Frequências de pastejo como estratégias de manejo do capim-zuri sob lotação intermitente

Abstract

Grazing management practices that modify the entry of light into the canopy promote changes in plant responses, generating the need for applied studies that seek to understand the cause-effect relationships. The objective of this work was to evaluate the effects of four grazing frequencies on the productive, morphogenic, structural characteristics and nutritional value of zuri grass. The experiment was carried out at Embrapa Beef Cattle, Campo Grande/MS, from October 2020 to March 2022. The experimental design was complete randomized blocks, with four treatments and four replications. The treatments consisted of four grazing frequencies, represented by the levels of light interception (LI) in the pre-grazing, of 80% LI, 85% LI, 90% LI and 95% LI in zuri grass under intermittent stocking. The grazing intensity was kept fixed at 50% of the entry height for the four treatments. For article 1, productive and structural characteristics and nutritional value were evaluated. In article 2, tillering dynamics and tissue flow were evaluated. In article 3, the dynamics of pasture lowering were evaluated, with the hypothesis that the different structures formed by the treatments could alter the efficiency of harvesting by the animals. Canopy height, forage mass (FM), forage accumulation (FA) and interval between grazing (IBG) were adjusted to a linear regression model, with increments as the LI increased by the canopy. The levels of 90% LI and 95% LI kept the pre-grazing height constant throughout the seasons, with averages of 65 and 75 cm, respectively. Tiller population density (TPD), percentage of crude protein (CP) and in vitro digestibility of organic matter (DIGOM) decreased with increasing IL levels in the canopy. The lowest TPD, CP and DIGOM for all grazing frequencies occurred in winter22. The highest MF (9626.1 kg/ha DM) and the highest FA (4738.4 kg/ha DM) were observed in summer21/22 for pastures managed with 95% LI, while the highest FAR was estimated in pastures managed with 90% LI. In spring, the highest leaf CP contents (15.53%) were found in pastures managed with 80% LI. For the dynamics of lowering, the frequency and intensity of defoliation was fitted to a linear regression model, with increments as the level of IL increased in the pre-grazing period. The efficiency of pasture use by the animals increased, with increases of 16.7%, 17.1%, 10.9%, and 4.1%, for expanded leaves, expanding leaves, pseudostem and extended tiller, respectively, when the canopy went from 80% LI to 95% LI. Zuri grass pastures managed with a higher frequency of defoliation have higher nutritional value and better morphological composition when compared to those managed with 95% LI in the pre-grazing. The gradual decrease in height and TPD for pastures managed with 80% LI may be indicative of compromised productive capacity and persistence of zuri grass. When the regrowth process was interrupted with 90% LI, the forage accumulation rate was higher and allowed a greater number of grazing cycles and better nutritional value. In the dynamics of lowering, IL influenced the structure of the zuri grass canopy and changed the way animals exploit the forage canopy. The IL of 80% resulted in a diet rich in leaves, a low proportion of stems and less time for reestablishment of the canopy. Pastures managed with 95% LI showed a lower leaf:stem ratio, but with a higher forage mass, which allowed a higher instantaneous stocking rate.