Lecler was the "mastermind" behind the project, who visualized the potential of ASFI and then worked to implement the system into the development of this project. The valve was then implemented according to design in the ASFI system during a trial at the University of KwaZulu-Natal's Ukulinga Research Farm.
INTRODUCTION
The performance of the ASFI system relative to a reference drip irrigation system was assessed by evaluating agronomic, economic and engineering considerations. These included: irrigation performance tests (Section 4.2), soil moisture monitoring analysis (Section 4.3), a yield analysis of the harvested crop (Section 4.4) and an economic comparison of ASFI and subsurface drip (SSD) irrigation systems (Section 5.4).
IRRIGATION SYSTEMS AND PERFORMANCE
Irrigation Performance Indicators
Vrz = volume of water per furrow spacing that is actually stored in the root zone (m3/m). AE is the amount of water per furrow spacing that is stored in the root zone divided by the total amount of water applied per furrow spacing (Walker, 2003).
Furrow Irrigation
- Factors impacting the performance of furrow irrigation systems
- Water application phases and irrigation performance
If the main slope of the land is too steep, furrows can be aligned across the main slope, thus reducing the front slope (Crosby et al., 2000). As illustrated in Figure 2.2, the advance phase begins when the irrigation event is first applied to the furrow and ends when it reaches the downstream end of the furrow.
Short Furrow Irrigation (SFI)
- Micro-flood: a type of Automated Short Furrow Irrigation (ASFI)
- Automation
A variation in the inlet pressure of the system will result in a system failure (Jumman and Mills, 2005). The valve is held in the closed position by the pressure of the water in the main pipe.
Conceptual Comparison of ASFI with Other Irrigation Systems
- ASFI compared to sprinkler irrigation
- ASFI compared to drip irrigation
For example, the field application efficiency shown in Figure 2.6 and proposed by the ARC (2003) is equivalent to the AE proposed by Mirriam and Keller (1987) and used in Chapter 2.1 The AE proposed by Mirriam and Keller (1987) in Chap. 2 is therefore different from the AE shown in Figure 2.6 and proposed by the ARC (2003). Koegelenberg and Reinders (2001) conducted studies in six regions of South Africa on the performance of drip irrigation systems under field conditions.
Computer Models for ASFI Design
The most difficult inputs to determine adequately are infiltration characteristics and furrow inflows, which are also the most sensitive inputs to the SIRMOD model (McClymont et al., 1996). 2006) found that furrow irrigation was adequately predicted by SIRMOD for soil conditions in MIA, with SIRMOD-predicted infiltration rates and measured infiltration rates being strongly correlated (r.
UKULINGA FIELD TRIAL
Site Investigation and Selection
ASFI Initial Development and Testing
- System requirements
- Preliminary field tests
- Development of a prototype valve
This is done to evaluate the impact of changing the flow rate on the combined efficiency of the system. However, the pressure in the valve allows the valve to remain open with the piston in the upper position, as shown in Figure 3.9c.
Trial Establishment
- ASFI design
- Drip irrigation design
- Land preparation
- Furrow shaper
- Planting and furrow shaping
- Furrow slope survey
- Irrigation installation
The ASFI system was then designed with the main line along the top of the field (as in Figure 3.14), with the lateral running perpendicular to the main line, down the slope. The seedling was planted along the length of the field with a slope of approx. 1:40.
Trial Management and Monitoring
- Irrigation scheduling
- Soil moisture monitoring
- Fertigation
One of the assessment tools was to assess trends in soil moisture over crops. Due to the different response times of the three logger channels, each channel was individually calibrated in the laboratory using watermark sensors. The watermark sensor was then placed in the hole using a PVC pipe of the same diameter as the top of the watermark sensor.
The configuration of the watermark sensors in the drip processing is shown in Figure 3.22b. One end of the tube was then connected to the venturi and the other end to a small filter.
Harvesting procedure
In March 2008, no fertilizer was applied because it would not significantly affect the sucrose content of the cultivated sugar cane. A total of approximately 1.2 bags of urea was used evenly for each irrigation. Twelve random samples of stems, approximately two stems from each bundle, were selected from each of the five species for each plot and weighed as shown in Figure 3.25.
The samples were then sent to the South African Sugar Research Institute (SASRI) laboratory for sucrose content analysis. The weight of the sugarcane bundles was combined as a total weight for each species selected for harvest.
FIELD TEST RESULTS
Valve Testing
The actual pressure drop across the valve was then measured with different pressures set at the hydrant. The pressure loss through the valve turned out to be 2 to 3 times higher than estimated from theory. The valve was then tested to estimate the pressure range in which it could open at the correct cut-off time.
In this pressure range the valve was able to open and close within the required trip time of 42 minutes. If the pressure is significantly higher than 10 m, it is expected that the valve can work normally.
Irrigation Performance Tests
- ASFI tests
- Drip irrigation tests
- Comparison of the performance of the irrigation systems
This includes the results of the Furrow B5 advance/recession front test at various stages of the crop cycle. A SIRMOD III simulation of ASFI Line 2 revealed that although the flow rate for Furrow D4 is significantly below the optimum value, the factor to which DU is most sensitive (Section 3.2.2), the test still produces a DU of 65. A comprehensive evaluation of the SSD irrigation trial was conducted as suggested in Koegelenberg and Breedt (2007).
There was a 6.8% change in sidewall pressure from the mean value of 112.7 kPa for the first line, which was within the acceptable limits of 20% as defined in Koegelenberg and Breedt (2007). BE is the ratio of the mean for the lowest 25% of the flow rate recording to the mean flow rate (or volume/time) recordings.
Soil Moisture Monitoring and Irrigation Scheduling
Front B soil moisture results, in Figure 4.4, had relatively little variation in the stress of Watermarks 1 and 2 and a large stress variation for Watermark 3. This is done for Front C in Figure 4.9, with the soil moisture content scale reversed, with drier soil at the top for easier comparison with the voltage. The soil moisture predicted using SAsched for the ASFI and SSD irrigation treatments is illustrated in Figure 4.10.
The plant water stress level in Figure 4.10 is for the point plot, which is very similar to the plant water stress level for the ASFI plot. The cumulative irrigation of SSD irrigation and ASFI treatment is shown in Figure 4.11.
Crop Yields
The irrigation performance analysis and soil moisture analysis were the first two major facets of the comparative performance analysis of the two irrigation treatments. The comparison of the soil moisture analysis results of the two treatments was inconclusive due to the limited resources and natural variation in soil conditions. From the sucrose sampling, the total weight of the stalks after top and litter was divided by the total weight of the cane before litter and top.
This resulted in a field average fraction of 0.7653, representing the weight of the clean stalks relative to the weight of the stalks together with tops and litter. The center of the green diamond represents the mean of the values for each treatment.
Re-establishment
The next step was to assess whether changes in DU affected soil moisture outcomes and crop yield outcomes. Due to the limited number of watermark sensors, soil moisture analysis using watermark sensors was inconclusive as to whether each of the irrigation systems had better soil moisture trends. However, soil moisture analysis showed that SAsched, the irrigation scheduling tool, accurately predicted trends in soil moisture.
The agronomic and engineering considerations (the irrigation performance analysis, soil moisture analysis and the crop yield analysis) are contained in Chapter 4. The economic considerations are included as a consideration for large-scale applications of ASFI in Chapter 5.
CONSIDERATIONS FOR LARGE-SCALE APPLICATIONS OF ASFI
- Sensitivity to Slopes
- Sensitivity to Flow-rates
- Sensitivity to Soils
- Economics
- Representative ASFI design and costs
- Representative sub-surface drip design and costs
- Life cycle comparison
- Design Considerations
Each of the furrow length options in Sections 5.1 through 5.3 were considered to be theoretically robust. Each of the scenarios in Table 5.1 was tested in SIRMOD III with notes discussed after Table 5.1. The details of the lateral and underwire design calculations are provided as an Excel file named "Sample_design" on the accompanying CD.
Due to the larger pump for the drip system, the network charge for the pump has a higher tariff. The fixed costs of the system are the cost of the drip sides for the drip irrigation system and the cost of the valves for the ASFI system.
DISCUSSION AND CONCLUSIONS
- Site Establishment
- Irrigation Design
- The Automatic Control Valve
- ASFI in the Context of Other Irrigation Systems
- Irrigation performance tests
- Soil Moisture analysis
- Yield analysis
- Economic analysis
- Labour and maintenance requirements
- Project Conclusions
The performance of the ASFI system was assessed relative to a reference drip irrigation system as part of the Ukulinga trial. It is recommended that a drier region should be selected for future comparisons of the ASFI and SSD systems. The purpose of conducting the Ukulinga trial was to compare the performance of the ASFI and reference drip systems.
Adding the burial cost to the ASFI system would significantly increase the capital cost of the system due to the amount of pipe required. The focus of the Ukulinga trial was on the development of a complete ASFI system and not on the optimization of the individual system components, such as the valve.
Evaluation of field irrigation system performance in the sugarcane industry in the south-eastern lowlands of Zimbabwe. Cost estimation procedures for micro, drip and furrow irrigation systems and economic analyzes of appropriate irrigation systems for large and small farmers in the Onderberg/Nkomazi region. The objective of the irrigation design for the ASFI and SSD irrigation system was to use the same water depth for both systems.
Side channels were then designed with a total of 27 water lines on each side, 9 side lines in the upper half of the field and 18 in the lower half. Pressure Pressure Pressure in the required length diameter Diameter o at side P1 Discharge Qemmiter tube Side d1 transmitter tube. Emitter Q Q L Diameter Velocity Hf (HW) Side pressure Number in side in side side side side side slope 1: at (initial segment segment segment segment segment Emitter.
Pressure Pressure in required diameter of length Diameter o Area emmi on lateral P1 Outlet Qemmitter pipe Emmitter pipe lateral d1 pipe A2.
