Drip irrigation systems are becoming the industry norm for vineyards due to their simplicity, ease of operation, and economical water distribution
Drip Irrigation Systems
A. Benefits and Characteristics of Drip Irrigation
Drip irrigation offers several benefits when utilised in vineyards, in terms of optimising water usage, meeting peak crop water requirements, and using the water-holding capacity of soil to optimise irrigation. By adopting drip irrigation systems, vineyard managers can achieve more efficient water management practices, leading to improved crop health, yield, and resource conservation.
Firstly, drip irrigation excels in water usage efficiency compared to traditional irrigation methods such as sprinkler or flood irrigation. This is due to the precise delivery of water directly to the root zone of the vines, minimising water loss through evaporation or runoff. With drip irrigation, water is applied slowly and evenly, allowing for better infiltration into the soil and reducing the risk of water wastage. As a result, vineyards can achieve higher water use efficiency, optimising water resources and mitigating the environmental impact of irrigation practices.
Secondly, drip irrigation systems can effectively meet the peak crop water requirements of vineyards, especially during critical growth stages such as flowering, fruit set, and ripening. Vineyards often experience varying water demands throughout the growing season, with peak water requirements occurring during periods of rapid vegetative growth and fruit development. Drip irrigation provides the flexibility to adjust water application rates and scheduling to match the specific needs of the vines at different growth stages. By delivering water directly to the root zone, drip irrigation ensures that vines receive adequate moisture when they need it most, promoting healthy growth and optimal fruit development.
Furthermore, drip irrigation can optimise the water-holding capacity of the soil, maximising the availability of water to the vines while minimising the risk of water stress. Soil type plays a crucial role in water retention and infiltration rates, with loamy or sandy soils typically having lower water-holding capacity compared to clay soils. Drip irrigation systems can be tailored to suit different soil types and vineyard conditions, allowing vineyard managers to optimise water application rates and frequencies based on soil moisture levels and crop water requirements. By maintaining optimal soil moisture levels throughout the growing season, drip irrigation helps to mitigate the effects of drought stress and ensures consistent vine health and productivity.
With drip irrigation, weeds are less of a problem, compared to other systems of irrigation.
Micro irrigation:
Micro irrigation is also widely used in the grape industry. It has certain advantages over drip irrigation. Blocked microjets can be easily identified and opened before damage to plants can occur, whereas with drip irrigation, blocked drippers are not identified easily and in time to prevent damage. Micro jets are better adapted to coarse sandy soils, because they emit water over a larger area, compared to drippers. On coarse sandy soils, lateral movement of moisture may be a problem with drippers.
The disadvantage is that more water is lost through evaporation, compared to drip irrigation systems.
B. Preparing an Operation Manual
Preparing an irrigation system operation manual involves documenting detailed instructions and guidelines for the proper functioning, maintenance, and management of the irrigation system. The manual serves as a comprehensive reference document for irrigation system operators, technicians, and stakeholders involved in system maintenance and operation.
An irrigation system operation manual typically consists of the following sections:
- Introduction and overview: Introduce the manual, outlining its purpose, scope, and intended audience. Give an overview of the irrigation system, including its components, design specifications, and operational objectives.
- System components and layout: Describe each component of the irrigation system, including pumps, pipes, valves, controllers, emitters, and sensors. Provide a detailed layout of the system, including maps, diagrams, and schematics depicting the arrangement of components and the water distribution network.
- System operation procedures: Outline step-by-step procedures for operating the irrigation system, including startup, shutdown, and routine operation tasks. Specify proper sequence and timing for activating pumps, opening valves, adjusting flow rates, and monitoring system performance. Include safety precautions and emergency procedures to be followed during system operation.
- Maintenance and troubleshooting: Provide guidelines for routine maintenance tasks, including inspection, cleaning, lubrication, and replacement of components. Identify common issues and troubleshooting procedures for diagnosing and resolving system malfunctions, such as leaks, clogs, or electrical faults. Include maintenance schedules, checklists, and recommended spare parts inventory to facilitate proactive maintenance planning.
- Water management practices: Discuss water management principles and best practices for efficient water use and conservation. Provide guidance on irrigation scheduling, irrigation frequency, and water application rates based on crop water requirements, soil characteristics, and weather conditions. Introduce strategies for water quality management, filtration, and treatment to minimise risks of clogging, sedimentation, or waterborne diseases.
- System monitoring and performance evaluation: Describe methods for monitoring system performance, including flow measurement, pressure monitoring, and data logging. Explain how to interpret performance data, identify trends, and assess system efficiency, uniformity, and effectiveness. Discuss tools and technologies for evaluating irrigation system performance, such as remote sensing, telemetry, and soil moisture monitoring systems.
- Regulatory compliance and record keeping: Provide information on regulatory requirements, permits, and codes related to irrigation system operation and water use. Outline record keeping procedures for documenting irrigation schedules, water usage, maintenance activities, and compliance with regulatory standards. Emphasise the importance of record keeping for tracking system performance, identifying areas for improvement, and demonstrating compliance with legal and regulatory obligations.
- Appendices and references: Include appendices with supplementary information, such as equipment manuals, technical specifications, design drawings, and contact information for suppliers or service providers. Provide references to relevant standards, guidelines, research publications, and resources for further reading or additional information.
By following these steps and organising the manual in a clear and structured format, irrigation system operators can create a valuable resource for ensuring efficient operation, maintenance, and management of the irrigation system. Regular updates and revisions to the manual will help to keep it current and relevant to evolving system requirements and operational practices.
C. Irrigation Scheduling
Irrigation scheduling methods are crucial for ensuring that crops receive the right amount of water at the right time. The aim is to maximise water use efficiency while promoting healthy plant growth and optimising yield. In the context of vineyards, where water management is critical for grape quality and vine health, various irrigation scheduling methods are employed.
A scientific approach to irrigation scheduling requires two variables to be verified, namely:
- The water holding capacity of the soil.
- The effective root depth.
The effective root depth can be verified by making inspection holes and identifying the possible root depth.
The water holding capacity can be determined from soil samples sent to a soil analysis laboratory. They use a gravimetric method. Saturated soil is placed in a calibrated tin and weighed. Then the tins with soil are baked for 24 hours in an oven at 120°C. From the difference in the two readings, the water-holding capacity of the soil can be calculated.
A quick field method can be used if the clay percentage of the soil is known or estimated. Multiply the water holding capacity per mm soil depth by the potential root depth to calculate the water holding capacity in the root zone.
Time-based scheduling:
Time-based scheduling involves irrigating crops at predetermined intervals, regardless of soil moisture levels or plant water needs. Vineyard managers may set up a regular irrigation schedule, such as irrigating four days or every week, based on historical weather patterns or grower experience.
Time-based scheduling is simple to implement and can provide consistent moisture levels, especially in regions with predictable weather patterns. This method may result in over-irrigation during periods of low water demand, leading to water waste, increased disease pressure, and reduced fruit quality.
Soil moisture-based scheduling (probes):
Soil moisture-based scheduling involves monitoring soil moisture levels to determine when irrigation is necessary. Soil moisture sensors or manual sampling methods are used to measure soil moisture content at different depths and locations within the vineyard. The data from the probes are transferred to a programme on your PC which shows when to irrigate. Irrigation is scheduled when soil moisture falls below a specified threshold.
Soil moisture-based scheduling allows for more precise irrigation timing, ensuring that water is applied only when necessary to maintain optimal soil moisture levels for plant growth. Soil moisture sensors and monitoring equipment may require initial investment and ongoing maintenance. Inaccurate sensor readings or improper placement can lead to incorrect irrigation decisions.
Crop evapotranspiration (ET)-based scheduling:
ET-based scheduling calculates crop water requirements based on estimates of evapotranspiration, the combined loss of water through evaporation from the soil surface and transpiration from plant leaves. ET-based scheduling uses weather data, such as temperature, humidity, wind speed, and solar radiation, to estimate crop water demand.
Evapotranspiration is the combined effect of both evaporation and transpiration
The daily evaporation from an A pan is measured and used together with a crop factor to calculate the water needed for a crop.
Crop coefficients are arbitrary figures based on the vine’s growth stage and canopy development. They are crop-specific and area-specific.
The daily evaporation is multiplied by the crop factor which gives the irrigation requirements, such as in the tables below.
Pan evaporation and crop factors for Upington and Vredendal.
|
Month |
Pan evaporation (mm) |
Crop factor |
Evapotranspiration (ET) |
ET/day (mm) |
Irrigation needs for drip (95% effective) |
Irrigation needs for micro (80% effective) |
|
Jan |
199.02 |
0.75 |
149.27 |
4.82 |
149.42 |
179.12 |
|
Feb |
161.84 |
0.70 |
113.29 |
4.05 |
113.43 |
135.95 |
|
Mar |
151.28 |
0.65 |
98.33 |
3.17 |
98.46 |
118.00 |
|
Apr |
107.70 |
0.50 |
53.85 |
1.80 |
53.95 |
64.62 |
|
May |
96.72 |
0.40 |
38.69 |
1.25 |
38.77 |
46.43 |
|
Jun |
66.30 |
0.30 |
19.89 |
0.66 |
19.95 |
23.87 |
|
Jul |
67.58 |
0.30 |
20.27 |
0.65 |
20.33 |
24.33 |
|
Aug |
85.80 |
0.30 |
25.74 |
0.83 |
25.80 |
30.89 |
|
Sep |
127.80 |
0.40 |
51.12 |
1.70 |
51.20 |
61.34 |
|
Oct |
155.31 |
0.50 |
77.66 |
2.51 |
77.76 |
93.19 |
|
Nov |
185.70 |
0.65 |
120.71 |
4.02 |
120.84 |
144.85 |
|
Dec |
209.87 |
0.75 |
157.40 |
5.08 |
157.55 |
188.88 |
Pan evaporation and crop factors for De Doorns.
|
Month |
Pan evaporation (mm) |
Crop factor |
Evapo transpiration (ET) |
ET/day (mm) |
Irrigation needs for drip (95% effective) |
Irrigation needs for micro (80% effective) |
|
Jan |
183.21 |
0.65 |
119.09 |
3.84 |
119.22 |
142.90 |
|
Feb |
155.12 |
0.60 |
93.07 |
3.32 |
93.19 |
111.69 |
|
Mar |
135.78 |
0.60 |
81.47 |
2.63 |
81.59 |
97.76 |
|
Apr |
74.10 |
0.50 |
37.05 |
1.24 |
37.15 |
44.46 |
|
May |
69.44 |
0.30 |
20.83 |
0.67 |
20.89 |
25.00 |
|
Jun |
39.90 |
0.20 |
7.98 |
0.27 |
8.02 |
9.58 |
|
Jul |
36.89 |
0.20 |
7.38 |
0.24 |
7.42 |
8.85 |
|
Aug |
33.90 |
0.30 |
10.17 |
0.33 |
10.23 |
12.20 |
|
Sep |
104.40 |
0.35 |
36.54 |
1.22 |
36.61 |
43.85 |
|
Oct |
127.41 |
0.45 |
57.33 |
1.85 |
57.42 |
68.80 |
|
Nov |
157.20 |
0.55 |
86.46 |
2.88 |
86.57 |
103.75 |
|
Dec |
167.40 |
0.60 |
100.44 |
3.24 |
100.56 |
120.53 |
ET-based scheduling accounts for variations in weather conditions and vine water demand throughout the growing season to provide a dynamic approach to irrigation management. ET-based scheduling requires access to accurate weather data and may involve more complex calculations compared to other methods. It also assumes uniform water distribution and soil moisture availability, which may not always be the case.
Tensiometers:
A tensiometer is a tube with a ceramic tip (see the Figure below). They come in different lengths: 30 cm, 60 cm, and 90 cm. They are “planted” in the soil at the border of the irrigation area. The tensiometers are then filled with water and closed. As the soil dries out, a vacuum develops in the tube, which is registered on a dial. Although they are “old school” technology, they are still in use.
A tensiometer is used to indirectly measure the soil moisture tension
The optimum tensiometer readings for different soils.
|
Month |
Max. tensiometer reading at 60cm depth |
|
|
<50 mm/m (sandy) |
>50 mm/m (loam/clay) |
|
|
Jan |
30 |
50 |
|
Feb |
30 |
50 |
|
March |
40 |
60 |
|
April |
50 |
70 |
|
May |
50 |
70 |
|
Jun |
50 |
70 |
|
Jul |
50 |
70 |
|
Aug |
40 |
60 |
|
Sept |
30 |
50 |
|
Oct |
30 |
50 |
|
Nov |
30 |
50 |
|
Dec |
30 |
50 |
Plant-based scheduling:
Plant-based scheduling involves monitoring plant water status or physiological indicators to determine when irrigation is needed. Methods such as leaf water potential measurements, stem water potential measurements, and canopy temperature measurements are used to assess plant water stress levels. Irrigation is scheduled when plants show signs of water stress.
Plant-based scheduling provides direct feedback on plant water status, allowing for timely irrigation decisions based on actual plant needs. Plant-based monitoring methods may require specialised equipment and expertise to implement. Interpretation of plant water status measurements can be subjective and may vary depending on environmental conditions and vineyard practices.
Combination methods:
Combination methods combine multiple factors, such as soil moisture, weather data, and plant water status, to determine irrigation timing and amounts. These methods integrate data from various sources, such as soil moisture sensors, weather stations, and plant monitoring devices, to develop comprehensive irrigation scheduling models.
Combination methods leverage the strengths of different approaches, providing more accurate and robust irrigation scheduling recommendations. Combination methods may require more resources and technical expertise to implement and maintain compared to individual scheduling methods. Integration of data from multiple sources can also introduce complexity and potential for errors.
By selecting the most appropriate scheduling method based on vineyard characteristics, growers can make informed irrigation decisions, minimise water waste, and maximise grape quality and yield. Regular monitoring, evaluation, and adjustment of the scheduling programme are essential for achieving optimal results and ensuring long-term vineyard sustainability.
D. Scheduling and Water Availability
Adjusting drip irrigation scheduling programmes based on water availability scenarios is crucial for optimising water use efficiency and crop productivity while conducting sustainable irrigation practices.
Low water availability:
- Reduce irrigation frequency by extending the interval between irrigation events to conserve water.
- Apply water for longer durations during each irrigation event to ensure adequate moisture penetration into the root zone.
- Concentrate irrigation during critical growth stages such as flowering and fruit development to minimise water stress and yield losses.
Moderate water availability:
- Adjust irrigation frequency and duration based on crop water requirements and soil moisture levels measured through sensors or field observations.
- Grapevines may benefit from deficit irrigation in some instances. Strategically apply water below full crop water requirements during non-critical growth stages to optimise water use without compromising yield.
- Regularly monitor soil moisture levels and crop conditions to make timely adjustments in irrigation scheduling as needed.
High water availability:
- Fine-tune irrigation scheduling to prevent overwatering and minimise water wastage.
- Utilise advanced technologies such as drip emitters with variable flow rates and soil moisture sensors to precisely match irrigation applications with crop water needs. This is known as precision irrigation.
- Explore options such as fertigation (combining fertiliser application with irrigation) to enhance nutrient uptake efficiency and minimise nutrient leaching.
E. Irrigation Scheduling Devices
Types of scheduling devices:
- Basic controllers: These controllers allow users to set simple irrigation schedules based on fixed time intervals or clock-based programmes.
Time-based controllers control the flow of water based on a fixed schedule
- Weather-based controllers: Also known as “smart” controllers, these devices automatically adjust irrigation schedules dynamically based on real-time weather data, including temperature, humidity, solar radiation, and rainfall.
- Soil moisture-based controllers: These controllers rely on data from soil moisture sensors to determine when and how much to irrigate, ensuring that water applications are tailored to the actual moisture needs of the soil and plants.
- Flow-based controllers: These controllers monitor water flow rates and can detect leaks or malfunctions in the irrigation system, helping to prevent water wastage and optimise system performance.
Features:
- Programmability: Users can define irrigation schedules and set parameters such as start times, duration, and frequency of irrigation events.
- Remote access: Many modern controllers offer remote access capabilities, allowing users to monitor and adjust irrigation settings from smartphones, tablets, or computers, even when they are away from the vineyard.
- Integration: Several controllers can integrate with other agricultural management systems, such as soil moisture sensors, weather stations, and ET models, to optimise irrigation scheduling and water management.
- Water conservation: By delivering water more efficiently and avoiding over-irrigation, controllers help conserve water resources, reduce water waste, and minimise environmental impact.
Evaluating and improving:
The efficiency and accuracy of irrigation controllers can be evaluated and improved through various methods and strategies, such as:
- Field testing
- Calibration
- Data analysis
- Adjustments and optimisation
- Continual monitoring and improvement
Field testing involves assessing the actual performance of the irrigation system under real-world conditions. One method of field testing is to conduct irrigation audits using catch cans or cups placed at various locations throughout the vineyard. Catch cans collect water during irrigation events, allowing growers to measure the uniformity of water distribution across different areas of the vineyard. Measure the depth of the water in the cans in mm at the end of the irrigation cycle. Make sure that the measuring device starts at 0 mm. By comparing the amount of water collected in each catch can, growers can identify areas with insufficient or excessive irrigation and adjust the system accordingly.
Calibration involves adjusting and fine-tuning the settings of irrigation controllers and related equipment to ensure accurate and precise operation. Calibration may include adjusting the flow rates of emitters or drip lines, setting the run times for valves or pumps, and verifying the accuracy of sensors and measuring devices. Flow meters, pressure gauges, and other components of the irrigation system should be calibrated regularly to maintain accuracy and reliability. Soil moisture sensors and weather stations may require calibration to account for changes in environmental conditions or sensor drift over time.
After conducting field tests and calibrations, growers analyse the collected data to evaluate the performance of the irrigation system. Data analysis may involve comparing actual irrigation application rates with target rates specified in the irrigation schedule. Growers also assess the uniformity of water distribution, soil moisture levels, and plant responses to irrigation to identify areas for improvement.
Based on the results of field testing and data analysis, growers adjust the irrigation system to optimise its performance. This may include fine-tuning irrigation schedules, adjusting emitter spacing or flow rates, repairing or replacing faulty components, and optimising the placement of sensors and monitoring devices. Growers may also explore advanced irrigation technologies, such as precision irrigation systems or automation solutions, to further improve efficiency and accuracy.
Field testing and calibration are ongoing processes that require continual monitoring and adjustment to ensure the long-term effectiveness of the irrigation system. Growers should regularly reevaluate their irrigation practices, update their irrigation schedules based on changing conditions, and implement modern technologies or techniques as they become available.
F. New Water Use Technologies
New irrigation water use efficiency technologies are continually emerging to address the growing need for sustainable water management in agriculture. These advancements leverage innovative approaches and innovative technologies to optimise water use, improve crop yields, and minimise environmental impact. One notable area of development is the integration of precision irrigation systems with advanced sensors and automation technology. Precision irrigation systems, such as drip irrigation and micro-irrigation, deliver water directly to the root zone of plants with high precision, minimising water losses due to evaporation, runoff, and deep percolation. By combining these systems with soil moisture sensors, weather stations, and remote monitoring capabilities, growers can precisely tailor irrigation schedules and water applications to match the specific needs of crops and soil conditions. This approach maximises water use efficiency by ensuring that water is applied only when and where it is needed, thereby reducing wastage, and optimising plant growth.
Another promising technology for improving irrigation water use efficiency is the development of smart irrigation controllers and management systems.
Smart irrigation controllers automatically adjust irrigation according to monitoring data from various sensors
These devices utilise real-time data from sensors, weather forecasts, and soil moisture models to dynamically adjust irrigation schedules and optimise water delivery. Smart controllers can automatically respond to changing environmental conditions, such as temperature, humidity, wind speed, and rainfall, to fine-tune irrigation timing, duration, and frequency. Some advanced systems also incorporate machine learning algorithms and predictive analytics to anticipate future water requirements based on historical data and crop growth patterns. By optimising irrigation scheduling in this manner, smart controllers help minimise water stress, improve crop health, and conserve water resources, enhancing overall water use efficiency in agricultural operations.
Additionally, the development of remote sensing technologies offers new opportunities for monitoring and managing irrigation water use at large spatial scales. Remote sensing platforms, such as satellites, drones, and unmanned aerial vehicles (UAVs), can collect high-resolution imagery and data on crop health, soil moisture, and water stress across vast agricultural landscapes. These data can be processed using advanced algorithms and machine learning techniques to generate insights for optimising irrigation practices. For example, remote sensing data can be used to identify areas of water stress or over-irrigation within a vineyard or field, allowing growers to target water applications more effectively and efficiently. By integrating remote sensing technologies into irrigation management strategies, growers can make informed decisions that improve water use efficiency, reduce input costs, and enhance sustainability in agriculture.
Furthermore, advancements in irrigation system design and materials are contributing to greater water use efficiency in agricultural irrigation. For example, the development of low-pressure drip emitters, high-efficiency pumps, and precision application technologies enables growers to deliver water with minimal energy input and losses. The use of recycled or alternative water sources, such as treated wastewater or rainwater harvesting systems, can supplement traditional irrigation supplies and reduce reliance on finite freshwater resources. Moreover, innovations in soil moisture retention and conservation techniques, such as mulching, cover cropping, and soil amendments, help improve water infiltration and retention in the root zone, reducing the need for frequent irrigation and promoting healthier soil ecosystems. Collectively, these advancements in irrigation technology and practices offer promising solutions for enhancing water use efficiency, sustainability, and resilience in agricultural systems, supporting the long-term viability of food production while mitigating the impacts of water scarcity and climate change.