Citation: Pereira, L.E.T.; Herling, V.R.; Tech, A.R.B. Current Scenario and Perspectives for Nitrogen Fertilization Strategies on Tropical Perennial Grass Pastures: A Review. Agronomy 2022, 12, 2079. https:// doi.org/10.3390/agronomy12092079 Academic Editor: Jianbin Zhou Received: 11 July 2022 Accepted: 28 August 2022 Published: 31 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agronomy Review Current Scenario and Perspectives for Nitrogen Fertilization Strategies on Tropical Perennial Grass Pastures: A Review Lilian Elgalise Techio Pereira 1, * , Valdo Rodrigues Herling 1 and Adriano Rogerio Bruno Tech 2 1 Department of Animal Science, Faculty of Animal Science and Food Engineering (FZEA), University of São Paulo (USP), Av. Duque de Caxias Norte, 225, Pirassununga 13635-900, São Paulo, Brazil 2 Department of Basic Sciences, Faculty of Animal Science and Food Engineering (FZEA), University of São Paulo (USP), Av. Duque de Caxias Norte, 225, Pirassununga 13635-900, São Paulo, Brazil * Correspondence: ltechio@usp.br Abstract: Traditional Nitrogen (N) fertilization practices for tropical perennial grass are still based on annual amounts, following flat N rates instalments. This strategy does not consider variations in climatic conditions along the growing season, their impacts on the plant’s demand and the soil N availability. At regrowth cycles where the amount of soil N released from mineralization or through animal excreta surpass the plant’s demand, most of the N may be lost (as ammonia, nitrate, and nitrous oxide), increasing production costs and environmental pollution. This paper examines current N fertilization and discusses possible gaps in knowledge for the definition of more precise fertilization guidelines in pasture-based livestock systems based on tropical perennial grasses. More precise fertilization practices, based upon site and seasonal-specific recommendations, will substantially contribute to the establishment of best fertilization guidelines. Sustainable approaches can be defined by combining the identification of regrowth cycles where high N rates are required, with enhanced efficiency fertilizers, and/or using grass species with the potential for biological nitrification inhibition. The lack of information on tropical grasses requirements, and soil and climatic factors driving the N fate into the mineralization and immobilization processes and how these factors affect plant’s N demand, still prevents opportunities for tactical applications and the establishment of best management guidelines. Keywords: environmental N losses; fertilizer management; litter quality; site-specific nutrient management; soil N mineralization 1. Introduction Grasslands, besides being the predominant forage source for grazing animals, also provide critical human goods (products from cattle, sheep, goats, and camels) and ecosys- tem services (climate change regulation, wildlife habitat, genetic resources, erosion control, water provision, air purification, and cultural and amenity services), thus are considered essential to sustain human societies [1]. However, all the socioeconomic, environmental, and ecological functions provided by grasslands are being progressively placed under severe threat or even being lost due to a long-term degradation process [2]. Despite the causes of grasslands degradation being multifactorial, [3] reported that, in a global scale, climate variation is associated with approximately 45.5% of the degradation processes in grassland areas, whereas human activities accounted for around 40.1% of this degradation. According to [1–3], overgrazing by livestock, land abandonment, extensive clearing for crop production, a heightened fire frequency, and inappropriate management and soil conservation practices that lead to soil erosion and woody plant encroachment, are included in the human activities that play critical roles in the degradation process. In this way, in a future scenario of climate change, equating human activities will be a decisive step towards the establishment of sustainable management practices. Agronomy 2022, 12, 2079. https://doi.org/10.3390/agronomy12092079 https://www.mdpi.com/journal/agronomy