Sistema silvipastoril na Amazônia Legal - Avaliação demográfica e agronômica em pastagens

Abstract

Silvopastoral systems in the Amazon become an important tool in the conscious use of natural resources. When studying alternative production systems, it is necessary to evaluate the changes that occur and to seek management alternatives that enable the use of these practices. Thus, silvipastoral systems reduce soil organic matter losses, increase nutrient utilization efficiency, the forage plant has higher crude protein content and higher leaf: stem ratio. when compared to conventional systems. On the other hand, there is a reduction in forage production, lower tillering, especially near the trees. Therefore, it is necessary to evaluate the possible impacts that height management, nitrogen fertilization and changes in light via tree management may have on the system. The present work aimed to evaluate the changes in soil chemical attributes over time; to evaluate the demographic changes of the plant as a function of nitrogen doses and cutting heights, and to study the distribution of Mombaça grass in response to tree shading. To evaluate soil chemistry, three experimental periods (2011, 2014 and 2017) and two production systems ( silvipastoral and monoculture ) at depths of 0-10 cm and 10-20 cm. The silvipastoral system obtained superior organic matter when compared to the monoculture , in the order of 1.28 and 0.71 g. dm -3 , respectively. Exchangeable cations were also superior in the integrated system. The spatial evaluation used geostatistical method to determine the distribution of the pasture in the area. In addition, a multivariate method was used to determine the main system variables. For this purpose, two periods were evaluated, 2013 and 2017. It was observed that forage production followed the same pattern of shading, areas with intense shading (close to 70%) were 2000 kg.ha -1 lower than areas with 35% of shading. Therefore, light restriction was determinant in forage production. Finally, the influence of nitrogen fertilizer ( 0, 125, 187.5 and 250 kg.ha -1 per year of nitrogen) and cutting heights (30, 40 and 50 cm) were evaluated. The appearance rate ( TxAp ) varied (P < 0.05) inversely to the residue height (Table 2). The height of 30 cm had a higher rate of appearance when compared to the heights of 40 and 50 cm of residue with values in the order of 1.5 5, 1.15 and 1.10, respectively, whereas for nitrogen doses only the appearance of tillers was significant, with higher tillering at the highest dose evaluated.