Evolution of forest soil properties after liming with a by-product derived from a sugar beet mill

Deciduous oak coppices (Quercus pyrenaica Willd.) of the “Sierra de Gata” mountains (central western Spain) are located on acid rocks and subjected to annual rainfall higher than 700 mm year⁻¹. Accordingly, the soils are acidic (soil pH is often below 5.0) and feature the presence of Mn²⁺ and Al³⁺ in the exchangeable complex. The aim of the present study was to assess the response of these soils to the addition of a lime residue from a sugar beet mill to reach pH values close to 7.0 and 6.0 with in situ and in vitro experiments, respectively. Initially, the quality of the lime by-product was evaluated, which showed content close to 75 % CaCO₃. Based on that analysis, calculations were accomplished to determine the dose of lime by-product necessary for achieving the targeted soil pH. We first performed an in vitro liming experiment, incubating 0.50 kg soil (0–20 cm layer) with 23.92 g CaCO₃ kg⁻¹ soil (20 °C and soil moisture equivalent to that of field capacity). Subsequently, another experiment was done adding an equivalent quantity of sub-product in lieu of the pure CaCO₃; the factors monitored were: soil pH, exchange acidity, CEC, and exchangeable bases, every 24 h. The in situ experiment was performed in a forest plot located in Western Spain (Navasfrías), liming with 16.0 Mg DM by-product ha⁻¹ (September 1999). Soil samples (two depths: 0–10 and 10–20 cm) were taken from both the control and the experimental forest plots for monitoring the liming effect. Sampling dates were September and December 1999; June 2000, January, June and September 2001; October 2002 and 2003, and March 2005). The dissolution of the lime by-product at the laboratory was almost immediate, but the effects in the field occurred approximately 2 years after initial liming, since lime dissolution depends on both the amount and distribution of rainfall and, also, on the application procedure. Graphical abstract Sub-products originated in the sugar-beet mills can be used for liming forest acid soils; nevertheless, rate of dissolution is important for managing efficiency