The stability and decomposition of biochar are fundamental to understand its persistence in soil, its contribution to carbon (C) sequestration, and thus its role in the global C cycle. Our current knowledge about the degradability of biochar, however, is limited. Using 128 observations of biochar‐derived CO2 from 24 studies with stable (13C) and radioactive (14C) carbon isotopes, we meta‐analyzed the biochar decomposition in soil and estimated its mean residence time (MRT). The decomposed amount of biochar increased logarithmically with experimental duration, and the decomposition rate decreased with time. The biochar decomposition rate varied significantly with experimental duration, feedstock, pyrolysis temperature, and soil clay content. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years with pool sizes of 3% and 97%, respectively. These results show that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long‐term C sequestration in soil. The second database (116 observations from 21 studies) was used to evaluate the priming effects after biochar addition. Biochar slightly retarded the mineralization of soil organic matter (SOM; overall mean: −3.8%, 95% CI = −8.1–0.8%) compared to the soil without biochar addition. Significant negative priming was common for studies with a duration shorter than half a year (−8.6%), crop‐derived biochar (−20.3%), fast pyrolysis (−18.9%), the lowest pyrolysis temperature (−18.5%), and small application amounts (−11.9%). In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This indicates that biochar stimulates microbial activities especially in soils with low fertility. Furthermore, abiotic and biotic processes, as well as the characteristics of biochar and soils, affecting biochar decomposition are discussed. We conclude that biochar can persist in soils on a centennial scale and that it has a positive effect on SOM dynamics and thus on C sequestration.

Biochar stability in soil: Meta-analysis of decomposition and priming effects

Brain tumor segmentation and classification from magnetic resonance images: Review of selected methods from 2014 to 2019

A full migration BBO algorithm with enhanced population quality bounds for multimodal biomedical image registration

Automatic segmentation methods are an important advancement in medical image analysis. Machine learning techniques, and deep neural networks in particular, are the state-of-the-art for most medical image segmentation tasks. Issues with class imbalance pose a significant challenge in medical datasets, with lesions often occupying a considerably smaller volume relative to the background. Loss functions used in the training of deep learning algorithms differ in their robustness to class imbalance, with direct consequences for model convergence. The most commonly used loss functions for segmentation are based on either the cross entropy loss, Dice loss or a combination of the two. We propose a Unified Focal loss, a new framework that generalises Dice and cross entropy-based losses for handling class imbalance. We evaluate our proposed loss function on three highly class imbalanced, publicly available medical imaging datasets: Breast Ultrasound 2017 (BUS2017), Brain Tumour Segmentation 2020 (BraTS20) and Kidney Tumour Segmentation 2019 (KiTS19). We compare our loss function performance against six Dice or cross entropy-based loss functions, and demonstrate that our proposed loss function is robust to class imbalance, outperforming the other loss functions across datasets. Finally, we use the Unified Focal loss together with deep supervision to achieve state-of-the-art results without modification of the original U-Net architecture, with a mean Dice similarity coefficient (DSC)=0.948 on BUS2017, enhancing tumour region DSC=0.800 on BraTS20 and kidney tumour DSC=0.758 on KiTS19. This highlights the importance of carefully selecting a suitable loss function prior to the use of more complex architectures.

Unified Focal loss: Generalising Dice and cross entropy-based losses to handle class imbalanced medical image segmentation

Study on the improved fuzzy clustering algorithm and its application in brain image segmentation

Biochar for cadmium pollution mitigation and stress resistance in tobacco growth.

Correlation between soil microbial communities and tobacco aroma in the presence of different fertilizers

Soil type regulates carbon and nitrogen stoichiometry and mineralization following biochar or nitrogen addition.

Excessive application of chemical fertilizer and continuous cropping in plastic greenhouse resulted in soil quality decline. The decrease of soil C/N ratio and the imbalance of soil carbon pool structure have brought new challenges to soil health, crop yield and sustainable agricultural development. The experiment was set up to explore the effect of modified biochar on soil bacterial community structure, and the correlation between soil environmental factors and bacterial community structure changes. Based on the plot experiment in the field, the effect of modified biochar was studied via high-throughput MiSeq sequencing. Compared with the control (CK), the modified biochar (T) significantly increased soil water content, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) content and the ratio of MBC and MBN by 7.92%, 24.58%, 2.07% and 18.95%. Diversity index analysis showed that the application of modified biochar significantly increased the Shannon index, ACE index and Chao1 index of the bacterial community by 3.05%, 5.07% and 5.24%. Compared with the control, the modified biochar decreased the relative abundance of Actinobacteriota and Chloroflex by 6.81% and 2.19%, and increased the relative abundance of Proteobacteria and Acidobacteriota by 7.34% and 12.52%. Correlation analysis shows that soil bulk density and water content may be important related factors that affect bacterial community structure. This study provides a theoretical basis for the directional control of modified biochar in the soil microecological environment in plastic greenhouse, which is conducive to healthy and sustainable farming.

Tianbao Ren

Papers

Study on the improved fuzzy clustering algorithm and its application in brain image segmentation

Biochar for cadmium pollution mitigation and stress resistance in tobacco growth.

Correlation between soil microbial communities and tobacco aroma in the presence of different fertilizers

Soil type regulates carbon and nitrogen stoichiometry and mineralization following biochar or nitrogen addition.

Soil amendment in plastic greenhouse using modified biochar: soil bacterial diversity responses and microbial biomass carbon and nitrogen.