Design of small gravity drip irrigation for smallholder farming in water scarce region of Indonesia

Many regions in Indonesia are suffering from a water crisis due to limited annual precipitation, especially in dry regions, which affects agricultural production. Climate change is becoming more severe, threatening global food and water security. Thus, the development of affordable irrigation for smallholder farms is crucial to increasing agricultural production. The study aims to provide a better design and management of a small gravity drip irrigation system for melon cultivation. Field experiments were conducted on a farmer’s field located in Sinjai Regency to analyze the performance of the small gravity drip irrigation system on melon cultivation. The technical design was determined by analyzing the water application uniformity and irrigation water productivity. The parameters of crop growth under small gravity drip irrigation were monitored during crop development stages, and the irrigation water productivity was calculated after the crop was harvested. As a result, the small gravity drip system performed well in crop performance, and the irrigation water productivity was 1.55 kg/m3. It can be concluded that a small gravity drip irrigation system is an effective strategy for irrigating melon cultivation on smallholder farms, minimizing water loss, and improving crop water productivity.


Introduction
Food and water demand are rising as the world population increases.Ensuring food security in high population countries such as Indonesia is a big issue.In most nations, agriculture is the largest consumer of water, generally using 70% or more of the water that is extracted from rivers, lakes, and underground sources.In Indonesia, the usage of freshwater resources is currently divided between drinking, municipal, industrial, and other purposes, accounting for around 93 km 3 (or about 82%) of the total [1].Therefore, it is important to establish methods that maximize the efficiency of water usage in agriculture.Furthermore, the threat posed by climate change to the security of global food and water has increased.As a result of unpredictable annual precipitation events, several regions now experience water scarcity and drought.Therefore, irrigation researchers and technicians are driven to develop and sustain irrigation technology that is reliable, affordable, and efficient in supplying crops with water and nutrients.
Drip irrigation is a micro-irrigation technique that provides water to plant roots slowly and evenly.Surface drip irrigation systems are commonly used by both large and small commercial horticulture farmers in developed countries.The system has taken rise attention from the growers due to its benefit in increasing crop yield and quality [2,3], improving water and nutrient efficiency [4], improving the 1230 (2023) 012139 IOP Publishing doi:10.1088/1755-1315/1230/1/012139 2 quality of products, and reducing incidence of foliar diseases [5].Meanwhile, where other irrigation techniques are problematic, the drip irrigation system has been employed effectively on saline soils and with saline groundwater [6].
Although drip irrigation system has tremendous advantages in increasing irrigation efficiency and yield, the adoption of this technology has been very slow among small-scale farmers in developing countries including Indonesia.The significant constraint in the adoption of drip irrigation technology includes the high investment costs, the complexity of installation and operation as well as emitter malfunction.Thus, it is essential to find irrigation techniques that are suited to the local conditions of small-scale farming in areas where water is scarce.
The objective of the present study was to develop a small-gravity drip irrigation system for smallholder farming in drought-prone areas for cultivating melon.In order to achieve this objective, the design of a small-gravity drip irrigation system was evaluated using the uniformity of water distribution (EU) and irrigation water productivity (IWP).

Site description
The study was conducted on the field farm of a farmer located in Salohe Village, Sinjai Regency.Sinjai Regency is located between 502 o 56' -5021 o 16' South Latitude and between 119056 o 30'-120025 o 33' East Longitude.The main land use in and around Salohe is for agriculture, where rice and maize are the primary crops grown during the rainy season.Sinjai has an arid climate with little rain and high temperatures, with temperatures ranging from 27.2-34.6°Cannually and relative humidity between 69-87%.The annual rainfall ranges between 78-860 mm.Rainy season occurs occasionally during the months of April-July, while dry season occurred in September to March.The irrigation water used during the study period was deemed to be of good quality, with electrical conductivity of 0.7 -1.12 dS/m.At various depths, soil samples were taken using an auger, and aluminum ring samples measuring 10 cm in diameter and 5cm in height were taken at six different depths.Then, Soil samples were subjected to various physical and chemical analysis in soil laboratory of Hasanuddin University.Values of the physical properties namely particle size distribution, bulk density, particle density, and porosity.Meanwhile, chemical properties such as electrolyte conductivity (EC), percentage of organic matter in soil including carbon and nitrogen as well as the ratio of carbon and nitrogen are presented in Table 1.Soil analysis revealed that the soil was classified as having a heavy soil texture and a high clay concentration.It showed that due to the densely compacted soil profile particles, water is absorbed very slowly and runoff can occur quickly if water is applied.In heavy soil, the water distribution will resemble a sphere and be wider and shallower [7].It suggested that drip emitter with 2 Lph (liter per hour) discharge would be used for heavy soils.The experiments were carried out in October 2021 to January 2022 for cultivating melon.The field experiments consisted of design and installation of small gravity drip irrigation system, field observations and samplings, as well as analysis data.

Description of small gravity drip irrigation system
A drip irrigation system was constructed and installed at the experimental site, as shown in Figure 1.The mainline pipes, flow meter, water filter, plastic water tank, sub-mainline pipe, valves/regulators, drip tape emitters, and an endcap made up the small gravity drip irrigation system.A typical emitter was used as a line source in this study.All pipes were made of PVC, and the system was a complete irrigation unit.It was powered by gravity and fed by a 300-liter plastic tank that was positioned at a 1meter height, providing sufficient head for water pressure.The sub-mainline had drip tape emitters (16 mm in diameter), laid on the soil surface along the plant rows with a dripper spacing of 50 cm.The small gravity drip irrigation system consisted of 4 laterals with the length of 10 m.Through a drip tape emitter, irrigation water was delivered at a rate of 2 liters per hour (Lph).A flow meter which was placed at the system allowed the water application easily to be controlled during irrigation events.It was considered that irrigation was used when the wetted portion of the soil was either completely dry or close to it.Thus, irrigation was applied every other day corresponding to the effective rainfall.On days without rain, the irrigation interval ranged from two to three days; on days with rain, it was longer.During the entire growing period, 18 m 3 of water were administered in a total of 0.33 irrigation cycles.
Analyzing the emission uniformity allowed for the evaluation of the drip irrigation system's performance.Calculations of the individual discharge rates of a few chosen emitters per lateral were made in order to assess the system's overall emission uniformity.In this study, 10 emitters from 20 emitters per lateral were randomly selected.The measurement of flow rate of each emitter was done by taking the volume of water to fill the can for 15 minutes water application.Then the EU was computed using the equation [8] as follow: Where; qn = the average of the emitter discharges that were at the lowest quarter of the field data (Lh -1 ) qa = average of all the field data emitted discharges (Lh -1 ) Figure 1.Schematic layout of small gravity drip irrigation system. (1)

Crop performance and irrigation water productivity
Golden melon Alisha F1, a commercial seed product by Panah Merah was cultivated in the field experiment.Melon was transplanted after 2 weeks seeding.While the crop was in the vegetative stage of its phenological development, growth indicators including the number of leaves and plant height were periodically assessed.Melon was harvested after the fruits turned to light yellow at the maximum maturity of 75 day after transplanting (DAT).Then, fresh weight of melon was observed on harvesting day using the digital weighing meter.The irrigation water productivity (IWP) was calculated using the total yield and total irrigation water application during the growing season using the following equation (Eq2.)[9].
The amount of water that plants need was calculated using meteorological data.A meteorological station closes to the experiment site recorded meteorological standard variables such as air temperature, relative humidity, wind speed, sun radiation, and rainfall.The FAO Penman-Monteith equation was used to compute daily values of ETo [10] using ETo calculator, a software was developed by the Land and Water Division of FAO.Then Daily crop evapotranspiration (ETc) was obtained by multiplying ETo with the crop coefficient (Kc) [10].The crop coefficient for melon based on FAO 56 paper [10], i.e., 0.81, 0.97, 1.16 and 0.85 for the initial stage, crop development, middle and late growth stage, respectively, was used.The development of crop progress was characterized by the increasing of crop water demand.The crop's evapotranspiration was computed using the crop coefficient (Kc) provided for each phenological stage as proposed by Allen et al. [10].The daily reference evapotranspiration (ETo) and crop evapotranspiration (ETc) during the growing season is illustrated in Fig. 3.The variables of meteorological information, such as air temperature, relative humidity, and solar radiation, have an impact on relative evapotranspiration.It is evident that during the growth season, the crop's evapotranspiration tends to increased.Rising from 1.5 mm/day to 5.2 mm/day.The crop water requirement was high in the middle phenological stage due to melon needs water for fruits development in this stage.Therefore, irrigation is crucial for providing plants with the right amount of water when precipitation is minimal during their development.According to Shukla et al. [11], as the crop developed, its evapotranspiration rose until it reached its optimum maturity.The cumulative crop water requirement during growing season was approximately 237 mm.

Discharge rates and emission uniformity
The main goal of a successful drip irrigation system is to deliver sufficient water or discharge to effectively irrigate the plant or area that receives the least amount of water.As a result, the most crucial aspect in the sub-unit of the system is the relationship between the minimum and average emitter discharge, which is shown by emission uniformity.Table 2 presents the emission uniformity (EU) from four laterals.As results, all the emitters had approximately the same discharge rates of 2 l/h in lateral 4 and lateral 1.Little variation discharge rate occurred in lateral 2 and 3.The slight discrepancy may be the result of pressure loss (head loss) brought on by the distance from the water source.The emission uniformity was excellent in the lateral 1 and 4 according to ASAE Classification which the value of emission uniformity above 90%.While the lowest EU was found in the lateral 3. It's possible that clogging caused a slight difference in the uniformity of the emitter flow rate, leakage or incomplete flushing.The uniformity or non-uniformity of the discharges from the individual emitters is typically attributed for the drip irrigation system's flow rate characteristics [12].Non-uniformity discharge rate result in non-uniformity water distribution of drip irrigation system.It can be occurred due to emitter clogging which reduced discharge from the emitter.Moreover, the installation of drip tape emitter in soil surface should be adjusted appropriately in order to reduce head loss in sub unit drip irrigation system.Cleaning filters on a regular basis, inspecting the pressure drop through the filter, looking over the screen holes, and flushing the laterals at least twice or three times a year could all help to prevent clogging, as also suggested by Storlie et al. [14], and as described in [15].

The effect of small gravity drip irrigation system on crop performance and irrigation water productivity
To maintain melon's regular growth and quality, an adequate soil water level within the root zone is necessary.Water application and irrigation planning are essential for providing the right amount of water for crop development.In this study design of small-gravity drip irrigation system was evaluated by the effectiveness of the system distribute water which meets the crop water requirement as the term of irrigation water productivity.Irrigation water productivity is summarized in Table 3.According to Table 3.The irrigation water productivity was 1.55 kg/m 3 water.Figure 4 shows the plant growth performance.The lateral 4 had the highest average number of leaves and plant height.This is due to the emission uniformity of water application distribution was excellent in the lateral 4. The system's ability to evenly distribute water throughout the emitter is a sign of a drip irrigation system's high performance.Thus, the system will be able to maintain the soil moisture properly in the plant root zone.Guan et al. [16] found that the lower uniformity of drip system resulted in a greater possibility of water and salt leaching out.Moreover, the study suggested that the determination of drip irrigation system uniformity should be considered in arid regions which can influence the soil water distribution and the potential salinity risk during growing season.

Conclusion
The small-gravity drip irrigation system is one of affordable irrigation technology which can be adopted by smallholder farmers in the areas where water is scarce.This system provided reduction of initial cost by using gravity force without cost of energy from pump unit.The productivity of irrigation water and the regularity of water distribution were used to evaluate the performance of the drip system.The fact that the diversity of discharge rate across emitters was minimal showed that the irrigation system generally offered good uniformity of water distribution throughout the rootzone.In addition, the plant growth performance was significantly affected by the water application uniformity.Therefore, the uniformity of drip system should be considered in designing of small-gravity drip irrigation system.

Figure 2 Figure 2 . 5 Figure 3 .
Figure 2. a) Daily average air temperature and relative humidity; b) linear correlation between daily average air temperature and relative humidity.

Table 3 .Figure 4 .
Figure 4. Plant growth performance i.e a) plant height; b) the number of leaves in different laterals.

Table 1 .
Physical and chemical properties of soils collected in the experimental site.