PSII-14 - Chemical composition of tropical forage fertilized with different sources of nitrogen fertilizers

Abstract: Nitrogen fertilization can improve the chemical composition of tropical forages, as nitrogen is required at all stages of plant development. The aim of this study was to verify the chemical composition of Urochloa brizantha cv. marandu fertilized with different sources of nitrogen fertilizers from the following treatments: without nitrogen fertilization (CO), fertilization with urea (UR), fertilization with ammonium nitrate (NI) and fertilization with ammonium sulfate (SA). The study was carried out from December 2021 to April 2022, in the cerrado biome of Brazil at the FCAV/UNESP Forage Sector, Jaboticabal Campus, during the rearing phase of Nelore cattle, non-castrated males kept on pasture, managed in a continuous stocking system and variable load capacity. In treatments with fertilization, 150 kg of N ha^-1 were applied, divided into 3 applications. The design used was in randomized blocks (DBC). The evaluation of the chemical composition of the forage was carried out from collections every 28 days of samples of the fraction of the forage consumed by the animals through the hand-plucking method. The samples were dried at 55ºC for 72 hours and ground in a mill of the type Willey, with a 1mm mesh sieve. The chemical composition of the forage was estimated by spectroscopy in the near infrared light region, NIRS (Near Infrared Spectrometer), using a modular FT-NIR spectrometer. The data obtained were submitted to ANOVA and Tukey's test (P≤0.05), using the statistical program R, version 3.4.4. Nitrogen fertilization significantly increased the organic matter content of the forage (P=0.001). The organic matter content of the non-fertilized treatment was 91.97%, while the average of the fertilized treatments was 92.22%. The percentage of crude protein in the forage also showed a significant difference (P< 0.001) between the non-fertilized treatment, which had an average of 10.64%, and the fertilized treatments, which had an average of 17.75%. The neutral detergent fiber and acid detergent fiber components also differed from the application of nitrogen fertilizer (P< 0.001) but did not differ between the types of fertilizers. The neutral detergent fiber content was significantly different (P< 0.001) between the non-fertilized treatment (59.21%) and the fertilized treatments (54.30%). The observed data for acid detergent fiber were 31.46% for the treatment without the use of fertilizers and 30.24% for the treatments with the use of fertilizers. Non-fibrous carbohydrates and liguinin components were also analyzed, but showed no difference between treatments, P=0.078 and P=0.209, respectively. This study confirms that the chemical composition of Urochloa brizantha cv. Marandu can be significantly improved through the application of nitrogen fertilizers. However, our results showed no significant difference between the types of fertilizers tested.