Effect of Biochar Type, Concentration and Washing Conditions on the Germination Parameters of Three Model Crops

Abstract

Biochar has been recognized as a promising and efficient material for soil amendment. However, its effects on seed germination are variable due to its alkaline pH and/or the presence of phytotoxic substances. In this study, two types of biochar (B1 and B2) were mixed with soil at different concentrations (0%, 5%, 10%, 25%, 50% and 100%, w:w), and both the solid and liquid fractions of these mixtures were tested on the germination of basil, lettuce and tomato seeds. Furthermore, solid fractions subjected to a pre-washing treatment (B1_W and B2_W) were also investigated for their effects on seed germination. Three germination parameters were then measured: seed germination number (GN), radicle length (RL) and germination index (GI). Biochar B2_W at 10% increased both RL and GI in basil by 50% and 70%, respectively, while B1 at 25% increased these parameters in tomato by 25%. No effects or negative effects were recorded for lettuce. Liquid fractions (L1 and L2) generally hampered seed germination, suggesting the presence of potentially water-soluble phytotoxic compounds in biochar. These results point to biochar as a suitable component for germination substrates and highlight that germination tests are critical to select the best performing biochar according to the target crop.

Keywords: basil; biochar; germination tests; lettuce; tomato.

Figure 1

Change in the number of germinated seeds (GN) (A), % change in radicle length (RL) (B) and % change in germination index (GI) (C) of basil seeds (mean ± SE) germinated in the solid fractions (B1, B1_W, B2 and B2_W) or in the liquid fractions (L1 and L2) relative to control (0% biochar). Asterisks (*) indicate significant changes relative to control, while different letters indicate significant differences among treatments within each biochar concentration. Abbreviations: ns: not significant; ng: not germinated.

Figure 2

Change in the number of germinated seeds (GN) (A), % change in radicle length (RL) (B) and % change in germination index (GI) (C) of lettuce seeds (mean ± SE) germinated in the solid fractions (B1, B1_W, B2 and B2_W) or in the liquid fractions (L1 and L2) relative to control (0% biochar). Asterisks (*) indicate significant changes relative to control, while different letters indicate significant differences among treatments within each biochar concentration. Abbreviations: ns: not significant; ng: not germinated.

Figure 3

Change in the number of germinated seeds (GN) (A), % change in radicle length (RL) (B) and % change in germination index (GI) (C) of tomato seeds (mean ± SE) germinated in the solid fractions (B1, B1_W, B2 and B2_W) or in the liquid fractions (L1 and L2) relative to control (0% biochar). Asterisks (*) indicate significant changes relative to control, while different letters indicate significant differences among treatments within each biochar concentration. Abbreviations: ns: not significant.

Figure 4

Changes in pH (A) and EC (B) in the different soil–biochar mixtures. Asterisks (*) indicate significant changes of both pH and EC relative to control, while different letters indicate significant differences among treatments in each soil–biochar mixture.