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Abstract: Conservation agricultural practices, such as no-tillage, crops rotation and balanced fertilization are increasingly adopted for maintaining soil fertility, improving crops health and reducing soil erosion. The aim of this study was to evaluate the effects of the long-term adoption of contrasting tillage (no-tillage or conventional tillage) and N-fertilization (0 or 90 kg/ha N) practices on soil porosity and active bacterial communities in cropping system plots (sunflower–wheat or maize–wheat rotation) established on a clayish soil and under Mediterranean climate. Soil porosity was evaluated by micromorphological observations of soil thin sections. The composition and structure of the active bacterial communities were estimated by a culture-independent approach (reverse transcription – polymerase chain reaction – denaturing gradient gel electrophoresis, RT-PCR-DGGE) exploiting the 16S rRNA of bacteria and nirK, nirS and nosZ transcripts of denitrifiers. Finally, canonical correspondence analysis (CCA) was used to correlate microbial data with soil physical and chemical characteristics. When repeated for a long period, no-tillage has significantly increased soil compaction compared to the conventional tilled soil. Soil compaction was likely responsible for creating a selective environment for active bacterial species. On the other hand, tillage favoured the richness and diversity of active soil bacteria by increasing the rate of diffusion of O2 and the energy sources availability. A wide variability of active nirK denitrifiers was found in each soil management, while nirS denitrifiers were more closely related to lower porosity conditions. N fertilizer management seemed to affect mainly the active nosZ denitrifiers. Our results suggested that conservation tillage practices on heavy clayish soils are not free of relevant side effects on soil porosity and bacterial soil communities. [Copyright &y& Elsevier]

Abstract: Severe slope denudation is one of the most important environmental problems in the Mediterranean region. In particular, badlands are widespread in central Italy as a result of extensive clayey outcrops, current climatic conditions and rapid Quaternary uplift. Human activity may significantly affect the development and evolution of these denudation hot spots, especially through changes in land use. This work is focused on a badland site that has developed over the last 30years on a gently sloping area of cropland in central Italy. The site, named Bargiano, underwent cropland abandonment in 1980 and was selected to evaluate the effects of external forcing (such as human impact and rainfall variations) on the development of water erosion processes. The remnants of the 1980 cropland surface and the present (eroded) surface were sampled using differential global positioning system techniques to perform a volumetric estimation of the eroded material and to calculate the average erosion rate for fairly large time spans. The DGPS survey was coupled with a 2-year monitoring with erosion pins in the region, which permitted comparisons between long- and short-term average erosion rates. In addition, the analysis of the rainfall series recorded at the Orvieto pluviometric station allowed us to assess and evaluate the role of critical rainfall events on denudation intensity. Finally, a further comparison of the measured and estimated erosion rates from the Bargiano site with the data recorded at other long-lasting monitoring stations that are set up in certain key areas of central Italy (the Tevere River and Ombrone River basins) revealed that the Bargiano experimental hillslope experienced considerably higher erosion rates than were noted at the other sites. Our investigations demonstrated that cropland abandonment caused an increase in the erosion rate relative to what happened in natural areas characterized by similar physiographic conditions. This finding is consistent with previously reported results for other badlands found in the Mediterranean area. Moreover, the results obtained suggest that, after the abandonment of its cropland, the Bargiano site evolved in a cyclical manner that was driven by intrinsic thresholds to a greater extent than it was affected by external (climatic) changes. [Copyright &y& Elsevier]

Regression models were developed to estimate the optimum moisture content and maximum dry density of clayey and fine-grained soils using physical and index properties from 30 soil samples collected in Central Italy and 41 soils described in the literature. The liquid limit of the soils analyzed ranged between 18 and 82%, the plasticity index between 1 and 51%, and specific gravity between 2.47 and 3.09. The most significant regression variables were the specific gravity and the Atterberg limits. The developed models are accurate and can be used as a simple tool to approximate the maximum dry density and optimum water content of clayey and fine-grained soils. [ABSTRACT FROM AUTHOR]