Use of Nitrogen Fertilizers Enriched with Selenium (Se-enriched N)

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Selenium-enriched nitrogen fertilizers are standard nitrogen products—such as urea, UAN, ammonium sulfate, or NPK blends—that have been coated or impregnated with small, controlled amounts of selenium, usually in the form of sodium selenate (Na₂SeO₄) or sodium selenite (Na₂SeO₃). When applied in the field, these fertilizers improve crop performance by enhancing stress tolerance, supporting healthier root growth, and strengthening plant defence systems. Selenium helps plants moderate oxidative stress, maintain better chlorophyll function, and cope with drought, salinity, and certain disease pressures. Because the selenium is delivered together with nitrogen, crops absorb it more efficiently, which often results in stronger early growth, improved vigour, and more uniform stands. This makes Se-enriched N fertilizers a practical, field-ready option for farmers looking to improve crop resilience and productivity without changing their existing fertilizer programs.

Principle

Selenium (Se) is not required in large quantities by plants, but small additions of Se through fertilizers can significantly improve crop performance under field conditions. The agronomic principle behind using Se-enriched nitrogen fertilizers is that selenium, when applied in very low, controlled doses, enhances plant physiological functions such as antioxidant capacity, stress tolerance, root development, and nitrogen-use efficiency. These improvements help crops maintain better growth under drought, salinity, high temperature, and other environmental stresses—leading to more stable yields.

In fertilizers, selenium is supplied mainly in two inorganic forms: selenate (SeVI) and selenite (SeIV).

• Selenate (SeVI) is highly soluble and moves easily through soil and plant tissues. It is taken up efficiently by roots and transported to leaves, where it supports photosynthesis and stress defense.
• Selenite (SeIV) is more strongly bound to soil particles and tends to stay near the root zone. It is absorbed more slowly but promotes root activity and oxidative stress reduction.

Once inside the plant, selenium participates in the sulfur metabolic pathway, where it boosts the plant’s natural antioxidant system (e.g., glutathione, peroxidases). This reduces cellular damage, delays leaf senescence, and helps plants maintain greener leaf area during critical growth stages.

Nitrogen fertilizers act as practical carriers for selenium because they provide uniform field distribution and improve Se uptake. Nitrogen application stimulates amino acid and protein synthesis in crops, which enhances the incorporation of selenium into plant metabolism and improves the plant’s physiological resilience. This Se–N synergy results in improvements such as better chlorophyll maintenance, stronger root systems, improved nutrient uptake, and greater tolerance to environmental stress (Ramkissoon et al., 2019).

Description of Formulations

1. Selenate-enriched urea granules (solid blends) These consist of urea granules impregnated or coated with sodium selenate. Upon dissolution, both N and Se are simultaneously available to the root zone. Premarathna et al. (2012) demonstrated that applying selenate-enriched urea in flooded paddy rice at the heading stage significantly increased rice grain Se concentration, with over 90% of total grain Se occurring as SeMet, indicating highly efficient biofortification.
2. Se-coated macronutrient granules (e.g., Se + ammonium sulfate, Se + NPK) These are manufactured through coating or blending processes. However, their performance depends on granule dissolution, soil pH, and redox conditions. In alkaline or reducing soils, selenate may be quickly converted to less available SeIV, reducing Se bioavailability. Ramkissoon et al. (2019) found that while granular Se-enriched macronutrients worked in some soils, pure soluble selenate applications were generally more effective for consistent Se uptake.
3. Foliar Se applications with N carriers (liquid urea or UAN) Foliar application of selenate or selenite solutions combined with 2% (w/v) urea enhances cuticular penetration and Se translocation to grains. Studies show that foliar Se + N mixtures can double grain Se accumulation compared with Se-only sprays, while reducing soil Se buildup and environmental risks (Ramkissoon et al., 2019).
4. Se-enriched compound fertilizers and slow-release/nano-Se formulations Recent innovations include nano-selenium and Se bound to organic or microbial carriers, designed to stabilize Se in soil, prevent leaching, and prolong availability (Kang et al., 2024). These formulations also improve soil microbial diversity and enzyme activity, enhancing nutrient cycling and Se bioavailability in the rhizosphere.

How to Use Se-enriched N Fertilizers

• Soil broadcast or base application: Apply Se-enriched granules as part of standard nitrogen dressing (either basal or side-dress). In rice, broadcasting Se-enriched urea into floodwater at heading dramatically improved Se accumulation in grain (Premarathna et al., 2012).
• Foliar application: Use low Se concentration solutions (typically <50 mg Se·L⁻¹) mixed with 2% urea or UAN. Apply at growth stages corresponding to grain/tuber filling to maximize Se transfer to edible tissues. Foliar routes offer high efficiency, using minimal Se mass while maintaining safe residue levels.
• Seed priming or dressing: For small-seeded crops, short-duration soaking in dilute Se solutions can enhance early seedling vigor and Se uptake. However, concentrations must be extremely low to avoid phytotoxicity (Danso et al., 2023).

Se biofortification promotes crop yields and quality parameters. Se-biofortification ap proaches include (1) genetic tools, (2) through foliar application, (3) soil amendment, (4) agronomic biofortification, (5) broadcasting into soils, (6) green manure with Se, enriched growth and development of plants, (7) nano-sized biofortification to leaves or soil, and (8) intercropping with Se- hyper-accumulator plants (Hossain et al., 2021).

When to Use It

• Cereals: Foliar sprays at heading or early grain filling maximize SeMet formation in grain. Soil-applied Se at heading in flooded rice is also effective (Premarathna et al., 2012).
• Root/tuber crops: Applying Se + N during bulking stages enhances Se translocation into tubers and may increase yield (Li et al., 2023).
• Leafy vegetables: Foliar Se sprays at late vegetative stages boost Se levels but require careful control to prevent taste or tissue damage (Schiavon et al., 2022).

Advantages

• Salinity resistance

Selenium efficacy in preventing such stress has been documented in a number of publications. Onions grown on silt loam soil with a salinity of 8 dS/m were less affected by salt stress after receiving an application of Se in the form of sodium selenite(0.5-1 kg/ha) (Bybordi et al., 2018).

• Human nutrition and bioavailability: Se-enriched fertilizers effectively raise dietary Se intake, with most of the accumulated Se in crops present as selenomethionine, a highly bioavailable form. Se acts as a strong antioxidant and protects the body from heart disease, Cardiovascular Problems, some cancers and beneficial for thyroid health (Hossain et al., 2021).
• Agronomic and physiological benefits: Proper Se application enhances antioxidant enzyme activities (e.g., glutathione peroxidase, ascorbate peroxidase), improves photosynthetic efficiency, and increases resistance to oxidative stress (Li et al., 2023).

Limits and Risks

• Toxicity risk: Selenium is an essential micronutrient for humans, and the recommended intake is 55–70 g per day (Schiavon et al., 2022). Excessive Se in food can lead to selenosis in animals and humans.
• Soil chemical constraints: pH, organic matter, redox, and clay content determine Se mobility. Selenate may reduce to SeIV or elemental Se under waterlogged or reducing conditions, limiting plant uptake (Sarwar et al., 2020).
• Environmental concerns: Leaching of soluble selenate into groundwater or runoff into aquatic systems can cause ecological harm. Buffer zones and precision dosing are essential.
• Regulatory and logistical challenges: Se fertilizer use is regulated in several countries, with limited commercial availability. Safe handling and strict adherence to national limits are required (Danso et al., 2023).

Field Testimonials

• Rice:  Two Se species, selenate (SeO4 2−) and selenite (SeO3 2−), were applied at a rate equivalent to 30 g ha−1. Four application methods were employed as follows: (i) Se applied at soil preparation, (ii) Se-enriched urea granules applied to floodwater at heading; (iii) foliar Se applied at heading; and (iv) fluid fertilizer Se applied to soil or flood water at heading. Premarathna et al. (2012) reported 5–6× higher grain Se concentrations after broadcasting selenate-enriched urea in paddy floodwater, with >90% Se as SeMet.
• Wheat: Ramkissoon et al. (2019) demonstrated that foliar Se + 2% urea doubled grain Se content compared to Se-only foliar application. A pot trial was set up to investigate whether the application of 3.33 µg kg−1 of Se (equivalent to 10 g ha−1) to wheat can be made more efficient by its co-application with macronutrient carriers, either to the soil or to the leaves.  In the soil, Se was applied either on its own (selenate only) or as a granular, Se-enriched macronutrient fertilizer supplying nitrogen, phosphorus, potassium or sulfur.  Co-application of foliar Se with an N carrier doubled the Se concentration in wheat grains compared to the application of foliar Se on its own,
• Potato: Li et al. (2023) found Se + N improved root function, photosynthesis, and tuber Se accumulation, increasing yield efficiency. Field experiments were conducted in 2019–2020 and 2020–2021. Three N levels, i.e., 0 kg N ha-1 (N0), 150 kg Nha -1 (N1) and 200kg Nha-1 (N2),and three Se levels, i.e., 0 g Se ha -1 (Se0), 500 g Se ha -1 (Se1) and 1000 g Se ha-1 (Se2), were set up.
• Leafy greens: Schiavon et al. (2022) observed dose-dependent Se enrichment in rocket leaves, altering phytochemical composition and nutritional value. Se was applied foliarly as selenate at 2.5, 5, or 10 mg per plant to two rocket species, Diplotaxistenuifolia and Eruca sativa, grown in soil and the effects in terms of Se enrichment and content of primary and secondary metabolites were comparatively analyzed. Foliar application of Seat the minimum dosage (2.5mg Se per plant) increased the fresh leaf and root biomass

Conclusions

Selenium-enriched nitrogen fertilizers are a proven agronomic tool that improve crop vigor, stress tolerance, and nutrient-use efficiency. Small, well-regulated doses of Se—especially when applied with nitrogen during reproductive stages—strengthen antioxidant activity, support root growth, and help maintain yield stability under drought, heat, or salinity. Because Se has a narrow safe range, applications must be tailored to soil conditions and crop needs. When properly managed, Se-enriched N fertilizers provide a cost-effective way to enhance plant resilience and overall fertilizer performance.

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References

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Hossain, A., Skalicky, M., Brestic, M., Maitra, S., Sarkar, S., Ahmad, Z., ... & Laing, A. M. (2021). Selenium biofortification: Roles, mechanisms, responses and prospects. Molecules, 26(4), 881.

Kang, Y., Ming, J., Fu, W., Long, L., Wen, X., Zhang, Q., ... & Yin, H. (2024). Selenium fertilizer improves microbial community structure and diversity of rhizospheric soil and selenium accumulation in tomato plants. Communications in Soil Science and Plant Analysis, 55(10), 1430–1444.

Li, S., Chen, H., Jiang, S., Hu, F., Xing, D., & Du, B. (2023). Selenium and nitrogen fertilizer management improves potato root function, photosynthesis, yield and selenium enrichment. Sustainability, 15(7), 6060.

Premarathna, L., McLaughlin, M. J., Kirby, J. K., Hettiarachchi, G. M., Stacey, S., & Chittleborough, D. J. (2012). Selenate-enriched urea granules are a highly effective fertilizer for selenium biofortification of paddy rice grain. Journal of Agricultural and Food Chemistry, 60(23), 6037–6044.

Ramkissoon, C., Degryse, F., da Silva, R. C., Baird, R., Young, S. D., Bailey, E. H., & McLaughlin, M. J. (2019). Improving the efficacy of selenium fertilizers for wheat biofortification. Scientific Reports, 9, 19520.

Sarwar, N., Akhtar, M., Kamran, M. A., Imran, M., Riaz, M. A., Kamran, K., & Hussain, S. (2020). Selenium biofortification in food crops: Key mechanisms and future perspectives. Journal of Food Composition and Analysis, 93, 103615.

Schiavon, M., Nardi, S., Pilon-Smits, E. A., & Dall’Acqua, S. (2022). Foliar selenium fertilization alters the content of dietary phytochemicals in two rocket species. Frontiers in Plant Science, 13, 987935.

White, P. J., & Broadley, M. R. (2009). Biofortification of crops with seven mineral elements often lacking in human diets. New Phytologist, 182(1), 49–84.

Bybordi, A., Saadat, S., & Zargaripour, P. (2018). The effect of zeolite, selenium and silicon on qualitative and quantitative traits of onion grown under salinity conditions. Archives of Agronomy and Soil Science, 64(4), 520-530.