ADUBAÇÃO NITROGENADA EM PASTAGENS TROPICAIS: EFEITO SOBRE A PRODUÇÃO DE FORRAGEM, DESEMPENHO ANIMAL E EMISSÕES DE GASES DE EFEITO ESTUFA

Abstract

The objective was to verify the effect of nitrogen fertilization in tropical pastures on forage production, animal performance and greenhouse gas emissions. The first chapter, through a narrative review of the literature, examines the main effects of nitrogen (N), its dynamics in the soil, plant and animal, and the relationship between N doses and greenhouse gas (GHG) emissions. The aim of the second chapter was to evaluate the effects of nitrogen fertilization on forage production, animal performance and greenhouse gas emissions in tropical pastures through a systematic literature review. A review protocol was drawn up, in which the search descriptors were previously tested and based on the PICOS mnemonic strategy to elaborate the guiding question where the population (P) was tropical forage grasses, the intervention (I) was nitrogen fertilization, the comparison (C) was the use of different doses of nitrogen, and the outcome (O) was forage production, animal performance and greenhouse gas emissions. The type of study, style (S), allowed only experimental studies. Thus, the following guiding question was developed: “What are the effects of nitrogen fertilization (types of N and doses) on forage production, animal performance and greenhouse gas emissions in tropical pastures?”. SCOPUS (Elsevier), Web of Science (Main Collection), Springer Link, SciELO, Science Direct (Elsevier) and the Cab Direct electronic library were used for the highly sensitive electronic search until November 23, 2023. The search identified 84,629 documents, of which 66,976 were scientific articles. Of the total, 54 articles were identified as potential sources of data of interest. However, only 34 were included for the extraction of results. Among the experimental conditions of the studies, 69.7% were carried out under grazing and 30.3% on plots. In the studies under grazing, 58.3% used the continuous stocking method and 37.5% intermittent stocking. Of the tropical forage genera and species studied, 52.9% were Brachiaria Brizantha and 26.5% Panicum maximum. The most commonly tested nitrogen (N) sources were urea (53.2%) and ammonium nitrate (25.5%). The doses tested ranged from 0 to 1,000 kg/ha of N. N promotes consistent increases in forage production and animal performance. Applying doses in line with the plants' assimilation capacity, choosing the time of application and the source of N, together with fractioning the annual dose of N, are essential strategies for reducing N losses, increasing utilization efficiency and potentially reducing environmental impact.