Evaluation of Automatic Irrigation System for Rice Cultivation and Sustainable Agriculture Water Management

Abstract

The water-resource policy of South Korea has been changing from that of securing water to that of saving water through sustainable water management. Moreover, population aging in rural areas is leading to agricultural water-management problems. In this study, an automatic irrigation system for rice crops was investigated and compared with conventional irrigation, and changes in water productivity and required labor power were quantified. The effect of the proposed system on economic feasibility was verified on farmland by monitoring irrigation water and rice yields for three years. Under the automatic irrigation system, on-site water productivity improved by an average of 12.7% and the labor power required for paddy water management decreased by an average of 21.8% compared to the conventional irrigation system. The internal rate of return was 8.6% higher than the discount rate of 4.5%. The net present value was 406,411 KRW, and the benefit-cost ratio was 1.23. The results can serve as a reference for the on-site introduction of irrigation water-supply automation for sustainable water management and are expected to benefit farmers in saving water and reducing labor demands through sustainable agricultural activities.

1. Introduction

The implementation of water-saving irrigation and efficient use of existing water resources are necessary for the sustainable utilization of agricultural water resources [1]. Because the demand for food is expected to increase with global population growth, food productivity must be increased [2]. Rice, a subtropical crop, is the main food source for half of the world’s population [3], and 90% of the total rice cultivation occurs in Asia [4]. As South Korea is a major rice-producing country, efforts are being made to provide a stable water supply for rice farming.

The global weather patterns have become increasingly unpredictable and extreme due to the phenomenon of climate change [5]. Extreme weather events are considered to increase or decrease the average values of climate factors, such as temperature and precipitation [6]. Abnormal climate phenomena, which have not occurred in the past, have recently been observed in the Korean Peninsula [7]. For example, in 2015, the amount of precipitation received in the Han River and Geum River Basins was, respectively, the lowest and the second lowest since 1966. Consequently, the water level in the Boryeong Dam was observed to be the lowest since its construction in 1998. Furthermore, in June 2017, the amount of precipitation received was the third lowest, although localized torrential rains were frequent for a short period, and in the summer of 2018, the highest average temperature was recorded due to a heat wave, which occurs every year. Moreover, it is becoming evident that the heat wave intensity is strengthening and its frequency is increasing.

Rice yield is decreasing due to climate change [8], stimulating a growing interest in irrigation technology. Water-saving methods for increasing water-use efficiency are required to help farmers with irrigation water management on rice paddy fields [9]. Various experimental studies regarding the conservation of agricultural water have been conducted. Tarlera et al. [10] studied the methods of alternate wet and dry irrigation for three irrigation seasons and reported that the water productivity increased only in two seasons. Mishra et al. [11] conducted an experimental study for three years by varying the paddy heights from 6 cm to 30 cm with a 4 cm increase interval and reported that the yield was not significantly affected by varying the paddy heights. Tabbal et al. [12] employed an intermittent irrigation method in a farm experiment in the Philippines, and the yield of wet-seeded rice increased by 6% to 36%. Belder et al. [13] conducted field experiments on the water use of alternately submerged and non-submerged irrigation systems. The irrigation water input was 15% to 18% lower under the alternately submerged and non-submerged systems than that under the continuously submerged system; however, this result was only significant in one experiment. Sohn et al. [14] studied the water-saving effect of three treatments for ponding depth management, and it was confirmed that shallow-pond and very shallow-pond irrigation methods saved approximately 18% and 26% more than the conventional deep-irrigation method, respectively. Park et al. [15] conducted an experimental study to examine the feasibility of applying the rice-intensification irrigation method and reported that water use reduced by 55.6% compared to the conventional method, which is effective in saving water resources. Humphreys et al. [16] argued that water productivity could be improved through technologies such as automated irrigation systems. However, the aforementioned studies focused on the effects of irrigation methods, and there is insufficient evaluation of the adoption of on-site technologies adopted to implement irrigation methods.

Sustainable paddy water management must account for a potential reduction in rural population while aiming to save water. The agricultural sector is facing a shortage of labor [17]. With the aging of farmers in rural areas, there is a need to introduce technology that can automate water management in rice fields. The population of farm households in Korea was 2,245,000 in 2019, which is 84.4% less than the population of 14,422,000 in 1970. The proportion of the population aged 65 and above in the total farm household population increased by 41.7%, that is, from 4.9% in 1970 to 46.6% in 2019 [18]. The aging problem in rural areas can be linked to the problem of labor required for water management in paddy fields. In particular, agricultural water in Korea is provided free of charge, and the efforts made by farmers to save water are insufficient. Moreover, the increase in labor wages for agricultural activities negatively affects farmer income [19]. For sustainable irrigation water supply practices in rural areas, a system for supplying agricultural water is being automated using Internet of things (IoT) sensors and images. Research has been conducted on irrigation systems for various crops [20,21,22,23,24,25,26,27]. The automation of irrigation systems is a water-saving technology [28]. However, few studies [29,30] have reported on automated irrigation systems for rice cultivation. In the future, a business model that can automate paddy water management will be required to counteract the aging problem of farmers. Therefore, it is necessary to examine case studies in the field of paddy-water management automation facilities considering water productivity. We hypothesize that using an automatic irrigation system for paddy rice crops in the field would save water and reduce labor demands, leading to economic benefits.

The purpose of this study was to evaluate the field introduction of an automatic irrigation system in terms of water productivity, the water management labor force, and the economic feasibility of water management for rice crops. To this end, water productivity and labor power were investigated by installing an on-site automatic irrigation system, which is a nonconventional water management method. The results were compared to those of the conventional water management method wherein farmers directly manage water by employing labor power. Based on the field data, an economic analysis of the automatic irrigation system was performed to examine the possibility of introducing sustainable paddy water management in rural areas.

2. Materials and Methods

2.1. Study Site

The site (Figure 1) used for the study was an irrigation area in Hwaseong City, located in central Korea. The main crop in this region is rice and the soil texture at the site is silt loam. We conducted experiments for three years (2017 to 2019) in two test fields; each had an area of 4000 m². The rice variety selected was Koshihikari, which is the main cultivated variety at the site. Irrigation water was supplied via an open canal from the reservoir to the test site. The site is in the monsoon climate zone, with 78.8% of the annual precipitation occurring during the irrigation period (April to September). Furthermore, this area has exhibited an annual average precipitation of 1 320.3 mm, average temperature of 12.5 °C, average relative humidity of 68.3%, average wind speed of 1.7 m/s, and average solar irradiation time of 6.1 h/day as the average climate values for the past 30 years (1991 to 2020). During the field experiment, the precipitation varied at 0.6% and −2.1% in 2017 and 2018, respectively, compared to the average climate value, and approximately 31% less rainfall was received in 2019. Conversely, the average temperature showed a gradually increasing trend, and in 2019, it was 13.2 °C, that is, 0.8 °C higher than the corresponding average climate value. The average humidity in 2019 was approximately 3% higher than that in 2017 and 2018. The average solar irradiation time was higher than its average climate value, and it was 6.8 h/day in 2019 and 7.1 h/day in 2017 and 2018. However, the average wind speed was the same as its average climate value during the entire experiment.

2.2. Automatic Irrigation System

An automatic irrigation system was installed to evaluate the benefits of the on-site introduction of water-conserving techniques in paddy fields. Figure 2 shows the layout of this system and photographs of its on-site installation. The system comprised a ponding-depth sensor, an intake gate, a controller, and a drive motor. The inlet device for supplying water to the paddy fields had a sluice-type gate design. This system automatically supplied water from the canal to the paddy field by using the ponding-depth sensor. Furthermore, an option to operate the sluice gate manually was enabled in the system. We combined a Thalimedes encoder with this system to monitor the irrigation characteristics in the test field.

2.3. Design of Field Experiments

In this study, we applied two methods for paddy water management: conventional and automatic irrigation systems. Figure 3 shows the layout of the field experiments for operating the irrigation systems.

In Test Field 1, a farmer manually supplied water using the conventional irrigation system, wherein the ponding depth did not exceed 80 mm. In Test Field 2, water was supplied using the proposed automatic irrigation system, a nonconventional system. For the automatic irrigation system, the ponding depth in the test field was designed to maintain a water level at half of the ponding depth for the conventional irrigation system. To evaluate the feasibility of the automatic irrigation system, we monitored the water consumption and labor required in water management in each test field. In the harvest season, the threshed rice crops from each test field were dried, and the amount of white rice produced was weighed.

2.4. Field Applicability Evaluation

We analyzed the water productivity, labor power, and economic feasibility to evaluate the applicability of the proposed technology. Water productivity and labor power were compared before and after the application of the automatic irrigation system. Water productivity ($WP$) is a measure of crop growth per unit of water consumption and can be expressed using Equation (1), where $Production$ denotes the weight of the produced crops and $Water consumption$ denotes the volume of the on-site irrigation water [31].

$$WP \left(\frac{\mathrm{kg}}{{\mathrm{m}}^3}\right)=\frac{Production\left(\mathrm{Kg}\right)}{Water consumption\left({\mathrm{m}}^3\right)}.$$

(1)

To compare the labor power required for water management with and without the automatic irrigation system, we analyzed the irrigation frequency. The labor power was calculated using the irrigation-monitoring information expressed in Equation (2), where $LP$ represents the total number of irrigation days during an irrigation period and $Rx$ is a representative number;$Rx=$ 1 if irrigation is performed on a given day and $Rx=$ 0 if irrigation is not performed on a given day.

$$LP \left(day\right)={{\displaystyle \sum }}^{ }Rx for irrigation period.$$

(2)

To evaluate the on-site introduction of the proposed technology, we analyzed the following economic evaluation indices: the internal rate of return ($IRR$), net present value ($NPV$), and benefit-cost ratio ($BCR$). $IRR$ is the discount rate that makes the $NPV$ of a project equal zero using Equation (3). $NPV$ is the total benefit on present value minus the total cost on present value. An investment is considered economically feasible when $IRR$ is greater than the discount rate. The $BCR$ is the ratio of the present value of the benefit streams generated by an investment divided by the present value of the cost streams, as expressed in Equation (4). An investment is considered economically feasible when the $BCR$ is greater than 1 [32,33,34]. The economic evaluation indices were calculated based on the experience data of on-site installation and operation of an automatic irrigation system. Here, a social discount rate was used as the most important input data for economic analysis [35]. A social discount rate is generally applied to calculate the value of funds for social public investment projects carried out by the government. Adjustment of the social discount rate was reviewed considering the changes in the economic and social conditions [36]. In addition, the results of the rice production-cost survey were used to calculate the cost of labor. According to the Statistical Act, a rice production cost survey is conducted annually for the purpose of providing basic data for the use of agricultural policies, such as the improvement of agricultural management and enhancement of competitiveness [37]. This survey is conducted by extracting paddy rice from farmlands with an area greater than 1980 m², and the survey items are divided into direct and indirect production costs. Direct production costs include labor, seedling, and fertilizer costs whereas the indirect production cost includes land service and capital service costs.

$$NPV={\displaystyle \sum }_{t=0}^n\frac{B_t-C_t}{{\left(1+r\right)}^t},$$

(3)

$$BCR=\frac{{{\displaystyle \sum }}_{t=0}^n\frac{B_t}{{\left(1+r\right)}^t}}{{{\displaystyle \sum }}_{t=0}^n\frac{C_t}{{\left(1+r\right)}^t}},$$

(4)

where $B_t$ represents the present value of benefit, $C_t$ represents the present value of cost, and r is the discount rate.

3. Results

3.1. Water Productivity from Irrigation Methods

Table 1. Comparison of irrigation water, rice yield, and water productivity for automatic and conventional irrigation methods during the irrigation period.

Year	Irrigation Method	Rainfall (mm)	Irrigation Water (mm)	Rice Yield (kg/103 m2)	Water Productivity (kg/m3)
					(IW) 1	(IW + R) 2
2017	Conventional	1120.4	428.9	717.2	1.67	0.46
	Automatic		356.9	708.7	1.99	0.48
2018	Conventional	806.4	699.0	858.9	1.23	0.57
	Automatic		621.5	839.1	1.35	0.59
2019	Conventional	606.2	708.1	854.9	1.21	0.65
	Automatic		604.1	799.2	1.32	0.66

¹ (IW) denotes irrigation water. ² (IW + R) denotes irrigation water with rainfall.

lists the irrigation water consumption, rice yield, and water productivity values obtained using the conventional and automatic irrigation methods from 2017 to 2019. With the conventional irrigation system, irrigation water consumption was 428.9 mm, 699.0 mm, and 708.1 mm in 2017, 2018, and 2019, respectively. Furthermore, the rice yields per thousand square meters ranged from 717.2 kg to 858.9 kg, and the average value was 810.3 kg. With the automatic irrigation system, the water consumption reduced by 16.8%, 10.4%, and 14.7% in 2017, 2018, and 2019, respectively, compared to those with the conventional irrigation system. However, the rice yield was decreased by 1.2%, 2.3%, and 6.5% in 2017, 2018, and 2019, respectively, compared to those with the conventional irrigation system. The average irrigation water saved using the automatic irrigation system was 14.2% higher than the conventional irrigation system. This indicates that the decrease in irrigation water consumption is higher than the decrease in rice production when the automatic irrigation technique is employed for rice cultivation. During the three years of this study, the water productivity obtained by the automatic irrigation system was higher than that obtained by the conventional irrigation system. Only considering irrigation water, the water productivity was 1.99 kg/m³, 1.35 kg/m³, and 1.32 kg/m³ with the automatic irrigation system, and its average value was 12.7% higher than that with the conventional irrigation system. This implies that every cubic meter of water consumed produced approximately 1.99 kg, 1.35 kg, and 1.32 kg of rice. The water productivity with rainfall showed a tendency to decrease when high precipitation during the irrigation period was considered. Mainuddin et al. [38] investigated the water productivity of 420 farmlands of rice cultivation from 2015 to 2017; the average water productivity was between 0.64 kg/m³ and 0.67 kg/m³ when rainfall was considered and between 0.8 kg/m³ and 0.95 kg/m³ when only irrigation water was considered. Water productivity of our test fields was lesser than or similar to that reported by Mainuddin et al. when rainfall was considered. However, in this study, the water productivity with only irrigation water was relatively higher, because the same amount of irrigation water was used more efficiently.

3.2. Labor Power for Paddy Water Management by Irrigation Methods

Figure 4 shows the labor-power characteristics of the water management for the irrigation methods employed in this study from 2017 to 2019. Over those three years, the number of days required to irrigate the paddy field using the conventional irrigation system was 94 days, 78 days, and 53 days, respectively, whereas that using the automatic irrigation system was 76 days, 61 days, and 40 days, respectively. The labor power with the automatic irrigation system was reduced by a minimum of 19.1%, a maximum of 24.5%, and an average of 21.8%, compared to those with the conventional irrigation system. By applying the proposed automatic irrigation technology, the number of days for irrigation is markedly reduced when compared to the conventional irrigation system. This implies that the automatic irrigation system can reduce the labor power for paddy water management, compared to the manual irrigation management system employed by farmers. In addition, the labor power for irrigation was required more frequently in the years with high precipitation and showed a tendency to decrease in the years with low precipitation. However, in the years with a higher amount of precipitation, the labor power for irrigation increased, but the amount of irrigation water used was small. In the years with low precipitation, the labor power decreased, but the total amount of irrigation water used tended to increase. To avoid drought damage caused by water shortage, it is necessary to induce local residents to practice water saving [39]. Customarily, farmers practice to save water when rainfall is insufficient. At the government level, farmers education for water saving has been implemented since 2016 as a comprehensive measure to cope with drought in rural areas [40]. Furthermore, farmers showed an interest in water-saving awareness through education, and most farmers agreed to save water [41]. Accordingly, in the case of a year with insufficient precipitation, it is judged that the labor force for water supply decreases to save water.

3.3. Economic Analysis of Automatic Irrigation Technology

Figure 5 shows the cumulative cash flows with the on-site introduction of the automatic irrigation system. The cost of automatic irrigation technology includes the initial investment and maintenance costs, and the benefit includes labor reduction and increase in yield. Its initial investment cost is approximately 1,360,000 KRW, and the durability is 15 years. The durability of the automatic irrigation technology was calculated based on the average durability values of the reservoir concrete structures [42] considered in this study, because the automatic irrigation system can be operated until the irrigation canal renovation project is completed. The maintenance cost is considered to be 40,800 KRW based on the experience of the trial-operation period. The labor cost could be 187,653 KRW based on a rice production-cost survey from 2021 [37], considering a labor-power reduction of 21.8% according to the results of the on-site operation. The rice yield benefit could be 1,293,998 KRW, and the increase in rice yield is considered to be 12.7% based on the increase in water productivity. The $IRR$ was 8.6% higher than the discount rate of 4.5%, based on the discount rate for public project evaluation [43]. The $NPV$ was 406,411 KRW, which converted to revenue after eight years of device installation. In addition, the $BCR$ was 1.23, which is greater than 1. Therefore, the automatic systems could achieve a break-even point based on the economic analysis results, suggesting that the introduction of this technology is economically satisfactory.

4. Discussion

To apply the proposed automatic irrigation technology to rice fields and to monitor the water-saving effect to realize sustainable irrigation water management, our experiments were set up in a shallow paddy field. We determined that the automatic irrigation method reduced water usage by an average of 14.2% compared to the conventional irrigation method. Wang et al. [44] conducted a two-year field experiment using shallow wet irrigation and shallow humidity-regulated irrigation methods, and the water-saving rates were 33.7% and 43% lower than those using the conventional irrigation method, respectively. They reported that shallow irrigation is more advantageous than deep irrigation in terms of water saving and can be realized using automatic irrigation technology. The application of the proposed technology enhanced water management in the paddy field with automatic irrigation that employed a sensor to estimate the paddy ponding depth. Kuo [45] also analyzed the relationship between water saving and production based on irrigation scheduling through field experiments in Taiwan and reported that 7-day and 15-day irrigation schedules reduced water requirements by 14.6% and 27.3%, respectively, and crop yields decreased by 7% and 15%, respectively. This indicates that the proposed automatic irrigation technology is necessary for shallow irrigation and can increase water productivity. The water-saving effect of the proposed method is relatively higher than the decrease in rice yield, which can help realize sustainable water management in preparation for water shortages.

The irrigation system in Korea generally supplies water from a reservoir to a paddy field through an irrigation canal. The proposed system can help automate the irrigation system because of its advantages, that is, it can be easily and directly installed in the irrigation canals and can use the supplied water directly from the irrigation canal. However, it has a disadvantage, that is, it cannot be controlled remotely. To compensate for these shortcomings, a study that integrates a smart phone capable of remote control with the proposed system will be conducted in the future. Taris et al. [46] studied an IoT-based smart irrigation system with a smart phone for rice fields that supplied water from a reservoir to a rice field through a valve. However, this is different from the proposed device in terms of using an additional pump and using a smart phone to remotely control the water supply. Parthasarathi et al. [47] studied a drip-irrigation system on upland rice, which was interesting because it provides an understanding of different water-supply systems for paddy rice in Korea. The drip-irrigation system is advantageous in terms of reducing water consumption; however, water supply for rice crops in Korea comprises a supply system for continuous irrigation using water canals. Sharma and Kumar [29] proposed an irrigation system for paddy crops using IoT, which supplied water via a water pump based on soil moisture. Barkunan et al. [30] proposed an automatic drip-irrigation system using a smart sensor for paddy cultivation. This system also supplied water based on soil moisture. However, the above-mentioned systems are different from the system proposed in this study because they used soil-moisture sensors for the water management of rice crops, and in Korea, water management is based on the ponding depth for the cultivation of rice crops. Therefore, the system proposed in this study utilized a ponding-depth sensor, as it is more advantageous than using a soil moisture sensor for rice cultivation in South Korea. The study findings indicate that for sustainable irrigation water management, on-site technology suitable for local characteristics should be applied.

In paddy fields, water management requires considerable labor. The proposed system makes it possible to reduce the labor power by 21.8% based on the data from the ponding-depth sensor compared to the conventional irrigation system. By using the automatic irrigation technology, the water supply was reduced compared to the conventional irrigation system. The proposed technology can maintain sustainable water management to cope with a decrease in labor power. Al Mamun et al. [48] proposed a prototype of an automatic smart irrigation model that operates a pump with a moisture sensor and presented the same opinion that an automatic irrigation system can solve the labor-power problem. As the labor supply on farmlands decreases, the importance of automation technology increases. Spencer et al. [49] reported that using automatic irrigation based on soil moisture on corn crops improved profitability.

The economic feasibility of the application of automation technology for rice cultivation is another important factor. Mdemu et al. [50] conducted a study to estimate the labor and water input for rice production and determine the water productivity in large rice-irrigation schemes. However, no economic analysis was conducted in terms of the applicability of irrigation technology that can be compared to our study results. Masseroni et al. [51] evaluated an automatic irrigation system for rice cultivation in Europe. Although this study did not have significant results for reduced water conservation or increased yield, it did report that the time spent by workers could be significantly reduced via automation. They also reported that the technology produced an investment effect according to the economic evaluation of $NPV$, and the $NPV$ for 20 years was a positive value. Their result is similar to that of the economic evaluation of the proposed automatic irrigation system in this study, where the $NPV$ index was evaluated to be a positive value while considering whether the field application of the technology is realistic for sustainable agricultural water management.

5. Conclusions

Owing to the limited availability of water resources, interests in sustainable management of agricultural water is increasing. In particular, agricultural water in Korea is provided free of charge, and the efforts to save water are insufficient. Furthermore, labor power for water management has potentially decreased due to the aging problem in rural areas. Therefore, the on-site introduction of an automatic irrigation system that improves the water productivity required for crop production by saving water and solving the labor problem for water management can be an important social alternative. In this social dimension, to implement sustainable irrigation water supply practices in rural areas, it is also necessary to consider the economic aspect of whether farmers can expand the automatic irrigation system to the field. In this study, changes in water productivity and the labor force were evaluated through a case study of an automatic irrigation system to practice sustainable paddy water management, and the economic feasibility of paddy expansion was analyzed. Under an automatic irrigation system, on-site water productivity improved by an average of 12.7% compared to that under the conventional irrigation system, whereas the labor power for paddy water management decreased by an average of 21.8%. Automatic irrigation in paddy fields proved to be advantageous because the technique prevents excess water supply. In addition, a reduction of labor power was observed while using the automatic irrigation system for paddy water management. The field introduction of this technology was found to be economically satisfactory based on an $IRR$ of 8.6% (greater than the discount rate of 4.5%), an $NPV$ of 406,411 KRW (>0), and a $BCR$ of 1.23 (>1). Comprehensively, the on-site introduction of the automatic irrigation technology was sufficient based on the water productivity, labor power, and economic indicators. Therefore, to ensure the sustainable practice of agricultural water management, an automatic irrigation system can be used as a business model to automate paddy water management, which is expected to address the issue of the aging farm households. The results of this study are expected to help farmers decide whether to introduce an automated irrigation water supply system for rice cultivation. Moreover, an automatic irrigation system could be beneficial to farmers in saving water, reducing labor costs, and practicing sustainable agriculture.