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Article

Yield and Bioactive Compounds of Asparagus (Asparagus officinalis L.) Grown in Open Field and Rain Shelter Systems on Reclaimed Land in Saemangeum

by
Ju Young Hong
1,
Hyo Jung Jang
1,
Han Na Lee
1,
Seung Wook Choi
1,
Hyun Hwan Jung
2,
Myung Suk Ahn
2,
In Bog Lee
3 and
Yang Gyu Ku
1,4,*
1
Department of Horticulture Industry, Wonkwang University, Iksan 54538, Republic of Korea
2
Floriculture Research Division, National Institute of Horticultural and Herbal Science, Wanju 55365, Republic of Korea
3
Horticulture and Herbal Crop Environment Division, National Institute of Horticultural and Herbal Science, Wanju 55365, Republic of Korea
4
Institute of Life Science and Natural Resources, Wonkwang University, Iksan 54538, Republic of Korea
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(9), 1067; https://doi.org/10.3390/horticulturae11091067
Submission received: 3 July 2025 / Revised: 22 August 2025 / Accepted: 22 August 2025 / Published: 4 September 2025
(This article belongs to the Section Vegetable Production Systems)
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Abstract

The aim of this study is to provide basic data on the yield and bioactive compound contents of the male asparagus cultivar ‘Avalim’ grown under two cultivation systems, i.e., an open field and a rain shelter house, in the Saemangeum reclaimed land. Spear sprouting, yield parameters, polyphenol and flavonoid contents, antioxidant enzyme activities (catalase, ascorbate peroxidase, peroxidase, and superoxide dismutase), and DPPH and ABTS radical scavenging activities of 22-month-old asparagus cultivated in each system were measured. Spear sprouting occurred approximately 10 days earlier in the rain shelter house than in the open field. The number of asparagus spears per 1000 m2 was approximately 600 higher in the rain shelter house, and the total weight was 21% higher than that in the open field. Polyphenol and flavonoid contents, antioxidant enzyme activities, and DPPH and ABTS radical scavenging activities were higher in the open field than in the rain shelter house. The temperature in the rain shelter house during the cultivation period was 0.6 to 17.4 °C higher than that in the open field, while light intensity was 359.7 μmol·m−2·s−1 higher in the open field. Consequently, cultivation in Saemangeum reclaimed land resulted in higher yields in the rain shelter house, whereas the bioactive compound levels were higher in the open field. Therefore, selecting an appropriate cultivation system based on the intended purpose, focusing on yield or functional quality, when cultivating asparagus on reclaimed land is important.

1. Introduction

Saemangeum, the largest area of reclaimed land in South Korea, is 293 km2 of arable land that has been developed over 30 years since the start of reclamation in 1991 [1]. Crops such as rice, barley, corn, and soybeans are typically cultivated, either as food or forage crops, in Saemangeum and other reclaimed areas across the country. Research in these areas has focused on the soil characteristics of the reclaimed land [2], rice productivity [3], growth characteristics of corn according to irrigation [4], and the effects of reeds on rice yield and herbicide efficacy [5]. However, due to the recent decline in rice consumption, there is a growing need to cultivate high-value-added horticultural crops [6]. Existing studies on horticultural crop cultivation on reclaimed land include the selection of suitable crop varieties for reclaimed soils [7], the growth of broccoli [8], and the growth and nutrient absorption characteristics of Chinese cabbage [9]. Reclaimed lands are susceptible to fluctuations in groundwater levels caused by precipitation, which in turn increases subsurface salt concentrations closer to the soil surface [10]. Therefore, selecting salt-tolerant crops for cultivation is essential. Representative salt-tolerant, high-value-added horticultural crops include asparagus (Asparagus officinalis L.), broccoli (Brassica oleracea L.), beets (Beta vulgaris L. var. vulgaris), and spinach (Spinacia oleracea L.) [11].
Asparagus is a perennial crop in the Asparagaceae family that is rich in secondary metabolites such as saponins, polyphenols, vitamin C, and rutin, making it a functional vegetable [12]. Asparagus spears are rich in various bioactive compounds, including flavonoids, phenolic compounds, nitrite scavengers, caffeic acid, and ferulic acid, which reduce cholesterol levels and inhibit cancer cell activity [13,14,15,16]. These compounds are representative secondary metabolites produced by plants to ensure survival and are a key reason why the World Health Organization (WHO) recommends regularly consuming fruits and vegetables to obtain diverse physiological benefits [17]. Research is being conducted continuously on the chemical components of horticultural crops, such as cabbage and garlic, when grown on reclaimed land [9,18]. These findings highlight continued research interest in understanding the chemical composition of horticultural crops cultivated on reclaimed land.
While open field cultivation is more common overseas, asparagus is primarily cultivated in rain shelter houses (unheated greenhouses) that are just protected from rain in Korea. This is because of the high temperatures, humidity, monsoon rains, torrential downpours, and dry periods during summer, promoting the occurrence of diseases, such as gray mold, Phomopsis asparagi (Sacc.), stem blight, and Fusarium, all of which severely impair asparagus production [19,20]. Rain shelter houses help prevent the spread of soil-borne diseases, such as crown rot, which is exacerbated by heavy rain. Compared to open field cultivation, rain shelter houses enable harvesting 2–3 months earlier and extend the harvest period, resulting in higher yields. Additionally, as Korea increasingly experiences abnormal weather patterns [21], such as extreme heat and excessive rainfall, continued research on environment-responsive cultivation systems is essential.
Studies comparing the production characteristics of the ‘Atlas’ cultivar under open field and rain shelter conditions [20], the yield of male and female cultivars in the two systems [19], and bioactive compounds from asparagus spears grown in rain shelter houses on lung cancer cell proliferation compared to those grown in open fields [14] have been conducted. However, research on the growth characteristics and bioactive compound contents in asparagus cultivated in reclaimed lands remains insufficient, mainly due to soil conditions, such as salt accumulation. We conducted a comparative analysis of open field and rain shelter house cultivation types to obtain basic data on the feasibility of cultivating the representative all-male cultivar ‘Avalim’ in the Saemangeum reclaimed land. Additionally, the bioactive compound content of asparagus was analyzed to assess its potential for high-value crop production on the Saemangeum reclaimed land.

2. Materials and Methods

2.1. Experimental Site, Asparagus Cultivar, and Cultivation System

The experimental site was located in the Gwanghwal test field of the Saemangeum reclaimed land, National Institute of Crop and Food Science, Gwanghwal-myeon, Gimje-city, Jeonbuk Special Self-Governing Province (35.83° N, 126.69° E). For asparagus (Asparagus officinalis L.) cultivation, compost (6 t/0.1 ha), rice straw (2 t/0.1 ha), rice husks (2 t/0.1 ha), and fused phosphate fertilizer (20% effective phosphoric acid, KG Chemical, Ulsan Metropolitan City, Republic of Korea) (0.4 t/0.1 ha) were applied, followed by plowing to a depth of 80 cm. The crop beds were formed at a height of 30 cm. A rain shelter house was installed in May 2021 after the soil preparation and maintained throughout the experimental period. Asparagus cultivar ‘Avalim’ seedlings were sown in plug trays with a commercial growing medium containing 68.5% coco-peat, 10% peatmoss, 10% vermiculite, 5% zeolite, 6% perlite, 0.18% fertilizer, 0.01% wetting agent, and 0.3% pH regulator (Alpha-Plus, Sang-Lim Company, Iksan city, Republic of Korea) in January 2021. After germination, one-month-old seedlings were transplanted into plastic pots (9 cm diameter × 9 cm high) containing a commercial growth medium and grown for four months in the rain shelter house. Asparagus cultivar ‘Avalim’ was planted at a spacing of 80 × 30 cm on 3 May 2021 and was cultivated as green asparagus with exposure to sunlight. Each plot measured 4.65 × 1.2 m, and 28 plots were designated for each of the rain shelter house and open field cultivation systems, resulting in 28 replications per system. Fertilization during the cultivation period before spring harvest and after fern establishment was applied to the soil base at an N:P:K ratio of 12:8:10 kg/0.1 ha. Irrigation was administered via drip irrigation in accordance with standard practices, with soil moisture content managed within the range of 5–30% in both the open field and rain shelter houses. Plastic vinyl was mulched in all plots to control weeds. Asparagus plants aged 22 months were harvested every two days from March to May 2023 to investigate their growth characteristics and bioactive compounds content. All these conditions were applied equally to both the asparagus in the rain shelter house and the open field. After harvest, asparagus plants continue developing to produce spears for future harvesting.

2.2. Abiotic Factors During the Cultivation Period

Agricultural environmental measuring instruments (aM-31; Wisesensing, Yongin, Republic of Korea) were installed both in the open field and inside the rain shelter house in the Saemangeum reclaimed land to collect data on atmosphere temperature (Figure 1A) and light intensity (Figure 1B). Soil moisture was measured using a soil moisture meter (6440FS; Spectrum Technologies, Bridgend, UK) every 2–3 days at a depth of 15 cm from the soil surface using time-domain reflectometry (TDR) (Figure 2).
In total, 18 random points within the Saemangeum reclaimed land cultivation area were selected before the experiment, and 1 kg of rhizosphere soil was collected from a depth of 30 cm at each point and mixed evenly for soil analysis. A total of 18 points were randomly selected in both the rain shelter house and open field during the experiment, and soil analysis was conducted using the same method in September 2023 (Table 1).

2.3. Determination of Yield Parameters

Starting in March 2023, asparagus cultivated in both the open field and rain shelter houses on reclaimed land in Saemangeum was harvested to compare their yield parameters. The measured parameters included the number of days to spear sprouting, total number of spears, spear diameter, and spear weight. The day spear sprouting first emerged at least 1 cm above the soil surface was defined as day 1 of sprouting and was recorded for all experimental plots. The asparagus was harvested when the spear length reached 23 cm. Spear weight was measured using a precision electronic scale (PX223KR; Ohaus, Parsippany, NJ, USA), and spear diameter was measured 1 cm above the base of the stem using a digital caliper (M12.500182; Mitutoyo, Kawasaki, Japan). Yield data were collected over a 2-month period, and all values were converted to a 0.1 ha area basis.

2.4. Determination of Polyphenols and Flavonoids

The polyphenol content of the lyophilized asparagus spear extracts was determined using the Folin–Ciocalteu method [22]. The total polyphenol content [mg gallic acid equivalent (GAE) per g dry weight (DW) of spears] was calculated based on a gallic acid standard curve. The flavonoid content [mg quercetin equivalent (QE) per gram (DW) of spears] was determined as described by Ku et al. [23]. Quercetin was used to plot a standard curve.

2.5. Determination of Antioxidant Enzyme Activities

Catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and superoxide dismutase (SOD) levels were determined as previously described by Cao et al. [22]. Briefly, CAT activity of ‘Avalim’ spears was determined spectrophotometrically based on the disappearance of H2O2. The reaction mixture was prepared by adding crude CAT extract to potassium phosphate buffer (50 mM, pH 7.0). The reaction was initiated by adding 11 mM H2O2. The decrease in H2O2 concentration was determined by measuring the decline in the absorbance of the reaction solution at 240 nm (ε = 36 M−1 cm−1). CAT activity was expressed as μmol H2O2 decomposed per min per mg protein.
APX activity was measured by mixing ascorbate (0.5 mM ascorbate and 0.2 mM H2O2 in potassium phosphate buffer (100 mM, pH 7.5)). The APX crude extract was added to the mixture prior to measuring the absorbance at 290 nm (ε = 2.8 mM−1 cm−1) to determine the speed of the ascorbate oxidation. APX activity was measured as μmol ascorbate oxidized per min per mg protein.
For the determination of POD activity, the reaction mixture (1 mL) contained potassium phosphate buffer (40 mM, pH 6.9), 1.5 mM guaiacol, and 6.5 mM H2O2. After adding crude enzyme extract, the speed of tetraguaiacol formation from oxidized guaiacol was determined by measuring the absorbance at 470 nm (ε = 26.6 mM−1 cm−1). POD activity was expressed as μmol tetraguaiacol formed per min per mg protein.
SOD activity was measured using a colorimetric method with Kit-WST and a UV–VIS spectrophotometer (Biochrom Ltd., Cambridge, UK). The absorbance of each sample and blank control was measured at 450 nm. SOD activity was calculated as described by Shawon et al. [21] and expressed as % inhibition per milligram of protein.

2.6. Determination of the Antioxidant Capacity

DPPH and ABTS free radical scavenging assays were operated as expressed by Ku et al. [24]. Different concentrations (250–20,000 μg mL−1) of the spear extract in methanol were prepared. The DPPH and ABTS reagents were added at each concentration. The reaction solutions were incubated in the dark for 10 min or 1 h, and the sample absorbance was measured at 734 and 517 nm for the DPPH and ABTS assays, respectively. Free radical scavenging activity (%) was defined as the decrease in the absorbance of the reaction solutions compared to that of the control.

2.7. Statistics and Analysis

All statistical analyses were performed using IBM SPSS Statistics version 26 (IBM Corp., Armonk, NY, USA). Significance was determined using Tukey test at a 95% confidence level.

3. Results and Discussion

3.1. Growth Characteristics of Asparagus

Spear sprouting occurred approximately 10 days earlier in the rain shelter house than in the open field (Figure 3). Because spear sprouting is closely related to temperature, the faster sprouting observed in the rain shelter house can be attributed to its relatively higher temperature compared to that of the open field. In winter, when temperatures drop, the shoots of asparagus turn yellow and die, and cold treatment is required to break dormancy for regrowth in the following year. The most suitable temperature range for cold treatment is 0–10 °C, with 5 °C being the most effective [20,25,26,27]. According to previous studies, when cultivation temperatures are above 20 °C, the duration of cold treatment has little effect on sprouting. However, when temperatures are below 15 °C, cold treatment of 3–6 weeks can accelerate sprouting by about 20 days compared to untreated conditions [26,28]. If cold treatment is insufficient, sprouting is delayed, and yield is reduced. Therefore, asparagus production is generally complex in Korea from November to February of the following year because of the extremely low winter temperatures below 0–5 °C [20,29,30]. Nonetheless, the results indicated that both open field and rain shelter house conditions provided adequate chilling temperatures during winter to satisfy asparagus dormancy-breaking requirements [25,27].
When sprouting is promoted, the growth of spears accelerates, increasing the number of spears that can be harvested within the harvest period, thereby enhancing overall yield [14,26,31]. Thus, the timing of sprout emergence is a critical factor in asparagus cultivation.
Comparing the average number of spears per plot and the yield distribution by spear diameter between the cultivation methods, the rain shelter house produced thicker spears and an approximately 23% higher yield than the open field (Figure 4). The mean spear weight was also higher in the rain shelters (Figure 5). These results are consistent with those reported by Ha et al. [20], who observed higher asparagus yields in rain shelter houses than in open fields when growing the ‘Atlas’ variety in inland areas. Similar results were obtained by Seong et al. [32], who reported higher yields from six varieties (Mary Washington, Mary Washington 500 W, UC 309, UC 500, Hybrid Imperial, and Excel) cultivated in rain shelter houses than in open fields. Moreover, the yield by harvest week revealed that a larger quantity of asparagus was harvested from the early sprouting stage in the rain shelter house, with spears exceeding 7 mm in diameter occurring approximately 22% more frequently than those in the open field (Figure 4B), indicating a higher market value [20]. In contrast, full-scale production in the open field began approximately 4 weeks later (Figure 6).
In inland regions, rain shelter house cultivation has shown advantages, such as a higher number of spears, buds, and roots of asparagus, compared to that in open field cultivation [33]. Sprout emergence was faster, the yield increased by approximately 78%, and the average spear weight was higher [20,32]. Similarly, this study confirmed that rain shelter house cultivation offers higher productivity than open field cultivation, even under reclaimed land conditions.

3.2. Polyphenols and Flavonoids

The polyphenol content of asparagus cultivated on the Saemangeum reclaimed land was higher under open field cultivation than under rain shelter house cultivation (Table 2). The polyphenol content of asparagus cultivated in the open field averaged 42.58 mg GAE g−1 of extract, which was approximately 16.6% higher than that of asparagus cultivated in the rain shelter house, which averaged 36.54 mg GAE g−1. These values are similar to those reported by Cao et al. [22], who measured polyphenol content ranging from 35 to 41 mg GAE g−1 in the ’Atlas’ variety cultivated under both open field and rain shelter house conditions in inland regions. This is also comparable to their finding that the polyphenol content was higher under open field cultivation than under rain shelter conditions. Kohmura et al. [34] also reported that asparagus grown under high sunlight conditions had higher polyphenol content than those grown under shade conditions. This is because phenolic compounds are metabolically produced through the increase in phenylalanine ammonia lyase activity when the plant receives irradiation of strong light or ultraviolet rays. It is thought that they function as absorption materials of ultraviolet rays to weaken the light reaching the photosynthesis organ and to protect DNA from the damage by strong light [34,35].
Polyphenols are bioactive substances, including flavonoids, phenolic acids, and lignans. They exhibit antioxidant, anticancer, and anti-inflammatory effects in the body [15] and have also been reported to regulate the gut microbiome [36].
The flavonoid content of asparagus cultivated in the reclaimed land averaged 28.27 mg GAE/g DW under open field cultivation, whereas asparagus cultivated in the rain shelter house averaged 24.69 mg, which was approximately 12.6% lower than that of open field cultivation (Table 2). The results of this flavonoid content analysis indicate a much higher level than the total flavonoid content of 2.4–5.8 mg/L reported by Kim et al. [33] for the Jersey Giant, Jersey Supreme, NJ953, and UC157 varieties and are also higher than the 12.62–16.39 mg/L range reported by Lee et al. [14] for the same varieties. This difference appears to be because the present study used spears harvested from two-year-old asparagus after transplanting, whereas Lee et al. [14] and Kim et al. [33] used spears from one-year-old plants. The flavonoid content in asparagus varies depending on the timing of harvest [37,38], and Takács-Hájos and Zsombik [38] reported that asparagus harvested in the third year had a significantly higher flavonoid content than that harvested in the second year. The report by Cao et al. [22], which used the ’Atlas’ variety at 19 and 30 months after transplanting—similar to this study, which used plants at 22 months after transplanting—showed comparable flavonoid levels ranging from 24.79 to 27.54 mg QE g−1. Flavonoids present in asparagus spears exert antioxidant effects by suppressing the action of reactive oxygen species (ROS) in the body and are effective in improving vascular and liver diseases, inhibiting the proliferation of cancer cells, and reducing lipid peroxidation [14,39,40].
According to a study by Ku et al. [24], the flavonoid content in asparagus cladodes was higher under open field cultivation than under conventional greenhouse or organic cultivation. Similarly, Cao et al. [22] showed that asparagus cultivated in an open field had a higher polyphenol content than asparagus cultivated in a rain shelter house, which is consistent with the findings of this study. These results suggested that differences in cultivation systems influence the polyphenol and flavonoid contents of asparagus. This can be attributed to the higher light intensity in the open field since increased light intensity can promote the synthesis of phenolic compounds in asparagus spears [22,37,41,42,43]. Since flavonoids are also included in phenolic compounds, it is thought that they were higher under conditions of strong sunlight, consistent with the results of Cao et al. [22] and Kohmura et al. [34]. Light intensity in the open field ranged from 1000 to 2500 μmol·m2·s−1 during the harvest period, whereas it ranged from approximately 300 to 2000 μmol·m2·s−1 in the rain shelter house, indicating that asparagus cultivated in the open field was exposed to relatively higher light levels (Figure 1).
In addition, asparagus grown in open fields, which had relatively smaller diameters than those in rain shelter houses, showed higher flavonoid contents. This is because metabolites that are produced in the epidermal tissues are always found at greater concentrations in small-sized fruits or vegetables, which have a greater surface area-to-volume ratio than large-sized fruit [44]. The results of this study are consistent with the report by Stoffyn et al. [44] showing that the content of rutin, a type of flavonoid, was higher in asparagus shoots with a small diameter. Therefore, careful selection of the asparagus cultivation system is necessary to utilize the polyphenol and flavonoid components.

3.3. Antioxidant Enzymes

An analysis of antioxidant enzyme activity in asparagus cultivated in the open field and rain shelter houses in the Saemangeum reclaimed land revealed that the activities of all four antioxidant enzymes, i.e., CAT, APX, POD, and SOD, were lower in asparagus grown in the rain shelter house than in those grown in the open field (Table 3). In plants, antioxidant enzymes play a crucial role in eliminating ROS, such as H2O2, which cause cytotoxicity, thereby preventing cell damage [45,46,47,48]. These enzymes also contribute to the prevention of various adult-onset diseases and exhibit anticancer and anti-aging properties [49,50].
The CAT activity in asparagus cultivated in the reclaimed land was as follows: the average CAT activity was 19.19 μmol·min−1·mg−1 protein in open field grown asparagus, whereas it averaged 17.55 μmol·min−1·mg−1 protein in rain shelter house-grown asparagus, approximately 8.6% lower than in the open field. CAT is a representative enzyme of the antioxidant system that primarily decomposes H2O2 into water and oxygen within the organism, thereby protecting the cells [51,52].
Such results indicate higher CAT activity than the levels of 8.1–12.3 μmol·min−1·mg−1 protein reported by Lee and Yun [53] for 2-year-old ‘Super Welcome’ asparagus and 10.73–14.43 μmol·min−1·mg−1 protein reported by Cao et al. [22] for ‘Atlas’ asparagus grown under rain shelter and open field conditions in inland regions at 19 and 30 months of age. These differences appear to result from variations in the cultivation environments. Excessive ROS can accumulate in plant cells under stress conditions, such as intense light, temperatures outside the optimal range, and UV exposure. This in turn leads to increased antioxidant enzyme activity to remove ROS [54]. ROS production and antioxidant enzyme activity increase when plants are exposed to ultraviolet (UV) radiation, including UV-B [55]. Eichholz et al. [56] reported that POD activity increased in asparagus when exposed to 1.08 kJ·m−2 of UV-B for 22 h. In this study, peak light intensity reached approximately 2700 μmol·m−2·s−1 in the open field and 2400 μmol·m−2·s−1 in the rain shelter house, whereas Cao et al. [22] reported lower intensities of 1766.3 μmol·m−2·s−1 in the open field and 1,408.8 μmol·m−2·s−1 in the rain shelter house. Furthermore, the maximum temperature recorded in this study was 39 °C in the open field and 55 °C in the rain shelter house. In contrast, Cao et al. [22] reported maximum temperatures of 49 °C in the open field and 28 °C in the rain shelter house, and Lee and Yun [53] reported an average temperature of 22 °C. These findings suggest that the asparagus was exposed to a more stressful and high-temperature environment in the present study.
APX activity in asparagus cultivated in the open field and rain shelter house within the reclaimed land averaged 789.53 μmol·min−1·mg−1 protein in the open field and 582.83 μmol·min−1·mg−1 protein in the rain shelter house, showing approximately 26.2% lower activity in the latter. APX, like CAT, mitigates the effects of hydrogen peroxide (H2O2) by oxidizing ascorbate, thereby inactivating H2O2 and protecting biological systems from ROS [52].
The POD activity analyzed in this study was also lower in the rain shelter. The average POD activity was 4.95 μmol·min−1·mg−1 protein in the open field and 3.49 μmol·min−1·mg−1 protein in the rain shelter house, representing a decrease of approximately 29.5%. PODs catalyze oxidation reactions by utilizing peroxides such as H2O2 [57,58], thereby contributing to the removal of H2O2 and playing a role in protecting plants from ultraviolet (UV) stress [59].
SOD activity, an antioxidant enzyme, was analyzed in the asparagus cultivated in this study. The average SOD activity in the open field grown asparagus was 82.19%, whereas that in the rain shelter house was 75.71%, which was approximately 7.9% lower than that in the open field. SOD is a catalytic enzyme that scavenges superoxide anion radicals by converting them into H2O2. It is present in all oxygen-consuming organisms and plays an important role in defending biological tissues against the ROS toxicity of reactive oxygen species [52].
This result is consistent with the findings of Cao et al. [22], who reported higher APX, POD, and SOD activities in open field grown asparagus than in those grown in a rain shelter house. These results were likewise considered to be attributable to differences in cultivation environments. In this study the daily maximum temperature and light intensity in the open field ranged from 12 to 32 °C and from 1000 to 2500 μmol·m−2·s−1, respectively, during the harvesting period, both of which were higher than those in the rain shelter house, where the temperature ranged from 13 to 43 °C and the light intensity ranged from approximately 300 to 2000 μmol·m−2·s−1 (Figure 1). Therefore, asparagus grown in the open field was cultivated under lower temperature, higher light intensity, and greater UV exposure than those grown in the rain shelter house. These environmental differences are thought to influence the antioxidant enzyme activity of asparagus depending on the cultivation system.
Additionally, during the experimental period, the monthly maximum atmosphere temperatures in Gunsan and Buan, inland areas adjacent to the experimental site, were 5.2–31.1 °C and 5.8–31.6 °C, respectively [60], which were lower than the temperatures of the reclaimed land measured in this experiment. Therefore, it can be guessed that the antioxidant enzymes activity of asparagus spears grown in the Saemangeum reclaimed land would be higher than that of asparagus spears grown inland, but this requires further study.

3.4. Antioxidant Capacity

The DPPH radical scavenging activity of asparagus grown on the Saemangeum reclaimed land was measured. Except for the treatment with 500 mg/L asparagus extract, spears cultivated in the open field showed higher scavenging activity than those grown in the rain shelters at all other concentrations (Table 4). Regarding ABTS radical scavenging activity, asparagus spears grown in the open field also exhibited higher activity than those grown in the rain shelter at all concentrations except for the lowest concentration of 500 mg/L (Table 5).
When various antioxidant substances, including the antioxidant enzymes mentioned earlier, act within plant tissues, the antioxidant capacity is typically evaluated by measuring their electron-donating ability. This method assesses the ability of donating electrons to inhibit the formation of oxidative free radicals involved in the lipid peroxidation chain reactions by donating electrons [49]. ABTS and DPPH are stable free radicals that are reduced by antioxidants and can be measured by spectrophotometry; therefore, they are frequently used to assess the antioxidant capacity [49,61]. Accordingly, this study analyzed antioxidant activity by measuring both DPPH and ABTS radical scavenging activities.
The experimental results show that asparagus cultivated in the open field had a greater ability to suppress oxidation by donating electrons to free radicals than asparagus grown in the rain shelter house. This result is consistent with the findings of Cao et al. [22], who cultivated asparagus of the ‘Atlas‘ cultivar in both the open field and the rain shelter house in an inland region and found that spears grown in the open field exhibited higher ABTS and DPPH radical scavenging activities than those grown in the rain shelter house. This result is also consistent with the findings of Cao et al. [62], who cultivated asparagus of the ‘Atticus’, ‘Avalim’, and ‘Herkolim’ cultivars in control, 30%, and 70% shade treatments and found that spears grown in the shade treatments exhibited higher ABTS radical scavenging activities than those grown in the non-shade treatments. Furthermore, the results are consistent with the research by Kohmura [34], who cultivated asparagus of the ‘UC157’, ‘Green Frecce’, ‘HK1’, and ‘Purple Passion’ cultivars in shade treatments with eight layers of netting in the greenhouse and found that spears grown in the plots without netting exhibited higher DPPH radical scavenging activity compared to those grown in the plots with eight layers of netting. These findings may be attributed to the higher light intensity and relatively lower temperature in the open field than in the rain shelter house, which promotes the synthesis of phenolic compounds, such as quercetin, rutin, and ferulic acid in asparagus spears, thereby enhancing the free radical scavenging activity [22,63]. Phenolic compounds such as p-coumaric acid, caffeic acid, and sinapic acid extracted from the stems of asparagus of the ’Atlas’ cultivar also contribute to antioxidant activity [64,65].
Moreover, the antioxidant activity values for both ABTS and DPPH radicals measured in this study were higher than those reported by Cao et al. [22]. These results are consistent with those of previous studies on various plants, such as red cabbage, onions, and grapes, which showed that a higher phenolic compound content was associated with greater electron-donating capacity [49,66,67,68,69,70]. Therefore, selecting an appropriate cultivation system is important when cultivating asparagus due to its antioxidant properties.

4. Conclusions

The yield and bioactive compound content in the ‘Avalim’ asparagus cultivar cultivated on reclaimed land in Saemangeum varied depending on the cultivation system. Higher yields were obtained from the asparagus grown in rain shelters. In contrast, polyphenols, flavonoids, antioxidant enzymes (CAT, APX, POD, and SOD), and DPPH and ABTS radical scavenging activities were all higher in asparagus spears cultivated in the open field than in those grown in the rain shelter. The Saemangeum reclaimed land exhibits higher temperatures and stronger light intensity than typical inland regions; as a result of these environmental influences, the bioactive compound content was higher. Therefore, when cultivating asparagus on reclaimed land, it is recommended to select a suitable cultivation system for the intended purpose, such as maximizing yield or functional properties, and carefully assess the climatic and cultivation conditions, including temperature and light intensity.
Further studies are needed to evaluate the bioactive compounds of asparagus, such as rutin and protodioscin, as well as the anti-obesity effects, metabolic activity, and gene expression of asparagus spears grown in rain shelter houses and open field cultivation systems.

Author Contributions

Conceptualization, Y.G.K. and J.Y.H.; methodology, Y.G.K. and J.Y.H.; software, Y.G.K. and J.Y.H.; validation, Y.G.K.; formal analysis, J.Y.H. and H.J.J.; investigation, J.Y.H., H.J.J., H.N.L. and S.W.C.; resources, J.Y.H.; data curation, Y.G.K. and J.Y.H.; writing—original draft preparation, J.Y.H.; writing—review and editing, Y.G.K.; visualization, J.Y.H.; supervision, Y.G.K.; project administration, Y.G.K.; funding acquisition, H.H.J., M.S.A. and I.B.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Rural Development Administration Joint Research Project (no: RS-2023-00231192) of the National Institute of Horticultural and Herbal Science of the Rural Development Administration (RDA).

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 11 01067 g001
Figure 1. Atmosphere temperature (A) and photosynthetic photon flux density (PPFD) (B) of both the rain shelter house and open field in the Saemangeum reclaimed land in 2023.
Figure 1. Atmosphere temperature (A) and photosynthetic photon flux density (PPFD) (B) of both the rain shelter house and open field in the Saemangeum reclaimed land in 2023.
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Figure 2. Soil moisture content of both the rain shelter house and open field cultivation at the Saemangeum reclaimed land in 2023.
Figure 2. Soil moisture content of both the rain shelter house and open field cultivation at the Saemangeum reclaimed land in 2023.
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Figure 3. Days to spear sprouting of asparagus (Asparagus officinalis L.) ‘Avalim’ plant grown in both the rain shelter house and open field cultivation in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show significant statistical difference between mean values with p ≤ 0.05.
Figure 3. Days to spear sprouting of asparagus (Asparagus officinalis L.) ‘Avalim’ plant grown in both the rain shelter house and open field cultivation in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show significant statistical difference between mean values with p ≤ 0.05.
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Figure 4. Mean spear number per plot of asparagus (Asparagus officinalis L.) ‘Avalim’ plants according to cultivation system (A) and spear diameter size (B) in both the rain shelter house and open field cultivation in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show significant statistical difference between mean values with p ≤ 0.05.
Figure 4. Mean spear number per plot of asparagus (Asparagus officinalis L.) ‘Avalim’ plants according to cultivation system (A) and spear diameter size (B) in both the rain shelter house and open field cultivation in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show significant statistical difference between mean values with p ≤ 0.05.
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Figure 5. Mean spear weight per plot of asparagus (Asparagus officinalis L.) ‘Avalim’ plant grown in both the rain shelter house and open field cultivation at the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show a significant statistical difference between mean values with p ≤ 0.05.
Figure 5. Mean spear weight per plot of asparagus (Asparagus officinalis L.) ‘Avalim’ plant grown in both the rain shelter house and open field cultivation at the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show a significant statistical difference between mean values with p ≤ 0.05.
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Figure 6. Mean spear number according to month of harvest (A) and total spear number according to weeks of harvest (B) of asparagus (Asparagus officinalis L.) grown in both the rain shelter house and open field in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show a significant statistical difference between mean values with p ≤ 0.05.
Figure 6. Mean spear number according to month of harvest (A) and total spear number according to weeks of harvest (B) of asparagus (Asparagus officinalis L.) grown in both the rain shelter house and open field in the Saemangeum reclaimed land. The error bars represent the standard deviation (n = 28). Different letters show a significant statistical difference between mean values with p ≤ 0.05.
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Table 1. Soil characteristics of Saemangeum reclaimed land before and during the experiment.
Table 1. Soil characteristics of Saemangeum reclaimed land before and during the experiment.
Cultivation
System		pH
(1:5)		EC
(dS/m)		OM
(%)		Av. P2O5
(mg/kg)		Ex. Cation (cmol/kg)
KCaMgNa
Before experiment
6.3 ± 0.3 z0.7 ± 0.19.8 ± 1.6118.0 ± 40.20.81 ± 0.082.63 ± 0.452.60 ± 0.790.15 ± 0.09
During experiment
Open field7.1 ± 0.20.2 ± 0.13.8 ± 3.0313.8 ± 101.91.27 ± 0.145.58 ± 0.472.82 ± 0.490.61 ± 0.11
Rain shelter house6.3 ± 0.40.9 ± 0.34.6 ± 2.9349.0 ± 132.61.05± 0.202.60 ± 0.832.62 ± 1.070.57 ± 0.23
z Each value represents the mean ± standard deviation (n = 18).
Table 2. Comparison of polyphenol and flavonoid contents of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Table 2. Comparison of polyphenol and flavonoid contents of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Cultivation SystemPolyphenol
(mg GAE g−1)		Flavonoids
(mg GAE g−1)
Open field42.58a z28.27a
Rain shelter house36.54b24.69b
z Means with different letters in a column are significantly different according to Tukey test at p ≤ 0.05.
Table 3. Comparison of catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and superoxide dismutase (SOD) of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Table 3. Comparison of catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and superoxide dismutase (SOD) of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Cultivation SystemCAT
(μmol H2O2 Decomposed
min−1 mg Protein−1)		APX
(μmol Ascorbate Oxidized
min−1 mg Protein−1)		POD
(μmol Tetraguiacol Formed min−1 mg Protein−1)		SOD
(% Inhibition
mg Protein−1)
Open field19.19a z789.53a4.95a82.19a
Rain shelter house17.55b582.83b3.49b75.71b
z Means with different letters in a column are significantly different according to Tukey test at p ≤ 0.05.
Table 4. Comparison of DPPH radical scavenging of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Table 4. Comparison of DPPH radical scavenging of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Cultivation SystemDPPH Radical Scavenging (%)
Asparagus Extracts (mg/L)
25050010002500500010,000
Open field15.44a z25.03a42.21a62.68a80.77a96.55a
Rain shelter house13.59b22.93a33.99b57.10b73.50b94.56b
z Means with different letters in a column are significantly different according to Tukey test at p ≤ 0.05.
Table 5. Comparison of ABTS radical scavenging of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Table 5. Comparison of ABTS radical scavenging of asparagus cultivated in an open field and rain shelter house in Saemangeum reclaimed land.
Cultivation SystemABTS Radical Scavenging (%)
Asparagus Extracts (mg/L)
50010002500500010,00020,000
Open field25.79a z35.83a49.48a74.79a90.34a95.21a
Rain shelter house23.00b30.14b42.31b69.06b86.48b92.33b
z Means with different letters in a column are significantly different according to Tukey test at p ≤ 0.05.
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Hong, J.Y.; Jang, H.J.; Lee, H.N.; Choi, S.W.; Jung, H.H.; Ahn, M.S.; Lee, I.B.; Ku, Y.G. Yield and Bioactive Compounds of Asparagus (Asparagus officinalis L.) Grown in Open Field and Rain Shelter Systems on Reclaimed Land in Saemangeum. Horticulturae 2025, 11, 1067. https://doi.org/10.3390/horticulturae11091067

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Hong JY, Jang HJ, Lee HN, Choi SW, Jung HH, Ahn MS, Lee IB, Ku YG. Yield and Bioactive Compounds of Asparagus (Asparagus officinalis L.) Grown in Open Field and Rain Shelter Systems on Reclaimed Land in Saemangeum. Horticulturae. 2025; 11(9):1067. https://doi.org/10.3390/horticulturae11091067

Chicago/Turabian Style

Hong, Ju Young, Hyo Jung Jang, Han Na Lee, Seung Wook Choi, Hyun Hwan Jung, Myung Suk Ahn, In Bog Lee, and Yang Gyu Ku. 2025. "Yield and Bioactive Compounds of Asparagus (Asparagus officinalis L.) Grown in Open Field and Rain Shelter Systems on Reclaimed Land in Saemangeum" Horticulturae 11, no. 9: 1067. https://doi.org/10.3390/horticulturae11091067

APA Style

Hong, J. Y., Jang, H. J., Lee, H. N., Choi, S. W., Jung, H. H., Ahn, M. S., Lee, I. B., & Ku, Y. G. (2025). Yield and Bioactive Compounds of Asparagus (Asparagus officinalis L.) Grown in Open Field and Rain Shelter Systems on Reclaimed Land in Saemangeum. Horticulturae, 11(9), 1067. https://doi.org/10.3390/horticulturae11091067

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