As an everyday beverage, coffee is consumed worldwide, generating a high amount of waste after brewing, which needs attention for its disposal. These residues are referred to as spent coffee grounds (SCGs), which have been shown to have applications as polymers/composites precursors, biofuels, and biofertilizers. This review focuses on agricultural applications usually based on organic matter to fertilize the soil and consequently improve plant growth. To date, SCGs have been shown to exhibit outstanding performance when applied as soil amendment and composting because it is a nutrient-rich organic waste without heavy metals. Therefore, this review presents the different options to use SCGs in agriculture. First, SCG composition using different characterization techniques is presented to identify the main components. Then, a review is presented showing how SCG toxicity can be resolved when used alone in the soil, especially at high concentrations. In this case, SCG is shown to be effective not only to enhance plant growth, but also to enhance nutritional values without impacting the environment while substituting conventional fertilizers. Finally, a conclusion is presented with openings for future developments.

Fertilizers are at the foundation of our modern society, and without them we would not be able to feed and sustain a majority of the world population. Of the major macronutrients necessary for agriculture, which include nitrogen (N), phosphorus (P), and potassium (K), nitrogen is essential for healthy plant growth, being vital for the production of amino-acids and proteins. For this reason, nitrogen is by far the most produced and applied fertilizer around the world, generally in the form of urea and ammonium salts, as well as through organic fertilizers, such as manures, composts, and digestates. Fortunately, in the early 1900s, the Haber-Bosch process was developed, allowing for the production of synthetic nitrogen fertilizers on an industrial scale – a process that is still responsible for over 96 percent of the world’s synthetic nitrogen production. However, despite the unimaginable benefits of nitrogen fertilizers on humanity, there have also been some significant impacts worldwide, notably ecologically and environmentally. Such impacts include soil acidification, eutrophication, nutrient run-off, reduced biological diversity, and substantial greenhouse gas (GHG) emissions. This chapter aims at exploring the environmental and ecological impact of nitrogen fertilizers, discussing the impact of their production and application to land.