Fertigation is a widely used farming practice. The fertigation technique allows growers to save time, resources, and efforts by completing two events at a time: fertilization and irrigation. Customization of modern fertigation systems and innovative satellite-based software enable pinpoint variable rate fertilizer (VRF) applications. The most efficient method is drip fertigation that reduces inputs and delivers nutrients to the root zone. The technology is suitable for farm enterprises of any size since there are large and small-scale fertigation systems, with manual or fully automated control.

What Is Fertigation?
In fertigation, liquid fertilizers are delivered to plants with irrigation. Compared to traditional fertilization methods, the fertigation technique proves to be more efficient. In particular, benefits of fertigation include:

  • saving costs on reduced fertilizer amounts;
  • eliminating nature pollution with decreased chemical applications;
  • controlling administered rates;
  • tackling soil erosion;
  • optimizing water consumption;
  • preventing fertilizer leakage due to heavy rainfalls or water supply;
  • promoting rapid root growth;
  • affecting soil microbial biomass.

The most commonly used water-soluble fertilizers for fertigation comprise ammonium nitrate, urea ammonium nitrate, calcium nitrate, ammonium thiosulfate, potassium chloride, potassium sulfate, potassium nitrate, phosphoric acid, sulfuric acid, etc. Apart from supplying nutrients proper, some fertilizers can perform acidulating functions and boost soil properties.

Thiobacillus bacteria in ammonium thiosulfate participate in the process of lime dissolving and turning it into gypsum, which improves the soil structure.

How Fertigation System Works
Fertigation technology suggests sprinkling fertilizers into the irrigation system from reservoirs with water-soluble fertilizers. Typically, it is done with injectors and a pressure-controlled valve.

Fertigation systems differ by several parameters:

  • Size and scale of applications: a large-scale fertigation system is used at a big enterprise. Correspondingly, small-scale fertigation systems are suitable for smaller farms or greenhouses.
  • Management: there are manual and automated fertigation control systems. Timers can be integrated into the irrigation system, enabling fertigation at the established times.
  • Irrigation methods: flood irrigation, nozzle and head sprinkling, drip fertigation.

Accuracy Of Nutrients Application In Fertigation
A significant advantage of fertigation is the liquid form of nutrients distribution. Thus, plants can absorb them immediately after administration, which enhances their availability and efficiency. Root fertigation allows optimal nutrient supplies to the root zone, with minimum losses. It essentially reduces runoffs and wastes, especially due to downpours or flooding.

Fertigation scheduling depends on the crop needs within required time frameworks and may be performed daily, weekly, etc., according to the nutrient management plan. Besides, for example, in the case of fertigation through drip irrigation, the absence of machinery soil disturbance during fertilizer applications prevents earth compaction.

Most fertigation systems are equipped with sensors to measure pH-levels and electric conductivity. This way, farmers can determine necessary fertilizer rates. Then, they can set the fertigation and irrigation system injectors correspondingly.

Since fertigation is not the only source of nutrients, it should be summed up to the total amount of planned nutrient supply when calculating the application rate.

Distribution Of Nutrients With Fertigation Implementation
As fertilizers are liquid, their delivery and distribution correlate with wetting patterns. In other words, nutrients will transfer to the areas within water reach. The most typical technique is drip fertigation. The optimal use of resources is achieved with root zone fertigation that provides moisture right at the plant root.

Typically, drip irrigation wetting patterns are oval or hemispherical, either on the soil surface or at the emitter level under it (depending on if the tape runs on or below the surface). The highest amount of water (and correspondingly, nutrients) will be around the emitter and under it. Horizontal spreading of moisture is conditioned by the soil properties, irrigation rate, and duration respective to plant needs. Another aspect that influences nutrient distribution is their type and the ability to adsorb to soil components. For example, nitrates and sulfates do not adhere to soil particles, while potassium and phosphorus do. In particular, phosphorus binds with calcium or aluminum, and positively charged potassium reacts with negatively charged clay.

What To Consider For Successful Fertigation
As mentioned above, fertigation suggests delivering liquid fertilizers via an irrigation system. Yet, merely adding them is not enough. Agronomists take several fundamental properties into account, including solubility, compatibility, acidity, and salinity (osmotic pressure).

First of all, the choice of fertilizers depends on their solubility in water. So, the suitable options are: 

  • Solid ones that can properly dissolve;
  • Lquid ones that are already dissolved.

Different fertilizer types have different solubility capacities. What is more, the degree and speed of solubility also relate to temperature. So, it matters if nutrients can dissolve under the current temperature in the field or not. Thus, the season should be taken into consideration as well since the solubility rate will differ.

Besides, some fertilizers may precipitate out of solution when added in high concentrations to hard water or when the temperature drops, e.g., in a cooler season or cold nights. This property counts when preparing solutions in advance and storing them. Precipitation is characteristic of monoammonium phosphate, urea phosphate, or phosphoric acid. Ammonium nitrate, potassium nitrate, urea, and ammonium phosphate refer to quick water-soluble fertilizers.

Typically, the higher the temperature, the higher the solubility is. For example, the solubility of ammonium nitrate rises more than twice when comparing the temperatures of 0°C and 30°C – from 1183 to 2420 g/L correspondingly. It means that a greater amount of nutrients will dissolve in the same amount of water.

However, there is another significant aspect to bear in mind. Solutions for fertigation systems can be endothermic or exothermic, i.e., the solution temperature either decreases or increases in the process of dissolution. Generally, most nitrogen-based fertilizers take heat from the water, so the solution temperature drops. Consequently, the preparation process will take more time, and more time will mean cooler liquid and reduction of estimated concentration.

When it comes to matching several components for fertigation, it is essential whether they are compatible or not. The basic rules are as follows:

  • Prepare separate solutions and store them in separate reservoirs if they may enter an undesirable reaction. 
  • Do not combine phosphorus or sulfur with calcium.
  • Do not add chelates to non-chelates.
  • Isolate chelates from acids because they break in acidic pH.

The basic rules to mix fertilizers are to avoid precipitations and reduction of solubility due to chemical reactivity.

Acidity Solution acidity causes corrosion, which deteriorates metal reservoirs, and irrigation system parts. This parameter is assessed as the pH level, and neither too high nor too low is good. Acid solutions have high corrosivity, while alkaline liquids represent the risk of precipitation. Chloride-based chemicals are also notorious for corrosive properties.

Fertilizers can decrease or increase the solution pH, for example:

  • Diammonium phosphate would create a higher pH than mono-ammonium phosphate.
  • Nitric acid would lower the pH of the solution even at relatively low concentrations.

Besides, agronomists consider the soil reaction to fertigation. In particular, muriate of potash or potassium sulfate gives a neutral reaction. With calcium nitrate or potassium nitrate, it is basic. Ammonium nitrate, urea, ammonium sulfate, monoammonium phosphate, diammonium phosphate produce an acidic reaction. Phosphoric acid applications cause the strongest soil acidity.

Osmotic Pressure
Typically, irrigation water is to certain degree saline, and adding salt-containing fertilizers contributes to salinity even more. Salinity relates to osmotic pressure. Negative osmotic potential complicates water absorption by plant roots, which results in a reduction of yield. Crops suffer from osmotic stress and cannot use moisture even when it is available in the soil because it flows from less saline areas to more saline ones. Plants spend more energy to absorb water and nutrients from fertigation, and if osmotic stress is critical, they die. For this reason, administered fertilizers should produce as low osmotic pressure as possible. As a rule, the salinity potential of fertilizers is not measured. It is assessed by electric conductivity and its correlation to osmotic pressure. Electric conductivity and pH are computed and then compared. It is specific for each chemical substance. For example, ammonium sulfate would generate a higher osmotic pressure in a solution (per amount of total nutrient applied) than ammonium nitrate.

Fertigation Scheduling
Plants require different nutrient volumes at different development stages. Either too early or too late applications almost turn into waste due to runoffs or volatilization. This particularly refers to nitrates that are not retained in the soil. As for phosphorus, it may leak too, though in many cases, about 50% of this fertilizer is administered before planting.

Fertigation allows agronomists to supply nutrients to crops in the right amount and at the right time, thus proving to be the most efficient method. It is even more beneficial to deliver nutrients to the root zone. This way, fertigation promotes root growth.

Furthermore, smaller fertilizer amounts save costs to farmers and prevent unjustified soil salinization due to saline water or when fertilizers salt out.

It also makes sense to apply nutrients slightly before the time the crop needs them to secure successful growth. Typically, the most intensive fertilization is required during plant growth and is reduced or completely stopped at the harvesting stage. Tracing weekly progress, farmers can schedule fertigation events.

Fertigation Compatibility With Irrigation Systems
There exist several options to carry fertigation out like surface and pressurized or non-pressurized irrigation, each of which contributes to crop production in its specific way.

Surface Irrigation
Surface irrigation is the most common type of water saturation, applied to 90% of all irrigated lands. However, it might not be a cost-efficient method as only 30-70% of water reaches the active root zone.

Typically, fertigation systems are not incorporated into surface irrigation since fertilizers are usually supplied via designated canals in established volumes. The equipment includes reservoirs with valves or openings for liquid and solid fertilizers correspondingly. It differs by operation complexity (from manual to fully automatic).

Fertigation with surface irrigation is not always efficient due to the loss of nutrients in tailwaters or seeping. This particularly refers to nitrogen-based fertilizers. However, the method practitioners state that high yields do justify the cost inputs even despite nutrient losses. The technique is suitable for zero slope and surge irrigation.

Pressurized Irrigation
As the name reveals, nutrients run through the system in this irrigation type thanks to the pressure differential. However, with anhydrous ammonia, no pressure is required since the solution possesses it naturally.

The force applied depends on the system type: it is stronger with sprinkler systems and weaker with drip ones. When using aggressive fertilizers, agronomists consider their corrosive impact on metal equipment parts as well as canopy burns.

The drip fertigation system is the most efficient option as it:

  • brings nutrients directly to the root zone, which optimizes water and fertilizer use;
  • requires less pressure compared to other techniques;
  • allows different automation settings.

Site-Specific Fertigation With Crop Monitoring
Modern fertigation systems have a wide array of customization features. This benefit enables farmers to step aside from uniform field treatment because, typically, different field zones have different nutrition needs. Generally, fertilizer rates depend on multiple factors:

  •  type of crop,
  • growth stage,
  • soil type,
  • fertilizer grade,
  • solution concentration,
  • soil moisture,
  • soil temperature,
  • osmotic potential,
  • fertigation effect on soil microbial biomass (microbial action).

Crop Monitoring with its zoning feature enables Variable Rate Fertilizer (VRF) application.

Farmers can identify zones in each field and manually set an appropriate amount of fertilizer for every zone (dividing a field into up to seven vegetation zones). Vegetation maps give actionable insights based on recent satellite data. Crop Monitoring shows the field productivity (or lack of productivity) in different zones with different colors. Thus, green highlights the areas with the healthiest vegetation. Red reveals the least healthy crops, summoning for immediate attention.

The possible deviance reason may be a lack of nutrition. So, green areas require a comparatively low fertilizer rate while red ones require the biggest dose. Furthermore, vegetation and productivity maps facilitate fertilizer inputs calculations, depending on the field needs. Growers enter fertilizer volumes for each zone and get the computed total amount for the field.

Correct fertilizer distribution essentially depends on weather conditions (air temperature, precipitation, wind speed, etc.). In sprinkler fertigation systems, winds may move the mist in the wrong direction, and high concentrations may negatively impact the crops (e.g., burn leaves or fruits). Crop Monitoring offers precision weather forecasts for up to fourteen days ahead. Being armed with wind speed information, soil fertility specialists can plan applications more efficiently, omitting wastes and unintentional crop leaves and fruit damage.

Thus, satellite-retrieved data from the Crop Monitoring software makes fertigation more accurate. It is a reliable assistant of every supporter of precisio