Plant absorption Inorganic forms of selenite ( \({\text{SeO}}_{3}^{2 - }\) ) and selenate ( \({\text{SeO}}_{4}^{2 - }\) ) comprise 73% to 76% of total soil. A soil is considered Se deficient if its Se concentration is <0.5 mg/kg. In agriculture, there are three main methods for applying se fertilizer: direct application, seed treatment, soilless culture application and nano application. These three primary applications can be further divided into seven sub-application techniques, such as hydroponics, foliar application, soil/root application, seed dressing, seed soaking, seed priming, and nano-selenium. Plants use between 5 and 30% of the selenium that is typically applied as a mineral fertilizer. Since individual plants may directly absorb exogenously supplied selenium and then efficiently moving it to other sections of the plant, particularly in the crop’s edible parts, foliar applications can result in a 20–50% higher absorption rate than soil methods. Se seed priming enhances plant tolerance in stressful conditions, particularly drought. It can improve water use efficiency by 25–40%, increase germination rates by 15–30%, and boost seedling growth by 20–50% compared to untreated seeds. Popularization of seed dressing and seed soaking is challenging because to its impracticality, low efficiency, and inconvenience. Modern application of Se nanoparticles (Se-NPs) is more active than other bulk materials and models. This chapter explores different selenium (Se) application methods in agriculture analyzing the efficacy of traditional techniques like soil application and foliar spraying and seed treatments against emerging technologies like nano-selenium (Se-NPs). It sheds light on the use of Se-NPs to optimally mitigate stress while improving bioavailability and uptake efficiency, which is critical to sustainable crop production and food security.