Abstract
Ginger (Zingiber officinale Rosc.) is a valuable sciophyte crop used as a spice or fresh herb in culinary dishes and for treating medical issues such as osteoarthritis, neurological diseases, vomiting, and asthma. The demand for ginger in the United States is remarkably high; it is produced commercially and exclusively in Hawaii but can only meet ∼20% of US demand. Light for ginger growth may be more important than is often assumed, but the roles of light in ginger growth and rhizome yield are not fully understood. We hypothesized that artificial shade would produce the highest yielding ginger compared with no shade. This study evaluated the impact of different shading suited for ginger growth and rhizome yield of different cultivars grown in a high tunnel. There were three levels (0%, 22%, and 40%) of shade using RCBD design. We analyzed the overall yield (weight) of ginger and the specific yield (weight) of different rhizome parts (biological root, edible root, and seed ginger) per plant in addition to plant growth data. Data were analyzed for 2018 and 2019, and shade conditions influenced ginger growth and yield. There was no significant difference between shade conditions or cultivars, but general trends found that data differed between the two growing seasons. In 2018, Chinese White and Hawaii Yellow produced a better (higher) yield under 0% and 40% shade. However, in 2019, Chinese White and Hawaii Yellow produced the highest total yield under 22% shade, but Bubba Blue produced the highest overall yield at 0% shade.
Ginger (Zingiber officinale Rosc.) is a tropical herb grown for its underground tuberous stem, which is cultivated annually. Due to its restorative and health-promoting properties, ginger has attracted increasing interest among dietitians, producers, and consumers (Majkowska-Gadomska et al. 2017). Ginger is known to be a complementary alternative medicine and a functional medicine because it has several medicinal benefits, such as for the treatment of cough, fever, sore throat, weakness, and fatigue (Baliga et al. 2011; Dehghani et al. 2011; Lewu et al. 2006). Ginger has been extensively grown in tropical areas, including southern Asia, the Caribbean Islands, Central and South America, Australia, and Africa (Randall 2012; Sutarno et al. 1999).
The most valuable part of the ginger plant is the underground rhizome, which is made up of three types of roots: seed (source used for planting), fibrous (biological, commonly not edible), and fleshy (edible), as seen in Fig. 1. The original seed piece is often harvestable as well. Fibrous roots are thin with root hairs and are the leading site for nutrient and water absorption. In contrast, fleshy roots are notably thicker and, depending on the cultivars, have few root hairs and no lateral roots (Medicinal Plants Archive 2018).
Freshly harvested Hawaii Yellow ginger rhizome from below ground (high tunnel) with its rhizome parts attached to the root, including the biological roots, edible roots, and seed.
Citation: HortScience 59, 10; 10.21273/HORTSCI18024-24
Ginger is an excellent plant for enhancing farm profitability because it is a low-input crop (Lyocks et al. 2013). Ginger grows 50 to 100 cm tall on average with a rhizome that can vary in shape and size depending on the cultivar (Zhang et al. 2022). However, depending on the cultivar and growing condition, it can exceed this height. Ginger is propagated vegetatively using small pieces of the rhizome known as the seed. It prefers growing in partial sun and well-drained soils in US Department of Agriculture (USDA) zones 9 through 12 (Starr 2019) and at a temperature range between 19 and 28°C with 70% to 90% relative humidity (Mahat et al. 2019; Sinha 2003). The growing season for ginger production in open field is 10 months, but it is possible to harvest it sooner, particularly in less temperate climates (Chan et al. 2017). Ginger thrives in a tropical environment with an optimal soil pH of 6.0 to 6.5 and a minimum soil temperature is 15.5 °C. Ginger crops need heavy manures and fertilizers for better yield and quality; foliar micronutrient spray at 60, 90, and 150 d can increase the yield by 5% to 6%. Nair (2019) reported that the average yield of ginger per acre is 300 bags of 60 kg, equivalent to 18 tons.
Fresh ginger is grown and harvested in two stages: baby ginger and mature ginger. US consumers of ginger are more familiar with golden-cured mature ginger (Wang 2020). Baby ginger is a nonfibrous, pink, and tender rhizome from young ginger plants typically grown for less than 8 months (Kumari et al. 2020). Baby ginger can be used for cooking, be pickled or candied, and preserves well in a freezer for culinary use all year round. Ginger harvesting is done almost entirely manually, although mechanical digging devices are available for large-scale production (Kaushal et al. 2017). Harvest maturity varies and depends on the end use and market demand. Ginger is highly productive, drought tolerant, and can be stored for a long time in the right conditions (Teferra et al. 2015).
Ginger has played a significant role in global trade markets. Value-added products, defined as commodities whose value is enhanced by adding other raw materials, receive considerable attention as their prices increase. Producers of niche market value-added products enjoy the benefit of higher prices and potentially higher income. The demand for ginger value-added products has skyrocketed globally (Unuofin et al. 2021). In the United States, ginger was introduced in Hawaii and has risen to rank among the top 12 spices consumed (CABI Compendium 2022). The Hawaiian ginger industry has enhanced its reputation for producing superior and quality products for the fresh market (Shaikh et al. 2017). Hawaii is the leading producer in the United States; however, it accounts for only about 20% of ginger used in the country, meaning the other 80% must be imported to meet demand. The United States is one of the top importers globally (Gaulier and Zignago 2021). Furthermore, ginger prices remain unstable and pose development challenges because it is sensitive to disease (Choenkwan 2017).
Ginger is a sciophyte and grows well in subtropical conditions (Balasubramanian 2014). Temperature and moisture can influence ginger growth and yield (Njoku et al. 1995). Low yields can result from a lack of suitable ginger varieties for shade agro-climatic conditions. Bhuiyan et al. (2012) reported that ginger exhibits shade-loving characteristics similar to turmeric under a multistoried agroforestry system. Our research aimed to investigate the impact of shading conditions on growth and yield performance of different ginger cultivars grown in high tunnel settings to provide more detailed information on producing high-quality ginger with appropriate cultivar selection.
Materials and Methods
This research was conducted at the Farm of North Carolina Agriculture & Technical State University, Greensboro, NC, USA, in USDA Plant Hardiness Zone 7b. The high tunnel (Fig. 2) for this research is 96 feet long and 30 feet wide and has 8-foot-tall sidewalls. It is Gothic style (Morgan Co LLC, Barnett, MO, USA). This high tunnel has drop-down curtains and two 8′ × 9′ doors on each end wall and is covered with a single layer of 6-mil greenhouse-grade polyethylene film. This high tunnel is oriented north to south and was constructed in 2015–16 specifically purchased by and for specialty crop research projects. The ginger plants were planted directly into the soil on raised beds in the high tunnel.
High tunnel ginger with different shading conditions from black cloth (40% shade), white cloth (22% shade), and no cloth (0% shade) in photo taken 16 Jul 2019.
Citation: HortScience 59, 10; 10.21273/HORTSCI18024-24
Initial sprouting in greenhouse.
For both the 2018 and 2019 growing seasons, ginger transplants were initiated from 20 to 25 g seed pieces in early March. Each piece contained 1 to 2 growth points (buds). Coconut husk has lignin, which was used as the sprouting media because it is highly porous and does not compact like traditional soil mix. After 1 to 2 d of curing, seed ginger pieces were ready to be planted. Each seed ginger tray (10′′ × 20′′) had a thin layer (∼0.5 cm in depth) of coconut husk on the bottom. Next, seed ginger pieces were placed roughly 1 inch apart with ∼20 to 25 pieces per tray, depending on seed size. Lastly, the seed ginger pieces were entirely covered with husk, thoroughly watered, and labeled. Heating pads were used to maintain warmth for the sprouting media to help with seed sprouting. The sprouting trays were watered daily or whenever the coconut husks became dry to maintain moisture and were carefully managed to prevent pests and diseases. The sprouts from seed ginger grew for ∼3 months in the greenhouse before being transplanted into the high tunnel trial in early June.
Field preparation for high tunnel.
During February, the soil was tilled with a tractor until it was loose and delicate enough to make raised beds. A tractor-operated Nolts bed layer made raised beds and lay drip tape. The North Carolina Department of Agriculture and Consumer Services soil test recommended 120 lbs of nitrogen, 120 lbs of phosphorus, and 55 lbs of potassium for ginger per acre. Broiler poultry nutrients were added and tilled in as a base fertilizer to enrich the soil, thus providing proper nutrients. With poultry liter, 45% nitrogen, 50% to 100% phosphorus, and 100% potassium were available for the first year. The drip tape was placed 1 to 2 inches beneath the soil surface with a 12-inch emitter spacing (Toro Micro-Irrigation, EI Cajon, CA, USA) with 0.45 gallons per minute (gpm)/100 feet.
Ginger plants were transplanted in the high tunnel in early June. Before transplanting, the beds were marked for appropriate planting based on the planting design. Irrigation was provided after transplanting through the drip tapes until the beds were saturated. On average, the ginger was watered four times a week at 1.5 h, 1 inch of water a week. Watering was intensive in the beginning weeks, but toward the end of sprouting, watering was reduced slightly to prepare seedlings for acclimation to a typical high tunnel environment. For this study, a netting mesh was suspended over plants using hoops to simulate levels of shading (Fig. 2).
Experimental design (2018).
The 2018 experiment included four beds that were 3′ × 62′ in size. The ginger was grown in a randomized complete block (RCBD) split-plot design, with shade treatment (0% or no shade, 22%, 40%) being the main factor and cultivars (Hawaii Yellow and Chinese White) being the secondary factor. The treatment design was split spot with eight plants per cultivar and 16 plants per replication (three replications per treatment).
Experimental design (2019).
The 2019 experiment included four beds that were 3′ × 62′ in size. The ginger was grown in a RCBD split-plot design, with shade 0%, 22%, and 40% (treatment) being the main factor and cultivars (Hawaii Yellow, Chinese White, and Bubba Blue) being the secondary factor. The treatment design was split spot with 10 plants per cultivar and 30 plants per replication (three replications per treatment).
For both years, three shading conditions were compared in the high tunnel throughout the experiment, including 0%, 22%, and 40% shading levels (Fig. 2). The shading material, Sun Blocker Premium, is constructed of high-density polyethylene shadecloth and was purchased from Greenhouse Megastore (Danville, IL, USA). The 40% shade is black, the 22% shade is white, and the 0% shade did not have shadecloth. The cultivars were purchased from Plum Granny Farm (King, NC, USA), which always separates and labels the cultivars so that they can each be identified individually.
Harvesting ginger rhizomes.
The ginger grown in the high tunnel was dug out from the ground using a broad fork to loosen the soil around the rhizome. The harvest process was done one block at a time, where all rhizomes were dug out and observed. Careful digging was performed diligently by leaving enough space between the broad fork and ginger rhizomes underground to avoid damage to the rhizome while scooping beneath it to raise it to the surface. The foliage was initially used as leverage to remove rhizomes from the soil. Next, the ginger was rinsed to remove any remaining soil, and then the rhizome was ready for further observation and weighing. After observations, the remaining rhizomes were stored at room temperature for drying.
Data collection.
Plant growth data were collected during peak growth season (October). Data included the length of stems (SL), diameter of stems (SD) (millimeters for both), and number of stems (SN) per rhizome. Plant yield data were collected when the rhizomes were harvested and weighed for the fresh weight (measured in grams). Yield data include fresh weights from different rhizome parts, including biological root weight, edible root weight, edible seed root weight, and overall total weight per rhizome.
Statistical analysis.
The overall fresh weight of ginger and the individual weight of the different rhizome parts, including biological, edible, and seed, were analyzed and investigated. Data collected from trials were pooled and averaged before analysis. Data were initially processed and organized for plant growth and yield data in Microsoft Excel. The Proc mixed model of SAS ver. 9.4 (SAS Institute Inc., Cary, NC, USA) was used for analysis of variance and other statistical analyses. Statistical significance was determined at P ≤ 0.05.
Results and Discussion
Plant growth data.
Shade affects plant growth differently between the aboveground and below-ground parts due to these plant sections’ distinct roles and functions (Lu et al. 2021). Aboveground parts of plants, such as leaves and stems, are directly exposed to sunlight. Shade can significantly impact the photosynthetic rate in these parts because less light leads to reduced energy production. This can result in slower growth, smaller leaves, and decreased biomass accumulation, which was demonstrated among different cultivars and shading conditions in this research.
Cultivars Chinese White (CW) and Hawaii Yellow (HY) were evaluated in the first year (2018), and Bubba Blue (BB), Chinese White (CW), and Hawaii Yellow (HY) were assessed in the second year (2019). Data were collected twice during the experiment, monthly between October and November. Ginger plant growth in different shade treatments and cultivar evaluation were examined in a high tunnel. Growth data among ginger cultivars were statistically analyzed at the same shade level to determine if there was any significant growth difference among cultivars by shade level.
Stem diameter.
For stem diameter (SD) in 2018 (Table 1), there was no significant difference between ginger cultivars under 0% and 22% shade levels. However, at 40% shade, CW had a slightly larger SD (8.9 mm) than HY (8.4 mm). Data collected in 2019 (Table 2), under 0% shade, found no significant difference between cultivars HY (6.6 mm) and BB (6.4 mm) for SD; however, CW (6.6 mm) produced the smallest SD. Under 22% and 40% shade, there was no significant difference in stem diameter size between cultivars and no trend of increased or decreased stem diameter size based on shade percentage or cultivar type. There was a general decrease in size of SD from 2018 to 2019.
Growth average comparisons of ginger stem diameter (SD), stem length (SL), and stem number (SN) in high tunnel for multiple cultivars by shade level (2018).
Growth average comparisons of ginger stem diameter (SD), stem length (SL), and stem number (SN) in high tunnel for multiple cultivars by shade level (2019).
Stem number.
For stem number (SN) in 2018 (Table 1), under 40% shade, there was a significant difference between cultivars, with HY significantly producing, on average, more stems (21.9) compared with CW (13.2). This same general trend occurred at 0% and 22% shade level, with HY producing more stems than CW. There was no significant trend in stem numbers as shade increased for either CW or HY. There was a significant difference between cultivars for ginger under 0% shade for SN in 2019 (Table 2); HY (13.9) significantly produced more stems, on average, compared with CW (7.6) and BB (9.8). Under 22% shade, there was no significant difference between cultivars; however, HY (11.4) and BB (11.3) produced the greatest number of stems compared with CW (9.1). Under 40% shade, BB (11.3) significantly produced, on average, more stems compared with CW (8.0) and HY (8.6). There was no significant difference in number of stems for cultivars as shade percentage increased in 2019, however it is important to note that each cultivar demonstrated a general trend response as shade increased, with CW and BB increasing number of stems and HY decreasing in number of stems. This suggests there were some cultivar specific reactions to shade that occurred, with the same general trend occurring with CW in 2018.
Stem length.
In 2018 (Table 1), although data were considered significant, the ginger demonstrated no significant patterns between cultivar or shade for stem length (SL) of plants. HY had the longest SL under 0% and 40% shade, whereas CW had longer stems under 22% shade. In 2019 (Table 2), HY had larger stems than CW under 0%, 22%, and 40% shade but shorter stems than BB under 40% shade. A general trend occurs that as shade level increases, ginger stem length also increases. However, more research is needed to determine whether this happens consistently. Sreekala and Jayachandran (2002) reported similar results from their study focusing on the influence of shade regimes on the physiological parameters of ginger. Under low shade conditions (20%), there was an increase in crop growth rate, leaf area index, and dry matter accumulation. Shading of crops typically alleviates foliage wilting because it reduces leaf temperatures and air and soil temperatures, which causes a decrease in transpiration rate and lowers the water requirement for normal leaf turgor pressure (Joshi et al. 2022).
Ginger yield in high tunnel.
Below-ground parts of plants (rhizome), such as roots and root hairs, are not directly affected by shade. However, the reduced photosynthetic activity in the aboveground parts can indirectly impact the growth and development of below-ground structures (Zhang et al. 2021). However, shade can also positively affect below-ground parts, as demonstrated in this research. Other examples include reduced evapotranspiration in shaded environments, which can increase soil moisture, benefiting root growth and nutrient uptake (Tang et al. 2022).
Ginger yield data are essential as they demonstrate the specific distribution of ginger rhizome yield (weights) among different parts of the rhizome. Edible rhizome weight would be most important to a farmer because this is the part that a consumer would buy and bring potential income to a ginger producer, especially small-scale growers. Data reported during 2018 and 2019 growing seasons (Tables 3 and 4) found no significant differences between cultivars and shade levels with the edible roots, seed ginger, edible root plus seed ginger, and total yield (weight). HY produced more biological roots by weight than CW under all shade levels (only 0% and 40% were considered significant) during the 2018 growing season. Similarly, during the 2019 growing season HY had higher biological root weight than CW under 0% and 22% shade, but not for 40% shade. BB measured during the 2019 growing season had a higher biological root weight than both HY and CW under all shades, except for HY 22% shade. However, there were some noticeable cultivar-specific trends within the data set that occurred. HY grown under 0% shade level produced the highest weight for bio, edible, seed, edible + seed, and total rhizome weight. CW and BB grown under 22% and 40% shade produced the highest yield (weight) for bio, edible, seed, edible + seed, and total weight. The cultivars (CW, HY, and BB) are ranked by yield performance from the highest to lowest number of ginger pieces per seed ginger. The outcome of yield data can benefit those who produce ginger in the mainland United States because it will provide knowledge about multiple cultivars that are high-yielding and can be produced in this region (Fig. 3). Also, these data will help producers better understand how to grow ginger in high tunnels for optimal yields with appropriate shading conditions.
Growth average comparisons and observations for yield parameters in the high tunnel concerning cultivars at the same shade during the 2018 growing season.
Growth average comparisons, number of observations for yield parameters in high tunnel concerning cultivars at the same shade during the 2019 growing season.
High tunnel ginger total yield comparison of Chinese White (left) and Hawaii Yellow (right) in 2019.
Citation: HortScience 59, 10; 10.21273/HORTSCI18024-24
Overall, our data demonstrate that shade conditions influenced ginger yield. Literature supports this with multiple studies indicating the beneficial effect of shade on growth and yield of ginger plants. For example, Jayachandran et al. (1991) demonstrated that shading affected ginger growth parameters and fresh yield, with the highest yield under 25% shade and the lowest yield under 75% shade. Furthermore, Jayachandran et al. (1998) reported that under 25% shade, ginger yield was increased by 11% to 29% compared with ginger plants grown in the open fields. Our 2018 data indicate that ginger yield was the highest under 40% shade for CW and 0% for HY; however, our 2019 data indicate that ginger plants under the 22% shade condition produced the highest yield for both CW and HY, and BB produced the highest yield under 40% shade. Aly et al. (2019) reported similar results in ginger growth and yield when ginger plants were grown under different shade conditions, with rhizome yield increased with shade levels (two shade levels using Saran 30% and Saran 60%). Babu et al. (2019) evaluated and identified different ginger varieties adapted for a particular agroecosystem for shade net cultivation and demonstrated significant growth parameters and yield differences among cultivars under shade net conditions. They also reported that ginger yield can be increased under shade net conditions (50% green shade). Our study demonstrated that rhizome yield rates were affected by different light intensities. Cockshull et al. (1992) reported that solar radiation received by crops is interrelated to crop growth. Paul (2021) reported that the field environment strongly regulates photosynthesis and growth of crop yields, which is significantly different from the laboratory or greenhouse. Cao et al. (2021) reported that higher photosynthesis rates can increase photosynthetic products and thus support the material requirements for increasing biomass and improving rhizome yield. Because light is a key component in photosynthesis, we can posit that changes in photosynthetic rate in ginger did occur as ginger was exposed to different shade netting. In our experiment, we observed higher yield from lower shade percentages in cultivars HY (0%) and CW (22%). Higher biomass and more vigorous plant growth were observed in increasing shade conditions but exhibited no significant difference in yield compared with no shade for all cultivars. Somasundaram (2015) conducted a similar study with turmeric, focusing on the effects of shade levels on growth and yield, and found that reduced radiation levels caused suppression of growth.
Shade affects plant growth differently between the aboveground and below-ground parts due to these plant sections’ distinct roles and functions (Lu et al. 2021). Aboveground parts of plants, such as leaves and stems, are directly exposed to sunlight. Shade can significantly impact the photosynthetic rate in these parts because less light leads to reduced energy production. This can result in slower growth, smaller leaves, and decreased biomass accumulation, which was demonstrated among different cultivars and shading conditions in this research. Below-ground parts of plants (rhizome), such as roots and root hairs, are not directly affected by shade. However, the reduced photosynthetic activity in the aboveground parts can indirectly impact the growth and development of below-ground structures (Zhang et al. 2021). However, shade can also positively affect below-ground parts, as demonstrated in this research. Other examples include reduced evapotranspiration in shaded environments, which can increase soil moisture, benefiting root growth and nutrient uptake.
Our growth and yield data indicated ginger could be successfully produced in North Carolina as a niche market cash crop using appropriate season extension techniques, such as high tunnels. Generally speaking, ginger grown under either 22% or 40% shade conditions demonstrated more vigorous (healthy looking) plant growth. Ginger grown under shade can potentially boost growth and yield, which can increase profit.
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