Short-term to mid-term effects of organic and inorganic soil amendments on carbon and nutrient dynamics in a clay-loam pear orchard soil (Ospital Monacale, Northern Italy)

The use of organic and inorganic soil amendments is increasingly promoted to enhance soil fertility and carbon sequestration in perennial cropping systems, yet field-based evidence on their temporal dynamics remains limited. This study investigates the evolution of soil chemical properties in a pear orchard located in Ospital Monacale (Ferrara Plain, Northern Italy), focusing on the surface layer (0–20 cm) of a fine-textured, clay-loam soil. The experimental design consisted of a randomized block layout aimed at assessing whether the application of biochar and zeolite-rich tuff could enhance the already known beneficial effects of compost. To this end, four treatments were established: i) an untreated control, ii) compost alone, iii) compost combined with biochar, and iv) compost combined with zeolite. Soil samples were collected at different times: immediately after amendment application (T0) and two years after application (T1). Different soil parameters were investigated: total carbon and nitrogen, inorganic nitrogen forms (ammonium and nitrate), total dissolved phosphorus, pH and electrical conductivity.

Results show a clear temporal signal in the surface horizon. Compost and compost–biochar treatments promoted a sustained increase in total soil carbon relative to the control, with differences already evident at T1, suggesting progressive stabilization of organic carbon pools. In contrast, compost–zeolite mainly influenced nitrogen dynamics, with higher ammonium retention and reduced short-term variability compared to other treatments. Dissolved phosphorus concentrations were consistently higher in the treated soils compared to the untreaded one.

Overall, the integration of a multi-temporal framework reveals that, under humid and fine-textured soil conditions, amendment effects strengthen over time in the topsoil. These findings underline the importance of long-term monitoring to capture amendment-induced shifts in soil biogeochemical functioning in orchard systems.