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Article

Comparison of Yield and Yield Components of Several Crops Grown under Agro-Photovoltaic System in Korea

by
Hyun Jo
1,
Sovetgul Asekova
2,
Mohammad Amin Bayat
3,
Liakat Ali
4,
Jong Tae Song
1,
Yu-Shin Ha
5,
Dong-Hyuck Hong
5,* and
Jeong-Dong Lee
1,6,*
1
Department of Applied Biosciences, Kyungpook National University, Daegu 41566, Korea
2
Department of Plant Sciences, College of Agricultural and Marine Science, Sultan Qaboos University, Muscat 123, Oman
3
Department of Food Security and Agricultural Development, Kyungpook National University, Daegu 41566, Korea
4
Department of Genetics and Plant Breeding, Faculty of Agriculture, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh
5
Upland-Field Machinery Research Center, Kyungpook National University, Daegu 41566, Korea
6
Department of Integrative Biology, Kyungpook National University, Daegu 41566, Korea
*
Authors to whom correspondence should be addressed.
Agriculture 2022, 12(5), 619; https://doi.org/10.3390/agriculture12050619
Submission received: 28 March 2022 / Revised: 22 April 2022 / Accepted: 26 April 2022 / Published: 27 April 2022
(This article belongs to the Special Issue Precision Agriculture Adoption Strategies)
Browse Figures
Versions Notes

Abstract

:
Renewable energy generation has attracted growing interest globally. The agro-photovoltaic (APV) system is a new alternative to conventional photovoltaic power plants, which can simultaneously generate renewable energy and increase agricultural productivity by the use of solar panels on the same farmland. The optimization of crop yields and assessment of their environmental sensitivity under the solar panels have not yet been evaluated with various crop species. This study aimed to evaluate the agronomic performances and crop yields under the APV system and the open field with crop species such as rice, onion, garlic, rye, soybean, adzuki bean, monocropping corn, and mixed planting of corn with soybean in South Korea. The results indicated that there was statistically no negative impact of the APV system on the forage yield of rye and corn over two years, suggesting that forage crops under the APV system were suitable to producing forage yield for livestock. In addition, the measured forage quality of rye was not significantly different between the open field and the APV system. However, rice yield was statistically reduced under the APV system. The yield of legume crops and vegetables in this study did not show consistent statistical results in two years. For further study, crop yield trials will still be required for rice, soybean, adzuki bean, onion, and garlic for multiple years under the APV system.

1. Introduction

Renewable energy generation has attracted increasing interest globally because of increased awareness of environmental issues, such as fossil fuel use and carbon emissions, resulting in climate change [1,2,3]. The greenhouse gas emission of renewable energy is considerably lower compared with coal and fossil fuels power generation [4]. According to the Paris Agreement of the United Nations Framework Convention on Climate Change, 32 gigatons of carbon dioxide will be reduced from the atmosphere by 2030 [5,6]. Renewable energy has been generated from photovoltaic panels, micro or small wind turbines to produce electricity, and from solar–thermal sources for heat production [7,8].
Recently, the agro-photovoltaic (APV) system has become an alternative to conventional photovoltaic power plants. The APV, an innovative facility, can simultaneously generate renewable energy and increase agricultural productivity by using a solar panel array on the same farmland [9,10,11,12,13,14]. Crops are cultivated on the ground under the solar panel arrays of the APV system. To create the APV system, the solar panel arrays should be installed high enough so that farm machinery can be moved for cultivation management [1]. The APV system may relieve food insecurity and become an alternative energy source to fossil fuels, which are the largest sources of carbon dioxide emissions. The expansion of renewable energy to reduce greenhouse gas emissions and increase farm household income through the installation of the APV system has received much attention from solar developers, policy makers, and agricultural communities worldwide [15].
The APV structure generates partial shading conditions during crop cultivation, resulting in decreased crop productivity. The amount of light is an important environmental factor in the growth and development of crops owing to their photosynthetic rates [12,16]. Light shortages may seem like a challenge for crops depending on the plant species in the shading condition of the APV system. In this regard, studies on crop yield and physiological changes in various crops are being conducted. A study reported that shading conditions created by the APV system led to yield reductions of spring and summer lettuces [17]. The APV system in rice paddies in Japan demonstrated a negative impact on rice yield and quality with a higher shading rate [18].
However, several studies have reported overcoming the effect of shading in crops under the APV system. Switching from open crop cultivation to an APV system requires minor adjustments for crop growth and development in the fluctuating shading conditions [11]. Marrou et al. [12] reported that the use of mobile panels can allow maximum light penetration in the juvenile stages to protect young seedlings from stunted growth. In addition, although shading effects could harm a plant, certain plant species can tolerate low light levels, which is shade tolerance. Acclimation is a growth process in which each newly produced leaf has a set of biochemical and morphological characteristics suited to the environment [19].
Crops cultivated under the APV system benefit from more effective water/rain redistribution [10], reduced evapotranspiration, increased carbon uptake and water use efficiency for plant growth and reproduction [20], decreased soil and crop temperature, improved soil humidity [12], increased land productivity [14], increased pollinator foraging behavior during hot, dry and late seasons [21], and protection against climatic uncertainty and extreme events, such as hailstones and excessive rain [22]. The protection provided by the solar canopy has been found to provide favorable microclimatic conditions such as soil radiation, soil and air temperature without adverse effects on crops, promoting soil and agricultural productivity [12,18,20,23]. Marrou et al. [12] reported that the light reduction caused by the APV system did not affect the production of cucumber and lettuce crops. Barron-Gafford et al. [20] monitored the physical and biological dimensions of the APV ecosystem on three different crops, chiltepin pepper, jalapeño, and tomato grown under the APV system and in traditional open field, resulting in multiple additives and synergistic benefits, including reduced plant drought stress, greater crop production, reduced heat stress, and renewable energy production. However, they reported that these positive effects under the APV system depended on the plant species.
The Ministry of Trade, Industry, and Energy of the Korean government announced that it will increase the proportion of renewable energy up to 20% by 2030 based on renewable energy expansion policies such as the Renewable Energy 3020 Implementation Plan and the 2050 Carbon Neutral Strategy, thereby increasing renewable energy generation to 84.4 GW by 2034, of which 39.3% will be generated from photovoltaic power. In 2020, 8072 photovoltaic power plants were built in rural areas, of which 10 were APV systems [24]. In addition, photovoltaic power plants have increased from 42 ha in 2010 to 2555 ha in 2019. Recently, the Korean government expressed interest in the expansion of photovoltaic power plants, including the APV system.
Shade-tolerant crop species such as Asian greens, chard, collard greens, kale, mustard greens, parsley, sorrel, spinach, scallions, broccoli, kohlrabi, hog peanut, alfalfa, yam, taro, cassava, and sweet potato are better cultivated under the APV system since they grow well in the low light environment [25]. Shade-intolerant crop species such as corn, cucumber, pumpkin, rice, tomato, turnip, and watermelon require sufficient daylight, whereas plants such as cauliflower, beans, carrots, coriander, onion, and pepper need moderate light [26]. However, the efficacy and number of beneficial effects of APV systems depend on the plant species. Production of shade-intolerant corn was increased by 4.9% with low density solar panels at 1.67 m intervals than in open fields [25]. Optimizing crop yields and assessing their environmental sensitivity under the solar panels have not been evaluated with various crop species in South Korea. The objective of this study was to evaluate agronomic performances and crop yields under the APV system and to compare them with crops grown in the open field condition, such as rice, onion, garlic, rye, soybean, adzuki bean, corn and intercropped corn and soybean.

2. Materials & Methods

2.1. Solar Panel

The APV system was installed at the affiliated field of Kyungpook National University (36°14′05″ N, 128°78′14″ E). The APV systems were built in a paddy field and a dry field. The APV systems in the paddy field and dry field covered approximately 1000 m2 (33,600 × 30,000 mm) with a dummy solar panel distance of 1500 mm at a height of 3300 mm (Figure 1A). A total of 320 dummy panels (1675 × 998 mm) were installed in the entire tested area of each field covered by the APV system with a shading rate of 30%, which was the ratio of the area (m2) shaded by the solar panels to the area (m2) of the installed APV system (Figure 1B). Brohm and Khanh [27] reported that the shading rate for the APV systems must be less than 33% to produce solar power in South Korea. Shading on the plant can be reduced by adjusting the angle of inclination, to form 35° angles. Figure 2 shows the APV system in a paddy field and a dry field. Rice was grown in the paddy field under the APV system and the open field (Figure 2A). Onion and garlic plants were grown in the dry field under the APV system and in the open field (Figure 2B).

2.2. Field Experiment with Crop Species

The study was conducted in an affiliated farm field (36°14′05″ N, 128°78′14″ E) of Kyungpook National University to assess the impacts of the APV system on crop performances and yield. Seven different crop species and a mixed planting of corn with soybean were selected, including rice (Oryza sativa L., var. “Wonkwang”), rye (Secale cereale L., var. “Elborn”), soybean (Glycine max L., var. “Hoshim”) [28], adzuki bean (Vigna angularis, var. “Saegil”), corn (Zea mays, var. “Kwangpyeongok”) [29], mixed planting of corn with soybean (G.max, var. “Chookdu 1”) [30,31], garlic (Allium sativum L., var. “Daeseo”), and onion (Allium cepa L., var. “Honmaru”). Rice and soybean are two of the most relevant cash crops worldwide. Adzuki bean is also a valuable pulse crop in South Korea. Onion and garlic are two of the most important vegetable crops. It was recently reported that mixed planting of corn with soybean in the same row improves forage yield and silage quality [30,31].

2.3. Rice Cultivation

All the rice seeds of the Wonkwang cultivar were planted on 23 April 2018 and 22 April 2019. Rice seedlings were transplanted to the paddy field on 19 May 2018 and 3 June 2019, respectively, at a planting density of 30 × 15 cm with approximately 15 plants per mound. The harvesting dates for rice were 23 October 2018 and 22 October 2019, respectively. Five blocks under the APV system and open field were harvested using a combined harvester. The harvested areas of each block were 28.8 and 18.0 m2 under the APV system and open field in 2018, and 28 m2 for the APV system and open field in 2019. Ten randomly selected hills from each block were measured for yield components such as number of ripened grains per hill, number of spikelets per hill, number of unfilled spikelets per hill, percentage of ripened grain, and 1000-grain weight. The percentage of ripened grain was the number of ripened grains per hill divided by the total number of spikelets per hill.

2.4. Soybean and Adzuki Bean Cultivation

Seeds of soybean (var. Hosim) and adzuki bean (var. Saegil) were planted directly by the planter on 12 June 2019 and 23 June 2020, respectively. Seeds were planted 70 cm apart between rows, and hills within the rows 15 cm apart with two seedlings per hill. The harvesting dates were 23 October 2019 and 27 October 2020, respectively. Three randomly selected plots (4 × 1.4 m) under the APV system and open field were harvested to determine yield and agronomic traits. Ten randomly selected soybean and adzuki bean plants per plot at maturity were used to measure plant height, number of branches per plant, number of nodes per plant, number of pods per plant, and the weight of 100 seeds.

2.5. Onion Cultivation

Onion seedlings (var. Honmaru) were transplanted into the holes of the plastic mulch at a planting density of 15 × 15 cm for two years on 30 October 2018 and 15 October 2019. The plots were 4 m long and 1.30 m wide with three replications under the APV system and open field. The onion harvest dates were 20 June 2019 and 11 June 2020, respectively. The total weight of onion harvested from each plot on the harvest dates was measured.

2.6. Garlic Cultivation

After sterilization, individual garlic clover (var. Daeseo) was directly planted in plastic mulch holes with one bulb per hill at a planting density of 15 × 13 cm for two years on 26 October 2018 and 15 October 2019. The plots were 4 m long and 1.30 m wide with three replications under the APV system and open field. The onion harvest dates were 20 June 2019 and 11 June 2020, respectively. The total weight of harvested garlic from each plot on the harvest dates was measured.

2.7. Rye Cultivation

Rye seeds (var. Elborn) were sown directly in the field under the APV system and open field using the scatter planting method on 10 November 2018 and 8 November 2019, respectively. The seeding rate was approximately 200 kg per hectare for two years. Four randomly selected plots (6 × 4 m) were harvested for forage yield and silage quality on 23 May 2019 and 20 May 2020, respectively. The fresh weight of the total harvested rye from each plot and the height of 10 plants at harvest dates were measured. Subsequently, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), digestible dry matter (DDM), dry matter intake (DMI), relative feed value (RFV), and total digestible nutrients (TDN) were measured as the components of forage quality parameters. Forage quality measurement and calculations were performed according to our previous study [32]. We found that there was no difference in forage quality from the first-year evaluation, we did not evaluate forage quality for the second-year test.

2.8. Monocropping Forage Corn Cultivation

Corn (var. Kwangpyeongok) was planted by a planter at a planting density of 20 × 70 cm on 12 June 2019 and 23 June 2020. The final stand in the hills was a corn plant. Fertilization and time of forage harvest were based on recommendations for forage corn production [30,31]. Harvesting dates were 18 September 2019 and 23 September 2020, respectively. Three randomly selected plots (4 × 1.4 m) under the APV system and open field were harvested for fresh weight as forage yield. In addition, plant height was measured for 10 individual plants from each plot.

2.9. Mixed Planting Corn with Soybean Cultivation

Soybean (var. Chookdu 1) and corn (var. Kwangpyeongok) were planted by hand in hills within the same row each at 10 cm intervals with 70 cm spacing between rows on 12 June 2019 and 23 June 2020. The final stand in hills was one corn plant and three soybean plants. Fertilization and time of forage harvest were based on recommendations for forage corn production [30,31]. Harvesting dates were 18 September 2019 and 23 September 2020, respectively. Three randomly selected plots (4 × 1.4 m) under the APV system and open field were harvested for forage yield. The corn with soybean was harvested separately at the recommended stage for forage corn. Corn and soybean were measured separately for plant height and fresh weight from each plot of the APV system and open field.

2.10. Statistical Analysis

All statistical analyses in this study were conducted in SAS v9.4 (SAS Institute, Cary, NC, USA, 2013). The t-test was performed using PROC TTEST in SAS.

3. Results

3.1. Effect of APV System on Yield and Yield Components of Rice

The mean values of rice yield and yield components over two years are shown in Table 1. Rice yield in the open field was significantly higher than the yield under the APV system over two years (p < 0.01). Rice grown in the open field produced a higher yield (7.5 t/ha) than that under the APV system (6.1 t/ha) in 2018. The rice yield was 7.9 and 7.2 t/ha for the open field and APV system, respectively, in 2019. In addition, the reduction in rice yield was 18.7% in 2018 and 8.9% in 2019 in the APV system compared with the open field. In two years, 1000-seed weight and the number of unfilled spikelets per hill were not significantly different between the open field and the APV system. Over two years, the numbers of spikelets per hill in 2018 and 2019 were 1309.1 and 1559.2 in the open field, respectively, which were significantly higher by 189.6 and 191.6, respectively, than the ones in the APV system. The numbers of ripened grains per hill for rice in the open field in 2018 and 2019 were significantly higher by 196.0 and 210.3, respectively, than those under APV. The plant height of rice was not significantly different between the open field (93.0 cm) and APV system (93.2 cm) in 2018. However, the plant heights of rice in the open field and APV system were 87.5 and 91.3 cm, respectively, in 2019, which resulted in statistical significance. The percentage of ripened grain was reduced in 2018 from 92.6% in the APV system to 90.9% in the open field, and in 2019 from 93.8% in the APV to 91.6% in the open field.

3.2. Yield and Yield Components of Legume Crops: Soybean and Adzuki Bean

Soybean and adzuki bean were evaluated for yield and yield components including plant height, number of branches, number of nodes, number of pods, and 100-seed weight (Table 2). In soybean, there were no significant differences for all measurements between the open field and APV system in 2019, whereas all measurements, except 100-seed weight, showed significance (p < 0.001) between the open field and APV system in 2020. Soybean grain yield in the open fields (1.6 t/ha) was significantly higher than that under the APV system (0.5 t/ha) in 2020. In addition, the yield components in the open fields showed a better performance than those in the APV system in 2020. In adzuki bean, there were no significant differences for all measurements except 100-seed weight between the open field and APV system in 2019 (Table 2). In 2020, the mean of yield, plant height, number of branches, number of nodes, number of pods of adzuki bean in the open field was statistically higher than the that under the APV system. Furthermore, the grain yields of adzuki beans in the open field and APV system were 1.5 and 0.4 t/ha, respectively.

3.3. Yield of Garlic (Allium sativum L.) and Onion (Allium cepa L.)

The yields of garlic and onion as vegetable crops were evaluated between the open field and APV system over two years (Table 3). There were significant differences in the yield performances of garlic and onion in 2018–2019, whereas the yields of garlic and onion were not significant in 2019–2020. The yield indexes of garlic and onion in 2018–2019 were 78.7 and 80.6%, whereas the yield indexes of garlic and onion in 2019–2020 were 82.9 and 90.6%, respectively. Overall, the harvested yields for garlic and onion for the APV system (14.4 and 71.3 t/ha) were 18.7 and 14.6% reduced compared to open fields (17.7 and 83.3 t/ha).

3.4. Forage Yield and Forage Quality of Rye (Secale cereale L.)

Forage yield (fresh weight) of rye was evaluated for two years (Table 4). Based on statistical analyses, there was no significant difference in forage yield and plant height of rye over two years. Under the APV system and open field, the forage yield of rye in 2018–2019 produced 19.1 and 19.7 t/ha, respectively. The mean difference in forage yield between the open field and APV system in 2019–2020 was 3.1 t/ha. Rye plant height in 2018–2019 and 2019–2020 averaged 155.4 and 148.0 cm under the APV system, respectively, compared with that in the open field (148.0 cm in 2018–2019 and 157.8 cm in 2019–2020).
In addition, there were no significant differences in all measured forage quality values of rye between the open field and APV system in 2018–2019 (Table 4). The mean values of rye in the open field for the CP, NDF, ADF, TDN, RFV, DMI, DDM forage quality characteristics were 9.1, 62.5, 37.9, 58.9, 88.5, 1.9, and 59.3, respectively. The mean values of rye on the open field for CP, NDF, ADF, TDN, RFV, DMI, DDM forage quality characteristics were 9.3, 64.0, 39.6, 57.5, 84.2, 1.8, and 57.9, respectively. Overall, forage yield, plant height, and forage quality parameters, such as CP, NDF, ADF, TDN, RFV, DMI, DDM, did not differ significantly between the open field and APV systems (Table 4).

3.5. Effect of APV Shading on Mixed Planting of Corn with Soybean, and Monocropping Corn

The forage yield was measured for the mixed planting of corn with soybean and monoculture corn between the open field and APV system in 2019 and 2020 (Table 5). In 2019, there were no significant differences between the open field and the APV system for forage yield and plant height of corn in the mixed planting cropping system, whereas soybean plant height in the mixed planting system was 136.5 cm, which was significantly taller than that under the APV system (119.5 cm). The total forage yield for the mixed planting system (corn + soybean) in the open field (60.7 t/ha) was statistically higher than that under the APV system (53.6 t/ha). In addition, the forage yields for monocropping corn in the open fields and APV systems were 55.1 and 55.2 t/ha, respectively. The forage yield indexes for a mixed planting in the open field and APV system were 110.2 and 97.1% for the corn mono-crop, respectively. In 2020, there were no significant differences between open field and APV systems for forage fields of corn, soybean, and total forage yield in a mixed planting. The total forage yields for mixed planting (corn + soybean) in the open field and APV systems were 46.8 and 39.6 t/ha, respectively. Forage yields for corn monoculture in the open field and APV systems were 41.8 and 31.0 t/ha, respectively. The yield indexes in 2020 of mixed culture in the open field and APV system were 112.0 and 127.7% of monocropping corn, respectively.

4. Discussion

Worldwide, people are concerned about the burning of fossil fuels to produce carbon dioxide, causing climate changes such as the heating and warming of the atmosphere. South Korea was one of the world’s top five importers of natural gas, coal, and petroleum liquids in 2019 owing to insufficient domestic resources and large-scale energy consumption [33]. In keeping with the Paris Agreement of the United Nations Framework Convention on Climate Change, the Korean government recently announced a policy to produce 20% of its electricity from renewable energy sources by 2030 [5,6]. In addition, mountains and highlands cover more than 60% of South Korea. In the limited cultivation areas of South Korea, it is necessary to use the APV system installed on the farmland to produce crops and renewable energy simultaneously. According to the Japanese Ministry of Agriculture, Forestry and Fisheries, crop yield should be higher than 80% under the APV system to ensure food security and electricity [14,15].
The implementation of an APV system for a long-term crop rotation system offers the farmer opportunities to increase crop productivity and generate electricity at the same time, thereby increasing the farmer’s income [15]. Furthermore, investigations on diverse species should be made to gain a broader understanding of which plant species are best suited for the APV system to optimize agricultural production. Research has shown that APV systems and light reduction are not always unsatisfactory for crop productivity as radiation interception efficiency was increased under the shade [12]. However, an understanding of plant growth and stress responses that affect the crop yield of various crop species is required to select the appropriate crop under the APV system. To date, not enough studies have been conducted on the performance of different crop species grown under APV systems in South Korea.
Crop yield is an important measurement and is determined by a combination of genetic, management, and environmental factors. In this study, we had similar results to other studies in that the shading effect negatively affected the rice yield of the APV system compared to that of the open field as a check treatment [18,34]. Gonocruz et al. [18] indicated that the soil–plant analysis development (SPAD) value of rice in the shaded area was higher than that in the unshaded area, resulting in the retardation of grain growth by the shading condition. There was a significant delay in flowering date and heading time under the shading conditions for grain cereals [34,35]. In this study, the number of spikelets per hill and the number of ripened grains per hill decreased by 14.5 and 16.2% in 2018, and 12.3 and 14.4% in 2019, respectively (Table 1). Wang et al. [36] showed that rice grown in the shade had an increased spikelet degradation rate. Homma et al. [34] found that the number of panicles and weight per panicle were significantly less compared to open field conditions, resulting in a 20.0% reduction in rice yields. Gonocruz et al. [18] also showed that the shading effect at different growing stages of rice affected grain yield, suggesting that crop yield under the APV system should be greater than 80.0%. Rice yield under the APV system in this study achieved the targeted yield, where the reduction of rice yield was 18.7% in 2018 and 8.9% in 2019 in APV system compared to open field.
In the summer of 2020, the experimental fields in this study received up to 835 mm of rainfall between July to August, much more than in 2019 (321 mm). A series of heavy rains in the summer of 2020 influenced crop yield and yield components for soybean, adzuki bean, and monoculture corn (Table 2 and Table 5). Although there was no significant difference in the yield components of soybean and adzuki bean between the APV system and open field, except for the 100-seed weight of adzuki bean in 2019, measured agronomic traits such as plant height, number of branches, number of nodes, and number of pods were statistically different between the APV system and open field in 2020. Egli [37] reported that reduced photosynthesis during pod formation did not affect the soybean pod production or seed number, whereas seed size showed phenotypic variations. There were no significant differences in soybean and adzuki bean yields and corn monoculture forage yield between the APV system and open field in 2019. However, studies showed that the performance of morphological and yield-related traits, vegetative growth, and kernel number in corn decreased significantly under artificial shade (80–90%) [38,39]. The result of this study in 2019 demonstrated that it was possible to grow soybean, adzuki bean, and monoculture corn under the APV system because the yield of each crop under the APV system was not statistically different from that in the open field. Several studies mentioned that crops cultivated under the APV system benefited from more effective water/rainfall redistribution [10], reduced evapotranspiration, greater carbon uptake and water use efficiency for plant growth and reproduction [20], decrease in soil and crop temperature, improvement in soil humidity [12], protection against climatic uncertainty and extreme events such as hailstones and excess rain [22]. In this study, a series of severe rains resulting in a shortage of solar radiation during summer had a dramatic impact on yield and yield components for summer crops. However, the forage yield of mono-crop corn under the APV system was not statistically different from that in the open field, suggesting that cultivation of mono-crop corn under the AVP system was suitable in heavy rain. For further study, crop yield trials for multiple years will be required for soybean and adzuki bean under the APV system.
Recently, our previous study reported the mixed planting of corn with soybean in the same row was a new cropping system that improved forage yield and quality by utilizing the viny growth habit of soybean [30,31]. The mixed planting of corn with soybean was evaluated under the APV system over two years. However, the forage yield of the mixed planting of corn with soybean was reduced under the APV system in 2019 (Table 5). Unlike monocropping corn, mixed planting of corn with soybean beneath the APV system was inefficient in providing the required yield.
In this study, crops growing over the winter season such as rye, onion, and garlic were tested over two years between the open field and APV system (Table 3 and Table 4). Light increases the rate of photosynthesis but only up to a certain extent. The interception of solar radiation and the utilization of radiant energy for plant biomass are the main processes in crop growth and forage yield. Crops with an enhanced photosynthetic mechanism better utilize the solar radiation that can be translated into yield. However, studies reported stressful growth conditions that limit photosynthate may improve forage quality and biomass [40,41]. Sekiyama and Nagashima [25] reported that the biomass of corn as a shade-intolerant crop under solar panels produced 96.6 and 104.9% at high density (0.71 m interval) of panels and low density (1.67 m interval) of panels, respectively, compared with the control field. Our study showed a similar result, where forage yields of monocropping corn and rye were not significantly different between the open field and APV system, resulting in their being applicable crops to produce forage yield and quality under the APV system. Averaging the yield over two years, harvested yields for onion and garlic in the APV system (71.3 and 14.4 t/ha) were 14.4 and 18.7% reduced compared with an open field (83.3 and 17.7 t/ha). However, since the statistical analyses for garlic and onion over two years were different, yield tests with those crops under the APV system are required for further research. Consequently, the APV system may have a different impact on the agriculture production of cereal crops compared with legume and vegetable crops, or on winter crops compared to summer crops. Future research should focus on determining the crop’s critical sunlight period requirements to better understand the physiological mechanisms during their growth, such as photosynthetic light use, net photosynthesis, photosynthetic nitrogen use efficiency, photorespiration, canopy light distribution, and associated gas exchange characteristics, under the APV system for various crop species.

5. Conclusions

In conclusion, different crops species such as rice, soybean, adzuki bean, corn, rye, garlic, and onion were evaluated under the APV system to facilitate improved adaptability under the APV system for seed, vegetable, and forage production. The results of this study indicated that there was statistically no negative impact of the APV system on the forage yield of rye and corn over two years, suggesting that forage crops under the APV system were suitable crops to produce forage yield for livestock. In addition, the measured forage quality of rye was not significantly different between the open field and the APV system. Rice yield was significantly reduced under the APV system over two years, and yield reductions were 18.7% in 2018 and 8.9% in 2019 in the APV system compared to the open field. Legume crops and vegetables in this study did not show consistent statistical results in two years. For further study, crop yield trials for multiple years will be required for rice soybean, adzuki bean, onion, and garlic under the APV system. In addition, the results of the present study suggest that employing APV systems, which provide 30% of the shading rate of a crop-cultivation environment, allows agriculture and renewable energy to cooperate for the purpose of maximizing the potential resources of energy and biomass of forage crops such as rye and corn.

Author Contributions

Conceptualization, D.-H.H. and J.-D.L.; Methodology, H.J., M.A.B., L.A., J.T.S., Y.-S.H., D.-H.H. and J.-D.L.; Formal Analysis, H.J. and M.A.B.; Visualization, D.-H.H. and J.-D.L.; Writing—Original Draft Preparation, H.J., S.A. and M.A.B.; Writing—Review and Editing, H.J., J.T.S., Y.-S.H., D.-H.H. and J.-D.L.; Supervision, J.-D.L.; Funding Acquisition, J.T.S., D.-H.H. and J.-D.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (IPET) through the Agriculture, Food and Rural Affairs Convergence Technologies Program for Educating Creative Global Leader Program, funded by the Ministry of Agriculture, Food and Rural Affairs (MAFRA) (716001-7), and this work was also partly supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (MOTIE) (20213030010140, for the study on 200 kW demonstration and development of fence-type photovoltaics in rural areas satisfying LCOE 140.8 (won/Kwh)).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to acknowledge the personnel from the Plant Genetics and Breeding lab at the Kyungpook National University for their time and work on the field experiments.

Conflicts of Interest

The authors declare no conflict of interest.

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Agriculture 12 00619 g001 550
Figure 1. Agro-photovoltaic structure and layout in the experimental paddy field and dry field. (A) Structure of the agro-photovoltaic system. (B) Layout of the 320 dummy panels in the agro-photovoltaic system.
Figure 1. Agro-photovoltaic structure and layout in the experimental paddy field and dry field. (A) Structure of the agro-photovoltaic system. (B) Layout of the 320 dummy panels in the agro-photovoltaic system.
Agriculture 12 00619 g001
Agriculture 12 00619 g002 550
Figure 2. Crop production of the agro-photovoltaic system and open field at the experimental farm field. (A) Rice cultivation on the paddy field. (B) Onion and garlic cultivation on the dry field.
Figure 2. Crop production of the agro-photovoltaic system and open field at the experimental farm field. (A) Rice cultivation on the paddy field. (B) Onion and garlic cultivation on the dry field.
Agriculture 12 00619 g002
Table
Table 1. Yield and yield component of rice between the agro-photovoltaic system and the open field over two years.
Table 1. Yield and yield component of rice between the agro-photovoltaic system and the open field over two years.
YearTreatmentYield (t/ha)1000-Seed Weight (g)Number of Spikelets/HillNumber of Ripened Grains/HillNumber of Unfilled Spikelets/HillPlant Height (cm)Percentage of Ripen Grain (%)
2018Open field7.524.11309.11213.295.893.092.6
APV system6.123.61119.51017.2101.693.290.9
T-Test (n = 5)**ns*****nsns
2019Open field7.924.91559.21463.395.987.593.8
APV system7.224.01367.61253.0114.591.391.6
T-Test (n = 5)**ns**ns*
* Significant at the 0.05, ** significant at the 0.01, and *** significant at the 0.001 probability level; ns: not significant. APV: agro-photovoltaic.
Table
Table 2. Agronomic traits and seed yields of soybean and adzuki bean between the agro-photovoltaic system and the open field.
Table 2. Agronomic traits and seed yields of soybean and adzuki bean between the agro-photovoltaic system and the open field.
CropsYearTreatmentYield (t/ha)Plant Height (cm)Number of BranchesNumber of NodesNumber of Pods100-Seed Weight (g)
Soybean2019Open field2.264.55.817.6109.115.9
APV system2.269.85.418.889.314.9
T-Test (n = 3)nsnsnsnsnsns
2020Open field1.677.63.515.085.9.
APV system0.558.12.713.245.3.
T-Test (n = 3)***************.
Adzuki bean2019Open field2.396.62.617.636.417.7
APV system2.0101.12.118.826.8715.8
T-Test (n = 3)nsnsnsnsns*
2020Open field1.572.62.618.232.5.
APV system0.447.11.915.214.6.
T-Test (n = 3)************.
* Significant at the 0.05, ** significant at the 0.01 and *** significant at the 0.001 probability level; ns: not significant. APV: agro-photovoltaic. Missing data are indicated by “.”
Table
Table 3. Mean of yield test for garlic and onion between the agro-photovoltaic system and the open field over two years.
Table 3. Mean of yield test for garlic and onion between the agro-photovoltaic system and the open field over two years.
CropsYearOpen FieldAPV SystemT-Test
(n = 3)		Yield Index (%)
(t/ha)(t/ha)(Yield of APV System/Yield of Open Field)
Garlic2018–201913.510.7*78.7
2019–202021.918.1ns82.9
Mean17.714.4ns81.3
Onion2018–201982.466.4*80.6
2019–202084.376.3ns90.6
Mean83.371.3ns85.6
* Significant at the 0.05 probability level. ns: not significant. APV: agro-photovoltaic.
Table
Table 4. Evaluation of silage quality for rye on a dry basis between the agro-photovoltaic system and the open field over two years.
Table 4. Evaluation of silage quality for rye on a dry basis between the agro-photovoltaic system and the open field over two years.
YearTreatmentForage Yield (t/ha)Plant Height (cm)CPNDFADFTDNRFVDMIDDM
2018–2019Open field19.7148.09.162.537.958.988.51.959.3
APV system19.1155.49.364.039.657.584.21.857.9
T-Test (n = 4)nsnsnsnsnsnsnsnsns
2019–2020Open field23.0157.8.......
APV system19.9162.0.......
T-Test (n = 4)nsns.......
ns: not significant. APV: agro-photovoltaic. Missing data are indicated by “.”
Table
Table 5. Mean of forage yield test for the corn mono-crop and the mixed planting of corn and soybean between the agro-photovoltaic system and the open field over two years.
Table 5. Mean of forage yield test for the corn mono-crop and the mixed planting of corn and soybean between the agro-photovoltaic system and the open field over two years.
YearTreatmentCorn (Mixed Cropping)Soybean (Mixed Cropping)Corn + SoybeanYield Index from Mixed Cropping (%)Corn (Mon-Crop)
Plant Height (cm)Forage Yield (t/ha)Plant Height (cm)Forage Yield (t/ha)Forage Yield (t/ha)Plant Height(cm)Forage Yield (t/ha)
2019Open field277.757.4136.53.360.7110.2291.155.1
APV system278.451.7119.52.053.697.1287.055.2
T-Test (n = 3)nsns*ns* nsns
2020Open field215.440.0100.36.846.8112.0217.641.8
APV system220.433.4125.66.239.6127.7210.431.0
T-Test (n = 3)nsns*nsns nsns
* Significant at the 0.05 probability level; ns: not significant. APV: agro-photovoltaic.
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Jo, H.; Asekova, S.; Bayat, M.A.; Ali, L.; Song, J.T.; Ha, Y.-S.; Hong, D.-H.; Lee, J.-D. Comparison of Yield and Yield Components of Several Crops Grown under Agro-Photovoltaic System in Korea. Agriculture 2022, 12, 619. https://doi.org/10.3390/agriculture12050619

AMA Style

Jo H, Asekova S, Bayat MA, Ali L, Song JT, Ha Y-S, Hong D-H, Lee J-D. Comparison of Yield and Yield Components of Several Crops Grown under Agro-Photovoltaic System in Korea. Agriculture. 2022; 12(5):619. https://doi.org/10.3390/agriculture12050619

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Jo, Hyun, Sovetgul Asekova, Mohammad Amin Bayat, Liakat Ali, Jong Tae Song, Yu-Shin Ha, Dong-Hyuck Hong, and Jeong-Dong Lee. 2022. "Comparison of Yield and Yield Components of Several Crops Grown under Agro-Photovoltaic System in Korea" Agriculture 12, no. 5: 619. https://doi.org/10.3390/agriculture12050619

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