Respostas do capim-quênia submetido a doses de nitrogênio sob lotação intermitente

Abstract

The objective of the study was to evaluate the effect of nitrogen (N) rates on canopy structure, forage accumulation and accumulation rate, nutritive value, and tillering dynamics in pastures of Panicum maximum cv. BRS Kenya. The design was randomized blocks. The treatments were four doses of N, 75, 150, 225 and 300 kg/ha/year of N (N75, N150, N225 and N300, respectively), with four replications. The grazing frequency was defined by the time when the canopy intercepted 95% of the incident light, and the grazing intensity was 50% of the pre-grazing height. The pastures were managed under intermittent stocking. Structural characteristics, forage mass (FM), accumulation (FA), accumulation rate (FAR), forage nutritional value, tiller population density (TPD), tiller appearance rate TAR), the tiller mortality rate (TMR) and the population stability index (SI) during the seasons. There was interaction between N doses and seasons for the interval between grazing (p<0.0001) and pre (p=0.0038) and post-grazing (p=0.0002) heights, which decreased with increasing N dose. Pre-grazing FM (p=0.0052), FA (p=0.0214) and FAR increased linearly with increasing N dose. Crude protein (CP) and organic matter digestibility (OMDIG) concentrations showed linear increases (p=0.0060). The highest TPD and TMR were observed at the highest N doses, regardless of the season. The increase in N caused changes in the structure of the canopy, increases in the accumulation and nutritional value of the forage, increased the period of use and promoted a greater appearance and mortality of tillers without compromising the population stability of the kenya grass pastures. When it comes to the use of Quênia grass in a pasture animal production system, the dose of 75N is considered insufficient for the correct use of the rainy season. The dose of 150N is the minimum dose for the cultivar evaluated. The 300N dose allowed greater use of the rainy season, with more grazing cycles, and anticipation of use after the dry period, due to the residual effect of N. However, the lower forage accumulation of the 300N dose when compared to the dose of 225N, indicates that the 225N dose provides greater support capacity, in addition to nutritional value similar to the 300N dose, being, of the doses evaluated, the most suitable for intensifying production systems. However, an economic assessment must be made to evaluate the increase in production x fertilizer price.