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What is subsurface drip irrigation and how does it differ from traditional systems?
Over the years, subsurface drip irrigation (SDI) has become one of the most advanced solutions for sustainable water use in agriculture, especially in a context increasingly affected by recurring droughts and growing pressure on water resources. The concept is simple: deliver water and nutrients directly below the soil surface, at root level, through driplines buried at different depths.
When water is distributed in the rhizosphere, it does not evaporate, it does not promote weed growth and it does not cause plant stress. Above all, SDI allows continuous, targeted and invisible irrigation — a major advantage for crops where field accessibility or orchard aesthetics play a crucial role.
Unlike surface or sprinkler irrigation, SDI is based on delivering water exactly where plants can absorb it most efficiently. This technology can be implemented in different ways.
In short-cycle crops, driplines are buried just a few centimetres below the surface, enough to protect them from wind and light field operations. In perennial systems, however, installation is deeper — often 30–40 cm or more — to follow root development and ensure long-term performance.
The optimal installation depth depends on soil hydraulic properties and on the depth and distribution of the crop’s root system.
Water moves through the soil by capillary action: the wetting pattern expands gradually around each emitter, forming a continuous moisture bulb that feeds the roots without dispersion. In SDI, the wetted volume is spherical, increasing the moist soil volume by about 46% compared to surface drip irrigation*, where a semi-spherical pattern forms.
The soil surface remains dry, foliage is not wetted, and soil structure is more stable, less prone to compaction or surface crusting. This represents a complete shift from traditional irrigation approaches and, over the past decades, has revolutionized water management in many orchard and forage crops.
Components of an SDI system
An SDI system is based on the same principles as micro-irrigation but requires particularly high-quality components and precise system design.
The system includes filters, PE pipes and fittings, valves, driplines, air release valves and fertigation units, all engineered by Irritec to ensure efficiency and long service life. When integrated with agrometeorological systems, satellite data, DSS platforms and remote automation, farmers can monitor water distribution and soil moisture in real time, optimizing irrigation scheduling and further reducing waste.
Filtration is always the starting point and one of the most critical elements, as it directly affects system longevity and flow quality. Screen or disc filters and hydrocyclones work together to protect the system from particles and impurities. In underground systems, clogging control is vital, since the network cannot be visually inspected as easily as surface systems.
The same applies to control valves, air vents and automation devices. Air release points prevent vacuum and suction phenomena that could draw soil particles into the emitters, while automation allows shorter and more frequent irrigation cycles — typical of SDI — and precise dosing of fertilizers and biostimulants.
In SDI, fertigation reaches extremely high efficiency levels: nutrients are delivered directly into the root zone, with minimal losses and reduced input quantities.
The core of the system remains the dripline itself. Irritec SDI solutions — such as Multibar® C Rootguard® and Multibar® F AS — are specifically designed to prevent root intrusion and soil particle suction. Unlike thin-walled tapes for seasonal crops, SDI driplines are expected to operate for many years. For this reason, they must feature pressure-compensating emitters, large turbulent flow paths and anti-siphon systems. Mechanical resistance is also essential, as buried pipes are continuously exposed to moisture and temperature variations.
The main benefits of subsurface drip irrigation
Irrigation efficiency is the first major advantage. With a dry surface, evaporation is almost eliminated and water is used directly by the plant. In traditional systems — especially sprinklers — up to 45% of water can evaporate before reaching the soil. With SDI, this loss virtually disappears, achieving irrigation efficiencies of at least 95%*.
Using the same amount of water, subsurface drip irrigates about 46% more soil volume compared to surface drip systems*. This not only improves soil aeration but also avoids saturation, favouring capillary water movement and reducing deep percolation losses.
The result is significant water savings (20–30% compared to traditional systems) and constant water availability for plants. Root systems benefit enormously from this continuity. In crops such as olives, almonds, grapes or hazelnuts, deep and stable moisture promotes denser, stronger roots, less exposed to thermal stress and surface dehydration. Deeper roots mean healthier plants, greater stress tolerance and more efficient nutrient uptake.
Another key benefit is weed control. Since the soil surface remains dry, weeds lose their main water source. This reduces mechanical operations, herbicide use and overall field maintenance. Fungal diseases are also limited, as foliage is never wetted. In sensitive crops such as table grapes, wine grapes, fruit orchards and almonds, this directly improves product quality and reduces the need for plant protection treatments.
Finally, eliminating surface pipes greatly improves field accessibility. Hazelnut orchards, almond groves, intensive fruit orchards and olive groves can be mechanically harvested without damaging the system. SDI also allows irrigation of forage crops during and immediately after mowing, and even while hay is drying in the field. While sprinkler systems cannot operate in these conditions, SDI promotes rapid regrowth and allows more cuts per year.
For lawns and green areas, SDI also offers clear aesthetic benefits: no visible pipes, no obstacles and full usability of the area even during irrigation.
Key design principles for SDI systems
Designing an SDI system starts from a simple principle: water must reach the zone where plants actually absorb it. To achieve this, several factors must be considered, including soil texture, water availability, crop type and plant spacing.
Sandy soils allow water to move downward more quickly and therefore require shallower installation depths. Silty or clay soils allow deeper installation. In mature orchards and vineyards, depths of 30–40 cm are common, while in highly draining soils shallower depths are preferred.
The spacing between driplines is also crucial: it must allow the formation of a continuous wetting strip covering the entire root zone. Another design choice concerns single or double lines: in tree crops with wide spacing, two lines per row improve early plant establishment and promote more balanced root development.
All these elements help create a system that combines water savings, uniform distribution and harmonious plant growth.
Burying the driplines: how it works and why it matters
Burying the driplines is a critical operation that largely determines system performance. A specialised trencher opens a narrow slit, places the dripline at the desired depth and closes the soil in a single pass.
During installation, it is essential to ensure that the pipe is laid smoothly, without stretching or bending, and that no soil enters the line. Proper installation prevents clogging, pressure losses and irregular water distribution.
The final section of the line is left above ground to allow connections to manifolds or flushing collectors. In sloping or irregular fields, air release valves and flushing points are added to maintain system cleanliness and uniformity over time.
Durability, maintenance and sustainability: why SDI is a long-term solution
One of the main reasons farmers and technicians choose SDI is its durability. A well-designed system with dedicated driplines can operate for over 20 years. Burial protects pipes from UV radiation, extreme temperatures and accidental damage.
Irritec recommends designing SDI systems in closed-loop layouts, with secondary pipes feeding the driplines and a flushing collector at the opposite end. Air release valves are installed at the highest points and flushing valves at the lowest points of each irrigation block.
System cleaning is carried out by opening the flushing valves, especially in the lowest areas of the field. The flushing collector should be installed deeper than the driplines and sized to guarantee flow velocities of at least 0.4–0.6 m/s. Ideal pressure at the flushing valve should be around 0.8–1.0 bar.
Flushing operations temporarily increase flow rate and operating pressure to clean emitter labyrinths. System design should therefore account for this additional demand, or include auxiliary power and flow sources for flushing operations.
In large irrigation blocks, dividing the flushing collector into multiple sections is recommended to maintain adequate pressure and flow velocity.
From an environmental perspective, SDI also improves soil sustainability. By limiting the downward transport of fine particles, it promotes more stable soil structure, better aeration and improved oxygen availability for roots. Lower water volumes also reduce salt accumulation in the soil — a common issue in irrigated areas with medium to high salinity water.
FAQ – Frequently asked questions about SDI
How long does an SDI system last?
With driplines specifically designed for burial, such as Rootguard®, root intrusion is prevented at source. System lifespan depends on material quality, but a well-managed SDI system can exceed 20 years. Performance is monitored through flow meters, soil moisture sensors and periodic inspections at the system headworks.
Can SDI be used in all soil types?
Yes, SDI can be applied in all soil types, provided that spacing between driplines, emitter flow rates and installation depth are correctly designed according to soil hydraulic properties.
Can reclaimed wastewater be used with SDI?
SDI is one of the safest and most effective methods for applying reclaimed urban wastewater in agriculture. Subsurface distribution eliminates contact between operators and edible plant parts, reducing health risks. Moreover, since emitters remain constantly moist, calcium carbonate crust formation is limited, reducing clogging risks.
What are the main rules for SDI design and installation?
Irritec recommends closed-loop systems with air release valves at the highest points and flushing valves at the lowest points of each irrigation sector. For proper system design, it is always advisable to consult Irritec specialists. For any support, contact us here.
*The information and/or results presented here are explained in greater detail and placed in context in our Sustainability Report.
