Effects of the Autumn Incorporation of Rice Straw and Application of Lime Nitrogen on Methane and Nitrous Oxide Emissions and Rice Growth of a High-Yielding Paddy Field in a Cool-Temperate Region in Japan

The effects of autumn plowing and lime nitrogen application on rice straw decomposition, CH4 and N2O emission and rice growth in the following year in a high-yielding rice cultivated paddy field were evaluated for two years. The experimental plots were set up, combining different times of rice straw (750 g m−2) incorporation into the soil by plowing (autumn or the following spring), with and without lime nitrogen application in autumn (5 g-N m−2). Autumn plowing promoted the decomposition of rice straw, but the application of lime nitrogen did not show a consistent trend. The soil pH was high (7.3) at the studied site, and the alkaline effect of lime nitrogen may not have been significant. As with straw decomposition, CH4 emissions were suppressed by autumn plowing, and no effect from the lime nitrogen application was observed. It was also suggested that the straw decomposition period may be shorter and the CH4 emissions may be higher in high-yielding cultivars that require a longer ripening period than in normal cultivars. The effect of both treatments on N2O emission was not clear. Both the autumn plowing of rice straw and lime nitrogen application were effective in promoting rice growth and increasing rice yield.

Nitrous oxide emission from conservation forest of Kampar Peninsula peatland ecosystem

Nitrous oxide (N2O) is a long-lived greenhouse gas with a warming potential of 300 times higher than CO2. Conserving of intact peat swamp forest can hold the natural physical and chemical properties of the soil, such that the N2O emission occurs naturally. To quantify N2O emission from peatland ecosystems, data availability is highly needed. The objectives of this study were to quantify the emission of N2O and determine the main factors controlling N2O emission from peatland conservation forests. This research was conducted from January to December 2020 in the Kampar Peninsula, Pelalawan Regency, Riau Province. This study found that N2O emission at peatland conservation forest was 0.23 ± 0.19 kg-N/ha/year. Substantial changes in soil and environmental factors such as water table, soil temperature, soil moisture, water-filled pore space, NH4-N, and NO3-N significantly affect the exchange of N2O between peatlands and the atmosphere.

Effects of Rock Powder Additions to Cattle Slurry on Ammonia and Greenhouse Gas Emissions

For several decades, farmers have been mixing rock powders with livestock slurry to reduce its NH3 emissions and increase its nutrient content. However, mixing rock powders with slurry is controversial, and there is currently no scientific evidence for its effects on NH3 and greenhouse gas (GHG) emissions or on changes in its nutrient content due to element release from rock powders. The major aim of this study was therefore to analyse the effects of mixing two commercially established rock powders with cattle slurry on NH3, CO2, N2O and CH4 emissions, and on nutrient release over a course of 46 days. We found that rock powders did not significantly affect CO2 emission rates. NH3 and N2O emission rates did not differ significantly up until the end of the trial, when the emission rates of the rock powder treatments significantly increased for NH3 and significantly decreased for N2O, respectively, which coincided with a reduction of the slurry crust. Cumulative NH3 emissions did not, however, differ significantly between treatments. Unexpected and significant increases in CH4 emission rates occurred for the rock powder treatments. Rock powders increased the macro- and micronutrient content of the slurry. The conflicting results are discussed and future research directions are proposed.

Rice Residue-Based Biochar Mitigates N2O Emission from Acid Red Soil

Biochar application is considered an effective approach to mitigating nitrous oxide (N2O) emissions from agricultural soils. However, the mechanisms of biochar to mitigate N2O emissions from acidic red soils are still unclear. Therefore, the present study aims to underpin mechanisms associated with rice residue-based biochar in mitigating N2O emissions from acid soils. Soil treated with different rates of biochar control, from 1%, 2%, and 3%, and different soil properties, including soil pH, microbial biomass carbon (MBC), NH4+-N, NO3−-N, genes abundance (nosZ, nirK, AOA, and AOB), and enzymatic activities ((nitrate reductase (NR) and urease (UR)) were studied. The application of 3% biochar increased the soil pH (5.21–6.48), MBC (565–685 mg/kg), NO3−-N contents (24.23–44.5 mg/kg), genes abundance (nosZ, nirK, AOA, and AOB) and UR activity. The highest N2O emission (43.60 μg kg−1) was recorded and compared with the application of 1% (26.3 μg kg−1), 2% (18.33 μg kg−1), and 3% biochar (8.13 μg kg−1). Applying 3% biochar effectively reduced the N2O emission due to increased soil pH, MBC, NO3−-N contents, genes abundance (nosZ, nirK, AOA, and AOB), and weakened NH4+-N and NR activities. Therefore, increasing soil pH, genes abundance, and weakened nitrification following the addition of rice residue-based biochar can effectively reduce the N2O emissions from acidic red soils.

Seasonal changes in the abundance and activity of bacterial and fungal denitrifying communities associated with different compost amendments

Composts can be efficient organic amendments in potato culture as they can supply carbon and nutrients to the soil. However, more information is required to the effects of composts on denitrification and nitrous oxide emissions (N2O) and the emission-producing denitrifying communities. The effect of three compost amendments (municipal source separated organic waste compost (SSOC), forestry waste mixed with poultry manure compost (FPMC), and forestry residues compost (FRC)) on fungal and bacterial denitrifying communities and activity was examined in an agricultural field cropped to potatoes in during the fall, spring and summer seasons. The denitrification enzyme activity (DEA), N2O emissions and respiration were measured in parallel. N2O emission rates were greater in FRC-amended soils in the fall and summer, while soil respiration was highest in SSOC-amended soil in the fall. A large number of <i>nirK</i> denitrifying fungal transcripts was detected in the fall, coinciding with compost application while the greatest <i>nirK</i> bacterial transcripts were measured in the summer when plants were actively growing. Denitrifying community and transcript levels were poor predictors of DEA, N2O emissions or respiration rates in compost-amended soil. Overall, the sampling date was driving the population and activity levels of the three denitrifying communities under study.