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Understanding irrigation costs in drip and SDI systems

Richard Arias for Progressive Forage Grower Published on 02 May 2016

The ag industry is one that doesn’t stand still. Everything from new technology to unexpected changes in weather affects operations and brings growers both new challenges and opportunities. Despite continual change, one thing remains a constant for all: the value of the dollar.

Smart growers know that achieving the most cost-effective operation is a balance of keeping costs in check while ensuring quality, yields and profit aren’t compromised. In the most general terms, this concept of maximized operation is best known as resource-use efficiency (RUE). Along with that, and most notably for alfalfa growers, the desire for better water-use efficiency (WUE) is top-of-mind.

Alfalfa growers looking at drip and subsurface drip irrigation (SDI) systems have already taken the first step toward greater RUE and WUE. These pressurized systems reduce water losses to runoff, evaporation and general over-irrigation most commonly seen in flood and traditional sprinkler methods, leading to greater WUE.

And over-irrigation wastes more than water; it also wastes fertilizer, energy and other precious resources and can often result in water and fertilizer traveling where it’s unwanted. In California, for example, nitrate poisoning of groundwater is a major concern. This is why growers looking to attain better RUE seek out these newer methods too.

Drip and SDI systems typically come at a greater initial cost per acre, so it’s often assumed that they’re more expensive to operate too. But that’s only one piece of the overall cost-of-irrigation puzzle. To determine if drip or SDI is the best solution for the bottom line, the grower must understand the complete cost of irrigation that comes with these types of systems.

Pros and cons of drip irrigation lateral and submain configurations

Click here or on the image above to view it at full size in a new window. (PDF, 43 KB )

Because every operation is different, there isn’t a one-size-fits-all formula to calculate this. There are, however, five primary areas one can explore to determine total cost of irrigation.

Permanent or seasonal

Drip and SDI systems consist of submains that deliver water from the source to lateral lines, which supply water to the crop’s root zone. Growers have the choice of a seasonal or permanent submain setup as well as seasonal or permanent lateral lines or a combination, leaving four possible options. Each comes with pros and cons that affect the overall cost of irrigation.

For alfalfa growers, the most commonly recommended setup is permanent submain (PVC pipe) and permanent lateral lines. When designed, installed and maintained properly, these systems are used successfully for 20-plus years.

Because alfalfa is grown for years at a time, with multiple cuttings in a season, this permanent setup offers a host of benefits, including the long life expectancy, automated flushing capabilities and overall reduced labor. As a trade-off, these systems typically come with a higher initial cost and maintenance requirements.

Compare this to a seasonal submain and seasonal lateral line configuration. This type is most popular for vegetable and fruit growers with short crop cycles, like strawberries, since the system allows for easy germination or plant setting, is portable and comes with the lowest initial cost.

And because of the short crop cycles, these growers don’t need the long life expectancy, hallmarked by the permanent configuration, and therefore wouldn’t benefit from the investment.

Component quality

Closely related to the choice of a seasonal or permanent system, the system’s components also affect the overall cost of irrigation.

The concept is simple: Higher-quality components last longer and, aside from misuse or neglect, won’t need frequent repair or replacement compared to cheaper components. Each grower must determine the life expectancy desired from the system, then weigh the cost-to-benefit ratio of different price points.

Alfalfa growers who choose the most common setup, permanent submain and permanent laterals, are advised to invest in high-quality, long-lasting components, like higher mil-wall-thickness drip tape with high-quality emission devices from reputable manufacturers. While this is another cost that’s higher up-front, it pays off later.

Let’s again compare the strawberry grower with a seasonal system. Drip tape in strawberry fields is often recycled after just one crop cycle, so the strawberry grower wouldn’t necessarily be advised to invest in a high mil-wall-thickness drip tape like an alfalfa grower should.

However, the grower is advised to invest in high-quality, low mil-wall-thickness drip tape from a reputable manufacturer. Poor-quality drip tape should not be confused with unnecessary features in a drip tape.

There are other components on which a grower, regardless of crop type, cannot compromise, as they directly relate to a significant factor outside his or her control, such as water – or more specifically, water quality.

Water quality determines how many filters are needed and the demands those filters must be able to meet. The more sand, organic matter and other particles naturally occurring in the water, the more filters, higher-quality filters and filter maintenance are required – and the higher the cost for the overall filter system.

Along these same lines, the size and quality of the system’s pump is directly related to what’s in the water. A simpler centrifugal pump is lower both in initial and operating costs versus a more powerful trash or diaphragm-style pump.

Emission uniformity

Just as it sounds, an efficient system with high emission uniformity applies water evenly throughout a field. Too little water compromises quality and yield while too much water, as mentioned earlier, is wasteful and often applies water and fertilizer where unwanted, so emission uniformity is directly tied to RUE and WUE. It’s also directly tied to the cost of the system.

A system designed to achieve high emission uniformity usually comes at a greater cost because it utilizes higher-quality emission device components like drip tape and drip line, requires accessories like pressure gauges and water meters, and may require more or larger submains to reduce pressure losses.

And this is only part of the equation. Ongoing maintenance, monitoring and adjusting of the system is required to ensure its emission uniformity potential is being met after the initial investment has been made, meaning additional resources – and costs – must be allocated.

This may sound expensive, but many growers have found the return on investment time frame of a well-designed, installed, operated and maintained drip system is relatively short due to the resulting increase in crop yield and quality (income) and reduction in required inputs (costs).

As water scarcity increases, this return on investment time frame will continue to decline. While a lower emission uniformity system may have lower up-front costs, this “savings” can quickly be lost to increased operational cost from over-irrigating to mask poor uniformity and the cost from compromising crop quality, uniformity and yield.

Irrigation schedule

Although it may not seem like it would, the grower’s irrigation schedule is directly tied to the operation’s overall cost of irrigation.

Alfalfa is a crop that, at most stages of growth, allows growers flexibility in choosing an irrigation schedule. On one end of the spectrum, a grower may choose daily, frequent, short intervals. On the opposite end, a grower may choose to run the system only every few days, for longer time periods, applying multiple days’ worth of water in a single day.

A grower willing to operate the system 22 hours a day (allowing two hours for unexpected downtime and breaks) can run a system that’s less expensive overall than a grower wanting to run a standard eight-hour day or less than daily.

A system designed to apply the daily water requirements over 22 hours has an overall lower flow rate and thus smaller pumps, pipes and values compared to a system that applies the daily water requirement in an eight-hour day or less frequently. However, operating more hours in a day might mean other costs go up.

Also, adding an automation system should be considered. While they come with an up-front cost, automation systems save time and labor. And, when managed properly, contribute to better RUE, WUE and overall profitability.

Regional conditions

Finally, there are a handful of factors that tie into an operation’s irrigation costs that are exclusively tied to location.

Again, water is a major factor. First off, water can be as high as $1,800 per acre foot in some areas. Even free water has a cost tied to it – energy. Water usually needs to be pumped; the question is how far and from what depth.

The greater the distance and depth from the original water source, the more in energy costs to move it. And energy costs vary from location to location as well.

Flat terrain is much cheaper to irrigate versus hilly. A system running in hilly terrain needs more submains, or pressure-compensating laterals – and perhaps more sophisticated control valves.

Conclusion

With so many variables affecting cost of irrigation, it’s nearly impossible to state that one method is the best for every grower. Considering RUE and WUE is a great place to start when weighing all the variables that affect the total cost and determining if drip or SDI is the best option.

Remember, spending $200 less per acre on a system sounds like a huge cost savings, and it would be easy to make a decision based on the initial investment cost. But keep in mind – that initial savings can easily be eaten up in just one season due to higher operating costs and missed ROI opportunities.  end mark

Additional contribution to this article was provided by Inge Bisconer, technical marketing and sales manager for Toro Micro-Irrigation.

Richard Arias is general manager of sales with RDO Water. Email Richard Arias

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