Práticas de maneja para otimizar a produção agropecuária: Fontes de adubação nitrogenada em sistema silvipastoril e frequêncai de suplementação em bezerros de corte desmamados precocemente.

Abstract

Two independent research projects were conducted and included in the dissertation. The objective of the first experiment was to evaluate the effect of N sources in cropping systems. This experiment was conducted at the Department of Animal Science Federal University of Tocantins, Araguaína, Brazil, from January to April 2019 and 2020. Treatments were the 2x4 factorial arrangement of two cropping systems [silvopastoral system (SSP) and monoculture (MN)] of ‘Mombasa’ guineagrass (Panicum maximum); and three fertilizer N sources [urea (UR); ammonium sulfate (SA); urea + Cu 0,15% + B 0,4% (UCB)] and control (CONT; no N fertilization), applying 200 kg N ha-1 ano-1, distributed in a randomized complete block design with four replicates. Response variables were forage accumulation (MSFT), leaf (MSF), stem (MSC) and dead material (MSMM), canopy height (ALT), and tiller density (NP). Overall, MN had greater NP than SSP (P = 0,003). There was no difference (P = 0,37) between N sources of SA, UCB and UR, but all had greater NP than CONT. Overall MSF, MSMM and MSFT was greater to MN than SSP (P <0,0001) and MSF, MSC, MSMM and MSFT were greater to all N fertilizer sources than CONT. The greatest MSF, MSC and MSFT were to SA. UCB treatment had intermediate values of MSF and MSFT and did not differ from SA and UR, which had the least and greatest values, respectively. The CONT had lower ALT than other treatments. There was a tendency (P = 0,07) to higher ALT to SA than UR, and the SA did not differ from the UCB (P = 0,27). The MN had the greatest N use efficiency (54 kg MS kg-1 N) (P <0,0001) than SSP (22 kg MS kg-1 N). The greatest N use efficiency was to SA in MN system (61 kg MS kg-1 N), and the least was on UR in SSP system (15 kg MS kg-1 N). The MN had 14% greater N use efficiency than SSP. The silvopastoral system had decreased N use efficiency and urea + Cu 0,15% and B 0,4% did not increase forage accumulation of Mombasa in the Amazon region. The second experiment was conducted at the Range Cattle Research and Education Center, Ona, FL, from February to July 2019 and February to June 2020 and the objective was to evaluate the effects of decreasing supplementation frequency on performance and physiological responses of early-weaned calves in pastures and drylot. In the grazing phase, Angus x Brahman crossing calves were weaned (age of 90 ± 15 days) and distributed in 8 annual ryegrass (Lolium multiflorum) pastures. At the drylot phase, animals from the grazing phase were selected and distributed in 24 pens. Treatments were concentrated supplementation offered daily (7X) or three times weekly (3X) distributed in a randomized complete block design with four replicates. There was no difference between treatments on herbage mass (HF), forage allowance (FA), crude protein (CP) and in vitro digestibility organic matter (IVDOM) (P ≥ 0,85); However, there was a month effect (P <0,001) on HM and IVDOM, which decreased from February to April. There was no treatment effect for body weight (BW) and average daily gain (ADG) (P ≥ 0,94) but PC increased from February to March and subsequent decreased from March to April (P ≤ 0,0001). There was no effect of treatments on plasma urea nitrogen (P> 0,88), but there was a day effect (P = 0,09). The concentration of blood glucose decreased over time from d 0 to 84 (P <0,0001). The 7X treatment had greater forage dry matter intake (CF) (P <0,0006) than 3x during the experimental period. The 3X treatment had greater total dry matter intake (DMI) than 7X on supplementation days but lesser on days when calves did not receive supplement (P <0,001). However, the 7X had greater total DMI than 3X (P < 0,0004). Decreasing the frequency of daily supplementation to 3 times per week decreases forage and total DMI but did not affect performance of early weaned calves receiving annual ryegrass.