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Soil microorganisms play a crucial role in organic matter decomposition and nutrient cycling in cropping systems. Compared to bacteria, fungal community composition and the role of fungi in organic matter decomposition and nutrient cycling in agro-systems are, however, elusive. Silicon (Si) fertilization is essential to improve agronomic performance of rice. The effects of the Si fertilizer application on the soil fungal community composition and their contribution in soil organic matter (SOM) decomposition are not yet studied. We investigated the short-term (120 days) slag silicate fertilizer (SSF) amendment impacts on plant photosynthesis and soil biochemical changes, soil fungal communities (assessed by ITS amplicon illumina sequencing), hydrolytic and oxidase enzyme activities, CO 2 emissions, and bacterial and fungal respiration in diverse eco-geographic races of rice (Oryza sativa L.), i.e., Japonica rice (O. sativa japonica) and Indica rice (O. sativa indica). The short-term SSF amendment significantly increased the relative abundance of saprotrophic fungi and accelerated organic matter decomposition. The increase in saprotrophic fungi was mostly attributed to greater labile C availability and Si availability. Higher organic matter decomposition was accompanied by an increase in both hydrolytic and oxidative enzyme activities in response to the SSF amendment. The stimulation of oxidative enzyme activities was explained by an increase in root oxidase activities and iron redox cycling, whereas stimulation of hydrolytic enzyme activities was explained by the greater labile C availability under SSF fertilization. We conclude that the short-term SSF amendment increases saprotrophic fungal communities and soil hydrolytic and oxidative enzyme activities, which in turn stimulates SOM mineralization and thus could have negative feedback impacts on soil C storage in submerged rice paddies.

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Straw incorporation is strongly recommended in rice paddy to improve soil quality and mitigate atmospheric carbon dioxide (CO 2), via increasing soil organic carbon (SOC) stock. However, straw application significantly increased methane (CH 4) emission during rice cultivation, and then its incorporation area was not expanded effectively. To find the reasonable straw management practice which can reduce CH 4 emission without productivity damage, the effect of straw incorporation season and method on CH 4 emission was investigated at six different textured paddy fields in South Korea for 2 years. A straw was applied right after rice harvesting in autumn, and the other right before rice transplanting in spring. In the autumn application, straw was applied with two different methods: spreading over soil surface or mixing with soil. Straw application significantly increased seasonal CH 4 flux by average 28-122% over 197-590 kg CH 4 ha −1 of the no-straw, but its flux showed big difference among straw applications. Fresh straw application before transplanting increased seasonal CH 4 flux by approximately 120% over the no-straw, but the autumn application reduced its CH 4 flux by 24-43% over 509-1407 kg CH 4 ha −1 of the spring application. In particular, the seasonal CH 4 flux was approximately 24% lower in straw mixing with soil after autumn harvesting than 423-855 kg CH 4 ha −1 in straw spreading over surface. However, CH 4 fluxes were not significantly discriminated by soil and meteorological properties in the selected condition. Straw application slightly increased rice grain yield by approximately 4% over the no-straw, but rice productivity was not statistically different among straw applications. Spring straw application increased CH 4 intensity which means seasonal CH 4 flux per grain yield by the maximum 220% over the no-straw. Autumn straw application significantly decreased CH 4 intensity by average 24-65% over the spring straw application. In particular, CH 4 intensity in straw mixing with soil treatment was not statistically different with the no-straw. Therefore, autumn straw application with mixing inner soil could be a reasonable straw management practice to decrease CH 4 emission impact with improving soil productivity.

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Paddy rice systems are characterized by waterlogged conditions with high potential for CH4 emissions and soil organic carbon (SOC) sequestration. Therefore, it is necessary to evaluate the net global warming potential (GWP) of soil management considering SOC stock changes, and CH4 and N2O fluxes. Green manure application and straw retention slightly enhanced SOC stock, but highly increased net GWP due to high CH4 emissions. Aerobic pre-digestion of organic matter amended soils and water drainage during cropping are practices which significantly decrease net GWP. Moreover, silicate fertilizers with electron acceptors like oxidized iron and manganese also decrease net GWP. Biochar rather than compost as a stable organic amendment significantly increases SOC while decreasing net GWP. In conclusion, the combined management of organic amendments, aerobic pre-digestion, water drainage, and fertilizers could be a promising way to mitigate greenhouse gas emissions and favor C sequestration in rice paddies.