Aim:  To evaluate the effects of soil physical and chemical factors (pH, conductivity, humidity, available phosphorus and organic matter) and environmental factors (temperature, relative air humidity, altitude and atmospheric pressure) on arbuscular mycorrhizal fungi (AMF)–Brachiaria decumbens grass relationship. Furthermore to establish patterns of microbiological responses that allow to differentiate the study sites in two relief types. Methods and Results:  Mycorrhizal characteristics (spore density, external hyphae and root colonizations by hyphae, vesicles and arbuscules), physical and chemical factors in soil and environmental factors were measured. Conclusions:  The effect of physical, chemical and environmental factors on microbiological variables was related to the type of relief ‘valley and hilly terrain’; the AMF behaviour was affected only over narrower ranges of evaluated variables. Similarly, the colonization of B. decumbens roots by AMF hyphae, vesicles and the mycorrhizal spore density follow different patterns according to the relief type. Significance and Impact of the Study:  The type of relief is one of the factors to be taken into consideration to evaluate the AMF inoculum and root colonization of these pastures, because of the influence of slope – as physical property of soil – on AMF.

Caqueta ´, Colombia, has a bovine population of 1,809,702 head, of which 88% are in dual purpose livestock systems; it ranks fifth in milk production at the national level. The aim of this study was to evaluate the effect of different levels of tree cover on milk production in dual-purpose livestock systems in the humid tropics of Colombia's Amazon region. The work was carried out in the Centro de Investigaciones Amazonicas CIMAZ Macagual. It is within the tropical humid forest life zone. Nine pastures of one hectare each were selected, covered by improved pastures (Brachiaria decumbes) and dispersed trees. Treatments were defined by the percentage of tree cover: (1) high (20.43 ± 0.47), ( 2) medium (14.83 ± 0.58) and ( 3) low (4.20 ± 0.85). The spatial distribution of the dispersed trees was obtained using the SexI-FS simulator. Nine milking cows with similar characteristics were selected and managed following a 3 9 3 Latin square experimental design (Cross Over), repeated three

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.

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