Ferti-irrigation

Technical articles - Water management, Reduction of IFT

Market gardening Market gardening Arboriculture Arboriculture Viticulture Viticulture Irrigation Fertilization fertigation Fertirrigation

A tank used for fertigation, allowing the injection of the desired dose of fertilizer into the irrigation water

Ferti-irrigation, also called fertigation or fertirrigation, consists of applying soluble fertilizing elements in water through an irrigation system. This method has been gaining popularity over the years by promising a significant increase in the efficiency of use of nutrients and water. In France, it is mainly used for fruit, market gardening and viticultural crops, but some producers of field crops are beginning to show interest.

Advantages of fertigation

Fertigation offers many economic and environmental advantages for crops.

Fertilizer supply according to needs

Fertilizer supply is done according to the needs of the crop. With conventional fertilization methods, supplies are made in large quantities several times during the crop growth. In fertigation, it is done by small doses throughout the cycle, according to needs. The quantity supplied as well as the type of nutrient are therefore optimized, which avoids damaging the roots with excessive fertilizer application.

Yield increase

Thanks to this optimized distribution, fertigation allows a yield increase. This increase varies depending on the crop studied, the climate, and the soil, but averages around 12%. This increase is linked to meeting crop needs at the right time. For example, a trial on a carrots crop in Normandy achieved a 32% yield increase (trial conducted by Yara France).

Increased efficiency of nutrient and water use

In fertigation, nutrients are supplied to the plant in a readily assimilable form, allowing rapid uptake. Moreover, the irrigation system used is designed to deliver water and solubilized nutrients as close as possible to the roots, improving absorption efficiency and limiting losses.

According to tests conducted by Yara, a company specialized in fertilizer production, this method would increase fertilizer efficiency by 16%.

Environmental issues

Fertigation is also a solution to address current environmental challenges. Indeed, optimizing nutrient and water use avoids waste and also limits leaching. According to tests by Yara, water savings are around 36%. There is also no fertilizer spreading, thus fewer passes of agricultural machinery, which avoids soil compaction, and limits the use of fossil fuels.

Limiting weed development

The fertilizer diffusion zone being reduced by fertigation, weeds have less access to the resources provided by these fertilizers and develop less.

Ease of use

Fertigation is compatible with most irrigation systems such as sprinklers or drip irrigation, whether associated with pressure tanks or dosing pumps. It is also suitable for most crops and different plant development stages. However, due to lack of information, time, and resources, many farmers hesitate to adopt it.

Disadvantages of fertigation

Equipment cost

The main disadvantage of fertigation is the cost of the necessary equipment:

Installation cost

€2500 to €3500/ha for equipment (filtration station, combs, fittings, dripper lines, tank, dosing pump…) plus €400 to €600 labor. The major factor affecting installation cost is the distance between the water source or well and the plot. System efficiency depends on the equipment used.

Fertigation equipment

Maintenance cost

€80/ha/year for cleaning, network repairs, and necessary labor.

Irrigation cost

€150 to €170/ha/year for the time required to operate and trigger irrigation.

Water cost

300 to 1000 m³/ha/year depending on the withdrawal method (water rotation, wells…).

Fertilizer cost

Its form can be soluble or liquid. Between €50 to €200 / 100 kg. Fertilizers used are specifically designed for fertigation and have the following characteristics:

• High solubility: Fertilizers must be completely soluble in water to avoid clogging the irrigation system.
• Purity: High purity is necessary to minimize risks of precipitation and clogging of drippers or micro-sprinklers.
• Nutrient concentration: Fertilizers for fertigation are often more concentrated to provide the required nutrient amount in a limited water volume.
• Chemical compatibility: Products must be compatible with other substances applied via the irrigation system.
• Appropriate pH and electrical conductivity: Chosen fertilizers must maintain these parameters within an acceptable range for crops.

Among the recommended fertilizer forms are:

• Soluble NPK solutions.
• Chelated fertilizers for micronutrients.
• Concentrated liquid formulas compatible with irrigation systems.
• Soluble magnesium nitrate, such as YaraTera® KRISTA MAG.
• Monoammonium phosphate.
  

On average, the costs incurred by the equipment are offset after about three years by increased yields and reduced input costs.

Equipment maintenance

To function properly, fertigation equipment requires frequent maintenance. Indeed, a system failure can lead to yield loss, poor crop growth, or damage to equipment. There is also a risk of chemical backflow into the water source, so a check valve must be installed to prevent this.

A filtration tool alone is not enough to maintain the conduits. It is recommended to perform winter maintenance by acidifying or chlorinating the irrigation network. The network must be drained, especially if drippers are buried, to avoid circuit blockage by roots, risks of frost or algae development.

Furthermore, the circuit must be thoroughly rinsed with clear water after each fertigation to prevent product reactions and precipitation, which would cause clogging. To avoid excessive water supply, the total water dose to be applied to crops must be carefully calculated. In a fertigation system, the steps are:

• Initial irrigation
• Opening the fertilizer tank and adding fertilizers into the system via the dosing pump,
• Once fertilization is complete, irrigation continues to rinse the system.

The final water dose must be calculated considering all three steps; careful planning is essential.

Water quality

Water quality used in fertigation is an important factor for the system. Various criteria must be checked to ensure proper system function.

Water salinity

Salinity corresponds to the total amount of soluble salt contained in a volume of water. This criterion is measured by electrical conductivity (EC), expressed in dS/m or mS/cm. The higher the total dissolved solids (TDS), the higher the water salinity. TDS (mg/L) is calculated as:

TDS = 640 x EC

Salt quantity must be controlled because if the solution applied to the soil is a hypertonic solution (solution with a higher molecular concentration than the medium), roots will no longer be able to absorb water and thus meet their water and nutrient needs.

Water quality depends on its electrical conductivity, which directly reflects its salt content. It is defined with the following thresholds:

• 0.05 dS/m to 0.4 dS/m: Very good quality.
• 0.4 dS/m to 0.75 dS/m: Good quality.
• 0.75 dS/m to 1.5 dS/m: Poor quality.
• Above 1.5 dS/m: Very poor quality.

Note: in fertigation, water salinity adds to that of the fertilizer. The water + fertilizer solution is therefore more saline than water alone. Fertigation must be adapted to the system and fertilizer application must be carefully managed to avoid applying overly saline water.

Specific salinity (sodium content)

The Sodium ion is highly soluble and can replace Calcium and Magnesium in soil aggregate structures. This causes their destruction and soil structure degradation, making it more impermeable and less aerated.

The Sodium Adsorption Ratio (SAR), expressed in meq/L, is used to determine water quality regarding sodium content. Quality is classified as follows:

• 0 meq/L to 3 meq/L: Very good quality.
• 3 meq/L to 6 meq/L: Good quality.
• 6 meq/L to 9 meq/L: Poor quality.
• Above 9 meq/L: Very poor quality.

Chloride (Cl–)

The chloride ion is abundant in saline solutions and can be absorbed by plants in large amounts. High Cl– concentration in leaves can cause burns or even complete leaf death. This can lead to loss of photosynthetic capacity and directly affect growth.

Hardness and alkalinity

Water hardness indicates the amount of calcium and magnesium present in the medium. It can cause future limestone formation. Alkalinity defines the water's buffering capacity and thus its ability to neutralize acidity and its carbonate content. Hardness and alkalinity indices are obtained through laboratory chemical analyses.

Magnesium and calcium precipitate in the presence of carbonates to form limestone, so there is a risk of clogging when hardness is high. Risk levels are:

• 0 to 100 eq carbonate: Low clogging risk.
• 100 to 200 eq carbonate: Moderate risk.
• Above 200 eq carbonate: Serious risk.

To mitigate clogging risk, it is necessary to acidify the network by lowering water pH below 7. Treatments with sulfuric or nitric acid break the bonds between carbonate and cations and thus clean the network of limestone.

pH

The soil acid-base profile depends on pH. In case of acidification, there is a risk of soil structure degradation, decreased biological activity, and increased risk of induced toxicity.

Irrigation water pH should be between 5.5 and 6.5. If pH is too high, an acidifying fertilizer can be added. Conversely, if pH is too low, care must be taken with fertilizer amounts because fertilizers tend to acidify the soil. In this case, it is better to apply smaller amounts of fertilizer to avoid soil degradation, preferring a low but regular supply rather than a large single dose.

Case of iron

In its Fe2+ (ferrous) form, Iron is soluble in water and poses no problem. Under the action of ferric bacteria, it can precipitate as ferric iron (Fe3+) and become insoluble in water. This creates a viscous brown gel that is a clogging factor in the irrigation network. Thus, water with more than 0.5 mg/L iron should not be used without prior treatment.

For this treatment, ferrous iron (soluble) must be oxidized before entering the network, either by strong agitation in the tank so it precipitates at the bottom, or by adding a highly oxidizing agent (Chlorine, e.g., bleach) to precipitate it and collect it in the system filter.

Ensuring water quality

In fertigation, self-monitoring at the beginning and end of the line can be effective to condition or adjust the nutrient concentration injected. If values do not match upstream and downstream, it indicates a distribution problem.