Plant fertilization is a sophisticated science that requires understanding both plant needs and the interactions between nutrients and the fertilizer salts used to supply them. Certain nutrient combinations can interfere with uptake, while improper fertilizer combinations may lead to precipitation or other reactions that make nutrients unavailable for absorption.
If you’re using pre-mixed fertilizers from a reputable brand, these incompatibilities aren’t a concern, as such products are formulated in a balanced way to ensure chemical compatibility. However, if you prefer to mix your own fertilizers, it is important to understand which combinations to avoid.
Understanding nutrient interactions
A nutrient interaction occurs when one nutrient affects the absorption or utilization of another. These interactions can be classified as either chemical or competitive:[1]
- Chemical: Nutrient ions form bonds that result in precipitates or complexes, reducing availability.
- Competitive: Nutrients with similar chemical properties—such as size and charge—compete for uptake, transport and function. This is common among calcium, magnesium, potassium and sodium, which share similar uptake pathways.
Nutrient interactions can occur in the root zone or within the plant and may be influenced by several factors, including:[2]
- Nutrient concentration
- Temperature
- Light intensity
- Moisture and aeration of the growing medium
- pH
- Root architecture
- Transpiration and respiration rates
- Plant age and growth stage
Nutrient interactions can occur in the root zone or within the plant and may be influenced by several factors, including:[2]
- Nutrient concentration
- Temperature
- Light intensity
- Moisture and aeration of the growing medium
- pH
- Root architecture
- Transpiration and respiration rates
- Plant age and growth stage
Synergism and antagonism
Nutrient interactions can be: [3]
- Synergistic: The interaction has a greater positive effect on the plant than the nutrients would have individually (e.g., 1 + 1 = 3, rather than 2).
- Antagonistic: The interaction reduces the availability or effectiveness of one of the nutrients, negatively impacting the plant. A common example is cation antagonism, where an excess of one nutrient limits the uptake of others. The number of cations a plant absorbs depends not only on their availability, but also on the presence of competing cations.
- Neutral: The interaction has no greater or lesser effect than each nutrient would have individually.
Mulder’s Chart (Figure 1) provides a quick visual reference for identifying synergistic and antagonistic interactions between nutrients.
Most macronutrients have synergistic effects with each other, and these interactions can increase yields by a factor of 1–3 compared to what individual nutrients provide. Since macros form the foundation of fertilizer programs, accounting for these synergies is essential.[4]
Figure 1. Mulder’s Chart. Red lines indicate antagonistic relationships; green lines indicate synergistic relationships.
Figure 1. Mulder’s Chart. Red lines indicate antagonistic relationships; green lines indicate synergistic relationships.
Most macronutrients have synergistic effects with each other, and these interactions can increase yields by a factor of 1–3 compared to what individual nutrients provide. Since macros form the foundation of fertilizer programs, accounting for these synergies is essential.[4]
Examples of synergistic interactions:
- Nitrogen and magnesium: When balanced, these promote chlorophyll formation, photosynthesis and nitrogen utilization. When imbalanced, they may reduce photosynthetic efficiency.[5]
- Nitrate and ammonium nitrogen with phosphorus: Both nitrogen forms affect root zone pH, improving root growth and phosphorus uptake.[6]
- Sulfur and nitrogen: Sulfur is essential for nitrogen use efficiency and protein synthesis.[7]
- Potassium and iron: Adequate potassium levels help promote iron uptake, though too much potassium can be antagonistic.[8]
- Iron and copper: These two micronutrients influence each other’s absorption.[9]
- Boron and calcium: These work together to support cell wall structure and function.[10]
- Phosphorus and magnesium: Magnesium aids phosphate transfer, and their synergy benefits early root development.[11]
Examples of antagonistic interactions:
- Ammonium nitrogen and potassium: Excess ammonium can reduce potassium uptake, especially when nitrate levels are low.[12], [13]
- Chloride and nitrate nitrogen: High chloride levels, often from saline irrigation water, can inhibit nitrate uptake.[14]
- Calcium, magnesium and potassium: Imbalances can interfere with uptake. For example, excess potassium may reduce calcium absorption, while too much calcium can inhibit magnesium.[15] These effects are especially pronounced in recirculating hydroponic systems, where growers should carefully monitor and balance these nutrients.
- Phosphorus and zinc, copper and iron: Excess phosphorus can cause zinc deficiencies[16] and reduce copper uptake.[17] Iron is antagonistic with phosphorus because it binds easily with phosphate in acidic conditions, forming an insoluble complex that reduces the availability of both. High phosphorus levels can therefore lead to decreased iron absorption, causing chlorosis.[18]
Since many growing media used in hydroponics have little to no cation exchange capacity, nutrient availability depends entirely on the nutrient solution. Providing the right nutrient balance is critical for promoting beneficial synergies and minimizing antagonisms.
Fertilizer compatibility
In addition to understanding how nutrients interact, growers need to consider fertilizer compatibility. Since nutrients are supplied as salts, chemically incompatible dry fertilizers may react with one another, leading to nutrient precipitation and clogged irrigation systems. To prevent this, growers can consult a fertilizer compatibility chart (Figure 2), which helps determine which dry fertilizers can be safely mixed without causing instability.
Figure 2. Nutrient compatibility chart. Notes on correlating box numbers below. Image source: Fertilizers Europe. 2014. “Guidance for Compatibility of Fertilizer Blending Materials.” Accessed April 7, 2025. https://www.fertilizerseurope.com/wp-content/uploads/2019/08/Guidance_for_compatibility2.pdf.
- Monitor moisture absorption, as its hygroscopic nature can weaken storage properties, depending on how the ammonium nitrate grade is stabilized.
- Assess the risk of detonability[19] when blending ammonium nitrate or ammonium sulfate and consider all related safety and legal implications.
- Assess the additional risks of free acid and organic impurities[20] when blending ammonium nitrate with ammonium sulfate, beyond detonability concerns.
- Expect this combination to absorb moisture quickly and form a liquid or slurry; manage the associated safety risks.
- Check for the presence of free acid, as it can significantly slow ammonium nitrate decomposition and compromise packaging.
- Consider the risk of self-sustained decomposition and evaluate the level of oil coating[21] on the material.
- Prevent sulfur from coming into contact with nitrates (e.g., ammonium nitrate, potassium nitrate or sodium nitrate) to avoid combustion.
- Monitor moisture absorption, as its hygroscopic nature can weaken storage properties, depending on how the ammonium nitrate grade is stabilized.
- Check the moisture content of single superphosphate or triple superphosphate when blending, as excessive moisture can cause caking.
- Avoid blending during periods of high humidity to minimize the risk of moisture absorption.
- Anticipate the risk of gypsum formation when calcium nitrate and other sulfate sources are blended.
- Confirm compatibility by conducting a test or chemical analysis before blending.
- Monitor impurities in ammonium sulfate and account for the reduction in the critical relative humidity of the blend.
- Evaluate the impact of additional nitrate[22] on nutrient balance and potential detonability.
- Prevent ammonium phosphate or potassium nitrate from reacting with urea by controlling relative humidity during blending.
- Check for free acid, as it can trigger urea hydrolysis and the release of ammonia and carbon dioxide.
- Expect sticky urea phosphate formation when blending urea with phosphate sources.
- Control moisture levels carefully to prevent caking.
- Manage the risk of reactions, such as neutralization with ammonia or acid attack with carbonates, if free acid is present.
Green boxes indicate compatibility; yellow shows limited compatibility; red indicates incompatibility. As shown in the chart, dry forms of urea and ammonium are incompatible due to their tendency to form slurry, while calcium nitrate combined with potassium or magnesium sulfate may lead to gypsum precipitation.
To prevent these kinds of reactions, always double-check compatibility before blending fertilizers. Precipitation can also occur when using concentrated fertilizers, but these can be avoided by using two stock tanks, with calcium-based fertilizers in one and phosphates and sulfurs in the other.[23]
Most pre-mixed fertilizers are already divided into two or three parts to maintain stability.
Choose a complete fertilizer line
Building a nutrient management program requires selecting fertilizers that are both chemically compatible and nutritionally balanced, thereby maximizing synergies, minimizing antagonisms and delivering the right concentrations and ratios for the plant’s needs at each growth stage.
Growers can avoid the headache of managing all this complexity by choosing a complete fertilizer line from a reputable brand like Emerald Harvest.
Choose a complete fertilizer line
Building a nutrient management program requires selecting fertilizers that are both chemically compatible and nutritionally balanced, thereby maximizing synergies, minimizing antagonisms and delivering the right concentrations and ratios for the plant’s needs at each growth stage.
Growers can avoid the headache of managing all this complexity by choosing a complete fertilizer line from a reputable brand like Emerald Harvest.
Sticking with pre-mixed fertilizers from one company ensures the products are chemically compatible and formulated to work in tandem, while providing the right nutrients in the optimal concentrations and ratios at the ideal times. Emerald Harvest’s line is also simple and compact, consisting of premium base nutrients and supplements designed to work together, so growers can achieve the biggest yields and highest possible quality.
Emerald Harvest Team
[1] Fageria, V.D. 2001. “Nutrient Interactions in Crop Plants.” Journal of Plant Nutrition 24 (8): 1269-1290. https://doi.org/10.1081/PLN-100106981.
[2] Ibid.
[3] Ibid.
[4] Fageria, Nand Kumar. 2014. Nitrogen Management in Crop Production. CRC Press. https://doi.org/10.1201/b17101.
[5] Mao, Yunxia, Xirong Chai, Min Zhong, et. al. 2022. “Effects of Nitrogen and Magnesium Nutrient on the Plant Growth, Quality, Photosynthetic Characteristics, Antioxidant Metabolism, and Endogenous Hormone of Chinese Kale (Brassica albograbra Bailey). Scientia Horticulturae 303: 111243. https://doi.org/10.1016/j.scienta.2022.111243
[6] Adams, Fred. 1980. “Interactions of Phosphorus with Other Elements in Soils and in Plants” in The Role of Phosphorus in Agriculture, edited by F.E. Khasawneh, E.C. Sample, and E.J. Kamprath. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
[7] White, Charles, John Spargo, Hanna Wells, Zachary Sanders, Tyler Rice, and Doug Beedle. 2021. “Sulfur Fertility Management for Grain and Forage Crops.” PennState Extension, September 15. https://extension.psu.edu/sulfur-fertility-management-for-grain-and-forage-crops.
[8] Celik, Hakan, Baris Bulent Asik, Serhat Gurel, and Ali Vahap Katkat. 2010. “Potassium as an Intensifying Factor for Iron Chlorosis.” International Journal of Agriculture & Biology 12 (3): 359-364.
[9] Rai, Snigdha, Prashant Kumar Singh, Samriti Mankotia, Jagannath Swain, and Santosh B. Satbhai. 2021. “Iron Homeostasis in Plants and its Crosstalk with Copper, Zinc, and Manganese.” Plant Stress 1: 10008. https://doi.org/10.1016/j.stress.2021.100008.
[10] Vera-Maldonado, Peter, Felipe Aquea, Marjorie Reyes-Diaz, et. al. 2014. “Role of Boron and Its Interaction with Other Elements in Plants.” Frontiers in Plant Science 15: 1332459. https://doi.org/10.3389/fpls.2024.1332459.
[11] Niu, Yaofang, Gulei Jin, Xin Li, et. al. 2015. “Phosphorus and Magnesium Interactively Modulate the Elongation and Directional Growth of Primary Roots in Arabidopsis thaliana (L.) Heynh.” Journal of Experimental Botany 66 (13); 3841-3854. https://doi.org/10.1093/jxb/erv181.
[12] Zhang, Fusuo, Junfang Niu, Weifeng Zhang, et. al. 2010. “Potassium Nutrition of Crops Under Varied Regimes of Nitrogen Supply.” Plant and Soil 335: 21-34. https://doi.org/10.1007/s11104-010-0323-4.
[13] High-quality liquid fertilizers tend to contain a higher portion of nitrate nitrogen vs. ammoniacal nitrogen, while dry fertilizers typically have higher ammoniacal nitrogen levels.
[14] Rosales, Miguel A., Juan D. Franco-Navarro, Procopio Peinado-Torrubia, Pablo Diaz-Rueda, Rosario Alvarez, Jose M. Colmenero-Flores. 2020. “Chloride Improves Nitrate Utilization and NUE in Plants.” Frontiers in Plant Science 11: 442. https://doi.org/10.3389/fpls.2020.00442.
[15] Currey, Christopher J. 2021. “Nutrient Antagonisms- The Potassium-Calcium-Magnesium Relationship.” E-GRO Edible Alert 6 (14). https://www.e-gro.org/pdf/E614.pdf.
[16] Cornell University. n.d. “Nutrient Management Competency Area 1: Basic Concepts of Plant Nutrition.” Accessed April 7, 2025. https://nrcca.cals.cornell.edu/soilFertilityCA/CA1/CA1_print.html.
[17] Javadi, Morteza, James E. Beuerlein, and Trevor G. Arscott. 1991. “Effects of Phosphorus and Copper on Factors Influencing Nutrient Uptake, Photosynthesis, and Grain Yield of Wheat.” Ohio Journal of Science 91 (5): 191-194. https://kb.osu.edu/server/api/core/bitstreams/3eb12057-4877-556e-979b-187659af8802/content.
[18] Yang, Xingqi, Chang Liu, Cuiyue Liang, Tianqi Wang, and Jiang Tian. 2024. “The Phosphorus-Iron Nexus: Decoding the Nutrients Interaction in Soil and Plant.” International Journal of Molecular Sciences 25 (13): 6992. https://doi.org/10.330/ijms25136992.
[19] Sanchez, Elsa, Francesco Di Gioia, Thomas Ford, Robert Berghage, and Nick Flax. 2024. “Hydroponics Systems: Nutrient Solution Programs and Recipes.” PennState Extension, updated March 18. https://extension.psu.edu/hydroponics-systems-nutrient-solution-programs-and-recipes.
[20] Detonability refers to a material’s ability to sustain a detonation—a rapid, supersonic chemical reaction accompanied by a shockwave and release of energy and gases.
[21] Free acids can decompose material, and organic impurities reduce purity and stability.
[22] Moisture absorption through damaged or insufficient oil coatings can lead to granule caking.
[23] Additional nitrate increases nitrogen content, which can cause nutrient imbalance and raise the risk of detonability.
