| Sumario: | pH values of different dilutions of the aqueous extracts (BC350AE and BC700AE) obtained from washing BC350 and BC700 (3% (w/v) with distilled water), respectively, for 24 h. Figure S1. SR-FTIR spectroscopy of grape pomace (GP) and biochars prepared at 350 °C and 700 °C (BC350, BC700, respectively). Full 2nd derivative spectra (wavenumber range between 3100 and 900 cm−1) along with the first two main principal components (PC-1 and PC-2) for different wavenumber ranges, which explain the largest contributions of signal shifts between samples. Numbers in red indicate the wavenumber values of the most representative peaks. Figure S2. SR-FTIR spectroscopy of grape pomace (GP), washed (BC350W) and unwashed (BC350) biochar prepared at 350 °C, and BC350 aqueous extract (BC350AE). Full 2nd derivative spectra (wavenumber range between 3100 and 900 cm−1) along with the first two main principal components (PC-1 and PC-2) for different wavenumber ranges, which explain the largest contributions of signal shifts between samples. Numbers in red indicate the wavenumber values of the most representative peaks. Figure S3. SR-FTIR spectroscopy of grape pomace (GP), washed (BC700W) and unwashed (BC700) biochar prepared at 700 °C, and BC700 aqueous extract (BC700AE). Full 2nd derivative spectra (wavenumber range between 3100 and 900 cm−1) and along with the first two main principal components (PC-1 and PC-2) for different wavenumber ranges, which explain the largest contributions of signal shifts between samples. Numbers in red indicate the wavenumber values of the most representative peaks. Figure S4. Effect of different concentrations (3%, 1.5% and 0.75%) of the unwashed biochar obtained at 700 °C (BC700) on 3-week old tomato plants 24 h and 6 days after its transplantation into biochar-amended sandy soils. Figure S5. Effect of different concentrations (3%, 1.5% and 0.75%) of the unwashed biochar obtained at 350 °C (BC350) on roots and shoots of tomato plants 3 weeks after its transplantation into biochar-amended sandy soils. Figure S6. Effect of different concentrations of BC350W on the percentage of seed germination (a), number of leaves (b), shoot length (c), relative water content (RCW) (d) and total fresh biomass (f) of 6-week-old tomato plants. Means ± standard errors (n ≥ 8). Significant differences with respect to the control according to Mann–Whitney U test. ***p < 0.001; **p < 0.01.
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