Implementation of Silvopastoral Systems under Nutrient Cycling in Secondary Vegetation in the Amazon

Abstract

Silvopastoral systems can be implemented in idle secondary forests; however, they may affect nutrient cycling in these ecosystems. This farming practice using babassu palms (Attalea speciosa Mart.) and Mombasa grass (Panicum maximum Jacq.) has been little studied, and the nutrient cycling occurred during this practice is yet unknown. The goal of this paper was to detect the leaf litter accumulation, decomposition, and nutrient release occurring in silvopastoral systems in a babassu secondary forest, and compared the results with those of a native forest and of a pasture grown under full sunlight. The data relating to deposition, chemical composition, decomposition, and macronutrient release of leaf litter and pasture litter were evaluated by multivariate analyses. The results showed that forest thinning reduced leaf litter deposition and overall nutrient cycling but had no effect on decomposition rates. Conversely, the presence of grass in the understory promoted increased overall nutrient cycling rates. The cycling in integrated systems occurs more similar to that of forests than that of monocultures. The greater the thinning intensity the more similar the cycling will be relative to that occurring in pastures and in monocultures. The nutrients Ca, Mg, and N were the most affected by thinning. Moreover, the presence of grass in integrated systems provided an increased N and Mg cycling, whereas the thinning reduced Ca cycling. K showed the highest release and return ratio to the soil. Lastly, leaf litter from pasture areas showed higher contents of nutrients, decomposition rates, as well as an enhanced nutrient cycling capacity.

Cutting Height of Mombasa Grass Under Silvopastoral and Monoculture Systems

“…The slower growth rate in the silvopastoral systems is also reported by Santos et al (2018), who found that shading significantly affected the dry mass content of forage under shade due to higher proportion of leaves and higher live:dead ratio in the grass. According to Gobbi et al (2011), another factor that reduces the dry mass content of the grass in a shading system is the modification in leaf anatomy; even with an increase of the specific leaf area there is a decrease in the mass density of the forage, with a reduction of sclerenchyma cells and the thickness of the palisade parenchyma.…”

“…In this sense, the growth rate of the grass in the silvopasture system was more slowly due to modifications imposed by the arboreal component, which interfered with dry mass availability. The DM decreased as the shading intensified, presenting negative correlation between shade and grass productivity due to the amount of light entering the lower canopy stratum (Santos et al, 2018). The number of cuts in the rainy season linearly decreased for both systems, with one cutting occurring for each 10 cm that rises at the height of the SSP system, whereas for the monoculture system the reduction is 1.3 cuts for every 10 cm of height increase (Table 2).…”