The Modified Hydroponic Kit Based on Self-Fertigation System Designed for Remote Areas

Abstract

Hydroponics has great potential to improve the sustainability of food supplies in various regions presently and in the future. However, studies on proposed hydroponic technology specifically for remote areas are still very limited, with the majority focusing on urban areas. Limited resources, such as electricity supply, are the main obstacles to implementing hydroponics in remote areas. Therefore, this study proposes a breakthrough in hydroponic technology based on a self-fertigation system that can work without electricity for effective and efficient plant growth. This study employs a descriptive quantitative methodology. The proposed hydroponic technology was applied to spinach (Amaranthus dubius) with green and red varieties, from January to April 2021 during the wet season in the tropical climate of Indonesia. Spinach seeds were sown and placed at the nursery for 10 days in net pots containing rockwool of 25 mm of cubes growth media, and then transferred to a hydroponic kit until harvesting. Based on the analysis, microclimate conditions had a safe range and were consistent with plant growth standards. The modified hydroponic kit provided good fertigation quality including temperature, electrical conductivity, potential hydrogen and dissolved oxygen for spinach plants. The total fertigation consumption amounted to 46.64 L during the 20 days of planting (equal to 0.012 L/plant day⁻¹) with low evapotranspiration (0.89 mm/day). In addition, green spinach had higher productivity of 1.34 kg/m² than red at 0.71 kg/m². The nutritional analysis results also showed that green spinach is superior for calcium, iron, phosphor, and vitamin C, while red is superior for potassium and magnesium. The hydroponic kit was used successfully to cultivate spinach plants with good morphological and nutritional qualities. This type of technology has a bright outlook for the near future and must be continuously developed.

1. Introduction

Hunger is the second-leading global challenge after poverty under the sustainable development goals set by the United Nations (2015). According to the latest estimates, 9% of the world’s population lives with malnutrition [1], especially in developing countries. Approximately 828 million people worldwide will be affected by hunger in 2021, with high hunger rates predominantly in rural areas [2]. In 2019, for the first time in history, there were more people in rural areas than in urban areas due to the coronavirus outbreak. In general, those who work in the informal sector, such as construction workers and street vendors, are willing to return to the countryside due to economic factors. Consequently, food supplies with good nutritional quality must be seriously ensured by the government. A brilliant step to avoid food shortages and poor nutritional quality in rural areas is the application of hydroponic-based agriculture [3,4].

Hydroponics is a method of growing plants without soil, using a continuous stream of water that contains mineral nutrients [5,6]. This method is simple, does not require special skills, and can be adopted by users with non-farming backgrounds. Furthermore, hydroponics provides several benefits, including saving water, energy, space, and costs. According to Atamurodov et al. [7], hydroponics can save 5 to 10 times more water and have up to 10 times more productivity than traditional soil-based farming methods. The systems are modular and can be placed outdoors or indoors in any spatial configuration, including vertical columns, walls, large tilting horizontal plants, etc. Given that the use of soil is not required, the plants suffer from fewer diseases and the use of pesticides is reduced. Therefore, hydroponics has great potential to improve the sustainability of food supply in rural areas today and in the future.

However, the main problem with the hydroponic method is its dependence on electrical energy sources. Well-known hydroponic methods, such as the deep flow technique (DFT), nutrient flow technique (NFT), drip irrigation, and floating raft, require an electrical energy source to circulate nutrients [8]. These methods also have a high investment cost. Andrea [9] reported that the percentage of the main utility costs for electricity in hydroponics is 6.8%, higher than the utility costs for water 0.2% and nutrients 3.4%. Hydroponics requires a fair amount of electricity to keep components active, such as pumps, lights, and fans. In many remote areas, electricity is still a scarce source of energy. Therefore, the hydroponic method with zero electricity will play an important role in solving this problem.

Various designs and types of hydroponic kits with the concept of zero electricity have been proposed by previous studies and companies, such as closed-type irrigation system, pocket fertigation, Autopot^®, Autopot^® Hydrotrays, Kratky method, and wick systems (Figure 1). Some of these hydroponic kits are still being developed in the laboratory, while others have been successfully commercialized. These types of hydroponics do not use electricity to transport nutrients. This study proposes a breakthrough in environmentally friendly hydroponic technology and zero electricity hydroponics based on a fertigation system. The proposed hydroponics system is supported by a smart valve component as a unique novelty for automatic nutrient distribution. This smart valve component is designed based on the principle of pressure and gravity.

Smart valves are an important component and are the latest technological concept in hydroponics based on self-fertigation systems. This component has been installed in various products released by Autopot^®. However, the major drawback is that the supply of nutrient stocks is relatively slow due to the complexity of the valve design. This will harm the plant and cause wilting because there is a time lag to replenish nutrients. In this study, the structural design of the smart valve components in the hydroponic kit was altered to enable a swift and constant supply of nutrients. This implies that nutrition will be given automatically when the altitude has reached a certain limit. This technology is expected to promote an effective and efficient plant growth process. Therefore, this study aims to modify a hydroponic kit based on its self-fertigation system designed for remote areas. It is hoped that various parties can adopt the proposed self-fertigation system-based hydroponic kit to increase their sustainable food supply.

The rest of paper is organized as follows: Section 2 describes the materials and methods, including location, horticulture cultivation, microclimate conditions, hydroponic kit evaluation, crop performance, and data analysis and statistics. Section 3 details the performance of the hydroponic kit based on a self-fertigation system and the results of morphological and nutritional contents in spinach. Finally, Section 4 explains our main conclusions.

2. Materials and Methods

2.1. Location

Experiments for designing a hydroponic kit were conducted on a rooftop greenhouse under natural solar radiation at the Faculty of Agricultural Industrial Technology, Universitas Padjadjaran. This site is located in Indonesia, with coordinates of 06°55′23.4″ south latitude, 107°46′19.3″ east longitude, and an elevation of 794 masl. This study was conducted from January 2021 to April 2021, when 94% of Indonesia had entered the wet season, with the peak occurring in January 2021 [15]. This condition will impact the microclimate conditions of the hydroponic kit installation based on the self-fertigation system. This study employs a descriptive quantitative methodology.

2.2. Horticulture Cultivation

The hydroponic system based on self-fertigation was significantly tested on horticultural plants, namely spinach (Amaranthus dubius). This is one of the most important vegetables because it contains mineral salts, such as calcium, phosphorus, and iron. Spinach can be harvested in about 20–23 days after planting, but according to the Indonesian Central Statistics Agency, the production, especially in West Java, has decreased by 1.03% from 2018 to 2019. This problem can be overcome by applying hydroponic cultivation, which optimizes productivity on narrow land.

In this study, green and red spinach varieties from the East-West Seed Indonesia company were used to evaluate the performance of the hydroponic kit. Spinach seeds were sown and placed in the nursery for 10 days in net pots containing rockwool planting media (25 mm cubes) to germinate or sprout properly. Each net pot contains 10 seeds based on expert recommendations, while the primary care required during seeding is maintaining a wet environment by properly watering the planting media.

Next, the spinach is transferred to the hydroponic kit until the harvesting stage; the growth medium used was a combination of roasted husk and cocopeat. This planting medium is categorized as a substrate hydroponic system, a hydroponic method that uses a solid material (substrate). To supply the nutritional needs during the spinach cultivation process, 10 mL of AB mix fertilizer was dissolved in 1 L of water. Furthermore, daily maintenance was performed by delivering nutrients at levels appropriate for plant demands and monitoring nutrition and pH, as well as by adding nutrients. The hydroponic and nutritional systems meet the standard requirements to support the growth and development of spinach.

2.3. Microclimate Conditions

The microclimate is a climatic condition measured in a local area in a square meter or a meter cube. Several climatic variables characterize the microclimate of a particular location. Traditionally, these variables describe the thermodynamic and dynamic state of the atmosphere [16]. This study’s microclimate variables include temperature, relative humidity (RH), light intensity, and wind speed. The microclimate inside the rooftop greenhouse was measured using the following measuring devices: (i) a thermohygrometer to measure temperature and humidity, (ii) a lux meter for light intensity, and (iii) an anemometer to measure wind speed. Meanwhile, the microclimate measurements on the rooftop were carried out at 07.00, 12.00, and 17.00 every day during the spinach planting period, and the observed values were averaged, as shown in Figure 2.

Microclimate conditions are very important in plant growth, as an unsuitable microclimate can cause physiological and morphological problems. Based on the analysis, the condition of each microclimate variable on the rooftop can be described as follows: (i) the daily minimum, average, and maximum of air temperature ranged between 25.43, 27.71 and 32.70 °C, respectively; (ii) the daily minimum, average, and maximum humidity were 45.67, 57.60, and 72.33%, respectively; (iii) the daily minimum, average, and maximum light intensity were 8403.33, 14,735.17, and 28,263.33 lux, respectively; (iv) the minimum, average, and maximum wind speeds were 0.40, 1.04, and 1.60 m/s, respectively. Although all microclimate variables fluctuate with time, the trend was reasonably steady because the interval for each parameter is not too vast.

Although spinach can grow well in humid and dry climates, microclimate conditions affect enzyme and gene functions, as well as the rate of plant transpiration. According to the literature review, the ideal microclimate conditions for the spinach growth process are detailed as follows: 20–30 °C of temperature [17], 50–80% of humidity [18], 8108.10–21,621.62 lux of light intensity [19], and 0.3–1.8 m/s of wind speed [20]. Based on the average value analysis, the rooftop greenhouse has a safe microclimate that meets plant growth standards.

2.4. The Modified Hydroponic Kit

Hydroponics based on a self-fertigation system can be designed to support the characteristics in remote areas. The proposed kit is capable of working without electricity and can be applied to substrate or non-substrate hydroponic processes. A complete visualization of this hydroponic system is given in Figure 3, which consists of (a) a reservoir 40 × 30 × 24 cm for storing a nutrient solution; (b) a polyethylene pipe with a 16 mm diameter for conveying the nutrient solution; (c) a valve for regulating the flow of nutrients; (d) a frame holder for supporting the hydroponic kit; (e) growing media for growing the plants; (f) a gutter (80 × 28 × 28 cm) for storing net pots; (g) a smart valve for automatically regulating nutritional needs. A total of three hydroponic kits were used, each having four gutters, two each for green and red spinach. Each gutter contains 32 net pots; hence, there were 192 net pots for red and green spinach.

The main modification of this self-fertigation-based hydroponic system lies in the smart valve support. This unique control valve allows nutrients from the reservoir to be delivered to the root zone by pressure and gravity, following the Archimedes principle. The smart valve uses water pressure from below to restrict the flow of nutrients from the reservoir. The systems have high efficiency because plants can absorb nutrients according to their needs. This indicates that the valve will open and close automatically based on a predetermined height. Compositionally, the smart valve contains a sponge with a diameter of 7.5 cm and a thickness of 8.5 cm for automatic replenishment of water and nutrients.

2.5. The Hydroponic Kit Evaluation

2.5.1. Fertigation Quality

Fertigation quality for spinach plants is measured using indicators including temperature, electrical conductivity (EC), potential hydrogen (pH), and dissolved oxygen (DO). Using an easy-to-use portable device, these parameters were measured three times each day at 07.00, 12.00, and 17.00. An EC meter was used to measure temperature and electrical conductivity in units of °C and µS cm⁻¹, respectively, while pH was measured using a portable pH meter with no units, and DO was calculated using a DO meter in units of mg L⁻¹. In general, this tool is very simple to use, as the operator only needs to dip the probe in the nutrient solution.

2.5.2. Fertigation Consumption

Fertigation consumption ($C_f$) is the amount of water and nutrient solution needed by plants (L/plant day⁻¹). This is illustrated as the difference between the total volume in the reservoir and gutter before ($V$) and after ($V^{\prime }$) using the hydroponics kit. The volume of fertigation consumption was converted and calculated based on changes in the height of the reservoir and gutter during plant cultivation. Fertigation consumption can be calculated using Equation (1). Based on the comparison between fertigation consumption and the cultivation area ($A$, m²), we can calculate the evapotranspiration value ($ETc$, mm/day) using Equation (2). In this study, the cultivation area with hydroponic kit based on self-fertigation system is 2.6 m².

$$C_f=V-V^{\prime }$$

(1)

$$ETc=\frac{C_f}{A}$$

(2)

2.6. Crop Performance

2.6.1. Growth and Yield

Spinach growth was identified through morphological changes from young to mature or ready to harvest. Plant growth parameters contained measurements of height and fresh weight. These two parameters were measured when the spinach was ripe for harvest, namely 20 days after planting, using a ruler and analytical balance. Spinach height was calculated from the stem base to the tip of the highest leaf, while fresh weight was measured by placing the spinach on an analytical balance. All measurements were carried out after the spinach was harvested to avoid shrinkage or wilting. The productivity ($P$) using a hydroponic kit can be calculated using Equation (3). It shows the comparison between the total production ($W$ in kg) per cultivation area.

$$P=\frac{W}{A}$$

(3)

2.6.2. Nutritional Quality Index

• Vitamin C

Ascorbic acid (vitamin C) was measured according to El-Ishaq and Obirinakem [21] using the iodometric method with slight modifications. Fine fresh leaves 10–30 g were homogenized in liquid distilled water into a volumetric flask. Next, 2 mL of 1% starch was added and titrated with 0.01 N iodine (I₂) solution until the end point of the titration was obtained, which was marked in blue. The percentage of vitamin C ($V_C$) in mg/100 g can be calculated using Equation (4), where $V_I$ is the iodine volume (mL), $w$ is the sample weight (g), and $D$ is the dilution factor.

$$V_C=\frac{0.88 V_I D}{w}100$$

(4)

2.

Calcium

Calcium analysis was carried out using the atomic absorption spectrophotometer method referring to Indonesian National Standard (SNI) 06-6989.56-2005 [22]. About 5 g of the sample was oven-dried at 200 °C and then stored in a desiccator until it reached room temperature. The sample was added with 5 mL HNO₃ and placed into an Erlenmeyer flask. Calcium levels were determined using a spectrophotometer at a maximum wavelength of 422.7 nm. The absorbance value obtained was used to calculate the sample’s calcium concentration based on the calibration curve’s regression line equation.

3.

Potassium

Potassium analysis was carried out using the atomic absorption spectrophotometer method, which referred to SNI 6989.69:2009 [23]. About 5 g of the sample was oven-dried at 110 °C and then stored in a desiccator. Potassium standard solutions were prepared in various concentrations, namely 0.5, 1.5, 2, and 3 ppm. The test solution was prepared by dissolving the sample using distilled water and then adding HNO. The potassium level was determined using a spectrophotometer at a maximum wavelength of 766.5 nm by substituting the absorbance value of the test solution into the linear equation curve.

4.

Magnesium

Magnesium levels were analyzed based on SNI 06-6989.12-2004 using the titration method [24]. About 50 g of the sample was dissolved in 200 mL of distilled water and filtered using filter paper. The solution was added with 2 mL of HCL, oven-dried, and then added with 1 mL of chloride solution. Furthermore, a standard solution of magnesium 100 mL/L was prepared by taking 10 mL from 1000 mL/L into a measuring Erlenmeyer flask, then diluted using distilled water to the mark. Similarly, a standard solution of 10 mg/L was prepared by pipetting 50 mL from 1000 mL/L into an Erlenmeyer flask, then diluted using aquadest to the mark. Magnesium levels were measured using atomic absorption spectrophotometry at a wavelength of 285.2 nm by multiplying the measured levels and the dilution factor.

5.

Iron

The iron content analysis was executed based on SNI 6989.4:2009 using the atomic absorption spectrophotometry method [25]. About 30 g samples were dried at 105 °C for 3 h. A standard solution of 10 mL of iron was placed into an Erlenmeyer flask, and distilled water was added to the mark. The iron content was determined using atomic absorption spectrophotometry at a wavelength of 248.3 nm by multiplying the measured level and the dilution factor.

6.

Phosphor

Analysis of phosphorus levels was carried out based on SNI 6989.31-2005 using atomic absorption spectrophotometry [26]. A sample of 0.5 g was added with H₂SO₄ and HNO₃ and then heated on a hot plate. Next, the sample was added with distilled water to 50 mL. Phosphorus levels were determined using a spectrophotometer at a maximum wavelength of 880 nm for 10 to 30 min.

2.7. Data Analysis and Statistics

The proposed self-fertigation system-based hydroponic technology was implemented on a field scale for disadvantaged areas. Data were statistically analyzed using mean and standard deviation with the Microsoft Excel spreadsheet software, hence, the values were compared between treatments.

3. Results and Discussion

3.1. The Modified Hydroponic Kit Evaluation

Fertigation quality was monitored over time to ensure that the conditions were suitable for plant growth. In the hydroponic kit, the fertigation quality was evaluated based on several parameters, including temperature, EC, pH, and DO (Figure 4). The nutrient temperature plays an important role in the fertigation quality. The recommended nutrient temperature for hydroponic plants is 18 °C to 28 °C [27]. Based on the analysis, the minimum, average, and maximum fertigation temperatures in this study were 24.63, 27.94, and 30.37 °C, respectively. The minimum and maximum fertigation temperatures occurred at 4 and 7 days after planting, respectively. On average, the nutrient temperature exceeded the safe limit to provide good plant growth, but the difference in values was not significantly different. The fertigation temperature must be maintained in the optimal range for effective plant nutrient absorption. Therefore, the nutrient solution must not be exposed to direct solar radiation.

The next evaluation parameter on fertigation quality is EC and, according to Baras [19], the optimal EC value for spinach is 1.0–1.8 µS cm⁻¹. Based on the analysis, the minimum, average, and maximum EC values in this study were 1.56, 1.71, and 1.89 µS cm⁻¹, respectively. At 1–14 days after planting the EC value was relatively constant, while a spike started at 15 days until the day of harvest. On average, fertigation EC was still within safe limits to provide good spinach plant growth. As harvest time approaches (15 days after planting), EC tends to rise, as plants absorb more water than nutrients, resulting in the accumulation of nutrient levels.

Spinach has an optimal pH for fertigation ranging from 6.0–7.0 [28] and, based on the analysis, the minimum, average, and maximum pH in this study were 6.33, 6.41, and 6.50, respectively. The minimum and maximum pH occurred 10 and 18 days after planting, respectively. These results confirm that the fertigation pH quality was still in the safe range to provide good spinach plant growth. In general, the pH of a nutrient solution depends on factors, such as temperature, ionic content, inorganic and organic matter, type of ion, and carbon dioxide content (CO₂).

The last parameter evaluated was DO. Values greater than 5 mg/L are highly recommended, because DO < 5 mg/L can be detrimental and fatal to plants [29]. The concentration might be difficult to maintain in a greenhouse environment because an increase in fertigation temperature culminates in decreased DO. Based on the analysis, the minimum, average, and maximum DO values in this study were 5.60, 6.54, and 6.77 mg L⁻¹, respectively. These results confirmed that the fertigation DO quality was still in the safe range to provide good spinach plant growth. In general, using a hydroponic kit, all fertigation quality parameters showed optimal values for spinach cultivation, hence, the spinach plant growth process can run efficiently.

Another parameter for evaluating a hydroponic kit is fertigation consumption, namely the amount of water and nutrients required by spinach during growth. Based on the analysis, spinach requires 46.64 L of water and nutrients for 20 days of planting (equal to 0.012 L/plant day⁻¹). In addition, this hydroponic kit is classified as very water efficient, as evidenced by its low evapotranspiration value (i.e., 0.89 mm/day). In the same horticultural commodity, the previous researcher reported that the spinach evapotranspiration for non-hydroponic agriculture was 11.57 mm/day and 6.16 mm/day using the lysimeter and CROPWAT model approach, respectively [30]. This study also competed with the hydroponic system based on a deep flow technique method with an evapotranspiration of 1.21 mm/day for spinach (reanalyzed) [31]. The application of hydroponics for other commodities also has a relatively low evapotranspiration, such as with melon (2.2 mm/day) [11], lettuce (2.3 mm/day) [32], and tomato plants (2.88 mm/day) [33]. In general, the hydroponic method produces less evapotranspiration than conventional agriculture. Hydroponic cultivation is one of the most efficient ways to achieve maximum results in minimal time with excellent quality. This is an efficient water-saving technique because the technology reduces high evapotranspiration, which is the total loss of water to the atmosphere through evaporation and transpiration. According to Arif et al. [11], low solar radiation has been proven to reduce evapotranspiration. Variables, such as plant type, cultivation method, planting media, sunlight, temperature, relative humidity, and wind speed, significantly impact evapotranspiration values.

The amount of water and nutrients needed by spinach fluctuates greatly every day and its consumption increases until harvest time (Figure 5). This phenomenon also occurs in other agricultural commodities, such as wheat, broad bean, corn, and millet [34]. Furthermore, nutrient consumption slowly decreases after the plant reaches the peak growth stage until maturity [34]. The basic principle for vegetable production in a hydroponic system is to provide all the nutrients that plants need. Several chemical elements are essential for plant growth and production, with a total of sixteen elements, namely carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo), and chlorine (Cl), being essential. Among these elements, there is a division according as to their origin, namely organic and mineral, including C, H, O; broken down into macronutrients, including N, P, K, Ca, Mg, S; and micronutrients, comprising Mn, Fe, B, Zn, Cu, Mo, and Cl. This division between macro and micro considers the amount of each nutrient the plant requires for its cycle. Plants in their composition have about 90–95% of their weight in C, H, and O [35]. These organic elements do not pose a problem because they come from air and water, which are abundant in the system. Therefore, greater emphasis must be placed on the mineral elements, that will make up the nutrient solution. Fertigation quality, such as temperature, EC, pH, and DO, can interact with chemical elements of nutrient. A clear example is reported by Sambo et al. [36] that a pH above 7 can cause the precipitation of nutrients, such as Fe, Zn, Cu, Ni, and Mn. Thus, extensive research activities are targeted at enhancing the concentration of fertilizer nutrients in hydroponic solutions. Techniques to overcome excessive precipitation in hydroponics can be accomplished using an ultrasonic atomizer [37], ultrafine bubbles [38], and an agitator [39].

3.2. Morphological and Nutritional

The morphological characteristics of spinach cultivated in a rooftop greenhouse are shown in Figure 6. Visually, spinach can adapt well to hydroponic technology based on a self-fertigation system, as demonstrated by the density of biomass during plant growth. This is also supported by nutritional factors and sufficient sunlight; hence, spinach can be harvested in a relatively short time of 20 days. The analysis results showed that green spinach has a greater biomass than red (Figure 7). The greater the biomass, the higher the level of productivity. Therefore, green spinach has higher productivity of 1.34 kg/m² compared to red at 0.71 kg/m².

Productivity is a key parameter in evaluating yield in plants; applying the hydroponic kit can produce yields of spinach of up to 1.34 kg/m². This productivity competes with traditional non-hydroponic farming methods which usually reach 0.91 kg/m² [40] and 0.88 kg/m² [41]. This suggests that, compared to traditional methods, hydroponic farming provides sufficient circumstances for spinach cultivation. Some of the latest techniques to increase productivity in hydroponic agriculture are the application of nanotechnology-based fertilizers [42], planting pattern setting [43], and the implementation of a light-emitting diode (LED) as artificial light [44]. Recently, the use of vertical farming in hydroponics has also led to an improvement in productivity. This pertains to the reality that increasing global population demand on agricultural land can optimize food output per unit area of agriculture. By farming upward instead of outward, this method tries to limit the amount of interference in conventional agriculture [45].

The complete morphological and nutritional characteristics of green and red spinach are shown in

Table 1. Morphological and nutritional characteristics of green and red spinach.

Characteristic	Parameter	Units	Spinach Type
			Green Spinach	Red Spinach
Morphological	Height	cm	39.55 ± 1.65	21.12 ± 3.99
	Fresh weight	g	46.03 ± 2.59	15.38 ± 2.1778
Nutritional	Calcium	mg/100 g	130.45 ± 1.38	99.67 ± 0.35
	Iron	mg/100 g	1.81 ± 0.00	1.64 ± 0.01
	Potassium	mg/100 g	112.95 ± 0.51	167.07 ± 1.80
	Magnesium	mg/100 g	117.34 ± 0.00	205.11 ± 0.00
	Phosphor	mg/100 g	100.79 ± 0.43	99.70 ± 0.06
	Vitamin C	mg/100 g	27.31 ± 1.70	21.33 ± 0.86

. Based on the analysis, green spinach had a height and fresh weight of 39.55 ± 1.65 cm and 46.03 ± 2.59 g, while red spinach has a height of 21.12 ± 3.99 cm and fresh weight of 15.38 ± 2.1778 g, respectively. These results indicate that green spinach has better growth than red. In terms of nutritional content, green spinach had 130.45 ± 1.38 mg/100 g of calcium, 1.81 ± 0.00 mg/100 g of iron, 112.95 ± 0.51 mg/100 g of potassium, 117.34 ± 0.00 mg/100 g of magnesium, 100.79 ± 0.43 mg/100 g of phosphor, and 27.31 ± 1.70 mg/100 g vitamin C. Meanwhile, red spinach had 99.67 ± 0.35, 1.64 ± 0.01, 167.07 ± 1.80, 205.11 ± 0.00, 99.70 ± 0.06, and 21.33 ± 0.86 mg/100 g for calcium, iron, potassium, magnesium, phosphor, and vitamin C, respectively. Based on the analysis, green spinach is superior for the nutritional content of calcium, iron, phosphor, and vitamin C. In contrast, red spinach is superior for the nutritional content of potassium and magnesium.

In general, the composition of plant nutrient content is influenced by various factors during the growth and post-harvest phases, including microclimate factors, namely temperature, light, and humidity, as well as nutritional quality, post-harvest treatment, and ethylene gas [46]. According to Wang et al. [47], pH level greatly affects plant leaf nutrient content as this leads to speciation and the availability of nutrients, such as P, Fe, Mg, Cu, and Mn in hydroponic solutions. Light intensity is also an important factor in regulating the biosynthesis of chemical constituents and their accumulation in plants [48]. Consequently, consumers can determine specific preferences regarding the nutritional content of green or red spinach.

The potential of hydroponics for remote areas is still a major concern according to previous studies. Limited resources, such as electricity supply, are the main obstacles to hydroponic implementation. Therefore, this study proposes a breakthrough in hydroponic kit technology that works without electricity for effective and efficient plant growth. The community eagerly anticipates this innovative and practical technology to address more difficult issues, such as climate change, which causes horticulture product shortages. Based on the evaluation, the proposed hydroponic kit proved capable of cultivating spinach plants with good morphological and nutritional quality to increase productivity.

This proposed technique offers promising near-term possibilities and needs to be continuously enhanced. The hydroponic system operates autonomously by utilizing a self-fertigation technology. In establishing a suitable environment for plants, this technology has proven beneficial, with great potential to improve production. Aside from recommending field testing for spinach, it is also recommended for other crops, particularly those with strong pricing prospects. The selection of plant species depends on local climatic conditions and user preferences, especially in disadvantaged areas. In Indonesia, this area is called the 3T, namely an underdeveloped, frontier, and outermost area. This region has a low quality of development compared to others on a national scale. The province of Papua is located in Indonesia’s eastern region and contains the highest concentration of 3T regions. Consequently, this region is ideally suited for a field evaluation of hydroponic kit technology.

4. Conclusions

Currently, studies on proposed hydroponic technology specifically for disadvantaged areas are still very limited because the majority only focus on urban areas. Remote and urban areas, obviously, both have different characteristics. This study describes a hydroponic kit technology created specifically for remote locations, with the absence of electrical electricity as its primary benefit. This hydroponic kit will make it easier for consumers to cultivate plants at a reduced cost per unit. The modified hydroponic kit might provide good fertigation properties, including temperature, EC, pH, and DO, for the growth of green and red spinach plants, as determined by the analysis. This plant requires a fertigation consumption of 46.64 L for 20 days of planting (equal to 0.012 L/plant day⁻¹) with low evapotranspiration (0.89 mm/day). In addition, green spinach has a higher productivity of 1.34 kg/m² compared with red spinach, with 0.71 kg/m². The proposed hydroponic kit facilitates the cultivation of spinach plants with good morphological and nutritional quality to increase productivity. Based on the analysis, green spinach is superior for the nutritional content of calcium, iron, phosphor, and vitamin C, while red spinach is superior for potassium and magnesium. Consequently, the community eagerly anticipates this innovative and applicable technology, particularly in impoverished areas.