The impact of water hyacinth biochar on maize growth and soil properties: The influence of pyrolysis temperature

Introduction

Options for managing water hyacinths (WHs) include converting the biomass into biochar for soil amendment. However, less has been known about the impact of WH-based biochar developed in varying pyrolysis temperatures on plant growth and soil qualities.

Materials and Methods

A pot experiment was undertaken in a factorial combination of WH biochars (WHBs) developed at three temperatures (350°C, 550°C and 750°C) and two application rates (5 and 20 t ha⁻¹), plus a control without biochar. Maize was grown as a test crop for 2 months under natural conditions.

Results

Our study showed that applying WHB developed between 350°C and 750°C at 20 t ha⁻¹ increased maize shoot and root dry biomass by 47.7% to 17.6% and 78.4% to 54.1%, respectively. Nevertheless, raising the biochar pyrolysis temperature decreased maize growth, whereas increasing the application rate displayed a positive effect. The application of WHB generated at 350°C and 550°C at 20 t ha⁻¹ resulted in significant improvements in soil total nitrogen (17.9% to 25%), cation exchange capacity (27.3% to 20.2%), and ammonium-nitrogen (60.7% to 59.6%), respectively, over the control. Additionally, applying WHB produced from 350°C to 750°C at 20 t ha⁻¹ enhanced soil carbon by 38.5%–56.3%, compared to the control. Conversely, applying biochar produced at 750°C resulted in higher soil pH (6.3 ± 0.103), electrical conductivity (0.23 ± 0.01 dS m⁻¹) and available phosphorus (21.8 ± 2.53 mg kg⁻¹).

Conclusion

WHBs developed at temperatures of 350°C and 550°C with an application rate of 20 t ha⁻¹ were found to be optimal for growing maize and improving soil characteristics. Our study concludes that pyrolysis temperature significantly governs the effectiveness of biochar produced from a specific biomass source.