The additions of straw and biochar have been suggested to increase soil fertility, carbon sequestration, and crop productivity of agricultural lands.  To our knowledge, there is little information on the effects of straw and biochar addition on soil nitrogen form, carbon storage, and super rice yield in cold waterlogged paddy soils.  We performed field trials with four treatments including conventional fertilization system (CK), straw amendment 6 t ha^–1 (S), biochar amendment 2 t ha^–1 (C1), and biochar amendment 40 t ha^–1 (C2).  The super japonica rice variety, Shennong 265, was selected as the test crop.  The results showed that the straw and biochar amendments improved total nitrogen and organic carbon content of the soil, reduced N₂O emissions, and had little influence on nitrogen retention, nitrogen density, and CO₂ emissions.  The S and C1 increased NH₄⁺-N content, and C2 increased NO₃^–-N content.  Both S and C1 had little influence on soil organic carbon density (SOCD) and C/N ratio.  However, C2 greatly increased SOCD and C/N ratio.  C1 and C2 significantly improved the soil carbon sequestration (SCS) by 62.9 and 214.0% (P<0.05), respectively, while S had no influence on SCS.  C1 and C2 maintained the stability of super rice yield, and significantly reduced CH₄ emissions, global warming potential (GWP), and greenhouse gas intensity (GHGI), whereas S had the opposite and negative effects.  In summary, the biochar amendments in cold waterlogged paddy soils of North China increased soil nitrogen and carbon content, improved soil carbon sequestration, and reduced GHG emission without affecting the yield of super rice.

Biochar has been shown to influence soil microbial communities in terms of their abundance and diversity.  However, the relationship among microbial abundance, structure and C metabolic traits is not well studied under biochar application.  Here it was hypothesized that the addition of biochar with intrinsic properties (i.e., porous structure) could affect the proliferation of culturable microbes and the genetic structure of soil bacterial communities.  In the meantime, the presence of available organic carbon in biochar may influence the C utilization capacities of microbial community in Biolog Eco-plates.  A pot experiment was conducted with differenct biochar application (BC) rates: control (0 t ha^–1), BC1 (20 t ha^–1) and BC2 (40 t ha^–1).  Culturable microorganisms were enumerated via the plate counting method.  Bacterial diversity was examined using denaturing gradient gel electrophoresis (DGGE).  Microbial capacity in using C sources was assessed using Biolog Eco-plates.  The addition of biochar stimulated the growth of actinomyces and bacteria, especially the ammonifying bacteria and azotobacteria, but had no significant effect on fungi proliferation.  The phylogenetic distribution of the operational taxonomic units could be divided into the following groups with the biochar addition: Firmicutes, Acidobacteria, Gemmatimonadetes, Actinobacteria, Cyanobacteria and α-, β-, γ- and δ-Proteobacteria (average similarity >95%).  Biochar application had a higher capacity utilization for L-asparagine, Tween 80, D-mannitol, L-serine, γ-hydroxybutyric acid, N-acetyl-D-glucosamine, glycogen, itaconic acid, glycyl-L-glutamic acid, α-ketobutyricacid and putrescine, whereas it had received decreased capacities in using the other 20 carbon sources in Biolog Eco-plates.  Redundancy analysis (RDA) revealed that the physico-chemical properties, indices of bacterial diversity, and C metabolic traits were positively correlated with the appearance of novel sequences under BC2 treatment.  Our study indicates that the addition of biochar can increase culturable microbial abundance and shift bacterial genetic structure without enhancing their capacities in utilizing C sources in Biolog Eco-plates, which could be associated with the porous structure and nutrients from biochar.

It is of great importance to solve the threats induced by cadmium pollution on crops. This paper examined the effect of biochar on cadmium accumulation in japonica rice and revealed the mechanism underlying the response of protective enzyme system to cadmium stress. Biochar derived from rice straw was applied at two application rates under three cadmium concentrations. Shennong 265, super japonica rice variety, was selected as the test crop. The results indicated that cadmium content in above-ground biomass of rice increased with increasing soil cadmium concentrations, but the biochar application could suppress the accumulation of cadmium to some extent. Under high concentrations of cadmium, content of free proline and MDA (malondialdehyde) were high, so did the SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) activity in the flag leaf of rice. However, the protective enzyme activities remained at low level when biochar was added.