Single and combined effect of soil amendment with biochar and wood distillate in young vine plants

Recycling plant biomass into bioproducts for agricultural practices, including biochar and wood distillate (WD), plays a key role in facing climate change and supporting global food security and circular economy (Tuck et al., 2012). However, the potential effect of biochar and WD, when co-applied as a soil amendment to maximize plant performance, needs to be further investigated (Becagli et al., 2022; Yuan et al., 2022). Pot experiments were performed in a climate chamber with the aim of evaluating the growth pattern of young vine plants (Vitis vinifera L. var. Sangiovese) in response to three soil amendments: 20% (w/w) woody biochar and 0.5% (v/v) WD weekly fertigation, alone (B and WD, respectively) and in combination (B+WD). At the end of the growth period (45 days), chlorophyll and primary metabolites (i.e., glucose, fructose and proteinogenic amino acids) were determined at shoot level, while the area and length at root level; fresh biomass, secondary metabolites as antioxidants (total polyphenols), and micro- and macronutrients (Ca, K, Mg, P, S, Cu, Fe, Mn, Mo, Zn, and Na) were determined in both shoots and roots. Finally, pH, electrical conductivity, cation exchange capacity (CEC), organic carbon and total nitrogen were determined in bulk soils, before and after the amendments. Results showed that plants fertigated with WD, irrespective of the combination with biochar, produced less leaf biomass, but more root biomass; in contrast, root expansion and length were positively affected by biochar application. Although the shoot glucose content was reduced by the application of both biochar and WD alone, their combination resulted in a glucose content similar to the control. The amino acid content, including that of phenylalanine (Phe) and tyrosine (Tyr), which are precursors of phenolic compounds, increased following WD application. In particular, WD reduced the content of Phe and Tyr only in the roots, whereas biochar, alone or combined with WD, lowered their concentration only in the shoots. The single or combined effect of biochar with WD strongly increased K content, but reduced Ca, Mg and P concentration in both shoots and roots. On the other hand, WD promoted an increase of P content in the roots. Although the Na content in soil amended with biochar was high, plants accumulated it mainly in the roots, whereas the root system of WD-treated plants showed a Na content even lower than the control. WD also increased the soil CEC, regardless of the biochar addition, while in the soil amended with biochar, the content of total nutrients (i.e., Ca, K, Mg, Fe, and Mo) was much higher than in the control. As expected, the organic C content increased in both the biochar-amended soil and in the WD-fertigated one. In conclusion, the synergic effect between biochar and WD was evident on plant physiology with a positive response especially in terms of root growth, suggesting that the combination of these bioproducts is a potentially feasible and eco-sustainable strategy for crop cultivation.