Jay Capasso, Alicia Halbritter, Luke Harlow

Introduction

Effective management of irrigation and fertigation is crucial to optimize blueberry production. When used together, especially with drip systems, water and nutrients are applied directly to the root zone, improving plant uptake while reducing nutrient losses from runoff or leaching. Spoon-feeding nutrients through fertigation enables growers to time fertilizer applications to match the crop demand, improving nutrient use efficiency and minimizing environmental impact. Blueberries thrive in acidic soils and prefer ammonium-based nitrogen fertilizers. Blueberries struggle to use the nitrogen in the nitrate form efficiently.  This is due to their low levels of nitrate reductase, the key enzyme required to convert nitrate into a usable form of nitrogen for the plant (Claussen & Lenz 1999).

Fundamentals of Fertigation

Fertigation systems work by mixing fertilizer into irrigation water and sending it through drip lines or other irrigation methods. Injectors move the fertilizer from a storage tank into the irrigation system, either manually or using automated equipment. One important thing to consider is how long it takes fertilizer to reach the farthest point in the field to determine how long the irrigation system needs to be run to completely flush out the fertilizer. This affects how evenly fertilizer is applied across the field. Fertigation systems require regular maintenance to prevent clogging, corrosion, or backflow contamination. Only water-soluble fertilizers should be used, and the system must be properly calibrated and maintained to work efficiently.

Fertilizer Injectors:

• Venturi Injectors: Affordable and simple, but cause pressure loss and offer limited precision.
• Positive Displacement Pumps: Provide accurate, adjustable injections regardless of changes in water pressure which is ideal for larger systems. Higher cost and power required.
• Pressure Differential Tanks: Inexpensive and easy to install, but fertilizer concentration declines over time, limiting consistency and scalability.
• Fertilizer Storage Tanks: Should be corrosion-resistant and appropriately sized. Multiple tanks may be needed to separate incompatible fertilizers. Use a jar test to check fertilizer compatibility before mixing.
• Backflow Prevention Devices: Legally required to protect water sources from contamination. In Florida, small drip irrigation systems used for fertigation or chemigation on blueberry farms must include backflow protection to prevent contamination of the water supply. Chemicals should never be injected into the irrigation system before the pump, because this can damage equipment or contaminate the water source. All chemical applications must follow label instructions (Bayabil et al., 2020).
• Filters: Remove particulates to prevent emitter clogging. Use screen, disc, or sand filters based on the water quality. Screen filters are good for filtering mineral particles while disc filters are preferred for filtering organic particles. Fertilizer injection should occur upstream of the filters and downstream of the backflow prevention device.
• Pressure Regulators and Gauges: Maintain consistent pressure within the emitter’s operating range (often for drip somewhere around 8 – 15 psi) to ensure uniform nutrient and water application. For larger operations, positive displacement pumps are recommended for consistent injection.
• Water flow meter: Know the water flow and pressure. Flow meters can help you record your injectors’ flow rate. Reduced flow rates but high pressure in the system could indicate a clog. Alternatively, situations with high flow rates and low pressure could be a signal that may have a leak in the irrigation system.

Fertilizers for Blueberry Fertigation

Blueberries require macronutrients (N, P, K, Ca, Mg, S) and micronutrients (Fe, Mn, B, Zn, Cu, Mo). Nutrient demand changes by growth stage, establishment, vegetative growth, flowering, fruiting, and post-harvest. Use water-soluble nitrogen, phosphorus, and potassium fertilizers suitable for acid-loving plants. Avoid chloride-based sources and incompatible mixes of fertilizer. When in doubt, conduct a jar to test to determine compatibility.

Emitter Clogging:

Emitter clogging can be caused by liquid fertilizer coming out of solution, algae growth, high pH, or mineral precipitation like iron and manganese. To reduce the risk of clogging, use fertilizers that are soluble and compatible. Water may need to be acidified, and chlorine can be injected to manage algae. Choosing clog-resistant emitters and flushing the system regularly are good maintenance practices. Flushing can be done manually or with automatic flush valves placed at the end of the drip tape to reduce maintenance time. Filters should be installed to remove particles from the water before they reach the emitters.

Uneven Nutrient Distribution:

Uneven nutrient distribution can result from poor system design, inconsistent water pressure, or fertilizer solutions that are not properly mixed or dissolved before injection. To improve uniformity, use pressure compensating emitters, which provide a consistent output even with pressure changes (but generally cost more).

Conclusion and Recommendations

Fertigation is an effective way to improve blueberry yields, enhance nutrient and water use efficiency, as well as minimize environmental impact. To maximize benefit, growers should assess their existing irrigation system and water quality. Use water-soluble, ammonium-based fertilizers, and ensure the system includes filters and approved backflow prevention devices. Develop a fertigation schedule based on crop growth stages. Regularly flush the system to prevent clogging. With proper irrigation system design and management, fertigation supports healthier plants, better fruit quality, and more sustainable production. If you need help with any part of the fertigation process, reach out to your local county extension agent for support.

References

Bayabil, H. K., Migliaccio, K. W., Crane, J. H., Olczyk, T., & Wang, Q. (2020). Regulations and guidelines for chemigation (AE542). University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension. https://edis.ifas.ufl.edu/publication/AE542

Claussen, W., & Lenz, F. (1999). Effect of ammonium or nitrate nutrition on net photosynthesis, growth, and activity of the enzymes nitrate reductase and glutamine synthetase in blueberry, raspberry and strawberry. Plant and Soil, 208, 95–102. https://doi.org/10.1023/A:1004457720197

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