What is Fertigation and How Does it Work?

Although fertilizers are heavily relied upon in agriculture, their traditional methods of application can be wasteful and their associated run-off often has negative consequences for the local ecosystem.

One of the many practices of precision farming, fertigation is a highly adaptable and scalable practice that is widely used as it simplifies the application of fertilizer and irrigation to plants by combining them into one waste-averse system.

It has been a popular practice amongst farmers and agricultural professionals for several decades and is only increasing in efficiency and efficacy as it becomes incorporated with modern technologies that continue to streamline and automate the process.

Defining fertigation

Fertigation is the application of fertilizers or nutrients into a farming system via the irrigation network, wherein the nutritious inputs are dissolved into water and then absorbed directly by plants when they uptake water.

The term combines the terms ‘fertilizer’ and ‘irrigation’ and has existed as a concept for hundreds of years, where farmers in ancient Rome would actually use sewage to water their crops, although it has evolved significantly since this time.

It can be used in conjunction with several different irrigation methods including sprinkler, drip, and soaker irrigation systems, although drip is the most compatible and beneficial irrigation type.

Compared to band or broadcast methods of applying fertilizer, it is considered to be the most precise and controlled method of application and typically uses an overall lower volume of fertilizer compared to other techniques.

It is also a common practice in hydroponic or soil-less growing systems, as it is by far the easiest technique for administering exact doses of the proper nutrition needed by plants in these systems.

Although a number of compounds are used in fertigation systems, the most common are phosphorus, potassium, and nitrogen due to their importance in the growth and development of many crop species.

How fertigation systems operate

The main principle of fertigation is to dissolve fertilizers that are water-soluble into the water used for irrigation so that their application is combined. Since wet roots are necessary for effective fertilizer absorption, it greatly increases the efficiency of fertilizer applications by making sure they are supplied to roots in already wetted soil.

The way that fertilizers are stored may vary from system to system, but they are often kept in a liquid form that is easier to combine with water than particles that must be dissolved. The specifics of each fertigation network are dependent on the scale of the farming operation and type of irrigation system, and more advanced operations may be on automated schedules while simpler, smaller-scale farms will do it manually.

Typically, a liquid form of fertilizer is stored in a large tank, and then a dripper or injector will imbue the irrigation water with precise volumes of the fertilizer.

Most regional agricultural bylaws dictate that fertigation systems must also have a backflow prevention device in place to avoid contaminating the original irrigation water supply with fertigated water, as this could risk contaminating drinking water sources with harsh chemicals.

Nutrient absorption patterns in fertigation

Fertigation systems have been popularly used by agricultural professionals for years because of the increased efficiency with which they are able to supply plants with nutrients.

Dissolving fertilizers in water and delivering them to plants in a liquid form allows them to be absorbed and utilized more quickly than traditional fertilizer applications, especially if being done at the root level through drip irrigation.

Although it has been around for decades, modern innovation in precision agriculture has created the ability to apply the precise amounts of fertilized irrigation to target specific crops and created automated systems that have advanced sensor, valve, and injection networks.

The way that fertigated water spreads changes between different systems and the unique soil biogeochemistry of each land area, but with drip irrigation it will typically spread outwards and down from the point of release, moving with gravity. Heavy clay soils are not ideal counterparts for fertigation systems, as fertilizers may get trapped and build up at the root level.

Creating successful fertigation systems

Efficient and successful fertigation systems depend on fertilizer choice and the design of the original irrigation network. Drip irrigation systems are the most common and most beneficial type to transform into fertigation systems, as they deliver water and nutrients directly to the root zone of the plant for quick absorption and utilization.

The main considerations in creating a successful system are the type of fertilizer being used, and how soluble, acidic, and compatible they are with the target crops. The compound being used should be based upon the nutrient needs of the plants being grown, and variable rate fertilizer (VRF) systems can pinpoint specific nutrient needs in the soil.

Table 1 breaks down some of the most common compounds used in fertigation and their chemical breakdown, as well as how their capacity to dissolve in water changes with higher temperatures. The majority of irrigation networks are now built from plastic or similar materials, which is important as certain fertilizers can be very strong and corrosive to metal piping.

The type and acidity of soil must be considered when planning its operations, and fertilizing in general, and it is vital to pair the correct compounds with your soil type to prevent it from becoming too acidic or alkaline.

Picking compounds with nutrients that have a solubility capacity well suited for the soil and water temperature of your region is another consideration for successful fertigation. For optimal fertigation planning geospatial mapping software should be used to create a multi-layered map that reflects the variations amongst different factors such as soil electrical conductivity, pH, nutrient density, and drainage patterns so that the appropriate inputs can be dissolved into your irrigation system in the correct amounts.

Table 1: Breaking down the common compounds used for fertigation

Fertigation compatibility with different irrigation systems

The best fertigation systems are those incorporated with drip irrigation lines, so that water and nutrients can be delivered directly to the root zone of crops – although it can technically be done through any irrigation system.

Sprinkler systems have several significant disadvantages, as much of the fertilized water lands on the leaves and foliage of plants, which wastes valuable resources and has the potential to burn fragile leaves or contribute to the spread of fungal disease through stagnant moisture.

Wind may also blow sprayed clouds of fertigated water into neighbouring fields or water sources, which is difficult to account for and may pollute water sources with potentially dangerous outcomes.

Supplying water and nutrients through subsurface drip irrigation is the best technique as there is minimal wastage and it can be absorbed quickly by the plant roots after release. Additionally, drip irrigation also allows for more controlled and precise amounts of fertilizers to be released at specific points in the soil to cater to each plant’s needs compared to sprinklers.

Drip irrigation also requires less pressure to operate than sprinkler systems, which is also true for soaker hose irrigation designs, however these are less ideal than subsurface drip irrigation as they still water on a surface level and don’t have the same precision as water is released from the entire surface area of the hose.

Advantages of fertigation

Properly installed fertigation systems can prove to be highly advantageous to farming professionals for several reasons. Firstly, it is a highly efficient way to distribute fertilizer in a ‘kill two birds with one stone’ approach by simultaneously watering and fertilizing crops.

This also means that the same piping equipment and infrastructure can be taken advantage of for two essential inputs, making it a cost-effective approach. It is also economically advantageous in that the precise application of fertilizer through an already efficient system such as drip irrigation means that resources are conserved and only exact volumes need to be used.

When compared to the traditional approach of broadcast spraying one monotonous fertilizer density across multiple fields, the wastage is minimal. Since fertilizer needs to be applied less frequently to crops than water, it can be scaled up or down as needed without having to switch to a different system as even heavy feeders won’t require more frequent fertilization than irrigation.

Smaller but more frequent volumes of fertilizer being applied to crops are also advantageous as they generally decrease the likelihood of salt buildup compared to higher volume but infrequent broadcast or band applications.

It has been used in arid climates that experience water scarcity to improve the potential of every drop of water being used and ensure that every patch of wet soil is utilized by providing the necessary fertilizers simultaneously.

Not only are the fertilizer concentrations highly controlled, but in drip fertigation systems the location of water release points is more accurate and results in the crop roots being able to quickly absorb the nutrition as it is applied, instead of it just absorbing into empty and dry soil patches where it is wasted.

The roots are also already moist when they receive the fertilizer, reducing root burning and increasing absorption capacity.

This technique of directly supplying fertilizer into the roots decreases the likelihood of nutrient leaching, as the amount of time the fertilizer spends ‘in limbo’ from when it is applied to when it is absorbed is very short, so there is a lower risk of run-off from rain events or similar weather occurrences.

Studies show that with the proper equipment and correct installation, drip fertigation can significantly boost crop yields, improve water productivity, and drastically reduce fertilizer wastage.

Disadvantages of fertigation

The disadvantages of fertigation systems are mainly linked to economic drawbacks, as systems with minimal investment are more likely to have infrastructure and leakage issues. Without a very high-quality preventative backflow device in place, there is a significant risk that the freshwater source being used for irrigation could become contaminated with fertigated water.

This poses obvious dangers for human health, but also for the health of local watersheds, flora, and fauna and may contribute to the general pollution of the local biome.

Lower quality or older equipment, or piping infrastructure that spans a long distance, may have inconsistent solutions running through them as the fertilizer becomes diluted in the water as it moves through the irrigation lines, decreasing the efficacy of the system and potentially causing overfertilization of certain crops and insufficient fertilization of others.

Depending on the chemical makeup of the irrigation water, there is also the possibility of reactions between magnesium or calcium-based fertilizers and any bicarbonates in the water.

This occurs more often when the water source is from a well or groundwater, and there may be slightly higher concentrations of lime or iron dissolved in the water that react with fertilizers or just build up and precipitate.

Chemical clogging can exacerbate issues of inconsistent nutrient applications to crops by blocking exit points in the irrigation system. Solutions include manipulating the water pH or injecting low concentrations of phosphonate into the water, or pumping it into a separate tank or reservoir where the precipitates can settle before fertilizers are applied.

A valuable practice of precision agriculture

Overall, it has proved itself to be a key part of modern agricultural systems and it has, and will continue to, play an important role in spreading the implementation of precision agriculture.

Fertigation overcomes the limits of traditional fertilizer applications by creating a higher level of control over the exact volumes and rates at which fertilizers are administered to crops, and it is done on a precise schedule with high levels of nutrient uptake success and minimal wastage.

Especially when used in a drip irrigation system, this practice embodies many of the foundations of precision agriculture, and assists land managers in making economic and sustainable decisions about fertilizer applications that not only boost yields but also contribute to the longevity of the farming operation.