Is There a Positive Synergistic Effect of Biochar and Compost Soil Amendments on Plant Growth and Physiological Performance?

M Seehausen,Norman Liu,Jane Michener,Nigel Gale,Charlene Williams,Sandy Smith,Emma Thurston,Sean Thomas,Virginia Hudson,Stefana Dranga

doi:10.3390/agronomy7010013

Abstract

The combination of biochar (BC) with compost has been suggested to be a promising strategy to promote plant growth and performance, but although “synergistic” effects have been stated to occur, full-factorial experiments are few, and explicit tests for synergism are lacking. We tested the hypothesis that a combination of BC and spent mushroom substrate (SMS) has a positive synergistic effect on plant growth and physiological performance in a nutrient-limited growing media. A greenhouse experiment with a full factorial design was conducted using mixed-wood BC (3.0 kg·m−2) and SMS (1.5 kg·m−2) (the combination was not co-composted) as organic soil amendments for the annual Abutilon theophrasti and the perennial Salix purpurea. Several measurements related to plant growth and physiological performance were taken throughout the experiment. Contrary to the hypothesis, we found that the combination of BC + SMS had neutral or antagonistic interactive effects on many plant growth traits. Antagonistic effects were found on maximum leaf area, above- and belowground biomass, reproductive allocation, maximum plant height, chlorophyll fluorescence, and stomatal conductance of A. theophrasti. The effect on S. purpurea was mostly neutral. We conclude that the generalization that BC and compost have synergistic effects on plant performance is not supported.

Highlights

Charcoal derived from wildfire plays an integral role in the re-vegetation and function of ecosystems following disturbances
Hypothesis, we found that the mixture of BC and spent mushroom substrate (SMS) generally had neutral or antagonistic we found that the mixture of BC and SMS generally had neutral or antagonistic interactive effects on interactive effects on plant growth and physiological performance
The generalization that BC and compost mixtures have synergistic effects on plant growth and performance is not supported by this study

Summary

Introduction

Charcoal derived from wildfire plays an integral role in the re-vegetation and function of ecosystems following disturbances. Soil pyrogenic carbon provides numerous services to plants, sorbing many growth-inhibitory compounds (e.g., phenolics, salts, metals) [1,2], basifying acidified soils concomitant with improving nutrient retention and exchange [3], delivering a pulse of water-soluble elements available for plants and soil fauna [4,5], and improving soil water holding capacity [6]. When charcoal is applied as a soil amendment, the term “biochar” (BC) is used [7]. BC has received much attention for its potential to improve soil fertility and to mitigate climate change by carbon sequestration (e.g., [8,9,10]). In recent meta-analyses, Jeffrey et al [11] and Biederman and Harpole [12] show that BC increases crop yields by an average of

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