Synergy effect of silicate fertilizer and iron slag: A sustainable approach for mitigating methane emission in rice farming.

Although silicate fertilizer has been recently recognized for its ability to suppress methane (CH4) emissions in paddy fields, the effects of its consecutive application during the rice farming period are still a subject of debate. Moreover, while it was known that silicate fertilizer can mitigate CH4 emissions through several electron acceptors, the effect of additional application of electron acceptors have not been extensively studied. This study evaluated the effect of silicate fertilizer with varying concentrations of iron slag on CH4 emissions and rice yield over the 3 years rice farming period. Seasonal CH4 fluxes exhibited a significant decrease with the application of silicate fertilizer, with the treatment containing 2.5 % iron slag showing the maximum reduction of 35 % in 2020. Additionally, in 2021 and 2022, the application of silicate fertilizer with 2.5 % iron slag resulted in a decrease of total seasonal CH4 emission by 22 % and 23 %, respectively. Rice grain yield exhibited a significant increase with the inclusion of iron slag in the silicate fertilizer, which resulted in a 37 % and 16 % higher yield compared to no-silicate fertilization and no­iron slag silicate fertilization, respectively. Therefore, iron slag-based silicate fertilizer could be a beneficial soil amendment to mitigate CH4 emissions in rice paddy fields and improve rice productivity without negative effects on the atmospheric and soil ecosystem.

Pyrolysis temperature and time of rice husk biochar potentially control ammonia emissions and Chinese cabbage yield from urea-fertilized soils.

Current agricultural practices are increasingly favoring the biochar application to sequester carbon, enhance crop growth, and mitigate various environmental pollutants resulting from nitrogen (N) loss. However, since biochar's characteristics can vary depending on pyrolysis conditions, it is essential to determine the optimal standard, as they can have different effects on soil health. In this study, we categorized rice husk biochars basis on their pH levels and investigated the role of each rice husk biochar in reducing ammonia (NH3) emissions and promoting the growth of Chinese cabbage in urea-fertilized fields. The findings of this study revealed that the variation in pyrolysis conditions of rice husk biochars and N rates affected both the NH3 emissions and crop growth. The neutral (pH 7.10) biochar exhibited effective NH3 volatilization reduction, attributed to its high surface area (6.49 m2 g-1), outperforming the acidic (pH 6.10) and basic (pH 11.01) biochars, particularly under high N rates (640 kg N ha-1). Chinese cabbage yield was highest, reaching 4.00 kg plant-1, with the basic biochar application with high N rates. Therefore, the neutral rice husk biochar effectively mitigate the NH3 emissions from urea-treated fields, while the agronomic performance of Chinese cabbage enhanced in all biochar amendments.

Evaluating methane emissions from rice paddies: A study on the cultivar and transplanting date.

Climate change, driven by increased greenhouse gas emissions, is a pressing environmental issue worldwide. Flooded rice paddy soils are a predominant source of methane (CH4) emissions, accounting for approximately 11 % of global emissions. Factors such as rice (Oryza sativa L.) cultivar, transplanting date, water management, and soil characteristics significantly influence these emissions. This study aimed to evaluate the CH4 emissions from rice paddies in relation to the cultivar and transplanting date. The experiment included two rice cultivars (an early-maturing cultivar, Unkwang, and a medium-late-maturing cultivar, Samkwang) and four transplanting dates (Times 1-4). In the present study, CH4 emissions were higher with earlier transplanting dates and decreased significantly with delayed transplanting. Weather conditions, such as cumulative mean air temperature, cumulative soil temperature, and total sunshine hours, were positively correlated with total CH4 emissions. The recommended regional transplanting date (Time 3) resulted in the highest rice grain yields for both cultivars. However, the earlier transplanting dates (Time 1 and Time 2) were more effective in improving plant growth characteristics such as rice straw weight, root biomass weight, and chlorophyll content. A significant positive correlation was observed between the root biomass weight of the rice and CH4 emissions in both cultivars, implying that an increase in root biomass weight led to an increase in CH4 emissions. Consequently, adhering to the advised regional transplanting dates is the most sensible approach for transplanting rice seedlings. This ensured lower CH4 emissions without compromising rice productivity or quality for both cultivars. Further research should focus on identifying the most appropriate rice-transplanting dates and management practices to effectively reduce CH4 emissions without compromising rice production.

Development of Models to Estimate Total Soil Carbon across Different Croplands at a Regional Scale Using RGB Photography.

A quick, accurate and cost-effective method for estimating total soil carbon is necessary for monitoring its levels due to its environmentally and agronomically irreplaceable importance. There are several impediments to both laboratory analysis and spectroscopic sensor technology because the former is both expensive and time-consuming whereas the initial cost of the latter is too high for farmers to afford. RGB photography obtained from digital cameras could be used to quickly and cheaply estimate the total carbon (TC) content of the soil. In this study, we developed models to predict soil TC contents across different cropland types including paddy, upland and orchard fields as well as the TC content of the soil combined from all the aforementioned cropland types on a regional scale. Soil colour measurements were made on samples from the Chungcheongnam-do province of South Korea. The soil TC content ranged from 0.045% to 6.297%. Modelling was performed using multiple linear regression considering the soil moisture levels and illuminance. The best soil TC prediction model came from the upland soil and gave training and validation r2 values of 0.536 and 0.591 with RMSE values of 0.712% and 0.441%, respectively. However, the most accurate equation is the one that produces the lowest RMSE value. Hence, although the model for the upland soil was the most stable of all, the paddy soil model which gave training and validation r2 values of 0.531 and 0.554 with RMSE values of 0.240% and 0.199%, respectively, was selected as the best soil TC prediction equation of all due to its comparatively high r2 value and the lowest RMSE of all equations.

Volatilisations of ammonia from the soils amended with modified and nitrogen-enriched biochars.

Biochar's capacity to abate NH3 emissions from fertilised agricultural soils may be enhanced through both modifications and formulation of slow-release biochar-based N fertilisers but there is a dearth of data in this area. Sulphuric acid (H2SO4), hydrogen peroxide (H2O2) and potassium hydroxide (KOH) were used to modify biochars which are denoted as BSAD, BHPO and BKOH, respectively. Nitrogen (N) enrichment was performed using urea and ammonium nitrate and the enriched biochars are denoted as BUR and BAN, respectively. The biochars were characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The ammonia abatement potentials of both the modified and N-enriched biochars were assessed in the incubation experiments which lasted for 30 days. Urea was used as a control while non-modified biochar (PrBC) was included for comparison. Compared to the control, PrBC, BKOH, BHPO, BSAD, BUR and BAN attenuated gaseous NH3 emissions by 57.62%, 63.06%, 73.23% and 74.85%, 79.93% and 82.88%, respectively. Biochar modifications increased the content of oxygen containing surface groups especially carboxyl and sulphoxide in the case of BSAD as depicted from the instrumental analysis data, which most probably increased the sorption of NH3 and its transformation to nitrates thus, resulting in a higher NH3 abatement capacity than that of PrBC. XPS data indicated that N-enrichment resulted in reactions of N with the surface groups of biochar which slowed its release, concomitantly lowering NH3 volatilisation better than even the modified biochars.

Characterization of the pyrolytic solid derived from used disposable diapers.

This paper confirms through physical and chemical analyses the possibility to reuse the solid pyrolytic residue derived from used disposable diapers (UDD), heated at different temperatures ranging from 500, 700 and 900 degrees C as a soil amendment. With an increasing pyrolytic temperature, the pH, electrical conductivity, available P2O5, exchangeable K+ and cation exchange capacity tended to increase; however, total-N and exchangeable Ca2+ and Mg2+ decreased. The pyrolytic diaper solid produced at 500 degrees C had a high volatile matter (60.22%) and low ash content (19.10%), which can negatively affect crop growth and productivity when added to soil. Heavy metal concentrations were less than the maximum allowable limits according to Japan standards. The surface of the pyrolytic diaper solid was coarse, porous and heterogeneous with higher temperatures. Hydrogen-containing functional groups, such as OH, C-H, N-H and CH2, decreased with increasing pyrolytic temperature. Based on these results, we concluded that the pyrolytic product derived from UDD at higher temperatures offers a potentially effective soil amendment option.