Whether combining rice-straw biochar (RSB) with leguminous cover crop (LCC) has synergistic effects in the rice production system or not, is still unknown. Two pot experiments were conducted to systematically explore the impacts of RSB on mass decomposition and nitrogen (N) release from LCC residues after incorporation into acidic paddy soil. Similarly, the effect of combining these two factors on soil nutrient status and microbial biomasses in the rice production system was also examined. Five treatments, namely, no N fertilizer (CK), 100% N fertilizer (150 kg N ha^–1 as N₁₀₀), 80% N fertilizer plus RSB (N₈₀B), LCC (N₈₀M), and a combination of RSB with LCC (N₈₀BM), were included. The results indicated that biomass decomposition and N release pattern followed a double exponential decay model such that the addition of RSB slightly stimulated the rates of both mass decomposition and N release during the initial rapid phase of decomposition. Thereafter, it notably slowed down the rates of both these parameters during the relatively slower stage of incorporating LCC residues to paddy soil during early rice season. Compared to 100% N, applying 80% N in conjunction with RSB and/or LCC residue increased grain yield and its components (i.e., effective panicles, 1,000-grain weight, and fully filled grains) that subsequently increased N accumulation and its physiological use efficiency (PUE_N) of rice shoot. Moreover, under 20% N, applying RSB and/or LCC residue remarkably increased the soil organic matter and total N, and soil microbial populations and biomasses, while the contents of NH₄⁺ and NO₃^– were decreased in RSB-amended paddy soil (N₈₀B and N₈₀BM), in comparison with N₁₀₀. Thus, combining RSB with LCC residue is a novel and promising management intervention for reducing mineral fertilizer use, improving soil fertility and rice production, and consequently minimizing the overall production cost in south China.

Endopolygalacturonase (EndoPGase), EC: 3.2.1.15. is one of the crucial pectinases belonging to the class of carbohydrase. The catalytic action of EndoPGase captivates the attention of the production of this extremely valuable catalyst in the industrial sector. The main focus was to ascertain a potential bacterial candidate for endoPGase production. The isolated bacterial strain was further identified by 16S rRNA gene sequencing. The parameters for enzyme biosynthesis were optimized by a single and multiple factor approach at a time. The results of our investigation led to the identification of a potent strain of Bacillus subtilis NR2 [strain 168]. The sequence of 16S rRNA amplified from the isolated bacterium has been submitted to GenBank under accession number ON738697. The strain was found active for pectic enzyme activity under shaking- flask fermentation at pH 5.0 and 50 °C temperature of incubation. Among all monomeric and polymeric substrates (inducer-substrates), citrus pectin, followed by potato starch and pectin (Sigma) were considered the best enzyme inducers at 1% concentration. In comparison, an increased wheat bran concentration at 5% was proved to be ideal for EndoPGase biosynthesis Moreover, an increasing trend in enzyme activity was observed with the increasing concentration of inducer. The combined effect of three variables (pH, inducer-substrates, and inducer-substrate concentration) was explored by response surface methodology (RSM) involving a Box–Behnken design (BBD). Based on the results, we concluded that the soil-isolated B. subtilis can be effectively utilized for commercial-scale pectinase enzyme biosynthesis.

Co-incorporating rice straw biochar (RSB) and milk vetch (MV) is a promising strategy for sustainable rice production. However, the appropriate nitrogen (N) reduction rate under RSB + MV, particularly when balancing multiple production objectives, remains unclear. This study evaluated five N-reduction rates (0–70% conventional N fertilizer) under RSB + MV. Grain yield, quality, nutrient uptake, and partial factor productivity of N fertilizer (PFP_N) were assessed in early and late rice. Entropy-weighted Technique for Order Preference by Similarity to Ideal Solution (EW-TOPSIS) model was used to integrate all indicators, when Gaussian model was applied to estimate the appropriate N-reduction rate. Pearson correlation and random forest analysis identified primary predictors of grain quality. Results showed that appropriate N-reduction (≤30%) under RSB + MV maintained or increased grain yield, quality, and PFP_N compared to conventional N fertilization alone. Among all treatments, N₈₀BM and N₇₀BM achieved the highest comprehensive scores in EW-TOPSIS analysis, and Gaussian model-estimated N-reduction of 18.2% and 21.0% for early and late rice, respectively. Nutrient uptake, effective panicle number and filled grains per panicle were identified as primary predictors of grain quality. Therefore, under the tested condition, RSB + MV with 20% N-reduction achieved the highest overall performance. However, these findings require further validation across multiple-year and multi-location.

Introduction: Biochar and milk vetch (MV) are known to improve soil fertility and crop yield. However, the effects of the combined application of rice straw biochar (RSB) and MV over multiple years on nitrogen (N) dynamics, microbial ecology, and rice yield remain unclear. This study is to evaluate the synergistic effects of RSB and MV over multiple growing seasons. Methods: A three-year field experiment was conducted with four treatments, N fertilizer alone (CK), N+RSB (B), N+MV (M), and N+RSB+MV (BM), and measured various indicators of soil health and rice yield. Results: Soil organic C, total N, inorganic N (NH ₄ ⁺ and NO ₃ ⁻ ), microbial biomass C/N, and enzyme activities (urease, nitrate, and nitrite reductase) were 14%–30%, 12%–25%, 18%–40%, 20%–45%, and 15%–50% higher in the B and M treatments than in the CK; the greatest increases in these parameters (by 14%–89%) were observed in the BM treatment. Microbial diversity (α-diversity of soil microbes) was increased and the expression of N-cycling functional genes ( nif H, amo A, nar G, nir S/ nir K, nos Z) was 9.1%–400% higher in the BM treatment than in the CK. High gene abundances (AOA amo A, AOB amo A, nar G, nir S, nir K, and nos Z) were associated with increased N uptake and grain yield. Microbial biomass C and N were key drivers of shifts in microbial communities influencing N-cycling genes. Increased soil C and N availability in the BM treatment stemmed from changes in the expression of microbial genes and enzyme activities enhancing N assimilation and rice yield. Discussion: Hence, combining RSB with MV can promote soil fertility, rice productivity and ecological benefits.

Although rice straw biochar (RSB) and milk vetch (MV) facilitate rice production and soil carbon and nitrogen (N) storage, their combined effects under N-reduction remain unclear, particularly at the aggregate-scale in reddish paddy soils. A two-year field experiment with four treatments: 100% N (N₁₀₀), 20% N-reduction + RSB (N₈₀B), 20% N-reduction + MV (N₈₀M), and 20% N-reduction + RSB + MV (N₈₀BM), was conducted in reddish paddy soil. Rice yield, soil organic carbon (SOC) and total N (TN) stocks, water-stable aggregate distribution and stability, and aggregate-associated C and N allocation were measured. Over the two-year study, N₈₀BM significantly increased grain yield by 11.2%, SOCs by 5.42%, and TNs by 6.92% compared with N₁₀₀ (p < 0.05). RSB and MV combined with N-reduction increased macroaggregate proportion by 7.92–11.8% and aggregate stability by 7.14–58.1%, while decreasing silt–clay fraction by 39.6–62.9%. Soil C and N enrichment occurred predominantly in macroaggregates. Pearson correlation and random forest analyses jointly identified aggregate distribution and stability as primary predictors of rice yield, SOCs, and TNs. Therefore, RSB + MV combined with 20% N-reduction sustained rice yield while enhancing soil aggregation and C, N sequestration, providing a rational strategy for N management in sustainable rice production.