Desempenho de Penisetum purpureum cv Kurumi e Panicum maximum cv Zuri sob rebaixamento drástico durante o outono-inverno em terras baixas no sul do Brasil

Abstract

When drastically lowered, perennial erect warm-season forage species expose their basal buds, which can result in the death of these plants during the cold seasons in southern Brazil due to the action of frost, a factor that can compromise the plant stand for subsequent harvests. On the other hand, intense defoliation during cold seasons allows for greater forage harvest at strategically important times. Thus, to verify the impact of this greater intensity of defoliation during the cold seasons in southern Brazil, an experiment was conducted at the Estação Experimental Terras Baixas - Embrapa Clima Temperado, located in the municipality of Capão do Leão, Rio Grande do Sul/Brazil. The following factors were studied: erect tropical perennial forage (Pennisetum purpureum - cultivar BRS Kurumi and Panicum maximum - cultivar BRS Zuri); drastic lowering of tropical species during the autumn and winter seasons (7cm), recommended lowering for these species (40cm); productive moments first harvest (spring-summer 2022-2023); autumn 2023; off-season (autumn and winter 2023); and second harvest (spring-summer 2023-2024). The experimental area consisted of 3 blocks. The plots had dimensions of 7m x 4m. Data were analyzed using analysis of variance and Tukey's test (p < 0.05). Soil preparation and cultivar management, except for drastic defoliation, occurred in accordance with technical recommendations, with sowing and planting carried out on December 5, 2022. Forage collections for the Kurumi cultivar were in an area of 80cm x 160cm (two plants) and for the Zuri cultivar in an area of 45cm x 50cm. The forage remained for 72 h in forced-air greenhouses (55°C) to determine the harvested forage mass. Zuri provided the highest forage harvest with 34,151 kg DM/ha, while Kurumi produced 21,602 kg DM/ha over two harvests in lowlands in southern Brazil. The intense drawdown during the fall-winter period (off-season) did not change the amount of forage harvested over the two harvests, only the time when the greatest amount of forage was harvested, in the fall-winter (6,006 vs. 3,339 kg DM/ha) in favor of the intense drawdown or in the following harvest (7,387 vs. 10,243 kg DM/ha) in favor of the recommended management. This indicates to the producer the best time to use these species to avoid forage gaps. Due to atypical temperatures and precipitation during the fall-winter of 2023 and during the second harvest (2023-2024), there is a need to continue the studies so that evaluations occur under environmental conditions closer to normal and, especially, during more extreme winters.