Micromorphological characterization and monitoring of internal drainage in soils of vineyards and olive groves in central Italy

Abstract

Internal drainage class is an interpretative soil quality that derives from the field evaluation of other soil qualities and characteristics, i.e. soil permeability, texture, structure, redoximorphic features, and may not match the results of measurements of the actual soil water status. The aim of this work was to investigate whether a better characterization of standard field assessments of internal drainage of 12 soils in vineyards and olive groves could be achieved through the qualitative and quantitative micromorphological analyses. The results of field and laboratory analyses, as well as of 34 months of monitoring of soil moisture and temperature, and 21 months of water table and redox potential, were related to the micromorphological estimation of the hydromorphy degree, following the methodology of Aguilar et al. (2003) [Aguilar, J., Fernandez, J., Dorronsoro, C., Stoops, G., Dorronsoro, B., 2003. Hydromorphy in soils. http://edafologia.ugr.es/hidro/indexw.htm], and to the quantification of porosity using image analysis. It was found that soils were only occasionally saturated with water and for short periods, although redox potentials during autumn and winter indicated probable Mn reduction. Water content monitoring differentiated soils with values far beyond field capacity throughout the year, and soils with values close to, or higher than, field capacity during rainy seasons. Results showed that hydromorphy degree was related to seasonal soil water content and redox potential. An improvement in this method should consider the presence and the nature of calcite pedofeatures. The statistical analysis associated the abundance of elongated and irregular macropores, which favor water drainage, to scarceness of macro- and microhydromorphic features and lower bulk density. The quantity of regular pores, which are less efficient for downward water transmission, was on the other hand correlated to an average high soil water content and to lower mean redox potentials. The relevance of elongated and irregular macropores for the internal drainage of this kind of soil (intensively cultivated, poorly structured, and with low total macroporosity) was also confirmed by the proportion of elongated and irregular macropores to total macroporosity (PR index). In soils of vineyards and olive groves, optimal drainage conditions in Mediterranean climate seem to be ensured by PR higher than 0.80. The study demonstrated, by means of a field experiment, the unfavorable effect of the common practice of deep plowing before tree planting in increasing the formation of redoximorphic features, micritic calcite nodules and infillings, within the deeper horizons of calcareous soils.