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Nanomaterials composed of non-nutritive elements are gaining momentum in agriculture. In view of these advances, this study aimed to synthesize and assess the effects of silver (Ag) and cobalt (Co) nanoparticles as seed treatment in maize crops. Nanoparticles were synthesized by coprecipitation and characterized by X-ray diffractometry, transmission electron microscopy, surface area analysis, and Fourier-transform infrared spectroscopy. An experiment was carried out according to a completely randomized design with a 3 × 5 factorial arrangement. The factors were Ag and Co source (soluble, microparticle, and nanoparticle) and concentration (0, 20, 40, 80, and 160 mg L−1). A total of 50 maize seeds were used per treatment. Seeds were placed on germination paper moistened with distilled water. Germination, biometric parameters (root and shoot lengths), and biomass production were evaluated. Characterization analyses showed that particles ranged from 20 to 100 nm in size and were composed of oxides, such as Ag2O and Co3O4. Nanoparticle treatment improved germination and reduced the incidence of defects. The best results were achieved with 98–106 mg L−1 Ag2O and 75–80 mg L−1 Co3O4. There was no significant change in biometric parameters between treatments.

ABSTRACT From 1913 onwards, the global situation changed from a scenario of nitrogen (N) scarcity to an abundance of ammonia (NH3) produced synthetically via the Haber-Bosch process. Several N compounds have been synthesized since then, with urea becoming the main source of N, accounting for 55 % of current N consumption. However, N efficiency in agroecosystems is low and, normally, N recovery in cultivated plants is less than 50 %. This occurs because a large amount of reactive N is lost to the environment, inducing various forms of pollution, threatening human and environmental health, in addition to causing a negative economic impact on the farmer. The main processes responsible for low N efficiency are NH3 volatilization, leaching, and N denitrification. Considering global NH3 volatilization losses of 14 %, it can be assumed that up to 8.6 million Mg of urea are lost every year in the form of NH3. For each ton of NH3 produced, 1.9 to 3.8 Mg of CO2 is emitted into the atmosphere. Therefore, increasing N use efficiency (NUE) without compromising yield is a necessity and a challenge for crop improvement programs and current management systems, in addition to reducing greenhouse gas emissions. In this context, enhanced efficiency fertilizers (EEFs), which contain technologies that minimize the potential for nutrient losses compared to conventional sources, are an alternative to increasing the efficiency of nitrogen fertilization. Currently, EEFs are classified into three categories: stabilized, slow-release, and controlled-release. This study aims to understand the technologies used to produce EEFs and the factors that govern their availability to plants. This review covers the following topics: the discovery of N, N dynamics in the soil-atmosphere system, N assimilation in plants, strategies to increase NUE in agrosystems, NH3 synthesis, NH3 volatilization losses, N fertilizer technologies, the importance of characterization of EEFs, conventional nitrate or ammonium-based fertilizers to reduce gaseous losses of NH3 and future prospects for the use of N fertilizers in agriculture.