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International Conference on

Recent Trends in Environmental Sustainability

ESCON22/ETERM/09
Assessments of the suitability of biochar produced from different feedstock as an
alternative rhizobial carrier and efficacy on soybean under drought stress

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Rahat Shabir , Yantao Li , Chengrong Chen
1 Environmental Biogeochemistry Research Lab, Australian Rivers Institute | School of
Environment & Science, Griffith University, Nathan Campus | 170 Kessels Road, Nathan
Qld, 4111, Australia
Correspondence: rahat.shabir@griffithuni.edu.au

Abstract
Here we tested the physical and chemical properties of six biochars made from various
feedstocks pyrolyzed at 600 ℃ using slow pyrolysis method. The potential of biochars as
inoculant carriers was tested using Bradyrhziobium japonicum (CB1809) strain for up to 90
days stored at 28 ℃ and 38 ℃ respectively. Peat was used for comparison. The relationship
between rhizobial shelf life and physicochemical properties of biochars was tested through
structural equation modelling (path analysis), principal component analysis (PCA) and Pearson
correlation. The results revealed that among different physicochemical properties, functional
groups (C=O, O-C=O), total carbon concentration, manganese concentration, specific surface
area (SSA), pore size and total pore volume (TPV) showed significant (p< 0.05) positive impact
on shelf life. Due to wide range of pH and water holding capacity of biochars, pH and WHC
showed non-significant (p>0.05) effect on shelf life of rhizobia. All biochars tested showed
good results and none of them caused detrimental effects on the CB1809 population. Pinewood
biochar (PBC) was the best as it sustained maximum rhizobial population as compared to peat
and other biochars. Furthermore, the role of PBC inoculants was tested on the growth of
soybean under drought stress using two soil types (100% garden soil + 0% sand and 50%
garden soil + 50% sand). Seed coating method was used to treat the soybean seeds and the
results were compared with control (without inoculant), peat and oak biochar (showed second
best performance on rhizobial shelf life). After emergence of the seedlings, depending upon
the water holding capacity of soils, three moisture levels (ML) i.e., ML 55% (normal watering),
ML 30% (moderate stress) and ML 15% (severe stress) were maintained. Changes in plant
growth parameters (e.g., shoot/root biomass, shoot/root length, number leaves, and number of
nodules), chlorophyll contents, relative water content (RWC), membrane stability index (MSI),
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nitrogenase activity through acetylene reduction assay (ARA), stable carbon (δ C) and
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nitrogen (δ N) isotopes, and leaf total nitrogen (LTN) were estimated under greenhouse pot
trial (completely randomized design). Moreover, drought stress also caused reduction in
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chlorophyll pigments, RWC, and MSI. Significant decline in δ C, δ N signatures and LTN
was also observed in drought stressed plants. High drought impact was observed in plants
grown on pure garden soil as compared to plants grown in mixture of garden soil and sand.
Finally, the application of PBC was found to reduce the negative effect of drought most and
maintained the highest growth in plants. Overall, the results of the study illustrated that
biochars (especially PBC) had the excellent physicochemical characteristics that are required
for rhizobial growth, and the pot trial results further revealed that biochars could be used as an
alternative promising rhizobia carrier material for the development of novel inoculant product.

Keywords: Biochar; Drought; Bradyrhziobium japonicum.

Department of Environmental Sciences, COMSATS University Islamabad, Vehari Campus

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