Potencial produtivo e estratégia de manejo da desfolhação para pastejo intermitente em três híbridos do gênero urochloa

Abstract

The objective was to evaluate the productive potential of three forage hybrids of the Urochloa genus and to define defoliation strategies based on the number of leaves that appeared in the tillers that allow the supply of forage material with good structural quality for grazing. The experimental period was from January to October 2018, accumulating a total precipitation of 1252.8 mm, in the periods of water (01/03/2018 to 06/04/2018) and drought (07/10/2018 to 26/10/2018). The experimental design was in randomized blocks in a split plot scheme, with the Marandu grass and the three hybrids being evaluated in the plots, and in the subplots the three regrowth times (2.5, 3.5 and 4.5 leaves from the tiller), with four replications, totaling 48 experimental units of 10 m² (2.5 x 4 m) each. The evaluations took place when the average of 15 tillers had reached the desired goal of the number of leaves, being then measured the canopy height, tillers count and the accumulation of forage above 20 cm from the soil. The value found for the number of leaves appeared was 2.4; 3.2 and 4.2 for the 2.5 treatments; 3.5 and 4.5 leaves emerged per tiller, getting close to what was intended, determining the height of the canopy with the appearance of leaves, with 33.61; 36.93 and 46.78 cm, respectively, with the forage 172 having the highest height (42.30 cm). Tiller population density (DPP) was higher in the lowest defoliation frequency (749 tillers / m²) and lower in forage 172 (597 tillers / m²). Forage accumulation (AcF), leaf blade (AcLF), stem (AcC) and dead material (AcMM) decreased with increasing defoliation frequency. Forage 171 presented the highest AcF (4.19), 173 the lowest AcLF (2.36) and 172 the lowest AcMM (0.19) t/ha per cycle in the water period. In the dry season, the height was 27.75; 31.30 and 34.22 cm when the plant was managed with 2.4; 3.2 and 4.2 leaves per tiller in the waters, with an average of 31.09 cm for forage. DPP averaged 291 tillers / m². The higher cutoff frequency promoted greater AcF and AcLF (0.96 and 0.72 kg/ha), respectively. On average, forages had 0.85 t/ha of AcF and 0.63 t/ha of AcLF, with an average of 2.73% AcC and 22.71% of AcMM. In the aggregate, the lower values were offset by greater numbers of cycles, with an average of 15.21 t/ha of AcFT and 11.45 of AcLFT. Forage 171 showed higher AcFT (16.68) and AcLFT (12.98) t/ha. The AcCT increased with the increase in the rest period, with 1.97 and 3.47 t/ha to 2.4 and 4.2 leaves per tiller, respectively, which promoted a decrease in the stalk ratio (RFC). The forage with the highest RFC was 172 (4.67) and forage density was 171 (236.03 kg DM/cm/ha), in the water period.