Alternatives to Mineral Nitrogen Fertilizers in Agriculture: State of the Art, Challenges and Future Prospects

Despite being one of the main components of the biosphere, nitrogen remains a limiting factor for agriculture. N-fertilizers produced using the Haber-Bosch process have addressed this issue, which has markedly increased crop yield and food production during the last century. Unfortunately, this process has unbalanced the soil nitrogen cycle due to the overapplication of mineral fertilizers in agricultural soils over several decades. Annually, thousands of tons of nitrogenous species are released, such as nitrogen oxides (NOx), ammonia (NH3), nitrous oxide (N2O), and the anion nitrate (NO3¿) into water, soil, and the atmosphere. Concomitantly, contamination events such as water eutrophication or greenhouse gas emissions, among others, are more frequent in the present era. In order to develop an environmentally friendly agricultural system, it is necessary to investigate alternatives that could result in a reduction in the use of mineral N-fertilizer without compromising yield productivity. In this Special Issue, we highlight investigations related to the minimization of environmental impacts of nitrogen application in agriculture and the optimization of fertilization.