Back to - Step 4.3 - What needs to be considered in the planning, design, cost and management of subsurface drip irrigation (SDI)?
18.104.22.168 Which manufacturer is the best?
There are a number of SDI manufacturers in the market. Some manufacturers provide a significant range of types of supply lines and a variety of configurations of emitters whilst others cater for more specialist needs. For example, less expensive, thin walled dripper tape meets the requirements of vegetable producers, while more resilient, thicker walled drip tapes are commonly used for perennial horticulture, viticulture, turf production and for parks and gardens. Thicker, more rigid drip tape improves life expectancy and helps counter damage by insects, rodents, stock, vehicles and disturbance associated with planting, harvest and seedbed preparation.
The best approach is to seek quotes from a range of suppliers before committing to a particular system and to evaluate options carefully with respect to your specific needs. Seek advice from other farmers with experience of particular manufacturers, suppliers and installers. A key factor to consider is the quality of ongoing backup and expertise provided should issues arise, particularly if you are new to these systems. You will want a good and ongoing relationship with experienced specialists in the technology, who are available when you need them. The cheapest price is unlikely to be the best option in the long run. In general it does not pay cut costs by mixing SDI components from rival manufacturers. Experience indicates that many of the components are not easily interchangeable, however particular manufacturers may have products with strengths in one area whilst others excel somewhere else.
22.214.171.124 What is the capital cost involved?
The initial investment for SDI is high and can vary considerably depending on the size, layout and topography of the field, proximity to power and water infrastructure, drip tape and emitter spacing, as well as the quality and price of individual components. Installation costs increase if the system needs complete automation and if fertigation equipment is to be included. Similarly, associated earthworks such as the construction of an on-farm storage dam or surface drainage system will also increase the investment. Installation cost will also increase if a new electricity connection is required. Initial per hectare cost is likely to be higher if a staged development is planned, because many key components such as pumps and filtration may be specified at capacities to suit the final development.
An economic analysis for grazed SDI pasture in northern Victoria found that the installation cost was approximately $8,950/ha (2008 prices) or around $226,000 for 25 ha (Heard and Finger 2009). This estimate used Python 250 tape (0.68 mm thickness) with non-pressure compensating emitters at 0.4 m spacing and a tape spacing of 1.0 m. The cost to access electricity was around $5,000. The capital costs for your farm will be different, depending on the design specification of the system and cost of the components. For example, increasing the distance between tapes to 1.4 m can reduce the initial capital cost by $1,000/ha, but increase the pumping cost (Table 5) to irrigate the area between tapes, failure of which can result in pasture striping and yield decrease.
126.96.36.199 How much does it cost to run the system?
The operating cost of the system depends on the block size and layout, pressure head to be maintained and pumping hours. These costs can vary widely depending on the system configuration. For example, for a seasonal water application of 6.5 ML/ha to grow pasture in northern Victoria, pumping cost increased by 150% and 327% when the tape spacing increased from 0.6 m to 1.0 m and to 1.4 m respectively (Table 5). The scale of the variation was in part due to increased duration of pumping needed to deliver the required irrigation depth through fewer drip lines and emitters per hectare, but also because the longer duration irrigations could not be completed within periods of off-peak electricity tariff.
Table 5. Impact of tape spacing on operating costs (Heard and Finger 2009)
Heard and Finger (2009) also compared SDI system labour costs with border-check irrigation of a 25 ha pasture. It was estimated that approximately 274 hours/year were required to run the border-check irrigation system, while with SDI the labour required was 98 hours/year (ie. 30 hours/year for irrigation scheduling and monitoring, 20 hours/year for flushing the system and 48 hours/year for acid applications).
188.8.131.52 Is there a trade-off between capital and operating cost?
Within any irrigation system there are always trade-offs between initial capital and ongoing operating costs. Decisions made at the SDI system design stage can have lasting financial impacts affecting the viability of the investment, so it will pay to understand these trade-offs at the outset. The key trade-offs relate to power supply, pump sizing, pipe sizing, and dripper line and emitter spacing. Operating costs will be lower if the system design allows irrigations to be completed during off-peak tariff periods. An inappropriate pump size can also increase the operating cost. If your plan is to stage the installation of the SDI system, your initial capital investment may be higher in order to install a pump capable of servicing the final development area and avoid the need to replace the initial pump. Generally, increasing the pipe and dripper line diameter will incur higher capital costs but reduce operating costs due to lower friction losses. Similarly, increasing the width between the drip tapes can reduce the capital cost (Table 6) but needs substantially more time to run the pump to fully irrigate the crop (Table 5). Again, consult other local growers who have had experience with these systems and learn from their experience.
Table 6. Impact of tape spacing on capital and operating costs (Heard and Finger 2009)
|Tape spacing (m)||Hours required to apply 8 mm||kWh required to apply 8 mm||Pumping cost per 8 mm irrigation ($)||Pumping cost for season when 8.5 ML/ha applied ($)||Pumping cost for season when 6.5 ML/ha applied ($)|
184.108.40.206 What will be the net economic return?
Given the high initial investment cost of these systems, SDI is most likely to be viable on the best soils, with good management achieving high levels of production growing a high value crop. The economics of SDI systems is highly variable, depending on the capital, operating and maintenance costs of the system, the costs associated with production and harvest of the crops grown with the system, yield and the market value of the crops.
A partial budget analysis over a ten year period for a 25 ha SDI pasture in northern Victoria has been prepared by Heard and Finger (2009). The irrigation water applied to perennial pasture was 8.6 ML/ha per year. Assumed annual average perennial pasture consumption was 14 tonnes of dry matter per hectare (t DM/ ha). The analysis showed that an increase in pasture production by 4 t DM/ha at a value of $400/t DM would be required to make the system economically viable (Table 7). An increase in pasture consumption alone would not justify the investment and risk involved in installing this technology for pasture production
In the Murray irrigation region, increases in production of 4% and 10% have been estimated to be needed to justify converting from furrow irrigation to SDI for vegetable crops if the gross return of the crop is $5,000/ha or $12,500/ha respectively. For lucerne, increases in production of 11% and 28% are required if the gross margin is $2,000/ha or $5,000/ha respectively. Similarly for summer crop production, increases of 25% and 10% are required when gross margins are $2,000/ha and $5,000/ha (Brook, 2007). The capital and operating costs used in these analyses were based on average costs taken from the literature and the past experience of the project team. They provide a useful guide, but the results do not necessarily mean that one particular irrigation system is better than the other under all conditions. Specific cases will usually require a specific and detailed analysis.
Table 7. Extra pasture grown and internal rate of return for SDI (Heard and Finger 2009)
|Tape spacing (m)||Total capital cost ($/ha)||Pumping cost per 8 mm/ha irrigation ($)||Pumping cost for season when 8.5 ML/ha applied ($)||Pumping cost for season when 6.5 ML/ha applied ($)|
|Extra pasture grown (t DM/ha)|
|Value of extra pasture ($/t DM)|
|Years to break even|
|Internal rate of return (%)|