Water and irrigation

Fertigation and beneficial nematodes in agriculture

Fertigation: definition, benefits and application

Fertigation is the application of fertilisers or nutrients through the irrigation system: the nutrients are dissolved in water and taken up directly by the plants as they absorb the irrigation water.

The concept is centuries old: farmers in ancient Rome already used wastewater for irrigation.

The most commonly applied nutrients are phosphorus, potassium and nitrogen, all essential for plant growth.

Benefits of fertigation

Efficiency: fertigation makes fertiliser applications more efficient, because roots take up nutrients more effectively when the soil is already moist, and fertigation delivers them straight to wet roots.
Less waste: it reduces fertiliser losses caused by rain washing traditional applications out of the soil, limiting negative effects on the ecosystem.
Even distribution: fertiliser is delivered evenly, steadily and gradually, easily reaching the roots.
Tailored feeding: nutrients can be supplied precisely to suit each crop, also thanks to modern precision agriculture systems.
Remote control: with automation, fertigation can be scheduled remotely from mobile devices and monitored with soil probes that track the water and nutrient needs of the plant.
Less leaching: because fertiliser and water go straight to the roots, the time between application and uptake is very short, so there is less risk of nutrients being leached by rain or similar weather events.
Versatility: fertigation works well on strawberries, processing tomatoes, vegetables in general, citrus, vines, stone fruit and pome fruit.

Fertigation systems

Drip irrigation: drip systems are the most common and effective for fertigation, as they deliver water and nutrients directly to the root zone.
Materials: irrigation networks are usually made of plastic or similar materials, since some fertilisers corrode metal pipes.
Spatial mapping software: for best planning, software is used to map soil variations (pH, conductivity, nutrient density) for targeted application.

Continuous or intermittent application

Continuous method: fertiliser delivery increases in proportion to the crop’s water demand.
Intermittent method: fertigation is split by growth stage, supplying specific amounts at set intervals.

Technical and operational aspects

Compatibility and interactions

Chemical interactions: when certain elements are in the same solution they can react and form substances that clog the irrigation system. For example, phosphates react with iron, calcium and magnesium, and sulphates react with calcium to form gypsum.
Water analysis: analysing the water is essential to identify potential problems and treat the water before fertiliser is added.

Fertiliser calculations

Terminology: N, P and K content is expressed as pure N, phosphorus pentoxide (P2O5) and potassium oxide (K2O), as a percentage by weight.
Conversions: formulas are used to convert from oxide to pure element and to calculate the amount of fertiliser needed for the required dose.
Example: a 15-5-30 fertiliser contains 15% nitrogen, 5% P2O5 and 30% K2O.

Injection methods

Pressure by-pass tank: installed in parallel, it uses a pressure difference to dissolve and carry the fertiliser.
Venturi injector: uses the Venturi principle to create suction and inject the fertiliser solution.
Pumps: there are pumps driven by water pressure, by combustion engines and by electric motors, each with pros and cons. Electric pumps come in a wide range of flow rates and capacities and are best suited to automating fixed installations, such as greenhouses or wells.

Filtration and control devices

Filters: screen, media and disc filters are essential to prevent clogging; with screen filters, irrigation water passes through a metal or plastic screen that acts as the filtration zone.
Non-return valves: they prevent fertiliser from flowing back into the water source. A non-return device upstream of the injection point is recommended and in some cases mandatory.
Vacuum relief valves: they prevent concentrated fertiliser from being sucked into the system when irrigation stops, which could harm the crops.

Maintenance

Tanks: they should be cleaned and rinsed regularly, and valves checked for leaks.
Injection systems: devices should be checked periodically and repaired if they leak.
Filters: filters must be cleaned and backwashed regularly; excessive dirt reduces filtration capacity and, in screen filters, can crack and damage the screen.

Measurements and checks

Pressure: check that pressure stays within the system specifications.
Flow rate: monitor the flow rate to detect significant leaks and blockages.
Pipe flushing: pipes should be flushed regularly to remove deposits.
Acid treatment: acid can be used to remove salt scale, but it is not effective on sulphate deposits.
Oxidising agents: chlorine or other oxidising agents can be used to control bacterial growth in irrigation systems.

Beneficial nematodes: biology, use and application

Definition and types

Nematodes: microscopic, worm-like, cylindrical organisms belonging to the phylum Nematoda, too small to be seen with the naked eye.
Entomopathogenic nematodes: beneficial nematodes have a unique relationship with insects. They are natural enemies of many insect pests and play a key role in biological pest control.
Harmless: entomopathogenic nematodes are not harmful to people, animals or plants.
Plant parasites: by contrast, plant-parasitic nematodes damage plants.

How beneficial nematodes work

Host seeking: nematodes actively search for insect hosts, attracted by chemical signals.
Attack: they enter the host through natural openings and release symbiotic bacteria.
Infection: the bacteria multiply rapidly, causing septicaemia and the death of the insect.
Reproduction: the nematodes feed and reproduce inside the dead host.
Emergence: new nematodes leave the insect’s body to look for new hosts.

Species of beneficial nematodes

Steinernema feltiae: cold-tolerant, effective against a wide range of soil-dwelling pests, including fungus gnats (sciarids), root flies, root weevils and other insect larvae, as well as thrips.
Steinernema carpocapsae: known for its effectiveness against pests such as bugs and various moth and beetle larvae.
Heterorhabditis bacteriophora: particularly effective against soil-dwelling insects such as the larvae of Japanese beetle and cockchafer, and root weevils.

Applying nematodes

Method: nematodes are applied with water. Once activated in water, the suspension can be spread with the spraying and irrigation systems commonly used in farms and gardens, including sprinkler and drip systems.
Filters: filters finer than 0.3 mm must be removed to avoid clogging.
Pressure: nozzle pressure must not exceed 20 bar.
Moisture: the soil must be moist before and after treatment and kept moist for several weeks, as nematodes are sensitive to dry soil and die in substrates that are too dry.
Temperature: the ideal spray water temperature is between 15 and 20°C and must not exceed 25°C.
Timing: apply early in the morning or in the evening, when relative humidity is high (above 75%) and sunlight is low.
Suspension: use the nematode suspension immediately after preparing it.
Substrates: nematodes do not survive long on clean rock wool.

Storage

Refrigeration: nematodes can be stored in a ventilated fridge until their expiry date.
Do not stack: for long-term storage, packs should not be stacked, to ensure good air circulation.

Regulation and organic farming

Licences: in most countries no licence is needed to apply nematodes, as they are considered natural enemies.
Registration: nematodes are exempt from pesticide regulations in most countries, although some may require local permits.
Organic farming: nematodes are generally compatible with organic farming.

Nematodes against specific pests

Fungus gnats: Steinernema feltiae is commonly used against sciarid flies, which damage plant roots.
Crane flies: Steinernema carpocapsae is effective against leatherjackets (crane fly larvae) in lawns and turf.
Wireworms: Heterorhabditis bacteriophora and Steinernema carpocapsae are used against click beetle larvae.
Delia spp.: nematodes can be used against various Delia species that attack onions and other crops.

Supporting technology: Nematool sensors

Precision sensor: Nematool is a soil sensor that, as well as monitoring and improving soil solarisation, measures the main physical parameters linked to the nematode life cycle and indicates the best time to intervene with nematicides.
Dedicated app: an app provides updates on solarisation and on the nematode cycle, flagging when action is needed.
Pre-transplant monitoring: Nematool is also useful before transplanting, to monitor solarisation.

Fertigation and beneficial nematodes are two key approaches to efficient and sustainable agriculture. Fertigation optimises fertiliser use, reducing waste and environmental impact, while beneficial nematodes offer an effective biological method of pest control. By combining these practices and using advanced technologies such as sensors, growers can improve production, reduce chemical use and contribute to a more sustainable future for farming.

Questions on fertigation and beneficial nematodes

What is fertigation and what are its main benefits?

Fertigation is a farming technique that applies fertilisers or nutrients through the irrigation system. The fertilisers are dissolved in water and taken up directly by the roots during irrigation. It allows even, controlled nutrient distribution, improves uptake efficiency and reduces waste and the risk of leaching, lowering environmental impact. Applying water and nutrients together also reduces root stress and improves uptake.

How does a fertigation system work and which irrigation systems suit it best?

The basic principle is to dissolve water-soluble fertilisers in a tank of irrigation water. Drip systems are the most common and effective, because they deliver water and nutrients directly to the root zone for rapid uptake. Fertigation can be continuous, matching fertiliser to the plant’s needs with every irrigation, or intermittent, split by growth stage. Automated systems with sensors and valves allow more precise, controlled application.

Which fertilisers are used in fertigation and how is the dose calculated?

The most common fertilisers contain phosphorus, potassium and nitrogen, and can be liquid or solid (crystalline, soluble). The dose is calculated according to the crop, its growth stage, the soil type and the irrigation water analysis, taking into account the percentage of N, P2O5 and K2O in the fertiliser and, for liquids, their specific gravity. Doses can be expressed by weight or volume per unit area, or as a concentration in ppm (parts per million) in the irrigation water.

What are beneficial (entomopathogenic) nematodes and how are they used in pest control?

They are microscopic worm-like organisms that act as natural enemies of many insect pests, especially at the larval stage. They are harmless to people, animals and plants and are an effective form of biological control. Applied to the soil, they enter the host insect through body openings and release symbiotic bacteria that kill it within a short time.

How do beneficial nematodes kill pests?

After locating a host, entomopathogenic nematodes enter the insect’s body through natural openings or by piercing the cuticle. Inside, they release symbiotic bacteria that multiply rapidly and cause septicaemia, killing the insect within a few days. The nematodes feed on the dead insect’s tissues and reproduce, emerging in large numbers ready to infect other pests. The process targets insect pests and does not affect beneficial insects or other organisms.

What are the main species of beneficial nematodes and which pests do they control?

The most widely used are Steinernema feltiae, effective against fungus gnats, thrips and some beetle and moth larvae; Steinernema carpocapsae, used against moth and beetle larvae; and Heterorhabditis bacteriophora, effective against beetle larvae in the soil. Each species suits different pests and settings, such as protected crops (greenhouses) or open-field crops (orchards, vegetable plots, turf).

How and when should beneficial nematodes be applied for best results?

They are applied with water using sprayers or irrigation systems. Ideal conditions are temperatures between 15 and 25°C, high humidity (ideally above 75%) and low sunlight, so preferably in the evening or early morning. Keep the soil moist for a few weeks after application so the nematodes can move and find hosts. Remove filters that are too fine and do not exceed 20 bar of pressure. Do not store the solution after mixing, as the nematodes settle and lose effectiveness.

What precautions should be taken when using beneficial nematodes?

Beneficial nematodes are safe for people, animals and plants, but they must be applied in the right conditions to work. Water temperature must not exceed 25°C, and they should not be applied to very dry soil or in direct sunlight. Remove filters finer than 0.3 mm from spray equipment and keep the mix agitated. Use them before the expiry date on the pack to ensure they are viable. They do not require plant protection product authorisation.