Estudio funcional de la materia orgánica del suelo en agroecosistemas vitícolas de la isla de Tenerife (Canarias, España)

Resumo

In general, agriculture leads to a simplification of the structure and diversity of natural ecosystems. The extent of the perturbation of the soil quality depends both on soil type and the intensity of the management practices. Despite this, agroecosystems provides several environmental services such as food production, carbon sequestration and erosion control. However, it is not completely understood to what extent clearing and cultivation could be associated to an irreversible loss of the functional attributes of the ecosystems, and retrogression from the climax status. In the case of volcanic regions, the influence of the geological substrate, the amorphous minerals and the organo-mineral complexes, have been considered as regards the dynamics of the different compartments of the ecosystem. In recent years, there is an increasing interest in the assessment of environmental sustainability in agricultural systems, focusing to improving agricultural productivity without decreasing the environmental services supplied by agroecosystems, which bear on social welfare. However, the development of such studies is largely limited by the lack of quantitative descriptors suitable for monitoring the impact of agricultural practices on soil. This research focuses on establishing scientific bases for the integrated management of ecosystems, by assessing the impact of different management practices on soil quality. The study area includes several vineyard systems in volcanic soils from Tenerife (Canary Islands, Spain). Special attention is paid to soil type, i.e., soils on original or allochthonous materials (sorribas), traditional or intensive conduction systems (espalier or traditional plantation) and use of vegetable or inert covers (jables) receiving inputs of organic amendments. In this research, the soil organic matter is used as source of analytical descriptors representing useful tools for soil functional analysis, and taking advantage or their character as an environmental record of recent and past changes in land use. This would lead to quantify differences between the cultivated soils and their corresponding undisturbed ecosystems, using spectroscopic techniques (spectroscopies in the visible, infrared and 13C nuclear magnetic resonance ranges) in addition to thermal degradation techniques combined with chromatographic and mass spectrometric analyses. In addition, the analysis of physical and chemical variables of minerals and humic fractions of volcanic soils, and their interactions, as well as the molecular characterization of the stable forms of C that have been accumulated in the soil during long periods of time (mainly humic acids) provide valuable information on past and present changes in land use. The experimental results were appropriate to infer indexes of similarity between the cultivated soils and their corresponding natural ecosystems. It has also been found that the more disturbed agroecosystems are those developed on Andosols where, in the long term, cultivation implies a trend to irreversible loss of andic properties but not to substantial change in the functioning of the biogeochemical cycle of C; this could be interpreted as these vineyards still behave as C sinks. This is not the case with the vineyards developed on pumice-covered soils, where cultivation increases diversity and complexity of natural ecosystems, despite lignin selective preservation were the dominant humification pathways. It was also observed that vineyards in coastal areas, developed on allochthonous materials (sorribas), showed comparatively better agroecological properties than those of the neighbour natural systems, which is interpreted as an effect of the volcanic materials transported in the past. From a functional point of view and at a macroscopic scale, cultivation causes significant changes in textural and structural properties of the soil, in association with a modified mineralogical composition. It was also observed the increased performance soil C cycle, concomitant to the enhanced aromaticity of the soil organic matter, i.e., an improvement in the quality of the soil C, which is accumulated in the form of humin, with the only exception of the vineyards on pumice-covered plots, where the occurrence of lignoproteins was considered a valuable agrobiological feature in terms of the slow release of N to the crops. In order to achieve the sustainability of these ecosystems, the different management practices should involve environmental criteria, where the soil were not approached as a black box (where a certain treatment is applied and the feedback is evaluated the shortterm) but considering the whole functional attributes of each agroecosystem and their suitability for cultivation. In the case of vineyards in the arid areas, the amounts of soil C and nutrient dynamics to large extent depend on the traditional application of manure under the pumice cover, whereas the andic character exerts the chief effect on the dynamics of C and nutrients in soils at the northern side. Considering the response to changes in land use, these ecosystems show a high capacity for self-regulation or resilience. In fact, in the case of soils on allochthonous materials, application of organic matter to soil is a requirement for its proper cultivation, for long-term conservation, as well as to avoid problems related to salinity or sodicity of the soil. Assuming the above considerations, it is proposed to include some new prefixes in the current Soil Classification systems which could shed any insight on the origin and Andic properties of anthropogenic soils from Canary Islands.