.2 a | 42.0 b | 56.3 bc | 5.2 a | 4.0 b | 1644.3 a | 91.6 b | 5.6 b | 2.2 ab |
| 7:2:1 | 37.1 a | 19.2 a | 71.2 a | 41.6 b | 61.5 a | 4.5 a | 4.1 b | 1637.7 a | 100.4 b | 6.1 b | 1.4 b | |
| 5:3:2 | 37.3 a | 19.3 a | 63.6 a | 41.7 b | 59.9 ab | 4.1 a | 4.8 a | 1578.6 a | 117.7 a | 7.5 a | 1.4 b | |
| G | 10:0:0 | 40.3 a | 20.8 a | 68.8 a | 41.2 b | 56.9 ab | 4.4 a | 3.9 b | 1606.4 a | 93.2 b | 5.8 b | 3.0 ab |
| 7:2:1 | 38.8 a | 19.3 a | 68.2 a | 48.6 a | 55.2 c | 4.3 a | 3.4 b | 1416.9 ab | 93.4 b | 6.6 ab | 3.4 a | |
| 5:3:2 | 36.9 a | 19.4 a | 58.0 a | 49.8 a | 56.3 bc | 4.1 a | 4.0 b | 1129.6 b | 92.5 b | 6.6 ab | 1.4 b | |
| A | ns | ns | ns | *** | ** | ns | * | * | * | ns | * | |
| B | * | ns | ns | ** | * | ns | * | ns | ns | * | ns | |
| A×B | ns | ns | ns | *** | * | ns | * | * | * | * | * | |
2. Plant growth parameters
At 10 weeks after treatment, plant height was not significantly different between the treatments. In the gypsum treatments, plant height was comparatively higher in G10:0:0 treated plants (Table 1). Among the treatments, no significant variations were observed in leaf width or the number of leaves of plants. These results reveal that all treatments similarly affected the growth of chinese cabbage. The chlorophyll content of leaves indicates the photosynthetic capacity and vigor of plants and it measured by SPAD value (Zhang et al., 2022a). In this study SPAD value was highest in G7:2:1 and G5:3:2 treated chinese cabbage than others (Table 1). In addition, it was not significantly different in quicklime-treated chinese cabbage.
The width of chinese cabbage was the lowest in G7:2:1. However, the highest width was observed in Q7:2:1. Stem length was not significantly different between the treatments (Table 1 and Fig. 4). The same growth (height, number of leaves and leaf width) of chinese cabbage (Table 1) in different treatments is the reason for the same stem length of plants.
Soluble solid (SS) content represents the quality and nutrient status of chinese cabbage (Kim et al., 2014). The highest SS (4.8 °Brix) was observed in Q5:3:2-treated plants (Table 1). It indicates Q5:3:2-treated chinese cabbage are comparatively better in quality than others. Furthermore, there was no significant difference between gypsum-treated plants. Our results also point out that based on SS, all treated chinese cabbage are good because these SS (brix levels 3.4 to 4.8, Table 1) are similar to conventionally grown chinese cabbage (Kim et al., 2014).
Fresh weight was significantly lower in G5:3:2 treated plants (Table 1) than others (except G7:2:1). It was significantly 30% lower than G10:0:0treated plants. There was no significant variation in quicklime-treated plants. Although growing substrates are different but same growing environment (temperature, humidity, Fig. 1) and same nutrient solution for irrigation are the reasons for similar growth and weight of chinese cabbage in different treatments. Among the quicklime-treated plants, dry weight was significantly highest in the treatment Q5:3:2 (Table 1). However, there was no significant variation in dry weight and dry rate of gypsum-treated plants. The presence of brix, fresh weight and dry weight of Q5:3:2-treated chinese cabbage may be correlated.
Tipburn is a major concern of chinese cabbage growers because, it develops dark lesions near the leaf margins and occurs during maturity or head formation, or storage resulting in a loss of quality and market acceptability (Li et al., 2022). Tipburn also occurred in our previous research where, plants grown in coir medium using hydroponic system. Therefore, to avoid tipburn association we attempted that added calcium in growing substrate before transplanted plants and observed their effect on plant growth. In this study, we also observed tipburn in all treatments and it was significantly highest in G7:2:1 treated plants than in others (except G10:0:0 and Q10:0:0) (Table 1 and Fig. 5). However, there was no significant variation in tipburn of quicklime-treated plants but comparatively lower in plants those were grown in Q7:2:1 and Q5:3:2 treatments. Maybe tipburn association in plants of different treatments due to facing low temperatures during night time (below 10℃) from the first day of treatment (Fig. 1A). Despite the fact, head formation in chinese cabbage is not completed in our present study, however, we found that more leaves in all treated plants compared to our previous research and it happened by the reason of added calcium in substrates. Because, in our previous research, we did not supply calcium-based fertilizer in growing substrates. In addition, irrigation volume and nutrient uptake ability of plants are another reasons for tipburn occurrence. Seeing, until 3 weeks of treatment drainage rate was higher (Figs. 2A, 2B, and 2C), and until 5 weeks of treatment supplied irrigation volume was lower (Fig. 1C). It indicates that maybe plants did not uptake enough water and nutrients during that period because of low root growth or less nutrients and water availability in the root zone. These findings support our concept that low temperature, less nutrient availability and less irrigation volume jointly played a crucial role in tipburn association in chinese cabbage along with calcium deficiency. Researchers noted that generally tipburn is related to calcium shortage in plants (Su et al., 2019). Although we added calcium in all treatments in different proportions, however, we also concerned about calcium deficiency. Furthermore, during the treatment period, the daily temperature in greenhouse was fluctuated approximately 15℃ where, maximum temperature was around 25℃ and minimum temperature was around 10℃ (Fig. 1A). Relative humidity in greenhouse was almost similar (60% to 70%), however, the daily solar radiation was highly fluctuated from 7 weeks after treatment compared to previous weeks (Figs. 1B and 1C). May be these environmental factors also the reasons for low plant growth and tipburn association in chinese cabbage (Table 1). Additionally, the presence of a higher proportion of peat moss and perlite in the growing substrate may be another reason for the low tipburn association in G5:3:2 and Q5:3:2 treated plants (Table 1). Further investigation is also required.
Conclusions
The present results indicate that drainage quality and growth parameters did not show highly significant variation among the treatments. Considering environmental factors for open field cultivation and assurance of quality and yield, this hydroponic method along with used coir dust as a substrate is applicable on chinese cabbage cultivation in Korea. Based on fresh weight, dry weight, soluble solid content and tipburn association, quicklime treatment Q5:3:2 is comparatively better than other treatments. On the other hand, treatment G7:2:1 is not preferable based on the width and fresh weight of chinese cabbage and their association with tipburn. More research is necessary to find a good combination of substrate, reuse possibility of substrate materials and nutrient solution for tipburn free profitable production of chinese cabbage in hydroponic system.
