Effects of Biochar on Soil Microbial Biomass after Four Years of Consecutive Application in the North China Plain

Qing-Zhong Zhang,Ning Lu,Xing-Ren Liu,Jian Huang,Feike A Dijkstra,Yi-Ding Wang,Andrew C Singer

doi:10.1371/journal.pone.0102062

Abstract

The long term effect of biochar application on soil microbial biomass is not well understood. We measured soil microbial biomass carbon (MBC) and nitrogen (MBN) in a field experiment during a winter wheat growing season after four consecutive years of no (CK), 4.5 (B4.5) and 9.0 t biochar ha−1 yr−1 (B9.0) applied. For comparison, a treatment with wheat straw residue incorporation (SR) was also included. Results showed that biochar application increased soil MBC significantly compared to the CK treatment, and that the effect size increased with biochar application rate. The B9.0 treatment showed the same effect on MBC as the SR treatment. Treatments effects on soil MBN were less strong than for MBC. The microbial biomass C∶N ratio was significantly increased by biochar. Biochar might decrease the fraction of biomass N mineralized (K N), which would make the soil MBN for biochar treatments underestimated, and microbial biomass C∶N ratios overestimated. Seasonal fluctuation in MBC was less for biochar amended soils than for CK and SR treatments, suggesting that biochar induced a less extreme environment for microorganisms throughout the season. There was a significant positive correlation between MBC and soil water content (SWC), but there was no significant correlation between MBC and soil temperature. Biochar amendments may therefore reduce temporal variability in environmental conditions for microbial growth in this system thereby reducing temporal fluctuations in C and N dynamics.

Highlights

Biochar is the product of the thermal degradation of organic materials in the absence of air and is distinguished from charcoal by its use as a soil amendment [1]
The microbial biomass carbon (MBC) in the B9.0 treatment increased by 118% to 763%, while the MBC in the straw residue incorporation (SR) treatment was 2% lower to 722% higher compared to CK, depending on the time of year (Fig. 1a, b)
Our results showed that MBC increased with biochar amendment compared to CK, which suggested that microbial growth could be accelerated by biochar addition

Summary

Introduction

Biochar is the product of the thermal degradation of organic materials in the absence of air (pyrolysis) and is distinguished from charcoal by its use as a soil amendment [1]. Positive and negative priming effects on native organic carbon mineralization in biochar-amended soils have been reported [3,4,5,6], and the priming direction is thought to be controlled by the biochar type (determined by production conditions and sources used) and soil pH. There is strong evidence that priming effect on soil organic matter decomposition relies on microbial biomass [7]. Research on soil microbial biomass dynamics with biochar application will help the understanding of priming effect on soil organic matter and biochar decomposition. Biochar addition can increase soil microbial biomass, and may affect the soil biological community composition, which in turn will affect nutrient cycling, plant growth, and greenhouse gas emission, as well as soil organic carbon mineralization mentioned above [1]

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