Abstract
Biochar from crop residues such as corncobs can be used for soil amendment, but its negative effects have also been reported. This study aims to evaluate the phytotoxic effects of different biochar treatments and application rates on cress (Lepidium sativum). Corncob biochar was produced via slow pyrolysis without using purging gas. Biochar treatments included fresh biochar (FB), dried biochar (DB), washed biochar (WB), and biochar water extract (WE). Biochar application rates of 10, 20, and 30 t/ha were investigated. Significant phytotoxic effects of biochar were observed on germination rates, shoot length, fresh weight, and dry matter content, while severe toxic effects were identified in FB and WE treatments. Germination rate after 48 h (GR48) decreased with the increase of biochar application rates in all treatments. The observed order of performance of the biochar treatments for germination, shoot length, and shoot fresh weight for every biochar application rate was WB>DB>WE>FB, while it was the reverse order for the shoot dry matter content. WB treatment showed the best performance in reducing the phytotoxicity of biochar. The mitigation of the phytotoxicity in fresh corncob biochar by washing and heat treatment was found to be a simple and effective method.
Highlights
Corncob is biomass residue, which is available and underused in many countries including Ethiopia [1,2]
fresh biochar (FB) and water extract (WE) significantly reduced the shoot length compared to dried biochar (DB) and washed biochar (WB)
A short-term application in this study showed, that FB had a negative effect on germination rate, shoot length, and shoot fresh weight, but the results might be different in a long-term application
Summary
Corncob is biomass residue, which is available and underused in many countries including Ethiopia [1,2]. It was reported in a previous study that in the corn belt areas of Ethiopia the average annual corn stover (i.e., cobs, husks, leaves and stalks) production per household was 2.09 tons [3]. Corncobs have a potential to be processed into biochar for both energy and soil improvement via a slow pyrolysis process. This can improve the resource use efficiency along the biomass-based value webs. Corncob biochar could have an innovative use as propagation substrate in agricultural production systems [4,5]
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