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The main purpose of the present study, conducted in the Piedemonte Llanero of Colombia, was to identify the role of covariates that influence soil properties under different land uses by analyzing the dynamics of selected soil properties in natural and agricultural areas. Soil samples were collected from 90 different sites throughout the region, 45 from areas with agricultural activities and 45 natural areas or areas with low anthropic intervention. The studied soils were strongly acidic (pH < 5.5), had low organic matter contents (1.73% and 2.34% on average in agricultural soils and natural areas, respectively) and, in general, represented poor conditions for agricultural production. The use of multivariate analysis showed that altitude was an important influence on soil properties. Moreover, it was found that land use influenced soil properties, which may limit productive capacity. The results presented here help to clarify the relationships between soils, climate, and landforms in an equatorial climate. [ABSTRACT FROM AUTHOR]

In this study, the control volume method is used to determine the air temperature at the outlet of an air-to-ground heat exchanger. Its implementation consists in dividing the duct of the ground-air heat exchanger into micro-volumes of identical size. An energy balance is then established for each micro-volume. The input parameters used to implement this model are related to the city of Yaoundé in the equatorial zone. The results show that when the total length of the air-to-ground heat exchanger duct varies between 0 and 100 m, the air temperature at the outlet also varies between 34.5 and 24 °C. The air-to-ground heat exchanger operates in cooling mode. As the length of the air-to-ground heat exchanger duct increases, the temperature of the air at the outlet of the air-to-ground heat exchanger decreases, approaching that of the ground. Based on the results obtained using the control volume model, the minimum total length of air-to-ground heat exchanger duct recommended for this zone is 40 m. Admittedly, air pressure drops, air humidity and the geometry of the air-to-ground heat exchanger are aspects that have not yet been taken into account in the implementation of this model. Nevertheless, the control volume method can be used to optimise the parameters influencing the thermal performance of an air-to-ground heat exchanger.•The control volume method is implemented here by dividing the air-to-ground heat exchanger duct into identical micro-volumes and then establishing an energy balance for each micro-volume;•In this work, the control volume method was used to optimise the total length of the duct of a ground air heat exchanger installed in an equatorial zone;•Some important aspects such as air pressure drops, air humidity, and the geometry of the air-to-ground heat exchanger are not yet taken into account in the implementation of the control volume method., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier B.V.)