3.1. Soils
Table 1 shows essential soil properties of the different Technosols (treatments and reference soil) from the two sites. All soil variables (particle size, pH, EC, CaCO3, TOC and TN) show significant degree of heterogeneity despite the analyses were done on composite samples.
Soil texture, not strongly impacted by the soil restoration, was classified as silt loam, and particle size proportions did not change much over time as expected. The natural soil has somewhat higher sand contents (from 37.1% to 38.9%) and lower clay contents (from 10.6% to 14.5%) than the experimental plots (from 26.6% to 35.4% and from 7.2% to 25.6% respectively).
We observed significant differences (P < 0.05) due to the treatments of organic amendments in all chemical properties after 6 years. Despite this, pH was quite similar in all plots (Table 1). EC was significantly higher in treatments of compost, reaching 3.8 dS/m at the first sampling. After 6 years, there was a decrease in EC on all amended plots up to contents similar to those of the reference soil. CaCO3 equivalent was higher in soils from control plots (without amendments) than in those with amendments and somewhat lower after six years. In all experimental plots, CaCO3equivalent was higher than in reference soils. Concentrations of TOC and total N were affected by treatments (Table 1). Higher organic C contents were observed in compost added treatments compared to those in other Technosols, both at the beginning and after six years. Further, there were also significant differences in N concentrations among treatments for both sampling periods. The highest N concentrations were observed in compost. While the highest values for TOC decreased slightly over time, the high concentrations of total N in compost plots were maintained.
The factorial ANOVA performed with the soil variables on the factorsorganic amendment and topsoil (Table S1) indicate that, primarily, the factor organic amendment contributes significantly to explain the differences for most of the tested variables.