Design of Micro Irrigation Systems for Vegetable Production in Amuria District, Uganda

Eng. Joshua Enyetu* Larmbert Ebitu

Eng. Enyetu Joshua graduated with a Bachelor’s degree in Agricultural Mechanisation and Irrigation Engineering at Busitema University. He has a passion for irrigation engineering and has been working on demystifying the concept of irrigation through public lectures, training farmers, and writing newspaper articles. His interaction with farmers has equally influenced his scholarly contributions in the field of sustainable agriculture, evidenced in his most recent co-authored Journal Publication titled “Citizen Science for sustainable agriculture – A systematic literature review”

Corresponding Author: 2ellertonjosh@gmail.com

1.    INTRODUCTION

Irrigation is crucial for agricultural development in Uganda, especially in areas where rainfall is erratic and insufficient to meet the growing demand for food. The government of Uganda is investing in both micro, medium, and large-scale irrigation systems (MAAIF/MoWE, 2017) to exploit the country’s vast but underutilized irrigation potential, mitigate climate change effects, and meet the food, fiber, and fuel demands of a rapidly growing population (UBOS, 2016). However, less than 1% of agricultural households practice irrigation in Uganda, and only 1% of the potential irrigable area (15,000 ha) out of 3,030,000 ha is under formal irrigation (BMAU, 2018). In the Amuria district, agriculture remains mostly rain-fed despite the abundance of surface and groundwater sources. This design considered the local context and constraints faced by smallholder farmers to design a system that is effective, affordable, and sustainable.

 1.1 Problem statement

In Amuria district, vegetable production is a crucial source of income for many households, but the reliance on rain-fed agriculture has become increasingly risky with the impacts of climate change. As a result, smallholder farmers, who make up the majority of agricultural producers in the district, face challenges in maintaining consistent crop yields and reliable incomes. While abundant surface and groundwater resources exist, many farmers lack the knowledge and resources to implement effective irrigation strategies. Micro-irrigation systems have been shown to be a promising solution for increasing water use efficiency and improving crop yields, but there is a need for systems that are tailored to the specific environmental and economic conditions of Amuria district. Such systems would need to be cost-effective, scalable, and suitable for different plot sizes and crop types. By improving access to efficient irrigation technologies, farmers could potentially increase their productivity, enable year-round crop production, and improve their overall livelihoods. Therefore, the purpose of this study was to design, implement, and evaluate a micro-irrigation system that is optimized for the specific needs and challenges of smallholder farmers in Amuria district.

1.2 Objectives of the project

The main objective of this project was to design a micro-irrigation system tailored to the specific environmental and economic conditions of Amuria district, with the goals of increasing crop productivity and enabling year-round crop production. The specific objectives were to:

• Identify the most suitable micro-irrigation system for vegetable production in Amuria district.
• Design a cost-effective micro-irrigation system tailored to various plot sizes that can be replicated by local farmers.
• Optimize irrigation scheduling to ensure that crops receive the right amount of water at the right time.

2.  MATERIALS AND METHODS

2.1   Project Area

The project area covered the 11 sub-counties of the Amuria district, located in North eastern Uganda. (Figure 1).

2.2 Identification of the most suitable irrigation method

A mixed-methods approach was used, including a site survey, community engagement, water sources assessment, and literature review. The site survey involved collecting climate data from the nearest meteorological station in Soroti, data on soil type using soil sampling and analysis, topography using a handheld GPS device, water availability through historical and hydrologic information, crop type through observation and farmer interviews, and plot size using a measuring tape. Focus group discussions and individual interviews were conducted with farmers and other stakeholders to understand the cropping patterns and preferences. Assessment of water sources was done to evaluate their quantity by measuring electrical conductivity and total dissolved solids, and soil tests were conducted to assess physio-chemical characteristics. The literature review included both peer-reviewed and grey literature and evaluated the performance and suitability of different micro-irrigation systems such as drip, sprinkler, and laser spray irrigation methods. Data collected were analysed to identify the most suitable micro-irrigation system design for vegetable production in Amuria district. Ethical considerations were considered, including obtaining informed consent and maintaining confidentiality and anonymity throughout the study.

2.3 System design:

Based on the results of the site assessment, micro-irrigation systems tailored to various plot sizes were designed. This involved selecting appropriate components, such as drip lines, emitters, valves, filters, pipes, pumps, and tanks, to meet the specific needs of the study area. The design took into account factors such as soil type, topography, water quality and availability, crop type, and plot size. The selected components were optimized for cost-effectiveness while still meeting the desired performance standards. Key design information, such as the layout of the irrigation system and the specifications of the components used, were documented in detail for future reference. The design was evaluated and refined through stakeholder consultation and expert review to ensure its feasibility and suitability for local adoption.

2.4 Irrigation scheduling optimization

To optimize irrigation scheduling, a crop water requirement was developed based on factors such as soil type, crop type, and climatic conditions. The crop water requirement was calculated using the crop coefficient (Kc) and evapotranspiration (ET). Kc takes into account the crop’s growth stage and the soil’s water-holding capacity. Soil tests were conducted to determine the soil’s physical and chemical characteristics, including water-holding capacity, and weather data was collected from a nearby weather station. The Kc values were obtained from published literature and adjusted based on local conditions. Crop-based scheduling was used to adjust the timing and amount of water to ensure that the crop received the optimal amount of water needed for growth and yield. The irrigation schedule was adjusted based on the crop’s growth stage, with more water provided during periods of high-water demand, such as the flowering and fruiting stages. After optimizing the irrigation schedule, it was documented, and training was provided to farmers on how to implement it effectively.

2.5 Equations for key calculations

The following are the equations that represent the key calculations used in the irrigation scheduling optimization process. They include:

3.  RESULTS AND DISCUSSION

3.1  System Selection

Drip irrigation was chosen to suit the requirement by the farmers for a more efficient and water-saving irrigation method. This is because it delivers water directly to the plant’s root zone, reducing water loss through evaporation and surface runoff. (Al-Jaloud et al., 2004; Sadler & Gilliam, 2019). It was also selected based on its usefulness in reducing the incidence of foliar diseases reported to affect vegetables in Amuria. It was also selected for its suitability on relatively flat terrain as characterized the study areas, as this would reduce water runoff, compared to sprinkler and other systems. (Kumar et al., 2019). Drip irrigation was also chosen to suit the farmer’s energy shortfalls. Drip irrigation systems have lower operating pressures and therefore lower energy requirements compared to sprinkler irrigation systems (Kumar et al., 2019). Drip irrigation systems also require less handling, making them preferable for farmers to whom irrigation was new. According to Kumar et al, (2019), drip irrigation systems have a longer lifespan compared to sprinkler systems, due to their having fewer moving parts that are prone to wear and tear. Overall, Drip irrigation was chosen based on literature findings, study area soil, water and climate conditions, and farmer preferences (Al-Jaloud et al., 2004; Sadler & Gilliam, 2019; Kumar et al., 2019).

Micro drip irrigation system design was subsequently selected to suit the small plots, the wide range of vegetables with different water requirements and the water sources in the study area. The system comprised several main components, each of which plays a crucial role in ensuring its effectiveness and efficiency, including the water source, mainline, laterals and emitters. A tank-based storage system was chosen to store water for use during periods of water scarcity. The farmers reported frequent and long seasons of drought or insufficient rainfall. They were variously sized for filling through a combination of surface runoff, harvested rainwater, or a borehole, depending on the availability of water sources in the study area.

For areas less than ¼ acre, the irrigators manually filled the water tanks. Water from the tanks flows by gravity to the driplines, which have emitters. The tanks were raised to a maximum height of 1.5m to allow for manual filling and provide a head for the operation of the emitters.

3.2  System design

3.2.1  Design area

 The irrigation system design was customized for seven categories of farmers based on the size of their farm land. The purpose of this approach was to tailor the design to the specific needs and capacities of each category, as farmers with different land sizes would have varying irrigation needs and capacities to adopt irrigation systems. The smallest land size considered was 64m2, while the largest was 2.5 acres, and the design was determined based on individual farmer capacity to adopt irrigation systems, as determined by the survey. Please refer to the Table 2 below for the number of farmers for each plot area category.

Table 2: Irrigation Area Distribution

3.2.2  Soil, crop and climate Information

Soil physical and chemical properties provided the basis for water infiltration calculation and planting depth estimations. The soil type was Sandy Clay Loam with a pH of 5.1, which was outside the range of 5.5 – 6.5, considered optimum for most vegetables. Thus, recommendations for liming with locally available alternatives to boost site productivity were made. The soil infiltration rate was 18mm/hr.

Tomatoes, Bell Pepper, Onions (dry paddy), Cabbages, and Eggplant were selected as the design crops. These are high-value and early maturing. The irrigation system design was based on their botany, as adopted from FAO paper 54.

The climate data collected from the nearest meteorological station in Soroti showed that the area experiences a bimodal rainfall pattern, with two rainy seasons from March to May and August to November, and two dry seasons from December to February and June to July. The average annual rainfall was 1055mm, which is generally considered to be low to moderate rainfall.

 3.2.3  System performance parameters

a) Reference Crop Evapotranspiration and Effective rainfall

The reference evapotranspiration (ETo) according to Penman-Monteith and the effective rainfall were calculated with CROPWAT 8.0 (option 1 in main menu) for the year 2019 using Equation 1. Figure 1 shows the monthly changes of reference evapotranspiration.

b) Crop Water Requirement (CWR)

The CWR for every design crop were computed for the two 2019/2020 growing seasons (option 2 in CROPWAT main menu). Crop coefficients provided with CROPWAT program were used (input: planting dates and growth length in days). Table 2 shows outcomes.

Table 3: Peak daily crop water requirements for the select crops in various month

The table 3 shows the CWR per day for respective crops, referring to the depth of water needed to meet their water loss through evapotranspiration under optimum growing conditions. Tomatoes and eggplants had the highest peak CWR of 6.57mm/day in February. In terms of seasonal crop water requirements, tomatoes and eggplant also showed highest CWR for the first season at 196.85 mm/month (6.35 mm/day×31 days=196.85 mm), occurring in March. Bell papers and Cabbages had the least CWR of 129.6 mm/month (5.00 mm/day × 30days = 150 mm.) in April. The second season showed a similar trend with tomatoes and eggplant showing the highest CWR and cabbage and bell peppers the least (Table 4).

Table 4: Seasonal crop water volumes required for different plot sizes in season 2

Acreage of 10,400m2 for Bell Peppers also required the highest crop water volume of 10,722.04m3 for both the first and second seasons.

c) Net Depth of Water Application (Dnet) and Gross Depth of Application (Dgross)

The net application depth Dnet was calculated as 48mm, which met the requirement of not being greater than the pre-determined soil moisture deficit provided in FAO design manual while Dgross was calculated as 51.1mm.

d) Irrigation Frequency (IF)

 Irrigation frequency was calculated as 7 days, and the irrigation cycle was computed as 6 days. To strike a balance between convenience and cost, the difference between irrigation frequency and cycle should ideally not exceed 1 day, with an extra day reserved for maintenance. However, in order to minimize material costs, the irrigation system was designed to operate on a daily basis.

e) Leaching Requirement (LR)

The leaching requirement was determined based on the yield reduction factors of different crops, and the highest leaching requirement was found to be 0.33 for onions. The other crops required a leaching requirement of approximately 0.2mm per day. This means that onions are more sensitive to salty soils than other design crops.

Table 5: Leaching requirement for design crops (Source 2: Max and Min. Electrical conductivities obtained from FAO manual- Module 9, ECe* – Electrical conductivity of soil, ECw** – Electrical conductivity of water)

f) Irrigation Requirement (IR)

The peak irrigation requirement was calculated as 5.3 mm/day in January at the mid stage of plant growth.

3.2.4   Final Micro Irrigation System Design

To meet the performance targets, irrigation component parts were sized and chosen. Write more words to describe what you mean and want to do.

a) Emitter sizing, selection and number per plant

A dripline with Vortex type emitters, having an outer diameter of 16mm and a discharge rate of 4 l/hr, spaced at 0.3m was chosen. Based on the soil parameters, the wetting diameter was determined to be 0.5m, covering 90% of the total wetting area, with a row spacing of 1m. Th e calculations indicated that each emitter is sufficient to irrigate 2 tomatoes plants, 5 eggplants, or cabbages or Bell pepper plants and 20 onion plants.

b) Precipitation rate and irrigation duration 

A precipitation rate of 13.33 mm/hr, calculated using equation 9 was below soil infiltration rate of 18mm/hr., implying discharge and spacing of the chosen drip line were within acceptable limits. To deliver the Dgross, an irrigation duration of 22.4 hours was computed, to be delivered in an irrigation cycle of 6 days. Thus, the irrigation systems would run for at least 3.7 hours per day, absent rainfall water. But at peak CWR of 5.3 mm/day and lowest IR of 1.1 mm/day, the maximum and minimum daily irrigation durations were calculated as 2.3 and 0.5 hours respectively.

c) Irrigation System Capacity 

System capacities (Table 6) depended on emitter choice and were calculated from equation 10.

Table 6: System capacities of different plots

d)    Hydraulic Design

i. Conveyance and distribution pipes

Water conveyance and distribution pipes, including the mainline (Table 8) and sub mains (Table 7) were sized and selected for each design area.

Table 7: Sub main pipe sizes.

Table 8: Main line pipe sizes

ii. Tank sizing and selection

The optimal tank size was calculated based on the peak ETc at the maximum and minimum months.

VT, Tank capacity, m3, A, area irrigated, m2, ETc, daily CWR, mm/day (Min: 4.485, Max: 6.57). Table 9 shows the volumes of water tanks for different micro-irrigation kits and recommended heights.

Table 9: Tank Capacities

3.3 Irrigation Scheduling Optimisation

To determine the optimal amount of water required for crop growth and yield, the crop water requirement was calculated for each design crop (as shown in Table 2), taking into account factors such as the crop’s growth stage and the soil’s water-holding capacity. We conducted soil tests to assess the physical and chemical characteristics of the soil, including its water-holding capacity, and collected weather data from a nearby station.

Using a crop-based scheduling approach, we adjusted the timing and amount of water to ensure that the crop received the ideal amount of water. To meet this requirement, we scheduled irrigation on a daily basis. Once we had optimized the irrigation schedule, we documented it and provided training to farmers on how to implement it effectively.

We calculated the net application depth (Dnet) to be 48mm, which met the requirement of not exceeding the pre-determined soil moisture deficit determined by the soil tests. To determine the total volume of water required for each crop per season, we calculated the gross depth of application (Dgross) by adding the net application depth and the water loss due to deep percolation and evaporation.

4.0 CONCLUSION

The study identified the micro drip irrigation system as the most suitable micro-irrigation system for vegetable production in Amuria district. This was selected through a mixed-methods approach, which included a site survey, community engagement, water source assessment, and literature review. The community engagement process was used to identify the cropping patterns and preferences of the farmers and other stakeholders, and this information was used to design a cost-effective micro-irrigation system tailored to various plot sizes that can be replicated by local farmers. The micro-irrigation system design for this project was customized for seven categories of farmers based on their plot sizes, ranging from 64m2 to 10400m2. The design was based on the specific needs and capacities of each category of farmers, considering factors such as soil type, crop type, and climate information. The crop water requirement (CWR) for the five selected crops was computed for the two growing seasons of the year 2019/2020. Tomatoes and eggplants had the highest peak CWR of 6.57mm/day in February, with tomatoes and eggplant also showing the highest CWR for the first season, occurring in March. The irrigation system was designed to provide the required water for the crops to achieve optimal yields while being cost-effective and replicable by local farmers.

5.0 RECOMMENDATIONS

The micro drip irrigation system identified in the design may be promoted among vegetable farmers in Amuria district to enhance crop productivity and reduce water use. Farmers and other actors should be trained on the installation, operation, and maintenance of the system to ensure its adoption and sustainability.

Local farmers should be encouraged to adopt the cost-effective micro-irrigation system design tailored to their plot sizes. The customized design will help to reduce the cost of irrigation and increase crop yields.

The optimized irrigation scheduling methods like the use of soil used in the study should be promoted among farmers to ensure that crops receive the right amount of water at the right time. This can be achieved by providing farmers with easy-to-use soil moisture sensors that monitor the real-time water needs of the crop.

Further research should be conducted to assess the economic viability of the micro drip irrigation system and to evaluate its impact on crop productivity, water use efficiency, and farmer income. This will help to strengthen the evidence base for the adoption of micro-irrigation systems in vegetable production in the Amuria district and other similar agroecological zones.

REFERENCES

Amuria district local government, 2015, District Development Plan II FY 2015/2016-2019/2020.

BMAU. (2018). BMAU BRIEFING PAPER (6 /18): Modernization of Agriculture in Uganda. How much has government done through irrigation (No. 6; 18).

FAO, (2007). Handbook on Pressurized Irrigation Techniques. Second Edition. Ed: Phocaides A

MAAIF/MoWE. (2017). National Irrigation Policy. In The Republic of Uganda.

Ministry of Agriculture, Animal Industry and Fisheries and Ministry of Water and Environment, (2017), A National Irrigation policy. 

Ministry of Water and Environment, (2010), A National Irrigation Master Plan for Uganda (2010 – 2035) Final Report. 

UBOS. (2016). National Population and Housing Census 2014 – Main Report

Al-Jaloud, A. A., Al-Amoud, A. I., & Al-Hamdan, O. T. (2004). Drip irrigation in the Kingdom of   Saudi Arabia: History and prospects. Agricultural Water Management, 66(3), 173-184. https://doi.org/10.1016/j.agwat.2003.11.006

Kumar, R., Singh, R., Rana, R. S., & Gupta, R. K. (2019). Effect of drip and sprinkler irrigation     on growth and yield of tomato (Lycopersicon esculentum) under open field condition.   Indian Journal of Agricultural Sciences, 89(9), 1623-1627. https://doi.org/10.31018/ijas.2019.8946

Sadler, E. J., & Gilliam, J. W. (2019). Agricultural Irrigation: Agronomic, Environmental, and Engineering Considerations. CRC Press.