Acúmulo e alocação da matéria seca e de nutrientes nas braquiárias decumbens e ruziziensis, em sistema intensivo de produção de forragem

Abstract

Pastures are the main source of roughage for ruminants and, in recent years, there has been an increase in intensive forage production systems. Thus, the objective of this study was to evaluate, in soil with adequate nutrient supply, the accumulation and allocation of dry matter and nutrients by Brachiaria decumbens (Urochloa decumbens) and Brachiaria ruziziensis (Urochloa ruziziensis), in three cuts, in the environment edaphoclimatic of Rio Largo - AL. The design used was randomized blocks, with five replications, and the plots consisted of five five- meter-long furrows, spaced 0.70 meters apart. The sowing of Brachiaria was carried out on May 15, 2019, applying 50 kg of P ha-1 at the bottom of the sowing furrow. Nitrogen and potassium, at a dose of 150 kg of N and 150 kg of K per hectare, were applied when the plants were about 5 cm tall. At 45 days after sowing, a leveling cut was performed, subsequently evaluating, every four weeks, the accumulation and allocation of dry matter and nutrients in the aerial part of the brachiaria. The Brachiaria cuts were carried out on July 25, August 22 and September 20, 2019. After each cut, the plants were again fertilized with 150 kg of N and 150 kg of K per hectare. The adopted system allowed obtaining high forage productivity and the average values of accumulation of natural matter (MN) and dry matter (DM) in the three cuts were, respectively, 41.0 and 6.53 t per hectare, every four weeks. It was observed that there was no statistical difference between the brachiaria; however, there was a significant effect of the cutting season on forage production, since in the second cut the average production of the two Brachiaria was 7.26 t of DM, exceeding the average of the first and third cuts by 11.77%. statistically equal. The higher DM productivity in the second cut was probably due to the greater water availability in the period and the beginning of the increase in the photoperiod. In the third cut, possibly the low rainfall in September (only 39 mm) associated with the high reference evaporation (118 mm) did not compensate for the increase in photoperiod. Regarding the allocation of dry matter in the plant, there was an effect of Brachiaria and cutting, however, there was no interaction between these factors. Brachiaria ruziziensis had higher DM allocation in leaves, about 12% more than brachiaria decumbens. Due to the high productivity of Brachiaria, there was also a great removal of nutrients, which on average was 107; 15.6 and 178 kg of N, P and K, respectively, per cut. Based on the results obtained in only three cuts, high productivity was observed for Brachiaria decumbens and ruziziensis, in this intensive forage production system.

Keywords: Livestock, forage quality, nutrient removal.