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Subsurface drip irrigation (SDI) is the most advanced method of irrigation

By Matt Clift

Did you know that subsurface drip irrigation (SDI) is the most advanced form of irrigation available to farmers today? SDI provides benefits across the entire farming operation beyond irrigation. It is for advanced growers who want to maximize their farm profits.

Although SDI can take various forms, here we are referring to drip irrigation that is installed generally at a depth of 30 cm (12”), for multi-season use with a lifespan of 10 – 20 years and beyond.


Addressing the challenges of labor shortages

Most people would expect that an article about drip irrigation would start with water use efficiency. However, when we talk to growers around the world, one of the biggest challenges we continually hear is their difficulty in sourcing and keeping good labor.

On the assumption that labor availability is not going to improve anytime soon, farmers need to adopt practices that reduce their reliance on labor. This is where SDI steps in.

To paint two very different pictures:

Picture 1: You need to apply fertilizer to your block. First you arrange a tractor prepared with the correct application implement. The fertilizer needs to be loaded and an operator needs to drive all the fields of your farm to apply the fertilizer. The tractor needs re-fueling and continual maintenance requiring more labor.
Picture 2: You have SDI and need to fertigate your block. You have fertilizer tanks prepared with the blend of fertilizers you need to apply. You press a button, the fertilizer is injected into the irrigation system and is applied directly to the root zone of the plants.

This is one example, but the same labor saving concept applies across numerous farm practices. From setting up siphon pipes for flood application, to un-bogging a pivot, to setting up solid-set sprinklers, the list goes on of the labor needs that are eliminated with SDI.

Even spraying herbicides for weeds in the interrow is reduced. SDI applies irrigation water below the soil surface. Overhead irrigation (pivots, sprinklers, etc) irrigate the whole field and encourage weed growth in the interrow. This creates extra work – attach sprayer to tractor, fill with herbicides, drive the fields, etc.  Many tasks add up to a lot of work.


Healthier crop = healthier profit

Study after study shows that SDI delivers superior yield results when compared to other irrigation methods. Why? Because the crop is healthier.

Most irrigation methods involve irrigating the soil to saturation point. In this state the plants are literally drowning as there is no oxygen in the soil. Then the soil dries to near wilting point, and the process is repeated.

SDI irrigation works on a Goldilocks method – not too little, not too much. The principal is a small application of water, delivered frequently. This keeps the soil moisture in the optimum range for uptake by the crop.

In addition to saving water through less leaching and evaporation, it provides the best conditions for growth of the crop. Water applied below the surface encourages the roots to ‘chase’ the water, leading to a stronger and healthier root structure.

Furthermore, water on the canopy is a recipe for fungal disease. Every overhead application (pivots and sprinklers in particular) increases this risk of disease and subsequent crop loss.


Input cost savings

We have already mentioned labor, and water saving is an obvious advantage with no loss to evaporation or run off. But you should also consider other savings such as fertilizer and energy costs.

Fertilizer cost is reduced simply by the efficiency of applying directly to the root zone. The saving can be significant (up to 30%).

Energy cost is reduced by the lower pressure requirement of drip irrigation compared to pivot irrigation in particular. Where a pressure requirement for a pivot is approximately 35 MHD (50 PSI), the pressure requirement for drip is only 9 MHD (13 PSI).   After head loss across the system is accounted for, the difference calculates to 72 MHD (102 PSI) for pivots and 53 MHD (75 PSI) for drip on the above assumptions. This is a big difference of pumping pressure which is then compounded because you also need to apply more volume with pivots due to less efficiency of application. So more pressure and more volume = more cost.


A note about financial analysis

So far we have talked about benefits, but it is important to make a comment about how to compare costs.

A common mistake when evaluating SDI is to use the wrong financial methodology. An SDI system will be more expensive than most other irrigation systems in installation. However, to accurately compare systems, you need to look at the lifetime cost. Unlike normal drip irrigation, in SDI you do not need to replace the tape every season. When comparing to pivots, you need to compare the long-term operation and maintenance costs. Pivots require expensive maintenance of gearboxes and tires and also incur costs mentioned above including labor, pumping costs, fertilizer and water. All this adds up and should be accounted for in conjunction with efficiency gains of SDI including higher yield that you achieve with SDI.


Where to next?

A good first step is to read our brochure on SDI which can be downloaded here.

Second. An advanced irrigation system needs an advanced irrigation company with the expertise to deliver SDI irrigation systems. Rivulis has many years of experience in delivering SDI systems that don’t just work for 1 year, but continue to deliver results for 20+ years. Find out more by talking to your local Rivulis representative.

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