Bridging the gap between biochar’s physicochemical characteristics and plant growth

Abstract

Industrialized farming relies heavily on the use of unsustainable synthetic fertilizers to attain their required plant production goals, this usage has several adverse side-effects e.g. eutrophication of water bodies or the increase of atmospheric nitrogen levels [1]. The last decade, the attention of the scientific community has shifted to biobased fertilizers, such as biochars, which can be produced via simple and low-cost methods, while being both energy-negative and carbon neutral. In this regard, Vercruysse et al. [2] synthesized biochars based on extracted common ivy trimmings. Physicochemical characterization of the biochars showed that they had great potential as effective fertilizers, however this was not supported by plant-growth experiments yet.

The aim of this study is to assess whether common ivy-based biochars would have beneficial effects on seedling development. To assess this, lab-scale plant growth experiments on Arabidopsis thaliana seedlings were performed and correlations between important biochar properties and plant development were established. Two different biochar pyrolysis temperatures were tested, 400 and 700 °C and the effect of two different valuable compounds extractions, ethanol extraction and steam distillation, on the biochar’s effectiveness was investigated. This was done via a lab-scale 96-well plant growth experiment, in which 0.5 and 1% of biochar were added to an adapted ¼ Murashee and Skoog plant growth medium. After 7 and 10 days of plant growth seedlings were harvested. After 7 days of growth, phenotypical analysis was performed and the plant’s cell cycle regulation was investigated [3]. Next, plants cultivated for 10 days were also phenotypically analyzed. Furthermore, changes in the plant growth medium due to biochar addition, were evaluated through leaching experiments.

K-leaching from the biochars caused the growth medium’s pH and conductivity to increase significantly in the first 7 days of plant growth. This leaching caused the plants to express initial growth stress responses (Pearson = 0.930), proven by changes in their cell cycle regulation. The second part of the investigated cultivation period, 7-10 days, showed total recovery of the seedlings subjected to biochars produced at 400 °C. Moreover, significant increases in plant fresh weight were established at 1% biochar application rate. Besides that, biochars produced at 700 °C did not significantly affect plant development compared to the control group. At high (1%) biochar loading, low-temperature biochars improved plant development significantly better than high-temperature biochars. This was due to the phosphate availability in high temperature biochars decreasing significantly, which would decrease several plant stress remediation mechanisms.

In conclusion, low-temperature (400 °C) biochars significantly outperform high-temperature (700 °C) in terms of plant development. Furthermore, valuable compound extractions are perfectly suitable as a pretreatment process for common ivy trimmings as they do not diminish the biochar’s performance as soil amendment.