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Georg-August-University Göttingen Allemagne (2008)

Biological and biochemical transformation of nutrients in agricultural soils of Yucatan, Mexico

Campos González, Adriana José

Titre : Biological and biochemical transformation of nutrients in agricultural soils of Yucatan, Mexico

Biologische und Biochemische Transformation der Nährstoffe in landwirtschaftlich genutzten Böden in Yukatan, Mexiko

Auteur : Campos Gonzalez, Adriana Jose

Université de soutenance : Georg-August-University Göttingen

Grade : Doctor of Philosophy (PhD) 2008

Résumé
The soils of the Yucatan Peninsula in Mexico, which are subject to diverse kinds of agricultural practices, have shown over time a decline in their fertility. The climate of the region (semi-arid) with scarce rainfall, rain in a concentrated short period, and a high mean temperature, play an important role in the soil processes and nutrient cycling. In addition, the high heterogeneity of the soils, where some of them present high organic matter content, does not allow a good diffusion of nutrients and limits their availability to the plants. Generally, in semi-arid ecosystems some nutrients are limiting and available to plant in short pulses following precipitation. Studies have shown that water input stimulates nutrient mineralization from accumulated organic mater. However, in a study carried out by Shang and Tiessen (2003) in Yucatan the hydrophobicity of some soil types with high organic matter content was observed, which affects water retention and consequently limits nutrient release. This thesis was focussed on the evaluation of the soil’s biological and biochemical characteristics involved in the nutrients transformation processes in the Yucatan Peninsula, which could contribute to understand the ecosystem functioning and to improve their management. Therefore, soil biological and biochemical indicators under different land uses systems and soil types were determined. Decomposition process, soil fauna (abundance and diversity), soil respiration, contribution of bacteria and fungi to the soil respiration, microbial biomass and enzyme activities were measured in order to evaluate the biological processes associated to the C-cycle. The study was carried under field conditions and artificial wetting in laboratory to asses the seasonal effect and the influence of soil moisture, respectively. Additionally, it was performed an incubation experiment upon artificial wetting to evaluate the potential source of the nutrients (N, P) through measures of enzyme activities. The main results of this research show that in general the rain and the moisture had a positive effect on the biological, microbiological and biochemical characteristics of soils. Decomposition process showed an increase and kept high rates during the rainy season, confirming that the rainfall has a strong effect. However, the soil fauna was another factor that determined the process, where termites and ants have high influence on it. Regarding biochemical characteristics, alkaline phosphatase and β glucosidase were found as potential indicators of activity due to under optimal moisture levels these enzymes showed the highest capacity of source of nutrient in the soil. The effect of the land uses was also detected on the microbiological and biochemical characteristics. It is important to highlight that both, field- and artificial wetting- conditions, the forest soils showed always the highest values compared to homegardens and milpa. Fungi play a greater role in the soil respiration, indicating that they could have a high influence on the decomposition processes in the different land uses but principally in the forests, where the litter input enriched the soil, and allow possibly an high immobilization of nutrients in their biomass. In general, milpa and homegardens showed similar characteristics and lower soil microbial biomass and activities in these systems were reported. The decrease in the microbial and biochemical parameters was attributed to the continuous remove of organic material in the soils. Thus, it is reflected in a negative effect on soil biological and biochemical processes that could be reflected in the productivity of these systems. Similarly, the black soils had higher values due to their high organic C content, which correlated with microbial and biochemical characteristics. Therefore, it stated the importance of the organic matter as soil chemical property and their effect and relationship with the biological and biochemical characteristics. Finally, the results of the incubation experiment help to understand the soil biological processes considering the influence of the moisture and the impact of the different land uses in the peninsula, which show a potential of nutrient that might be liberated only when the moisture conditions are optimal. This could contribute to understanding the functioning of the systems and maybe to develop a better management based on the water control.

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Page publiée le 11 mars 2009, mise à jour le 2 janvier 2019