Fine root density and vertical distribution of Leucaena leucocephala and grasses in silvopastoral systems under two harvest intervals

Abstract

Understanding belowground morphological mechanisms of trees and grasses is a complicated task but can help in the design and management of silvopastoral systems. In this study, we evaluated the effect of the harvest intervals (i.e. 30 and 50 days) of aboveground biomass on the fine root density and vertical distribution in two silvopastoral systems (SPS): one comprising Leucaena leucocephala (legume tree) and Cynodon plectostachyus (grass) and the other L. leucocephala and Panicum maximum. We used a completely randomized design with four repetitions. We sampled fine roots by using a metal cylinder (8 cm diameter and 50 cm length) 7 days after each harvest. We washed the samples with pressurized water to separate them from the soil. The roots were digitalized at a resolution of 600 dpi to determine the diameter and specific root length by using IJ Rhizo® software. Samples were subsequently dried to quantify fine root mass. We found that the greater percentages of fine roots were between 0.4 and 0.8 mm for the legume and between 0.2 and 0.4 mm for grasses. The fine root length and mass density of P. maximum was higher (P 0.05). The effect of harvest interval was significant only in some soil layers in both SPS (P > 0.05). Most of the pasture roots were found in the upper soil layer (0–20 cm), while L. leucocephala roots were present to deeper soil layers. We conclude that P. maximum has a greater rooting capacity and a more rapid recovery than C. plectostachyus, which has greater diameters and lower root density. However, L. leucocephala presented deeper and thicker fine roots in both SPS, which is a good indication of its belowground recovery capacity to aboveground disturbances.