Abstract
Trees dispersed in grazing areas are contribute to the sustainability of livestock systems. The interactions between trees and soil are ecological processes that allow the modification of the biology, fertility, and physics of the soil. This study was aimed to assess the influence of dispersed trees in pastures on soil properties in grazing areas for dual-purpose cattle systems in the Piedmont region of the Colombian Amazon. The work was done in grazing areas with scattered trees at the Centro de Investigaciones Amazónicas CIMAZ–Macagual in Florencia—Caquetá—Colombia. We evaluated the effect of five tree species, Andira inermis, Bellucia pentámera, Guarea Guidonia, Psidium guajava and Zygia longifolia, on soil properties (up to 30 cm soil depth) under and outside the influence of the crown. Under the tree crown, three points were systematically taken in different cardinal positions. This was done at a distance corresponding to half the radius of the tree crown. The sampling points in the open pasture area (out of crown) were made in the same way, but at 15 m from the crown border. The ANOVA showed significant interaction (P < 0.0001) between tree species and location for macrofauna abundance up to 30 cm soil depth. For this reason, we performed the comparison between locations for each tree species. Chemical soil variables up to 10 cm soil depth only showed interaction of tree species-location for exchangeable potassium (P = 0.0004). Soil physical soil characteristics up to 30 cm soil depth only showed interaction of tree species-location at 20 cm soil depth (P = 0.0003). The principal component analysis for soil properties explained 61.1% of the total variability of the data with the two first axes. Using Monte Carlo test, we found crown effect for all species. Trees help to control exchangeable mineral elements that can affect the soil, potentiate basic cations such as magnesium and potassium, increase the abundance of soil macrofauna; but some trees with high ground level of shade in grazing areas could increase soil compaction due to the greater concentration of cattle in these areas.
Highlights
The department of Caquetais located in the northwest of the Amazon region
There were differences between tree species (P = 0.0378), where A. inermis was the one with the highest richness (4.82 ± 0.63), followed by Z. longifolia (4.52 ± 0.62), B. pentamera (4.14 ± 0.59), P. guajava (2.91 ± 0.49), and ending with G
The greater abundance of the macrofauna below the crown of A. inermis, G. guidonia, P. guajava, and Z. longifolia trees than abundance outside of crown in grazing areas of pastures is presumably due to two factors: the quality of litter and microclimatic conditions
Summary
There were changes in land use cover that started from the forest to agricultural production systems (annual crops, palm, and pastures) which were sponsored by state policies This process has been called by some authors as the empowerment of the Amazon, causing the loss of ecosystem services, as well as reduced livestock systems efficiency [3]. In this context, deforestation and the conversion of Amazonian forests into pastures and croplands can have negative effects on the soil due to an excessive stocking, turning grazing areas into degraded pastures [4]. The soil macrofauna in particular has proven to be a sensitive indicator of the alteration of the vegetation cover [8,9,10,11,12], and it can considerably affect the decomposition and cycling processes of soil nutrients [13,14,15]
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