Construyendo materia orgánica en suelos degradados bajo clima semiárido mediante el uso de enmiendas orgánicas

Resum

The overall objective of this Doctoral Thesis work has been the evaluation of the capacity and effectiveness of the management of different organic amendments, at different doses, different scenarios (non-agricultural and agricultural soils), and different time scales (short, medium and long term), to build new and stable pools of organic C in the soil, and thus, ensuring the sustainability of agricultural and non-agricultural soils in semiarid areas. Different management strategies have been considered: i) a sole application of organic amendment at high dose, with the objective of restoring seriously degraded non-agricultural abandoned soils; ii) application of organic amendments at low doses and on a continuous basis, to agricultural soils in semi-arid areas. To this end, the following specific objectives have been established: Evaluation of the construction of organic matter (C pool), generated over time, as a direct consequence of the organic amendment. Contribution to sustainability through parameters that allow us to describe the quality and health status of degraded, non-agricultural and agricultural soils. Search for new models of representation and interpretation of results obtained in short-, medium- and long-term organic amendment application trials, using regression analysis techniques. Monitoring of these soil recovery, both agricultural and non-agricultural, was carried out according to the following parameters: -Agronomic parameters: physical-chemical (texture, pH, density, water holding capacity, aggregate stability), organic matter content and nutritional parameters (total carbon, total nitrogen, total organic carbon, soluble carbon, humic substances, macro and micronutrients). - Environmental parameters: electrical conductivity, Na+, nitrates, water soluble nitrogen and heavy metals. - Microbial diversity related parameters: enzyme activities, microbial respiration and analysis of the structure of the microbial community. With data from such a diverse spectrum of parameters, we can get information on the ability of these soils to build new pools of organic C, increasing fertility and ensuring the sustainability of these degraded soils. As a General Conclusion of this work of Doctoral Thesis it can be noted that the addition of organic amendments of different origin and degree of stability to degraded semi-arid soils, both agricultural and non-agricultural, gives them a higher quality and a general improvement in their agronomic properties and in those related to microbial diversity, without adversely affecting the environment, always on the basis of the use of quality amendments and with appropriate management. This impact on soil quality will depend on the type of management of the amendment, its nature and application dose, and the characteristics (texture, physical and physical-chemical properties) of the soil on which it is applied. The study at different time scales, has allowed us to observe that semi-arid soils do not lose their capacity to respond to exogenous organic matter inputs, being able to develop and maintain a pool of C over time, thanks to the development of a stable plant cover in those soils devoid of vegetation. It is important to note that the effect of the amendments on soil quality is not ad hoc but persistent over time, restoring and maintaining edaphic fertility in these ecosystems. The addition of exogenous C sources (quality organic amendments) to semi-arid soils with an adequate management can be considered, after our study, as a sustainable and necessary strategy to conserve and maintain in optimal conditions a Natural Resource as important as SOIL.