Steel slag amendment impacts on soil microbial communities and activities of rice (Oryza sativa L.).

With the increase in iron/steel production, the higher volume of by-products (slag) generated necessitates its efficient recycling. Because the Linz-Donawitz (LD) slag is rich in silicon (Si) and other fertilizer components, we aim to evaluate the impact of the LD slag amendment on soil quality (by measuring soil physicochemical and biological properties), plant nutrient uptake, and strengthens correlations between nutrient uptake and soil bacterial communities. We used 16 S rRNA illumine sequencing to study soil bacterial community and APIZYM assay to study soil enzymes involved in C, N, and P cycling. The LD slag was applied at 2 Mg ha-1 to Japonica and Indica rice cultivated under flooded conditions. The LD slag amendment significantly improved soil pH, plant photosynthesis, soil nutrient availability, and the crop yield, irrespective of cultivars. It significantly increased N, P, and Si uptake of rice straw. The slag amendment enhanced soil microbial biomass, soil enzyme activities and enriched certain bacterial taxa featuring copiotrophic lifestyles and having the potential role for ecosystem services provided to the benefit of the plant. The study evidenced that the short-term LD slag amendment in rice cropping systems is useful to improve soil physicochemical and biological status, and the crop yield.

Different response of plastic film mulching on greenhouse gas intensity (GHGI) between chemical and organic fertilization in maize upland soil.

Since plastic film mulching (PFM) can deplete soil organic carbon (SOC) stock but increase greenhouse gas (GHG) emissions, PFM utilization is still debating. To determine the influence of PFM on global warming, PFM and no-mulching treatments were installed under chemical and organic fertilizations. In organic fertilization, cover crop was cultivated during the fallow season, and its biomass was incorporated as green manure. To estimate net global warming potential (GWP), two GHG (N2O and CH4) fluxes and SOC stock changes were determined. SOC stock changes were estimated using net ecosystem carbon budget (NECB), which implies the difference between C input and output. GHG intensity (GHGI) was calculated using net GWP per unit of grain yield. PFM increased maize grain yields by approximately 45-95% over no-mulching under the same fertilization, but it was more effective in organic fertilization, due to higher nutrient input. In contrast, PFM increased seasonal N2O and CH4 emissions by 5-10% and 130-260% over no-mulching under the same amendment, respectively. Compared with no-mulching, PFM decreased more highly SOC stock in organic fertilization (around 140-200%) than chemical fertilization (20-30%), due to higher harvest removal and respired C loss. Irrespective with fertilization and mulching background, net GWP was decided by SOC stock change, which covered about 75-90% of net GWP, and then followed by N2O. PFM differently influenced net GWP and GHGI between chemical and organic fertilizations. In chemical fertilization, PFM increased net GWP by 20-30% over no-mulching, but decreased GHGI by 25-35%. However, in organic amendment, PFM highly increased net GWP and GHGI by approximately 115-160% and 30-80% over no-mulching, respectively. PFM in chemical fertilization could be very powerful tool to decrease GHGI via crop yield increase. However, in organic farming, PFM should be carefully selected to increase crop yields, due to more highly increased global warming impact.

Beneficial effect of compost utilization on reducing greenhouse gas emissions in a rice cultivation system through the overall management chain.

Livestock manure application can stimulate greenhouse gas (GHG) emissions, especially methane (CH4) in rice paddy. The stabilized organic matter (OM) is recommended to suppress CH4 emission without counting the additional GHG emission during the composting process. To evaluate the effect of compost utilization on the net global warming potential (GWP) of a rice cropping system, the fluxes of GHGs from composting to land application were calculated by a life cycle assessment (LCA) method. The model framework was composed of GHG fluxes from industrial activities and biogenic GHG fluxes from the composting and rice cultivation processes. Fresh manure emitted 30MgCO2-eq.ha-1, 90% and 10% of which were contributed by CH4 and nitrous oxide (N2O) fluxes, respectively, during rice cultivation. Compost utilization decreased net GWP by 25% over that of the fresh manure during the whole process. The composting process increased the GWP of the industrial processes by 35%, but the 60% reduction in CH4 emissions from the rice paddy mainly influenced the reduction of GWP during the overall process. Therefore, compost application could be a good management strategy to reduce GHG emissions from rice paddy systems.

Composted Cattle Manure Increases Microbial Activity and Soil Fertility More Than Composted Swine Manure in a Submerged Rice Paddy.

Livestock waste composts with minimum inorganic fertilizer as a soil amendment in low-input intensive farming are a feasible agricultural practice to improve soil fertility and productivity and to mitigate soil degradation. The key benefits of the practice rely on the activities of soil microorganisms. However, the role of different livestock composts [composted cattle manure (CCM) vs. composted swine manure (CSM)] on soil microbes, their activities and the overall impact on soil fertility and productivity in a flooded paddy remains elusive. This study compares the effectiveness of CCM and CSM amendment on bacterial communities, activities, nutrient availability, and crop yield in a flooded rice cropping system. We used deep 16S amplicon sequencing and soil enzyme activities to decipher bacterial communities and activities, respectively. Both CCM and CSM amendment significantly increased soil pH, nutrient availability (C, N, and P), microbial biomass, soil enzyme activities indicative for C and N cycles, aboveground plant biomass and grain yield. And the increase in above-mentioned parameters was more prominent in the CCM treatment compared to the CSM treatment. The CCM amendment increased species richness and stimulated copiotrophic microbial groups (Alphaproteobacteria, Betaproteobacteria, and Firmicutes) which are often involved in degradation of complex organic compounds. Moreover, some dominant species (e.g., Azospirillum zeae, Azospirillum halopraeferens, Azospirillum rugosum, Clostridium alkalicellulosi, Clostridium caenicola, Clostridium termitidis, Clostridium cellulolyticum, Magnetospirillum magnetotacticum, Pleomorphomonas oryzae, Variovorax boronicumulans, Pseudomonas xanthomarina, Pseudomonas stutzeri, and Bacillus niacini) which have key roles in plant growth promotion and/or lignocellulose degradation were enhanced under CCM treatment compared to CSM treatment. Multivariate analysis revealed that soil pH and available carbon (C) and nitrogen (N) were the major, while total organic carbon (TOC), total nitrogen (TN), and available phosphorus (P) were the minor drivers of variation in bacterial communities. Overall, our observations suggest that CCM amendment is better than CSM amendment to improve soil fertility and crop yield in a submerged rice cropping system.