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

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.

Plant-biochar interactions drive the negative priming of soil organic carbon in an annual ryegrass field system

“…The initial positive priming in our study can be partly explained by the addition of fresh labile C in biochar (containing 30% Alkyl-C, Table 1), serving as an energy source for the microbial community (Lehmann et al, 2011). This hypothesis was supported by the rapid increase in MBC shortly after biochar application (Table 4), which was also observed in other studies (Lehmann et al, 2011;Zhang et al, 2014). At the four-month sampling we also showed that biochar addition increased soil pH from 4.6 to 5.2 compared with the controls (Table 4).…”

Nitrogen immobilization may reduce invasibility of nutrient enriched plant community invaded by Phragmites australis

“…The MBN significantly decreased in the AC-amended soil in all populations in our study, which is supported by other studies 93,94 . For example, Zhang et al 93 found the MBN decreased with AC addition at a rate of 4.5 t/ ha/yr in the field at most sampling dates and soil depths compared to the unamended soil treatment, whereas Zavalloni et al 95 and Dempster et al 96 found AC amendment had no significant impact on MBN. Again, AC increased soil MBC in our studies supported by Ma et al 97 and Gebhardt et al 98 whom found addition of carbon as a soil amendment significantly increased MBC and thereby, altered plant biomass.…”

A model for mechanistic and system assessments of biochar effects on soils and crops and trade‐offs

“…The default value for fr_bcbiom was set so a small portion (0.05 × 0.4 = 2%; Table ) of the decomposed biochar C was partitioned to BIOM. This assumption is reasonable given experimental findings that the size of the microbial pool increases following biochar application (Clough et al ., ; Bruun et al ., ; Zhang et al ., ; Liu et al ., ). The parameters described in this section have either not been experimentally measured or have been measured for only a limited range of biochar‐soil‐weather conditions (e.g.…”