Comparative Analysis of Leaf Vegetable Productivity, Quality, and Profitability among Different Cultivation Modes: A Case Study

Abstract

In recent years, vegetable production has been in the transitional stage from traditional cultivation mode to modern cultivation mode. Therefore, evaluating the actual productivity and economic benefits of different cultivation modes is instructive for leafy vegetable production. This research chose a vegetable production company (Shanghai, China) as a demonstration case to cultivate various leaf vegetables under different cultivation modes (hydroponic, substrate, and soil cultivation). By investigating the yield and quality of vegetables, as well as all production costs and selling prices, we drive a comparative evaluation of comprehensive features and economic benefits of different cultivation modes. The results showed that leafy vegetables cultivated by hydroponic mode gain the highest fresh weight at the early growth stage, but the greatest unit yield (0.98~1.21 kg·m⁻²) emerged under the soil cultivation mode. Vegetables grown under substrate mode had the best comprehensive quality with high soluble solids content and low nitrate content. The unit costs of the soilless cultivation modes (8.26~10.3 CNY·m⁻²) were 3–4-fold higher than that of soil cultivation, mainly due to the high fixed costs and input costs, especially for substrate mode. According to actual prices, the soil cultivation mode had the highest economic benefits as a whole (4.83~8.83 CNY·m⁻²), and only hydroponic cabbage which had comparable yield gained considerable benefits (8.94 CNY·m⁻²). Quality-based pricing scheme can make substrate mode achieve profitability. The pricing scheme that guarantees a 40% revenue is within acceptable limits for consumers. Based on this actual production case, it can be concluded that a low unit yield of hydroponic mode and a high unit cost of substrate mode are the predominant factors affecting their profitability and economic viability.

1. Introduction

Since the beginning of the 21st century, the development of vegetable production in China has been particularly rapid. Vegetable production increased from 424 million tons to 721 million tons, and the total sown area increased from 15,237 thousand hectares to 20,863 thousand hectares from 2000 to 2019, second only to food crops [1]. Leafy vegetable is one of the main types of vegetable, including cabbage, green leafy vegetables, green onions, chives, and sprouts [2]. Leafy vegetables contain a lot of nutrients and are the main source of people’s inorganic salts and vitamins. Since leafy vegetables are difficult to store and transport over long distances, the supply of fresh leafy vegetables mainly relies on local production. According to data from the Ministry of Agriculture and Rural Affairs, the area of facility vegetables in China has expanded from 2667 ha in the year of 1978 to more than 387 million ha in the year of 2018. Facility cultivation has gradually replaced traditional agricultural production methods as the main method of leafy vegetable cultivation. However, due to the pursuit of excessive fertilization, the safety and quality of leafy vegetables produced in facilities are more prominent [3]. Therefore, how producers can improve productivity while improving production quality is the core of improving leafy vegetable production benefits.

The current planting and cultivation modes of leafy vegetables can be divided into traditional soil cultivation modes and modern soilless cultivation modes. Modern soilless cultivation modes include nutrient solution cultivation (hydroponics, spray cultivation) and solid substrate cultivation. Different cultivation modes have respective advantages and disadvantages and lead to different environmental conditions which would affect yield and quality. Therefore, choosing a suitable cultivation mode according to local conditions is critical for vegetable production. Till now, many scholars have compared various aspects of different cultivation modes. Modern soilless cultivation could certainly increase the space utilization rate, and shorten the growth period and annual production compared with soil cultivation. While there are no unanimous conclusions about the difference in yield and quality of vegetables under various cultivation modes. Several studies have found that compared to soil cultivation, substrate cultivation could increase the yield and overall quality of green vegetables and spinach [4], and hydroponic cultivation elevated the vitamin C content and reduced nitrate content of lettuce [5]. However, Roman cauliflower cultivated in substrate cultivation had lower fresh weight and soluble solids content than those cultivated in soil [6]. It was also reported that substrate cultivation caused a few visual defects and obvious heartburn in lettuce [7].

In addition to the differences in the quality and yield of leafy vegetables among different cultivation modes, there are also great differences in their production costs and economic benefits [8]. For traditional vegetable production in China, planting area and the inputs of labor, chemical fertilizer, and farm manure have significant contributions to vegetable production output [9]. In Nigeria, the main input of vegetable production comes from the cost of materials such as seeds and fertilizers [10,11]. For modern soilless cultivation mode, the early investment in facilities and soilless cultivation system is substantial. In addition, greenhouse heating and power supply costs account for the highest proportion of vegetable production costs [12]. In the production of leafy vegetables by hydroponics, the cost can be reduced by adjusting the concentration of nutrient solution to improve production efficiency [13].

How to improve the benefits of vegetable production has always been the research goal. Based on regional economic research, technological progress has a significant impact on the benefit of vegetable production [14,15]. Improving technical efficiency is an important measure for agricultural enterprises in the operating environment and high-level competition [16]. The cultivation environment and the efficiency of management methods also affect the economic benefits of vegetable production [17,18,19]. Based on the research on cultivation mode, greenhouse cultivation has higher economic benefits, while open-field cultivation has higher energy efficiency [20]. In addition to production cost considerations, technology level [21], seed diversity [22], climate change [23], etc., are also factors that affect the efficiency and benefit of vegetable production. In the above-mentioned studies, the evaluation of vegetable production benefits was based on cost and output value. However, the potential economic values brought by the difference in vegetable quality under different cultivation modes will also have a certain effect on the production benefits, which were often ignored. Therefore, the analysis of vegetable production benefits should integrate the influence of vegetable quality and cost.

In addition to the cost, economic benefits also highly depend on the selling price. At present, there are pricing references for pollution-free, green, and organic vegetables, but there is no uniform pricing standard for vegetables produced by modern cultivation modes. The market price for modern cultivation products is various. In some cases, the price is set in accordance with the traditional soil cultivation mode, which lowers the economic efficiency and hence limits the development of modern cultivation.

Till now, although modern soilless cultivation modes have greater potential in vegetable production than soil cultivation, the actual production efficiency is often not as high as expected [24], which will bring an obvious negative impact on the economic benefits. Based on this situation, this study took a commercial vegetable production base in Shanghai, China, as the case, compared and analyzed the productivity and nutritional quality of leafy vegetables, as well as the production cost and sales information under different cultivation modes. This study aimed to explore the advantages and disadvantages of different cultivation modes in actual production and identify critical factors that affect production efficiency and economic benefits, thus providing a reference for growers.

2. Materials and Methods

2.1. Plant Material and Germination Condition

In this study, two types of leafy vegetables, Hang cabbage (Brassica campestris L. ssp. Chinesis) and lettuce (Lactuca sativa L.), were cultivated. The cultivar of Hang cabbage (C) used is Precocious No. 5, which was bred by the Zhejiang Academy of Agricultural Sciences, China. Two cultivars of lettuce, Rosa green (LG) and Rosa red (LR), were selected, which are loose-leaf lettuce, and purchased from Beijing Dingfeng Modern Agricultural Development Co., Ltd. (Beijing, China).

The experiment was conducted in a commercial vegetable production base (Shanghai Xinhui Vegetable Co., Ltd., Shanghai, China) in Shanghai (30.9° N, 121.6° E), China, from April 2021 to May 2021. All cultivars were germinated under unified conditions. Seeds were mechanically sown in 200-hole plug trays and then moved to the germination room for germination which was carried out for 24–30 h at a temperature of 25 °C and humidity of 70~80%. After the germination was completed, trays were placed on the shelf for the seedling period. When the seedlings reached the transplantation standard (on the 28th day after sowing), they were randomly transplanted to three kinds of cultivation modes, i.e., hydroponics cultivation mode (Hyd), substrate cultivation mode (Sub), and soil cultivation mode (Soi) (Figure 1).

2.2. Cultivation Modes

2.2.1. Greenhouse Structure and Cultivation System of Different Cultivation Modes

For Hyd mode, the nutrient film technique (NFT) system was applied in a Venlo-type plastic greenhouse (8064 m²) that was equipped with internal and external shading net, skylight, and wet-curtain fan-cooling system for environment control; for Sub mode, water-storable seedbed combined with tidal irrigation system was applied in the greenhouse (10,000 m²), which had the same type as Hyd mode; for Soi mode, soil was covered by the plastic tunnel (210 m²). The actual cultivable areas of the three modes were 3917 m², 6169 m², and 180 m², respectively.

2.2.2. Cultivation Management of Different Cultivation Modes

The cultivation management of different cultivation modes during the experimental period was consistent with actual production. Hyd mode: The hydroponic seedbed was first covered with non-woven fabric, and then covered with a planting plate. Water and nutrients were supplemented through the continuous flow of nutrient solution (N:P:K = 20:10:20, 1200~1900 μS·cm⁻¹, pH 5.8~7.0) on the non-woven layer. Sub mode: the seedlings were transplanted to plug trays and placed on a seedbed and watered thoroughly on the day of transplanting. Nutrient solution (N:P:K = 20:10:20, 1300~1600 μS·cm⁻¹) and disinfected and filtered rainwater were alternately used for irrigation. During the experiment, irrigation was carried out four times; Soi mode: the planting area was divided into three blocks, one for each variety. Seedlings were watered thoroughly on the day of transplanting. To grasp the variables between different cultivation modes, vital environmental parameters, including light intensity, temperature, and relative humidity, were monitored by an environmental monitoring instrument (Xiaomi Technology Co., Ltd., Beijing, China).

2.2.3. Cultivation Design of Different Cultivation Modes

Each cultivar was cultivated in three above-mentioned cultivation modes. In total, there were 9 treatments. The planting density and length of the growing period were adjusted according to the actual production situation of the base and shown in

Table 1. Cultivation design for different treatments of varieties and cultivation modes.

Treatment	Number of Seedlings	Planting Area	Planting Density	Growing Period after Transplant
	(Plants)	(m2)	(Plants·m−2)	(Days)
Sub-C	2240	64.3	34.9	24
Sub-LG	1920	55.1	34.9	24
Sub-LR	640	18.4	34.9	24
Hyd-C	1600	38.4	41.7	25
Hyd-LG	1200	28.8	41.7	28
Hyd-LR	400	9.6	41.7	28
Soi-C	1029	60.0	17.2	30
Soi-LG	465	30.0	15.5	35
Soi-LR	180	10.0	18.0	35

Note: Sub, Hyd, and Soi stand for plug substrate cultivation, hydroponic cultivation, and soil cultivation, respectively; C, LG, and LR stand for Hang cabbage, lettuce of Rosa green, and lettuce of Rosa red, respectively.

.

2.3. Plant Quality and Fresh Weight Assessment

The plant quality was assessed at the time of transplanting and on the 15th day after transplanting, including the content of chlorophyll, soluble protein, soluble solids, ascorbic acid, and nitrate by using the methods of ultraviolet spectrophotometry, coomassie brilliant blue G-250 staining, anthrone-sulfuric acid colorimetric, molybdenum blue colorimetric, and salicylic acid-sulfuric acid colorimetric, respectively [25]. The plant’s fresh weight was measured on the 18th day after transplanting. When the base manager started to make arrangements for harvesting according to the sales plan and labor availability, the yield of each treatment was calculated at the stage of harvest. Leaves or plants without commercial quality were not counted for yield.

2.4. Fuzzy Comprehensive Evaluation

As it would be biased to evaluate vegetable production based on a certain indicator, we used the fuzzy membership function to comprehensively evaluate the properties of leafy vegetables. The assessment indices include fresh weight and quality indexes (chlorophyll, soluble protein, soluble solids, vitamin C, and nitrate contents). The membership function value (U_ij) of beneficial indexes was calculated using Equation (1) and that of unfavorable indexes (i.e., nitrate contents) was calculated using Equation (2).

U_ij = (X_ij − X_i,min)/(X_i,max − X_i,min)

(1)

U_ij = 1 − (X_ij − X_i,min)/(X_i,max − X_i,min)

(2)

where X_ij represents the original value of i-th comprehensive indicator of the j-th sample. X_i,min and X_i,max represent the minimum and maximum value of the i-th comprehensive indicator among the same cultivar, respectively.

2.5. Production Benefit Analysis

All production cost data were recorded in real time from pre-production seedling to mid-production management and to post-production packing under each cultivation mode, including fixed cost, labor cost, input cost, management cost, and other costs, which are listed in

Table 2. List of production cost data collection.

Cost Category	Seedling Period	Growing Period	Harvest Stage
Fixed cost	Production depreciation
Input cost	Number of seeds Seed varieties and price Substrate consumption and price	Transfer area Transfer density Fertilizer or nutrient solution price	Packing quantity and cost
Labor cost	Labor unit
Management cost	Electricity consumption Water consumption

. Fixed costs included land transfer fees, facility depreciation, and depreciation of cultivation facilities and equipment. Input costs mainly included the cost of agricultural materials such as seeds, substrates fertilizer, and so on. Management cost meant the cost of electricity and water. Production cost was calculated by integrating the above costs into unit cost, that is, the cost per square meter of production area. The fixed cost was calculated based on 20 years of depreciation. The input cost, labor cost, and management cost were calculated according to the actual use, where one labor unit (one person per hour) was recorded as 11 CNY (Chinese currency unit).

The unit cost is calculated as follows:

$$\mathrm{Unit} \mathrm{cost}=\frac{(Fixed cost+Input cost+Labor cost+Management cost)}{Relative Planting area}$$

$$\mathrm{Relative} \mathrm{planting} \mathrm{area}=\frac{ Planting area\times Total planting area}{Greenhouse area}$$

The unit yield is calculated as follows:

$$\mathrm{Unit} \mathrm{yield}=\frac{Total yield }{Rlative Planting area}$$

The cost per unit of yield is calculated as follows:

$$\mathrm{Cost} \mathrm{per} \mathrm{unit} \mathrm{of} \mathrm{yield}=\frac{Unit cost}{Unit yield }$$

Three pricing strategies were defined and assessed, named actual selling price (SP), quality-based price (QP), and benefit-based price (BP). The SP was the actual selling price and was provided by the vegetable production base. The QP was defined according to fuzzy comprehensive evaluation, calculated as follows:

$$\mathrm{QP}(\mathrm{x})=\frac{24\times Score\left(x\right)+6\times Score\left(max\right)-30\times Score\left(min\right)}{Score\left(max\right)-Score\left(min\right)}$$

where Score(x) is the PCA score, and Score (max) and Score (min) are the highest and lowest prices in the market for leafy vegetables grown in facilities, respectively. Since soil-cultivated leafy vegetables have a fixed market price and it is difficult to increase the price, only soilless-cultivated leafy vegetables will be evaluated in the subsequent economic evaluation based on QP pricing. Referring to the market pricing of soilless leafy vegetables, the highest price is 30 CNY·kg⁻¹, and the lowest price is 6 CNY·kg⁻¹.

The BP was defined as the price which could obtain the targeted production benefit. The levels of targeted benefit were simulated as 20%, and 40% of cost per unit of yield. The BP is calculated as follows:

BP = Cost per unit of yield × (1 + targeted benefit)

After subtracting the unit cost, the unit benefit based on different pricing strategies was obtained and calculated as follows:

$$\mathrm{Unit} \mathrm{benefit}=Unit yield\times price-Unit cost$$

2.6. Data Analysis

The data were organized and plotted using EXCEL (Student Edition 2016) software. For multiple comparisons, IBM SPSS Statistics (V23.0) software was used to perform a one-way analysis of variance on the treatment.

3. Results

3.1. Environmental Conditions under Different Cultivation Modes

During the experimental period, the light intensity was highest under Soi mode and lowest under Hyd mode. However, the relative humidity showed an opposite trend, which was the highest under Hyd mode and lowest under Soi mode. The daily mean temperature under different cultivation modes remained broadly consistent. As a whole, temperature under Hyd mode was less affected by external environmental changes, with smaller temperature fluctuations (Figure 2).

3.2. Plant Growth and Biomass Assessment under Different Cultivation Modes

The plant growth appearance and biomass indexes of the three leafy vegetable varieties grown under different cultivation modes are shown in Figure 3 and

Table 3. Fresh weight and yield of each leafy vegetable under different cultivation modes.

Treatment	Fresh Weight (g·Plant−1)	Total Yield (kg)	Daily Biomass Integral (g·d−1·Plant−1)
Hyd-C	47.08 ± 8.54 a	68.0	1.70
Sub-C	24.42 ± 3.04 b	62.7	1.17
Soi-C	52.97 ± 11.48 a	85.0	2.75
Hyd-LG	25.04 ± 4.20 a	27.0	0.80
Sub-LG	10.45 ± 1.51 c	75.0	1.63
Soi-LG	19.62 ± 4.74 b	34.4	2.11
Hyd-LR	17.41 ± 2.77 a	7.5	0.67
Sub-LR	9.92±1.83 c	25.0	1.63
Soi-LR	14.18 ± 3.17 b	11.5	1.82

Note: Fresh weight was assessed on the 18th day after transplanting. Total yield was counted at harvest, and leaves or plants without commercial quality were not counted. Daily biomass integral was calculated based on total yield and number of plants. Different letters in the same column indicate a significant difference among different cultivation modes at p < 0.05.

, respectively. All cultivars cultivated by the Sub mode had the smallest plant size and lowest fresh weights, which were significantly lower than those cultivated under Hyd and Soi modes. The fresh weights of two lettuce cultivars under Hyd mode were significantly higher than those under the other two modes, whereas the daily biomass integral, calculated based on the total yield, of lettuce was lowest under the Hyd mode. All three leafy vegetable varieties grown under Soi mode had the highest daily biomass integral.

3.3. Plant Quality Assessment under Different Cultivation Modes

3.3.1. Photosynthetic Pigment

The photosynthetic pigment contents of the three cultivars under different cultivation modes are shown in Figure 4. There were no significant differences in the chlorophyll a content between different cultivation modes for all three cultivars. Cultivation mode only had a significant influence on the chlorophyll b content in LG and carotenoid content in LR. The chlorophyll b content of LG was significantly lower in Hyd mode compared with Soi mode. In contrast, the carotenoid content of LR in Hyd mode was significantly higher than that in Soi mode.

3.3.2. Nutritional Quality

As shown in Figure 5, cultivation modes had varying effects on different nutritional qualities of different types of leafy vegetables. For soluble protein, Hang cabbage cultivated in substrates had significantly lower content compared to Hyd and Soi modes. The soluble protein contents in Rosa green lettuce were significantly reduced both by Hyd and Sub mode in comparison with Soi mode; for soluble solids, almost all cultivars had the highest contents under Sub mode, which were significantly higher than that under Soi mode. The soluble solids contents in cabbage and Rosa green lettuce cultivated under hydroponic mode were significantly lower than those cultivated under Sub mode; for nitrate, Sub mode significantly reduced the nitrate contents in cabbage and Rosa green lettuce compared to the other two modes. The nitrate content in LR was lowest under Hyd mode, which had a significant difference in comparison with both Sub and Soi modes; for Vitamin C, different cultivation modes had no significant effect on the vitamin C content of cabbage. The vitamin C contents of two lettuce cultivars were lowest under hydroponic cultivation which had significant differences with Sub mode.

3.3.3. Comprehensive Analysis and Evaluation of Leafy Vegetable Properties

In order to have a unified standard for evaluating the comprehensive properties of leaf vegetables cultivated under different cultivation modes, the fuzzy comprehensive evaluation method was applied. Only indexes that had significant differences among different cultivation modes were considered. The results are shown in

Table 4. Fuzzy comprehensive evaluation of leafy vegetables under different cultivation modes.

Treatment	Membership Function Values							Average Score	Overall Ranking
	Soluble Protein	Soluble Solids	Vitamin C	Total chl	Carotenoid	Nitrate	Fresh Weight
Hyd-C	0.82	0.25	/	/	/	0.05	0.56	0.42	7
Sub-C	0.25	0.83	/	/	/	0.97	0.06	0.53	2
Soi-C	0.76	0.11	/	/	/	0.40	0.66	0.48	4
Hyd-LG	0.16	0.51	0.05	/	/	0.46	0.64	0.36	9
Sub-LG	0.20	0.80	0.46	/	/	0.80	0.04	0.46	5
Soi-LG	0.66	0.13	0.76	/	/	0.10	0.56	0.44	6
Hyd-LR	/	0.86	0.20	/	0.74	0.91	0.83	0.71	1
Sub-LR	/	0.80	0.79	/	0.30	0.52	0.23	0.53	3
Soi-LR	/	0.30	0.49	/	0.15	0.40	0.66	0.40	8

Note: The membership function values of the indexes that have no significant differences among cultivation modes were not calculated (/). The ranking is based on the average membership function value.

. The overall property of hydroponic LR was the best (0.71) with high scores on soluble solids, carotenoids, nitrate, and fresh weight. However, the Hang cabbage and Rosa green lettuce cultivated under Hyd mode had the lowest comprehensive properties attributed to the high nitrate content and low vitamin C content, respectively, with average scores of 0.42 and 0.36. These two cultivars both obtained the highest comprehensive scores under Sub mode, with high scores on soluble solids and nitrate. And the comprehensive property of LR cultivated under Sub mode was second only to that cultivated under Hyd mode, which was the highest among all treatments. On the whole perspective of the three leafy vegetable cultivars, the comprehensive properties of the Sub mode were the best. Therefore, the selection of the substrate cultivation mode can positively improve the comprehensive properties of leafy vegetables.

3.4. Cost–Benefit Evaluation of Leafy Vegetables in Different Cultivation Modes

Data related to the production cost of leafy vegetables in different cultivation modes were classified as fixed costs (depreciation of greenhouses or greenhouses, depreciation of supporting facilities and equipment for cultivation), input costs (consumption costs, substrates, fertilizers, etc.), labor costs, and management costs (water Fees, electricity bills, etc.). These costs were calculated into unit costs according to the relative planting area and actual planting cycle of leafy vegetables.

Table 5. The cost composition of each leaf vegetable under different cultivation modes.

Treatment	Unit Fixed Cost CNY·m−2	Unit Input Cost CNY·m−2	Unit Labor Cost CNY·m−2	Unit Management Cost CNY·m−2	Unit Cost CNY·m−2
Hyd-C	4.00	1.47	1.39	1.40	8.26
Sub-C	3.36	4.17	2.60	0.17	10.30
Soi-C	0.30	1.31	0.79	0.06	2.45
Hyd-LG	4.48	1.47	1.39	1.41	8.75
Sub-LG	3.36	4.02	2.27	0.15	9.80
Soi-LG	0.35	1.44	0.94	0.09	2.82
Hyd-LR	4.48	1.47	1.39	1.39	8.73
Sub-LR	3.36	4.02	2.27	0.15	9.80
Soi-LR	0.35	1.57	0.94	0.09	2.95

shows the production cost composition for different cultivation modes. Comparing the total cost of leafy vegetable production in different cultivation modes, Sub-C treatment had the highest total cost of 10.3 CNY·m⁻², and Soi-C treatment had the lowest total cost of 2.45 CNY·m⁻². On the whole, mainly due to the high cost of supporting infrastructure and equipment, the total cost of hydroponics and substrate cultivation are much higher than soil cultivation mode. Moreover, the Sub mode had higher input and labor costs, but lower management costs than the Hyd mode.

3.5. Analysis of Production Benefits Based on Different Pricing Strategies

3.5.1. Benefit Analysis Based on SP

Taking the actual selling prices under each cultivation mode as the pricing standard, the production cost–benefit table of each leaf vegetable in different cultivation modes is shown in

Table 6. Production income based on the actual selling price of the case.

Treatment	Unit Cost CNY·m−2	Unit Yield kg·m−2	Cost per Unit of Yield CNY·kg−1	SP CNY·kg−1	Unit Income CNY·m2	Unit Benefit CNY·m2
Hyd-C	8.26	0.86	9.61	20.00	17.20	8.94
Sub-C	10.30	0.60	17.12	10.00	6.02	−4.28
Soi-C	2.45	1.21	2.02	6.00	7.29	4.83
Hyd-LG	8.75	0.46	19.21	20.00	9.11	0.36
Sub-LG	9.80	0.84	11.67	12.00	10.08	0.28
Soi-LG	2.82	0.98	2.87	10.00	9.81	7.00
Hyd-LR	8.73	0.38	23.01	20.00	7.59	−1.14
Sub-LR	9.80	0.84	11.67	12.00	10.08	0.28
Soi-LR	2.95	0.98	3.00	12.00	11.78	8.83

. The actual selling price of vegetables cultivated under Hyd mode was the highest, leading highest unit benefit of Hyd-C. However, due to the low unit yield, the unit benefits of two lettuce varieties cultivated under Hyd mode were much lower. Both LG and LR had the highest unit benefit under Soi mode due to low cost and high yield. In general, producing cabbage under Sub mode and producing Rosa red lettuce under Hyd mode were at a loss.

3.5.2. Benefit Analysis Based on QP

According to fuzzy comprehensive evaluation, the QP of vegetables cultivated under soilless cultivation mode is sorted from high to low as shown in

Table 7. Production benefits based on quality principal component analysis and custom pricing.

Treatment	Score	QP (CNY·kg−1)	Unit Benefit (CNY·m−2)
Hyd-C	3.02	10.11	0.44
Sub-C	3.74	17.66	0.29
Soi-C	3.25	/	/
Hyd-LG	2.08	6.00	−5.99
Sub-LG	3.11	12.86	1.00
Soi-LG	3.87	/	/
Hyd-LR	4.00	30.00	2.67
Sub-LR	3.44	17.66	5.03
Soi-LR	2.19	/	/

. The QP of Hyd-LR was the highest, and the QP of LG cultivated in the Hyd mode was the lowest. Based on quality-based pricing, the unit benefit of Sub-LR was the highest, and the unit benefit of Hyd-LG was the lowest. In general, based on the quality pricing, the unit benefit of lettuce cultivated under the Sub mode is higher than that in hydroponic cultivation mode, while the Hang cabbage cultivated in the Sub mode had higher quality but lower unit benefit compared with the Hyd mode.

3.5.3. Benefit Analysis of BP

Taking the unit cost under each cultivation mode as the base, the custom benefits are 20% and 40% pricing, as shown in

Table 8. Production benefits after custom pricing based on cost–benefit.

Sort	Treatment	Unit Cost CNY·m−2	Cost per Unit of Yield CNY·kg−1	20% Revenue Pricing CNY·kg−1	Unit Benefit CNY·m−2	40% Revenue Pricing CNY·kg−1	Unit Benefit CNY·m−2
1	Sub-C	10.30	17.12	20.54	2.03	23.97	4.08
2	Sub-LG	9.80	11.67	14.00	1.96	16.34	3.92
3	Sub-LR	9.80	11.67	14.00	1.96	16.34	3.92
4	Hyd-LG	8.75	19.21	23.05	1.85	26.89	3.62
5	Hyd-LR	8.73	23.01	27.61	1.76	32.21	3.51
6	Hyd-C	8.26	9.61	11.53	1.66	13.45	3.31
7	Soi-LR	2.95	3.00	3.60	0.58	4.20	1.17
8	Soi-LG	2.82	2.87	3.44	0.56	4.02	1.12
9	Soi-C	2.45	2.02	2.42	0.48	2.83	0.97

. The three types of leafy vegetables had the highest unit benefit under the hydroponic mode, and the lowest unit benefit under the soil culture mode. When the cost is considered as the standard, due to the high cost and the low unit yield in the substrate mode, its BP was higher than SP. The cost of leafy vegetables in the hydroponic cultivation mode is also relatively high, and the SP of the two lettuce cultivars in the hydroponic cultivation mode was lower than the BP. While the BP of leafy vegetables under soil cultivation was lower, which was similar to SP. In general, the cost of leafy vegetables in modern cultivation mode was higher than that in traditional soil cultivation mode. Based on the cost-based pricing, the unit benefits of substrate cultivation and hydroponics leafy vegetables were much higher than the soil cultivation mode.

4. Discussion

4.1. Growth Differences of Leafy Vegetables in Different Cultivation Systems

In principle, soilless culture can provide optimal conditions for plant growth to obtain consistently higher yields compared to traditional soil culture [24]. But in actual plant production, the yield under soilless culture is sometimes not as high as expected. In the present study, fresh weight data indicate that leafy vegetables had the highest growth rate under Hyd mode but the lowest growth rate under Sub mode at the early growth stage. This might be because the hydroponics mode keeps the plant roots in the liquid environment, which is beneficial to the absorption of nutrients and water, and hence improves the growth rate of leafy vegetables [24]. But for Sub mode, the volume of the root zone limits the total amount of available nutrients, and the nutrition supply of Sub mode depends on the irrigation frequency and volume of the substrate [26], which might be inadequate in this case. Based on the growth trend during the first 18 days and planting density, leafy vegetables cultivated under Hyd mode should gain the highest yield at harvest. But, unexpectedly, Hyd mode produced the lowest daily biomass integral of the two lettuce cultivars according to the final yield. This is partly due to the increased growth rates of leafy vegetables cultivated under Soi and Sub mode at the later stage. In addition, it was observed that many smaller plants and old leaves developed chlorosis and wilted at harvest under Hyd mode, especially lettuce. These leaves with low commercial property were not counted as yield. This might have a certain correlation with the high planting density of Hyd mode. It should be noted that the planting density of the hydroponics and substrate cultivation modes tested in this study is the actual planting density used in commercial production which is different among cultivation modes. High planting densities not only limit root development but also affect the air circulation at the plant canopy, which will easily cause the chlorosis of old leaves [27,28]. In addition, the inconsistency of the planting cycle could also be one of the important reasons behind the difference in the final yield. In general, under hydroponic mode, plants can gain a high growth rate attributed to sufficient nutrition supply, but attention should be paid to cultivation density and environment management to ensure uniformity and growth status in the later stage. For substrate cultivation mode, it should be noted that the growth rate highly depends on the nutrient supply, which is controlled by irrigation frequency and substrate volume.

4.2. Comprehensive Evaluation of Leafy Vegetable Quality and Suggestions for Quality Improvement

The cultivation mode also has great effects on the quality of vegetables. It has been reported that the soilless cultivation mode reduced the chlorophyll content and increased the nitrate content in leafy tissue [7,29], while substrate cultivation can improve some of the quality of leafy vegetables, such as VC content [30]. In this study, Sub mode had positive effects in promoting the soluble solids content and reducing nitrate content simultaneously. The plants cultivated under Sub mode had 44~92% higher soluble solids content and 8%~82% lower nitrate content compared to those cultivated under Soi mode. This is consistent with previous research; nitrate content has a negative correlation with carbon [31]. Soi mode had visible advantages in improving the soluble protein and vitamin C content, especially for LG. The soluble protein and vitamin C contents for LG were found to be 63% and 42% higher, respectively under Soi mode compared to Hyd mode. This should be attributed to the high light intensity level under Soi mode (Figure 2). It has been widely reported that soluble protein and vitamin C content could increase with light intensity [32,33,34].

As different leafy vegetable under different cultivation modes had their own superior quality indicators, the fuzzy comprehensive evaluation needed to be applied to provide a comprehensive evaluation of the overall performance of leafy vegetables under different cultivation modes. Taking different cultivars as a whole, the comprehensive properties of vegetables under substrate cultivation mode were the best. The substrate is rich in organic fertilizers and minerals, as well as inorganic substances such as perlite, which improves the air permeability and water-holding capacity of the medium, and hence accelerates the absorption of water and nutrients by the root system [35,36]. In contrast, the comprehensive quality of hydroponic leafy vegetables was the lowest in this case. The mechanism of this might be related to the dilution effect caused by excessive growth rate on one hand. On the other hand, the lowest level of light intensity should also bear part responsibility, as light intensity has a great influence on plant quality [33]. This suggests that the quality differences of different cultivation modes not only correlate with the characteristics of cultivation modes themselves but also highly depend on the regulation of the whole cultivation system. Regrettably, till now, cultivation system management in actual production relies more on the experience of the person and lacks systematic management strategies. Fortunately, prior research can provide some references for quality regulation. For example, it has been proposed that irrigation with a nitrogen-free solution before harvest [37], changing the nutrient solution formula [38], and using quartz porphyry as a water treatment agent [39] can significantly reduce nitrate content and increase the yield.

In the present study, only nutritional quality indicators were considered when comparing the quality of leafy vegetables under different cultivation modes. In fact, vegetables produced by soilless cultivation have great advantages in terms of safety. Further improvement could focus on the safety quality indicators such as microbial biomass and pesticide residues in leafy vegetables for a more comprehensive analysis of production quality.

4.3. Analysis of Production Cost of Leafy Vegetables

By collecting and analyzing the cost composition of leafy vegetable production under different cultivation modes, fixed cost was found as the main cost in soilless cultivation. The fixed cost of Hyd and Sub modes, respectively, accounted for about 50% and 34% of the total cost, which was more than ten times the fixed cost of soil cultivation. For soilless cultivation, the construction of greenhouses and supporting facilities requires a large investment at the initial stage. Reducing the cost of soilless cultivation facilities is one of the important issues to be solved in the promotion of soilless cultivation mode [40]. Notably, the proportion of cultivable area under Hyd (48.6%) and Sub (61.7%) mode was much lower than that under Soi mode (85.7%) in our case, leading to a further increase in unit fix costs of soilless modes. Unit cost is more referable in economic benefit evaluation than total cost. Thus, the proportion of cultivable area needs to be elevated under soilless mode. In addition, unit costs also can be reduced by appropriately increasing the construction area [41].

In addition to fixed cost, another main cost of Sub mode was input cost, which occupies about 40% of the total cost, which was nearly three-fold of Hyd and Soi mode. The main composition of input cost in substrate cultivation is plug and substrate consumption, this can be reduced by optimizing substrate composition, growing leafy vegetables with relatively small sizes, recycling plug and substrate, and using locally available materials [42]. In addition, the input costs of fertilizer can be reduced by improving fertilization and irrigation methods [43] and efficiently using organic nutrients [44]. For hyd mode, nutrient solution preparation and the continuous operation of irrigation systems consumed much more electricity, thereby leading to an obviously higher management cost (1.39~1.41 CNY·m⁻²) than the other two modes. Optimizing the management of water pumps can be an effective way to reduce the management cost while bringing more preferable root microclimate for plant growth [45].

The labor cost of vegetable production in China has been high for a long time [9]. In this study, the input cost and labor cost of soil cultivation accounted for the vast majority of the total cost, accounting for about 50% and 30% of the total cost, respectively. It can be seen that the soil cultivation mode is a labor-intensive production method [46]. Among them, the input cost of soil cultivation mode is mainly composed of fertilizers, pesticides, and seedlings. At present, the mechanization of vegetable production is still a bottleneck restricting the high-level development of the vegetable industry [47]. To reduce the cost of leafy vegetables cultivated in soil, it is first necessary to reduce labor costs by strengthening the degree of mechanization and automation of production.

Furthermore, it must be aware that, although production costs of soilless cultivation have space for further reduction, commercial-scale soilless cultivation is bound to be a high-cost production mode. And with the application of intelligent control and mechanical equipment, combined with the high demand for skilled labor, the total cost will further improve. Therefore, what we need to pursue is to reduce the cost of unit yield.

4.4. Economic Benefit Analysis of Leafy Vegetables Based on Pricing Scenarios

Based on the actual market price, the overall production benefit of soil cultivation was stable and considerable (4.83~8.83 CNY·m⁻²), although the Soi mode had the lowest price. This should be attributed to the low cost and high yield under Soi mode. The hydroponic vegetables had the highest selling price, but only hydroponic cabbage obtained the most appreciable economic benefit (8.94 CNY·m⁻²), as the yield of hydroponic lettuce was much lower. For hydroponic lettuce and leafy vegetables cultivated in substrates, due to the low yield and high cost, profits cannot be obtained. Therefore, we hope to improve the economic benefits of soilless cultivation of leafy vegetables by adjusting the pricing plan.

At present, there is no uniform standard pricing plan for leafy vegetables produced under soilless cultivation mode. Based on the QP pricing plan, the economic benefit of substrate cultivation was elevated, as well as that of hydroponic Rosa red lettuce. QP pricing plan is more suitable when produced vegetables have high comprehensive quality. Notably, this study uses a simple linear model for the setting of QP and evaluates all quality indicators equally. Further improvement can give corresponding weights to the quality of leafy vegetables according to consumers’ preference for the quality of leafy vegetables, so as to better optimize the model and obtain a pricing plan that is more in line with consumers’ wishes. For the BP pricing plan, under the premise that the BP price range (2.42~32.21 CNY·m⁻²) is close to the investigated market price range (6.0~30.0 CNY·m⁻²), the loss can be avoided, but the benefits of Soi mode are very low, with a maximum of only 1.17 CNY·m⁻². Above these, each pricing scheme has its superiority. Pricing strategies can comprehensively consider cost and vegetable quality to further increase benefits while ensuring revenue.

Of course, increasing yield and quality is the precursor to improving pricing and achieving benefits. Meanwhile, it is also important to improve consumers’ willingness to pay for high-quality and high-priced vegetables. Although the effect of soilless cultivation on vegetable quality has been generally recognized by researchers [48], customer perception and approval still need to be promoted. Balqiah et al. [49] conducted an online survey on consumers’ purchase intention of hydroponic vegetables and obtained eight factors that can promote consumption intention via multiple regression and cluster analysis. In general, to improve the economic benefits of leafy vegetable production, it is not only necessary to improve the cultivation method and the quality of leafy vegetables, but also the market pricing scheme and consumers’ willingness to pay for vegetables, and the demand for high-quality vegetables are also important factors.

Notably, as this study was conducted mainly in May, a season that has optimal environmental conditions for soil cultivation in Shanghai, the advantage of soilless cultivation modes cannot be reflected. The most prominent advantage of soilless cultivation under environment-controlled greenhouse conditions is stable and provides continuous production throughout the year. At the same time, vegetable selling prices also fluctuate with seasons, thus the statistics and analysis of annual productivity, cost, and marketing information should be conducted in the future to obtain a comprehensive and accurate benefit analysis of soilless cultivation modes.

5. Conclusions

In general, hydroponic cultivation has great potential in obtaining high yields, but optimization of planting density and meticulous management are required to ensure final yield and improve nutritional quality. Substrate cultivation mode can effectively improve the comprehensive quality of leafy vegetables but needs adequate irrigation of nutrient solution to gain considerable yield. Cost analysis indicates that the unit cost of the soilless cultivation mode is about 3-4 times more than that of the soil mode, which is mainly caused by fixed cost and input cost. In addition, the low proportion of cultivable area plays another critical factor in the high unit costs of soilless cultivation. The economic benefits assessment based on the three types of pricing scenarios shows that the actual selling price of hydroponic vegetables (20 CNY·kg⁻¹) can make hydroponic mode obtain considerable benefits when yield is comparable, such as the hydroponic cabbage. However, to achieve profitability, substrate mode needs a higher price, which can be established according to the high-quality feature of substrate-cultivated vegetables. Based on the market-acceptable price range and production costs of soilless cultivation, a maximum revenue of 40% can be guaranteed.

This study helps us identify the critical factors that affect productivity and economic benefits of soilless cultivation mode in actual production, as well as the advantages and disadvantages of different soilless cultivation models. These conclusions can give references for growers in cultivation management, cost control, and marketing strategy, thereby improving benefits.