Implementing Internet of Things for Real-Time Monitoring and Regulation of Off-Season Grafting and Post-Harvest Storage in Citrus Cultivation: A Case Study from the Hilly Regions of Nepal

Abstract

Citrus fruit cultivation, especially mandarin oranges, is crucial to the economy of Nepal’s hilly regions due to their ideal geoclimatic conditions. Despite its economic importance, the sector faces several challenges, such as inadequate grafting techniques, low-quality saplings, and ineffective post-harvest storage. This paper explores these issues and proposes innovative solutions through the use of Internet of Things (IoT) technology. To address these challenges, we identified key areas for improvement. First, we focused on extending grafting practices during the off-season to ensure a higher success rate and better-quality saplings. Second, we examined different post-harvest storage methods to determine their effectiveness in terms of shelf life, decay loss, and quality of fruit. In addition to exploring post-harvest strategies, this paper provides preharvest recommendations for farmers, emphasizing methods to enhance fruit quality and longevity through effective pre-storage practices. Our IoT-based approach introduces off-season grafting in polyhouses and advanced monitoring for post-harvest storage. The results are promising: We achieved grafting success rates of 91% for acid lime and 92% for local mandarin orange varieties. Additionally, our research compared different post-harvest storage methods for mandarin oranges, including room, cellar, and cold chamber. We assessed these methods based on shelf life, physiological weight loss, and the total soluble solids (TSS) to titratable acidity (TA) ratio. The cold chamber proved to be the most effective method, offering superior conditions for storing mandarin oranges. The IoT-based monitoring system played a crucial role in maintaining optimal temperature, humidity, and gas content within the cold chamber, resulting in reduced post-harvest losses and extended shelf life. These findings highlight the transformative potential of IoT technology in mandarin orange cultivation and post-harvest storage.

1. Introduction

Citrus fruit, mainly mandarin orange cultivation in Nepal’s hilly regions, has been a source of economic prosperity and sustainability for many farmers.

The geoclimatic conditions in these areas are highly suitable for farming, with approximately 62 out of 77 districts actively involved in citrus production [1,2]. The demand for grafted saplings has been steadily rising, and both smallholder and commercial farmers are drawn to the profitability of local mandarin orange cultivation [3]. However, several pressing challenges have hindered the sector’s growth and sustainability, necessitating innovative solutions.

1.1. Citrus Cultivation and Post-Harvest Storage in Nepal

The hilly areas of Nepal exhibit a varied topography, ranging from subtropical to temperate zones, with altitudes fluctuating between 800 to 3000 m above sea level [4]. One of the key factors contributing to Nepal’s suitability for citrus fruit cultivation in hilly regions (800–1600 m) is the favorable temperature range. The hilly terrains experience moderate temperatures throughout the year, with warm summers and cool winters. This temperate climate is well suited for the growth and development of citrus trees, as they thrive in temperatures ranging from 15 to 30 degrees Celsius [5]. The ample sunlight in the hilly areas of Nepal further enhances the citrus cultivation prospects. Citrus fruits require a significant amount of sunlight for photosynthesis and fruit maturation. The sloping landscapes of the hills ensure that citrus orchards receive optimal sunlight exposure, contributing to robust and healthy fruit production. Additionally, the well-drained soils in the hilly regions are conducive to citrus cultivation. Citrus trees prefer soils with good drainage to prevent waterlogging, and the diverse range of soils in Nepal’s hilly areas, including loamy and sandy soils, provides suitable options for citrus cultivation. As the number of orange orchards continues to flourish, the peak of production often results in a surplus supply, leading farmers to face the challenge of selling their oranges at reduced prices. An effective alternative to this predicament is the implementation of proper orange storage techniques. By successfully storing oranges for 60 to 90 days, farmers can take advantage of a substantial price increase, nearly tripling their earnings. A recent study in regions with cold storage facilities showed that farmers experienced considerable benefits from this approach [6]. Thus, having a reliable and efficient storage method is of paramount importance for the prosperity of farmers, offering them a strategic advantage in the market.

1.2. Economic Significance

The citrus sector significantly enhances the income and food security of rural communities, with most districts actively engaged in citrus production. Citrus cultivation holds significant economic importance in Nepal, contributing to the country’s agricultural sector and overall economic well-being. Citrus cultivation serves as a source of income generation for numerous farmers across Nepal, especially in the hilly regions where the conditions are favorable. The cultivation of citrus fruits such as oranges, lemons, and limes provides a steady income for farmers who rely on the sale of these fruits in local and regional markets [7]. Additionally, it generates employment opportunities at various stages, such as planting, pruning, harvesting, and packaging during the cultivation process. The recent trends in production shows that Nepal’s orange production has potential for export if improved cultivation practices and the adherence to quality standards can be maintained [8]. Citrus orchards, with their scenic beauty and fragrant blossoms, can attract tourists, contributing to the growth of agro-tourism in the region.

1.3. Challenges

Despite the favorable geoclimatic conditions, the production and post-harvest storage of citrus crops in Nepal encounter significant challenges, posing a notable impact on overall productivity. One primary issue arises from insufficient grafting seasons and the provision of substandard saplings by local nursery vendors. This results in a mismatch between the demand for citrus crops and the available supply, adversely affecting productivity levels. Inadequate grafting seasons hinder the proper establishment of citrus orchards, impacting the growth and yield of these valuable crops. The use of substandard saplings further exacerbates the problem, as it compromises the overall health and resilience of the citrus plants, leading to reduced productivity and unmet market demands [9,10]. Furthermore, post-harvest challenges pose a significant hurdle to the citrus industry in Nepal. Inadequate storage practices contribute to substantial fruit losses after harvest [11]. Without proper storage facilities and techniques, citrus fruits are susceptible to spoilage, deterioration, and decay, rendering a considerable portion of the harvest unsuitable for consumption or commercial purposes. This not only results in economic losses for citrus farmers but also affects the overall supply chain and market availability of citrus products [12,13]. The National Research Citrus Program (NCRP), a government body of Nepal, is working towards uplifting citrus farming overall. Standard grafting procedures have been given to produce disease free and quality saplings [14]. However, the use of cutting-edge technologies such as the Internet of Things (IoT) remains essential. This not only facilitates remote monitoring and control of environmental parameters but also enables the recording of sensor data for insightful data analytics [15].

This paper aims to provide a suitable implementation of Internet of Things (IoT) technology as one of the crucial transformative solutions for the grafting and post-harvest storage of mandarin orange in Nepal. By leveraging IoT system, the aim is to address the shortcomings in grafting practices, optimize irrigation through microclimate regulation, and introduce real-time monitoring and control mechanisms for post-harvest storage conditions. The main contribution of this work is the demonstration that the integration of an IoT system in citrus farms and crops can improve productivity, reduce waste, and contribute to the long-term food security of the region.

The two challenges considered to be of main interest were off-season grafting and post-harvest storage. For this purpose, an IoT system was implemented, and the performance was evaluated.

The remaining of the paper is organized as follows. Section 2 discusses the related work, and Section 3 presents the proposed system, materials, and methods. We present the experimental analysis, results, and discussion in Section 4 and Section 5, followed by the limitations of the current work. Finally, we discuss the main conclusions of our research work and possible future lines of research.

2. Related Works

Over the years, there have been significant technological developments in areas such as managing nurseries, orchards, protecting plants, and handling post-harvest processes. Strano et al. discussed the challenges of post-harvest losses in citrus, primarily in the Mediterranean Basin, where it is a significant fruit source. These losses, attributed to diseases and metabolic disorders, can reach up to 30 to 50% of the total production. To mitigate this, there is a critical need for innovative post-harvest technologies aimed at preserving quality and extending shelf life. The emphasis lies on the proper handling, treatment, storage, and transport of harvested produce. Strano et al. intended to provide a critical review of current knowledge regarding safe and sustainable strategies as well as advanced post-harvest handling and storage technologies [16]. Mario et al. presented the effectiveness of two treatments, namely hot water dipping (HWD) at 50 °C for 3 min and hot air treatment (HAT) at 37 °C for 48 h, in managing chilling injury and decay in blood oranges during cold quarantine and subsequent storage. The study proposed HWD as a commercially viable option for mitigating chilling injury and decay in quarantined fruit while advising caution against the use of HAT to enhance the keeping quality of blood oranges following cold disinfestation [17]. A study conducted in Khuzestan, Iran, aimed to reduce post-harvest losses in Valencia and local Siavarz orange cultivars. Treatments following optimal harvesting included hot water dipping, thiabendazole (TBZ) fungicide, wax, and combinations. After fruit storage at 6 ± 1 °C and 85–90% humidity for 3 months, the results showed hot water, wax, and TBZ effectively reduced post-harvest decay, particularly against penicillium molds. For Siavarz, these treatments notably reduced decay to 2% compared to the control’s 26.7%. While wax preserved fruit weight, ascorbic acid, and firmness, hot water treatment maintained weight and firmness but lowered ascorbic acid content [18]. Raithore et al. explored a sensor-based electronic tongue system’s (e-tongue) ability to differentiate between orange juices from healthy and Huanglongbing (HLB)-affected oranges. By analyzing key chemicals impacting flavor and health, the e-tongue detected variations in orange juice spiked with sucrose, citric acid, potassium chloride, and secondary metabolites [19]. Lafuente et al. suggested that blue light-emitting diode (LED) light, under the specified conditions, has positive effects on the post-harvest storage of Lane Late oranges, including enhancing resistance against pathogens and influencing beneficial metabolic activities. However, it is essential to note that the effectiveness of such treatments can depend on various factors, including the specific conditions, duration of exposure, and the type of fruit being studied [20]. Hu et al. studied the effect of light on ripe Hamlin sweet oranges after harvesting. They used light-emitting diodes (LEDs) and ultraviolet (UV) light for six days. By examining important ripening factors and analyzing the contents of sugars, acids, and color components in the orange pulps, it was found that LED and UV light not only made the oranges ripen faster but also changed their sugar, acid, and color content significantly [21]. Zhang et al. examined the impact of blue LED light intensity on carotenoid accumulation and gene expression related to carotenoid biosynthesis in satsuma mandarin and Valencia orange juice sacs in vitro. It was found that 100 μmol m⁻² s⁻¹ blue LED light was effective in increasing carotenoid content, particularly β-cryptoxanthin in satsuma mandarin, while 50 μmol m⁻² s⁻¹ blue LED light induced carotenoid accumulation, specifically all-trans-violaxanthin and 9-cis-violaxanthin, in Valencia orange. The value μmol m⁻² s⁻¹ expresses the light saturation point (LSP). The LSP is the point at which the photosynthesis rate does not increase any further despite increasing light intensity. When this point is reached, the photosynthesis-rate curve becomes flat.

Gene expression analysis revealed concurrent upregulation of key carotenoid biosynthesis genes, corresponding with increased carotenoid accumulation under specific blue LED light intensities. These findings contributed to understanding the regulatory mechanisms of carotenoid accumulation influenced by blue LED light [22].

Hussain et al. explored the specific ramifications of climate change on citrus cultivation, focusing on temperature variations, water availability, light intensity, atmospheric CO₂ concentration, and salinity stress. Innovative strategies such as advanced monitoring systems, precision irrigation, molecular priming, and shade netting were discussed as potential solutions to mitigate the adverse effects of environmental stressors, fostering a more resilient citriculture capable of addressing the challenges posed by climate change [23]. Luca Preite et al. explored the significant challenges facing agriculture, notably the need to produce more food due to population growth, which increases pressure on natural resources like water and land. To investigate how innovative strategies can reduce water consumption in agriculture, the authors conducted a systematic review of studies from the last ten years, using PRISMA guidelines and the Scopus database [24,25]. The review focused on approaches like controlled-environment agriculture, hydroponics, and precision farming for field crops. The findings suggested these strategies could potentially reduce water consumption, but additional research is needed to evaluate their full impact and potential trade-offs. The results aimed to establish a framework for assessing sustainable agricultural practices and how these strategies can be applied in real-world scenarios [26].

Cao et al. revealed that the combined treatment of blue light and ethylene facilitated chlorophyll degradation, hastening fruit color change through gene expression modulation. These results contributed to understanding the regulatory mechanisms of blue LED light irradiation on enhancing the coloration of ethylene-degreened satsuma mandarin fruit [27]. J.H. Bower et al. investigated the impact of ethylene on Bartlett pear quality during storage at −1 or –2 °C. The study suggests that while minimizing ethylene is desirable, effective temperature management plays a more critical role in preserving fruit quality [28]. Sheik et al. in their review paper explored the distinction between traditional and smart agriculture. They also identified various sensors crucial for smart agriculture and their integration with emerging technologies, emphasizing the need to address research challenges for enhanced adoption and deployment in the future [29].

The significance of using the Internet of Things (IoT) to enhance productivity and cost effectiveness in agriculture was highlighted by Rehman A. et al. in their paper. The research focused on evaluating smart agriculture through IoT approaches, showcasing applications, benefits, current challenges, and potential solutions [30].

N.N Mishra et al. in their review explored the transformative impact of the Internet of Things (IoT) and big data on agri-food systems. The review discussed their roles in agriculture, and supply chain modernization as well as social media’s influence on the food industry, food quality assessment, and safety measures [31]. M.N. Mowla et al. in their study advocated for sustainable agriculture through automation, focusing on integrating the Internet of Things (IoT) and wireless sensor networks (WSNs). The research emphasized the need for advanced technology adoption to ensure efficient annual production. It provided a comprehensive overview of IoT-WSNs and wireless network protocols, addressing recent challenges and proposing mitigation strategies for the future development of smart agriculture systems [32]. M. Ayaz et al. in their review identified current trends, future prospects, and potential research challenges in the integration of IoT with traditional farming practices [33]. Kour et al. in their study highlighted the transformative role of the Internet of Things (IoT) in enhancing both the quality and quantity of the agriculture sector. They emphasized globally collaborative efforts involving scientists, research institutions, and nations, aiming to harness IoT’s potential for resource optimization [34]. R.K. Singh et al. in their study introduced Agri Fusion, a multidisciplinary architecture for efficient agriculture solutions, highlighting industrial solutions and proposing a step approach for performance evaluation in precision agriculture (PA). the study also outlined open research issues and future scopes in implementing precision agriculture [35]. S. Qazi et al. in their survey paper offered a comprehensive tutorial on advancements in smart agriculture through IoT and AI, critically reviewed challenges in their deployment, and discussed future trends, both technological and social, anticipating widespread adoption by farmers globally [36]. G. Burchi et al. in the paper [37] highlighted the importance of upgrading greenhouse cultivation technology in Mediterranean countries like Italy, Turkey, Greece, and Spain. These regions are crucial for fresh food production and ornamental plant export, yet they lack advanced techniques. The “HouseGarden High Tech” project addressed this gap by introducing a network of sensors and information and communication technology (ICT)-based automation. This high-tech greenhouse, with its sophisticated data-driven control system and non-thermal plasma (NTP) technology, aims to optimize crop management, improve yields, and streamline operations. The project underscored the need for modern technology to enhance productivity and sustainability in greenhouse cultivation.

Zhang, R. et al. used machine learning to provide a theoretical basis for determining the shelf life of blueberries under different storage temperatures, offering technical support for predicting their remaining shelf life [38]. Strano, M.C. et al. emphasized the significant post-harvest losses in Citrus spp., which can reach 30 to 50% of the total production due to diseases and metabolic disorders. To address these issues, the paper explored innovative post-harvest techniques and sustainable strategies aimed at reducing losses, improving quality, and extending shelf life. These approaches included improved handling, storage, and transport practices, along with a focus on reducing synthetic fungicide residues and their environmental impact [16].

3. Materials and Methods

In this section, we delve into the details of the methods and materials employed in the grafting of citrus fruit within a polyhouse and the subsequent post-harvest storage of local mandarin oranges. The key aspects of monitoring and regulating temperature, relative humidity, and gas play a crucial role in both these processes. To ensure precision and efficiency in this regard, an IoT-based system was designed and implemented. The IoT system was developed, and the generated data were hosted in the cloud server. Users can login with verified credentials to access the system and use web or mobile application for real-time data visualization and monitoring. Figure 1 depicts the IoT system architecture for polyhouse grafting and post-harvest cold storage applications. The subsequent sections provide a comprehensive breakdown of the specific methods and materials essential for the successful conduction of these experiments.

3.1. Off-Season Grafting in Polyhouse

The study was conducted by designing a controlled environment inside a polyhouse facility equipped with sensors and IoT-controlled systems, which include an exhaust fan, fogger, heater, and cooling pads. The facility provided an ideal setting for grafting experiments, ensuring optimal conditions for citrus plants. Additionally, ambient temperature and relative humidity were continuously monitored using dedicated sensors strategically placed inside the polyhouse. A data-logger system facilitated real-time logging of climatic data, and a cloud server platform was employed for storing and retrieving the logged information. Quality scions and rootstocks of citrus plants suitable for grafting were also procured for the experimental setup. The methodology employed in this study involved the deployment of temperature and humidity sensors in the citrus orchard during the regular grafting season, which usually is November–January. These sensors continuously monitored and recorded ambient temperature and relative humidity, with data being sent to a cloud server for storage. To ensure accuracy, periodic checks were conducted to verify the sensors’ functionality and the reliability of the recorded climatic conditions. Grafting activities took place during the regular season, usually in an open field within a low tunnel. The monitoring data showed that temperature fluctuated between 15 and 30 degrees Celsius, while humidity ranged from 80% to 95%. However, the ambient temperature and humidity was not ideal for open-field grafting after the month of February. To extend the grafting operation period, experiments were conducted inside the polyhouse with a controlled environment mimicking the optimal conditions observed during the regular season.

3.2. Post-Harvest Storage of Mandarin Orange

The materials utilized in this experimental study included local mandarin oranges harvested at the optimal ripening stage. The oranges were graded to ensure uniformity and quality. The experiment involved five different treatments labeled T₁–T₅. In treatment T₁, oranges were stored in open trays without any additional covering. Treatments T₂ through T₅ used clean low-density polyethylene (LDPE) plastic bags, with each treatment having a different number of holes in the bag to control the airflow around the oranges during storage. The objective was to determine the best storage method among those commonly used in the region. To this end, the study evaluated three distinct storage facilities, which are illustrated in Figure 2. This setup aimed to assess which storage approach provided the optimal conditions for preserving oranges.

The description for the three storage facilities is given below:

Table 1. Description of storage facility.

Storage Facility	Dimensions (m)	Temperature Range (°C)	Relative Humidity Range (%)	Description
(a) Room Storage	4 × 5 × 9	20–25	75–85	Standard room storage with ambient conditions.
(b) Cellar	3 × 4 × 7	15–19	75–85	A controlled cellar environment.
(c) Cold Chamber	3 × 4 × 7	10–12	75–85	Cold chamber for cooler storage.

outlines the key characteristics of each storage facility, including their dimensions, temperature range, relative humidity range, and a brief description.

The methodology employed in this experiment aimed to evaluate the post-harvest storage conditions of mandarin fruits, focusing on different treatments and storage setups. Initially, a meticulous fruit selection process was conducted, ensuring uniformity and the absence of damage in the chosen mandarin fruits. Subsequently, five distinct treatments (T₁–T₅) were established, incorporating varying storage conditions and utilizing trays and plastic bags with different numbers of holes to regulate airflow. The post-harvest storage experiment spanned a duration of 12 weeks, with each treatment being replicated three times to ensure result reliability. For T₁, mandarin fruits were placed directly on open trays, while T₂–T₅ involved bagging the fruits in clear plastic bags with two, four, six, or eight holes, respectively, for controlled airflow. The treatments were allocated to specific storage conditions, including room storage, cellar storage, and cooling storage. Throughout the experiment, environmental conditions within each storage facility, encompassing temperature and humidity, were regularly monitored and recorded. Destructive sampling was implemented, extracting three fruits as samples from each treatment per week to assess quality attributes such as firmness, color, and taste (data not included here). The collected data, including observations of decay or spoilage, were meticulously recorded, and a comprehensive statistical analysis was undertaken to discern the impact of different storage treatments on the post-harvest quality of mandarin fruits.

3.3. Proposed IOT System and Implementation

Figure 3 illustrates the architecture of the proposed IoT system. This system is specifically designed for two applications: polyhouse grafting and post-harvest storage of mandarin oranges. The proposed IoT system integrates various sensors, including the DHT22 for temperature and humidity, a light intensity sensor, and a CO₂ sensor, all interfaced with a NodeMcu-12E, an ESP8266-based controller. The Figure 3 depicts the IoT system architecture of the proposed IoT system. The system was designed for two specific applications: polyhouse grafting and post-harvest storage of mandarin oranges. In the polyhouse grafting phase, sensors continuously monitored temperature, humidity, and light, essential for successful citrus grafting. The ESP8266-based microcontroller preprocessed the sensor data and transmitted to a cloud server at regular intervals. The proposed IoT system incorporates various sensors: the DHT22 for temperature and humidity, a light intensity sensor, and a CO₂ sensor, interfacing with a NodeMcu-12E, an ESP8266-based controller. Actuators such as exhaust fan, humidifier, and fogger adjusted conditions based on sensor data to maintain optimal temperatures between 15 to 30 degrees Celsius and optimal humidity levels of 75 to 85%. Full-spectrum light-emitting diode (LED) lights ensured an adequate 12–16 h of light exposure in the polyhouse.

For post-harvest storage, a cold chamber was equipped with real-time monitoring sensors for temperature, humidity, and CO₂ concentration. The system allowed remote monitoring, and actuators adjusted conditions to maintain recommended storage parameters for mandarin oranges. The temperature was kept between 7 to 10 degrees Celsius, and relative humidity was maintained between 75% to 90%. The stored data were not only accessible remotely but could also be visualized and downloaded for further analysis. This feature enables growers to make informed decisions and fine-tune environmental parameters. The Figure 4 shows the implementation of the IoT system for grafting inside a polyhouse and cold chamber storage for postharvest. The use of IoT technology in both grafting and post-harvest storage facilities enables remote monitoring and automatic control, thereby reducing manual intervention and ultimately contributing to improved citrus cultivation practices.

4. Result and Discussions

4.1. Offseason Grafting in Polyhouse

Figure 5 depicts temperature and humidity variations in a polyhouse during the months March–April, without any internal regulation. Temperature and humidity readings showed clear fluctuations over time, indicating a range of environmental conditions. The temperature readings, taken over several days, varied significantly, with low readings in the range of 16 to 25 degrees Celsius during early morning and late-night hours. Temperatures tended to peak during the daytime, reaching 40 degrees Celsius or sometimes even higher to 50 degrees Celsius. Humidity readings displayed a contrasting pattern. Early-morning and late-night readings tended to show high humidity levels, often above 90%. However, as the temperature rose throughout the day, humidity generally decreased, sometimes falling below 20%. This cyclical pattern of temperature and humidity throughout the day suggests that environmental conditions are influenced by daily weather changes and sunlight. Understanding these variations is crucial for applications inside a polyhouse, as they directly impact plant growth, irrigation needs, and other critical processes.

For the successful cultivation of graftage plants, it is imperative to maintain specific climatic conditions and selection of a proper scion, i.e., root stock. Ideally, the temperature should be regulated within the range of 15 to 35 degrees Celsius, and relative humidity levels should be maintained between 70% to 90%. These optimal conditions are crucial for the healthy development and grafting success of citrus plants. Therefore, the necessity of implementing an internal microclimate regulation system within the polyhouse is evident. To counter the substantial temperature and humidity fluctuations observed within the polyhouse, a control system was implemented using the proposed IoT system. Using exhaust fans, cooling pads, and foggers, this system acted swiftly to regulate the internal microclimate. Sensors continuously monitored temperature and humidity, activating the exhaust fan and fogger systems when deviations occurred, ensuring they remained within the optimal range of 15 to 35 degrees Celsius for temperature and 70% to 90% for humidity. Additionally, the integration of a cloud server enabled remote monitoring of sensor data, allowing real-time insights and facilitating prompt decision making for optimal polyhouse conditions.

An experiment was conducted to assess the success rates of different grafting types for acid lime (Sunkagati-2 scion on trifoliate rootstock) and mandarin orange (Avana Aprino scion on trifoliate rootstock). Three grafting types, namely veneer, splice, and cleft, were employed, and the results are summarized in the

Table 2. Summary of grafting and success rate.

#	Crop	Scion	Rootstock	Grafting Type	Total Grafted Plant	Success	Success Rate (%)
1	Acid Lime	Sunkagati-2	Trifoliate	Veneer	109	99	90.8
2	Mandarin Orange	Avana Aprino	Trifoliate	Veneer	36	33	91.7
3	Mandarin Orange	Avana Aprino	Trifoliate	Splice	36	26	72.2
4	Mandarin Orange	Avana Aprino	Trifoliate	Cleft	36	22	61.1

below:

The veneer grafting type demonstrated remarkable success rates for both acid lime and mandarin orange, at 90.8% and 91.7%, respectively. The splice and cleft grafting types for mandarin orange, while yielding acceptable success rates of 72.2% and 61.1%, revealed a comparatively lower efficacy than the veneer method. These findings emphasize the importance of selecting an appropriate grafting method, with the veneer technique standing out as highly effective for both acid lime and mandarin orange. This result suggests that for off-season grafting for acid lime and mandarin, trifoliate orange rootstock and the veneer grafting method is recommended. This result also contributes valuable insights for citrus-grafting practices, enabling farmers and horticulturists to make informed decisions for optimal yield and success rates in citrus grafting.

4.2. Post-Harvest Storage of Mandarin Orange

The experiment conducted involving different storage facilities, such as a normal room, cellar, and cold chamber, and with varying treatments and replications revealed significant insights into the storage of oranges. Figure 6 is shows the comparative results obtained. Among the storage options, the cold chamber emerged as the most suitable for preserving the quality and extending the shelf life of oranges compared to normal room and cellar storage. Figure 7, Figure 8 and Figure 9 depict the reduction in the weight and shrinkage of mandarin oranges, indicative of physiological weight loss (PWL). PWL was found to be at its minimum when stored in a cold chamber, followed by cellar storage and room storage over a 49-day period. Figure 10 corresponds to decay loss in different storage facilities. The least loss, at 8%, occurred in cold chamber storage, while the highest, at 13%, was observed in normal room conditions. In a parallel storage experiment using LDPE poly bags (25 microns), the least effective method for preserving was found to be normal room storage with fruit on a plastic tray, yielding a shelf life of 32 days. In contrast, storing fruit inside an LDPE poly bag with eight holes and under the same storage conditions extended the shelf life to 62 days.

The cold chamber demonstrated the highest overall shelf life among the three storage structures, and when using LDPE poly bags with eight holes under the cold chamber, the shelf life was extended to three months. In summary, the cold chamber emerged as the most suitable storage option for maintaining orange quality and extending shelf life compared to room and cellar storage. Notably, the inclusion of eight holes in the plastic bags was crucial for enhancing airflow, contributing significantly to prolonged shelf life and reduced decay.

Total Soluble Solids (TSS) to Titratable Acidity (TA) ratio

Table 3. Effect of storage conditions and TSS/TA ratio of local mandarin orange.

Treatments	TSS/TA Ratio
	15 DOS	30 DOS	45 DOS	60 DOS
Storage conditions (Factor A)
Normal room	8.12 a	9.97	11.4	15.24 a
Cellar storage	8.68 a	9.89	10.92	12.76 b
Cold storage	6.79 b	9.56	10.88	11.43 c
Sem (±)	0.22	0.32	0.16	0.38
F-value	***	ns	ns	***
LSD0.05	0.65			1.1
Plastic packaging (Factor B)
Control	8.76 a	10.35	12.08 a	15.95 a
Two-hole plastic packaging	7.74 b	8.92	11.05 b	13.26 b
Four-hole plastic packaging	7.59 b	10.05	10.58 b	12.16 bc
Six-hole plastic packaging	7.61 b	9.52	11.10 b	13.27 b
Eight-hole plastic packaging	7.63 b	10.19	10.52 b	11.08 c
Sem (±)	0.29	0.42	0.21	0.49
F-value	*	ns	***	***
LSD0.05	0.87	-	0.61	1.42
CV, %	11	12.8	5.7	11.2
Grand mean	7.87	9.81	11.07	13.15

Means with the same letter are not significantly different at p = 0.05 by DMRT. * Significant at 5% (p < 0.05). *** Significant at 0.1% (p < 0.001). ns: not significantly different.

presents detailed information on the TSS/TA ratio at various storage durations (15, 30, 45, and 60 days of storage (DOS)) across different conditions, namely normal room, cellar, and cold storage, as well as with different LPDE plastic packaging types (control, two holes, four holes, six holes, and eight holes). The results highlight that normal room storage and cellar storage generally maintain higher TSS/TA ratios, indicating better preservation of fruit sweetness compared to cold storage. Additionally, the table provides statistical metrics including SEM (standard error of the mean), F-values from ANOVA (analysis of variance), LSD (least significant difference) values, and significance levels determined by DMRT (Duncan’s multiple range test). The SEM values (e.g., 0.22 and 0.32) reflect the precision of the TSS/TA ratio measurements at different DOS. F-values (***, **, *, and ns) indicate the significance of differences between treatment groups, with *** indicating highly significant differences. LSD values (e.g., 1.1) determine if mean differences are statistically significant at a significance level of 0.05 (5%), while “ns” denotes no significant difference between means at the specified level. DMRT aids in identifying specific treatments that significantly differ in TSS/TA ratios, contributing to a comprehensive understanding of citrus fruit quality and stability under varied experimental conditions.

TSS/TA ratio (total soluble solids to titratable acidity ratio): This ratio is a measure used in fruit quality assessment. Total soluble solids (TSS) typically represent sugars and other dissolved solids in the fruit juice, while titratable acidity (TA) measures the acidity level, usually as citric acid. The ratio provides insights into the balance between sweetness (TSS) and acidity (TA) in the fruit.

SEM (±): The standard error of the mean (SEM) indicates the precision of the sample mean as an estimate of the population mean. It shows how much the sample mean is expected to vary from the true population mean. The values (e.g., 0.22 and 0.32) denote the SEM for each TSS/TA ratio measurement at different DOS.

F-value: The F-value is from the analysis of variance (ANOVA) and indicates whether the differences between treatment groups (e.g., storage conditions or packaging types) are statistically significant. Asterisks (***, **, *, and ns) indicate the significance level of the F-value, with *** meaning highly significant and ns meaning not significant.

LSD value (LSD0.05): LSD stands for least significant difference. It is a measure used in statistical hypothesis testing to determine if the difference between two means is statistically significant. The value (e.g., 1.1) represents the LSD at a significance level of 0.05 (5%), which is used to compare means and determine if they are significantly different.

ns: “ns” stands for “not significant”. In the context of the table, it means that there is no statistically significant difference between the means compared at the specified significance level (typically p = 0.05).

DMRT (Duncan’s multiple range test) is a statistical test used after ANOVA and shows significant differences among treatments. It compares the means of all treatment pairs to see which ones differ significantly.

Real-time monitoring and control of commercial cold storage

Previously, farmers encountered challenges when mandarin oranges stored in large cold chambers began to deteriorate within just a month [12]. Manual operation of temperature and humidity controls in cold storage facilities, along with the absence of a real-time and automated system for gas exhaust, significantly contributed to the degradation of the oranges. Consequently, recommendations were made for enhancing both pre-harvesting and post-harvesting procedures, highlighting the critical need for integrating advanced automation systems to effectively regulate storage environments. These findings underscore the importance not only of selecting optimal storage facilities but also of implementing cutting-edge technologies to ensure the longevity and quality of stored produce. Figure 11 showcases the 5 days of sensor data obtained at 10 min intervals from the deployed IoT device from 27 January 2024 to 31 January 2024, illustrating the real-time monitoring capabilities. The temperature and humidity sensor data were securely logged in to the cloud server for monitoring purposes every 10 min. Notably, the variation in temperature and humidity was consistently regulated within the desired range of 7 to 10 degrees Celsius with a relative humidity of 80–95%, ensuring optimal conditions for the preservation of mandarin oranges. A mobile application and web-based platform were developed to provide users with real-time monitoring and visualization of sensor data. Access to the applications requires login credentials comprising a user ID and password. Figure 12 illustrates the implemented version of dashboard interface of both the mobile and web-based applications and data visualization at different dates and time intervals.

5. Discussion

This paper demonstrates the implementation of IoT technology in off-season grafting of citrus in polyhouses, an innovative and relatively new concept in agricultural practices in Nepal. The proposed system extends the traditional regular-season grafting period, enabling the production of quality saplings and meeting the demand for citrus fruits outside the regular season. By regulating and monitoring climatic conditions, the system facilitates successful grafting practices when natural conditions are less favorable. IoT devices monitor temperature, humidity, and other environmental factors to maintain optimal conditions in the polyhouse. This precision reduces risks such as poor graft union and low survival rates of grafted plants. This study highlights the importance of selecting appropriate grafting methods, scion, and rootstock to enhance success rates during off-season grafting. The veneer grafting type with trifoliate rootstock demonstrated remarkable success rates for both acid lime and mandarin orange at 90.8% and 91.7%, respectively. The other aspect of this research includes pre-harvest recommendations to the farmers to optimize the quality of mandarin oranges. This aspect is significant because many farmers may not be aware of these practices or may neglect them when preparing fruits for storage, which has previously led to decay and spoilage. First, a preliminary surface washing with clean water is recommended to remove contaminants. Following this, immersing the fruit in a 4% calcium chloride solution for 4 min helps improve the fruit’s texture and durability during storage. To ensure effective drying, treated fruits should either air dry overnight or be dried with warm air to avoid excess moisture during storage. Applying a protective layer of citrus wax is crucial in maintaining freshness and preventing moisture loss. After this, fruits should be swiftly stored in sanitized trays within 24 h of harvest to minimize contamination. Storage conditions are critical; maintaining a temperature between 7 and 10 degrees Celsius and relative humidity of 75–95% preserves fruit quality and reduces spoilage. In this study, we compared various post-harvest storage methods to identify best practices. We identified several key recommendations and best practices for post-harvest storage of fruit, focusing on the cold chamber environment. These practices aim to maintain fruit quality and extend shelf life, emphasizing the importance of hygiene, temperature control, and real-time monitoring. The results revealed that normal room storage and cellar storage maintained a higher total soluble solids to titratable acidity (TSS/TA) ratio, indicating they preserved fruit sweetness better than cold storage. In terms of plastic packaging, the control group (no holes) consistently yielded the highest TSS/TA ratio, suggesting that limiting airflow could help maintain fruit quality. At 60 days of storage (DOS), normal room storage and the control group performed best, indicating their effectiveness in preserving fruit quality over time. However, for longer-duration storage with less decay and spoilage, cold storage may be preferable due to its controlled environment, reducing the risk of mold and other decay-related losses. These results suggest that a combination of room storage for short-term quality retention and cold storage for long-term preservation may offer the best approach. Physiological weight loss (PWL) is at its minimum in cold storage. It was found that cold storage provided the highest shelf life compared to cellar and normal room storage. Cold storage is recommended for long-term storage due to its ability to minimize decay and spoilage through controlled conditions. In conclusion, the proposed system’s integration of IoT technology in real-time monitoring of cold storage enables precise control and quick responses to deviations, which helps in taking immediate corrective action. This also ensures optimal storage conditions.

6. Limitation of the Study

This study has some limitations that should be acknowledged. First, the research was conducted within the specific climatic conditions of Nepal’s hilly regions, which may limit the generalizability of the findings to other regions with different climates. Second, the study focused primarily on mandarin oranges and acid limes, and further research is needed to validate the applicability of the proposed methods to other citrus varieties and fruit types. Additionally, while the IoT technology demonstrated significant benefits, the initial cost of implementation and the need for technical expertise may pose challenges for small-scale farmers.

7. Conclusions

Citrus fruit cultivation, particularly mandarin oranges, holds significant economic importance in Nepal’s hilly regions, benefiting from favorable geoclimatic conditions. However, challenges such as inadequate grafting techniques, poor sapling quality, and ineffective post-harvest storage practices hinder the sector’s growth. This paper explores these challenges and proposes innovative solutions through the integration of Internet of Things (IoT) technology. The research emphasizes two critical areas for improvement: enhancing off-season grafting techniques and optimizing post-harvest storage methods. Off-season grafting, facilitated by IoT-monitored polyhouse, demonstrated remarkable success rates for acid lime and local mandarin orange varieties. This approach not only extends the grafting season but also ensures higher-quality saplings, addressing a longstanding issue in the citrus-farming community. Farmers are encouraged to follow pre-harvest recommendations for preparing the fruits for post-harvest storage. Furthermore, the study meticulously evaluated various post-harvest storage methods—normal room storage, cellar storage, and cold chamber storage—for mandarin oranges. Farmers can plan how they store their fruit after harvesting, as the farmers may have varying production capacities. Farmers can strategically prioritize their post-harvest approach for short-term, medium-term, and long-term storage. The cold chamber emerged as the most effective method, maintaining optimal conditions that minimized physiological weight loss (PWL). Analyzing various storage methods, the study found that normal room storage and cellar storage maintained higher total soluble solids to titratable acidity (TSS/TA) ratios, indicating better fruit sweetness retention, while cold storage was more suitable for long-term storage with reduced decay. Crucially, IoT-enabled real-time monitoring within the cold chamber played a pivotal role in regulating temperature, humidity, and gas composition, thereby significantly reducing post-harvest losses and extending shelf life. These findings emphasize the transformative potential of IoT technology in revolutionizing mandarin orange cultivation practices in Nepal. By integrating IoT solutions in both grafting and post-harvest stages, farmers can enhance productivity, improve product quality, and ultimately uplift their livelihoods. Moreover, the study’s recommendations for pre-harvest practices offer practical insights for farmers to optimize fruit quality and longevity. Looking ahead, continued research and adoption of IoT applications hold promise for further enhancing agricultural practices in Nepal’s citrus sector. Future efforts should focus on expanding IoT’s role in monitoring and optimizing other aspects of citrus farming, ensuring sustainable growth and resilience in this vital agricultural industry.