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Earthworms’ activities not only increase soil nitrogen (N) uptake by crops but also lead to N losses to environment. However, it remains unclear whether earthworms’ impact on the fate of fertilizer N differs based on the type of fertilizer application. Therefore, the present pot experiment examined the transformation and fate of two types of 15N-labeled fertilizer (synthetic fertilizer urea and organic fertilizer compost applied at rate of 400 mg N/pot) with and without earthworms (Amynthas corticis) in a soil-lettuce system over three seasons of cultivation. Results showed that earthworms increased the fresh biomass of lettuce in all three seasons, regardless of the type of fertilizer used. However, the effect of earthworms on fertilizer N uptake varied depending on the type of fertilizer. With earthworms present, lettuce took up an additional 20.97 mg/pot of synthetic fertilizer N in the first season, which sharply decreased to 2.72 mg/pot and 4.63 mg/pot in the second and third seasons, respectively. In contrast, the uptake of organic fertilizer N by lettuce increased by 10.08–11.24 mg/pot throughout the entire experiment when earthworms were present. The presence of earthworms increased the percentage of synthetic fertilizer N lost to the environment by 0.8 %, due to increased N leaching, N2O emission, NH3 volatilization, etc. In contrast, earthworms decreased the percentage of organic fertilizer N lost to the environment by 1.9 %, primarily through reduced NH3 volatilization, etc. This study underscores the pivotal role of earthworms in modulating fertilizer N dynamics, with organic fertilizer offering superior ecosystem services compared to synthetic fertilizer. Given that only one earthworm species was studied and nearly half of the organic fertilizer remained in the soil, future long-term experiments incorporating diverse earthworm species and changes in the soil’s native N pool are essential to fully understand the role of earthworms in agro-ecosystem N cycling.

Global warming can accelerate soil organic matter (SOM) decomposition resulting in faster carbon (C) loss and positive climate-C feedback. Previous studies on response of SOM decomposition to climate change mainly focus on plow soil layer. However, the effects of elevated CO2 and soil warming on soil organic carbon (SOC) and total nitrogen (TN) contents and mineralization are rarely studied in subsoil layer. In this study, soil samples were collected from the 0–50-cm paddy soil layer of the Tsukuba free-air CO2 enrichment experimental site with elevated CO2 (+200 ppm) and soil warming (+2 °C), Japan, after 5-year rice growth season. The amounts of SOC, TN, δ13C, and δ15N were analyzed. A 4-week anaerobic incubation experiment was conducted to measure C decomposition and N mineralization potentials. Due to the intrinsic variation in SOC and TN contents in soil layers and fields, the effects of elevated CO2 and soil warming on C decomposition and N mineralization potentials could not be determined here. However, the effect of elevated CO2 on δ13C was only found in 0‒10-cm soil layer. In the 0–50-cm soil profiles, significant correlations were observed among SOC and TN, δ13C and δ15N, decomposed C and mineralized N, and δ13C of decomposed C. The variables associated with soil C and N pools, and dynamics showed large spatial heterogeneity within paddy field, due to variation in the original land use history. Therefore, great caution should be exercised when evaluating the effects of elevated CO2 and temperature on SOM decomposition and sequestration in paddy soil profiles.

Abstract Indoor air conditioning systems play a crucial role in regulating the environmental conditions of enclosed spaces. The noise generated by such systems can significantly impact human comfort. The multiblade centrifugal fan, as a crucial component of indoor air conditioners, has a significant impact on the performance of the air conditioner. The vortex, which is the primary noise source inside the fan, hinders the aerodynamic noise reduction of the indoor unit. During experimental research and numerical simulation of the indoor unit, the researchers identified the presence of a vortex flow at the outlet of the multiblade centrifugal fan. By analyzing the velocity vector of different cross‐sections in the fan, the researchers determined the formation mechanism and influencing factors of the vortex at the fan's outlet. The addition of fairing sheet plates on the volute wall was explored as a vortex suppression method, which proved effective in weakening and suppressing the vortex. The test results showed that under the same air volume, the noise reduction amplitude of the fan equipped with fairing sheet blades was 1.2 dB at an outlet static pressure of 30 Pa and 0.7 dB at an outlet static pressure of 100 Pa. The research findings suggest that the addition of the fairing sheet can effectively reduce the vortex's intensity, improve the performance of the multiblade centrifugal fan, and reduce the noise.

Soil pH significantly impacts microbial activity and community assembly, which in turn determines the temperature sensitivity (Q10) of soil respiration. Due to the high soil acidification in China, it is necessary to understand how soil acidification impacts Q10. Here, the Q10 of soil respiration was examined in a long-term field experiment (1982–present) with different soil pH caused by fertilization management. In this experiment, we selected treatments with neutral pH: (1) no crops and fertilization (CK); (2) crops without fertilization (NF); low pH with (3) crops with chemical fertilization (NPK); and (4) crops with chemical fertilization combined with wheat straw incorporation (WS). Under natural soil temperature changes, we observed that soil acidification lowered the Q10 value of soil respiration. Considering only temperature changes, the Q10 of soil respiration was strongly associated with microbial community composition, alpha diversity, and soil ammonium nitrogen. Considering the interaction between soil pH and temperature, warming strengthened the negative effect of soil pH on the Q10 of soil respiration, and the pathway through which soil pH mediated Q10 included not only microbial community composition, alpha diversity, and biomass but also the soil’s available phosphorus. This work enhanced our insights into the relationships between Q10, temperature, and soil pH by identifying important microbial properties and key soil environmental factors.

Appropriate weeds control is needed against weeds constraints in field, especially the organic field. With the appropriate management, weeding would benefit the organic field not only in reducing weeds but also in increasing nitrogen (N) availability in organic rice fields. This research aims to observe soil available N changes affected by weeding frequencies in organic paddy fields. Treatments applied were five weeding frequencies (WF) such as 0 WF, 2 WF, 4 WF, 6 WF, and 8 WF, to study the effect of various weeding frequencies on soil total N and available N ( NH4+ and NO3–) in the organic rice field. The soil in the conventional field was analyzed as a comparison to organic field soil. The results showed that soil C and N contents are similar in all treatments. Meanwhile, 6 WF performed the highest soil NH4+ among organic plots (10.36 mg N kg–1) and 8 WF enhanced soil NO3– to the highest average among all plots (10.12 mg N kg–1). The treatment of 6 WF and 8 WF also maintain the increase of soil NH4+ to 51 days after transplanting (DAT), meanwhile 0 WF, 2 WF, and 4 WF decreased after 40 DAT. Water samples from fields inlet-outlet and river showed that NH4+ content found in water sample was higher than NO3–. We concluded that the more frequencies of weeding applied to organic fields potentially preserved soil inorganic N longer, which is very important in supporting rice growth.

Plants have evolved various mechanisms for low P tolerance, one of which is changing their membrane lipid composition by remodeling phospholipids with non-phospholipids. The objective of this study was to investigate the remodeling of membrane lipids among rice cultivars under P deficiency. Rice (Oryza sativa L.) cultivars (Akamai, Kiyonishiki, Akitakomachi, Norin No. 1, Hiyadateine, Koshihikari, and Netaro) were grown in 0 (−P) and 8 (+P) mg P L−1 solution cultures. Shoots and roots were collected 5 and 10 days after transplanting (DAT) in solution culture and subjected to lipidome profiling using liquid chromatography-mass spectrometry. Phosphatidylcholine (PC)34, PC36, phosphatidylethanolamine (PE)34, PE36, phosphatidylglycerol (PG)34, phosphatidylinositol (PI)34 were the major phospholipids and digalactosyldiacylglycerol (DGDG)34, DGDG36, 1,2-diacyl-3-O-alpha-glucuronosylglycerol (GlcADG)34, GlcADG36, monogalactosyldiacylglycerol (MGDG)34, MGDG36, sulfoquinovosyldiacylglycerol (SQDG)34 and SQDG36 were the major non-phospholipids. Phospholipids were lower in the plants that were grown under −P conditions than that in the plants that were grown under +P for all cultivars at 5 and 10 DAT. The levels of non-phospholipids were higher in −P plants than that in +P plants of all cultivars at 5 and 10 DAT. Decomposition of phospholipids in roots at 5 DAT correlated with low P tolerance. These results suggest that rice cultivars remodel membrane lipids under P deficiency, and the ability of remodeling partly contributes to low P tolerance.

We investigated temporal changes in paddy rice phenology and yield under climatic and varietal changes in Shonai region, Yamagata Prefecture, northeast Japan across a period of 1982–2017. In the study region, the dominant variety shifted from Sasanishiki to Haenuki in mid 1990s. Temporal trends across the study period were significant in mean air temperatures for the months from May to July, and the temperature rise has accelerated heading, which was delayed by the varietal shift. We built models of the effects of climatic and varietal changes on phenological events and yield components: number of grains per land area, percentage ripened grains, and 1000-grain weight. Combining the yield component models, we built a yield model, with which we estimated the effect of the temperature rise from May to July on the yield. The temperature rise in May and June has reduced the yield by accelerating phenology, while that in July has increased the yield by raising 1000-grain weight. The net effect was no change in the yield across the study period, which, however, does not indicate an insensitivity of the yield to the temperature rise. Rather, the finding points to the dependency of the net change in the yield on seasonal pattern of the climate change. Climate change impacts on rice should therefore be quantified on the changes at monthly or shorter time scale rather than a seasonal mean. Our finding also points to the need to pay attention to the changes in agronomic practices such as varieties.

Poultry-litter biochar and Azolla as green manure amendments are reported to enhance paddy soil fertility and rice yields. However, whether their co-application in lowland rice paddies has synergistic effects and whether those benefits are accompanied by greenhouse gas (GHG) emissions remains unknown. The objective of this study was to determine the effects of poultry-litter biochar (hereafter: biochar) and its co-application with Azolla as green manure (hereafter: Azolla), on the simultaneous methane (CH4) and nitrous oxide (N2O) emissions from a lowland paddy soil planted with rice during a single rice growing season in Tsuruoka, Yamagata, Japan. Biochar and Azolla amendments were applied once before rice was transplanted at a density of 20 t ha−1 and 133.9 kg N ha−1, respectively. Compared with NPK, NPK + biochar, and Azolla only treatments, Azolla and biochar co-application (i.e., Azolla + biochar) significantly increased CH4 emissions by 33%–197.6% in the early stages of rice growth (before 63 days after transplanting, DAT), but did not significantly influence CH4 emissions at both late rice growth stages (after 63 DAT,) and whole rice growth period (112 DAT). Conversely, Azolla + biochar significantly reduced N2O emissions by 83.0%–97.1% before 63 DAT, and by 76.4%–95.9% during the whole rice growth period at 112 DAT, with a significantly high interaction between biochar and fertilizer amendments. There were no significant N2O emission differences among all treatments after 63 DAT. Additionally, Azolla + biochar significantly increased rice grain yield by 27.3%–75.0%, and consequently, decreased both yield-equivalent CH4 emissions by 24.7%–25.0% and N2O emissions by 81.8%–97.7%. Our findings suggest that the co-application of poultry-litter biochar and Azolla as green manure offers a novel approach to increase rice yield while reducing the emissions of non-carbon dioxide greenhouse gases.

Compound specific isotope analysis (CSIA) and enantiomer specific isotope analysis (ESIA) are powerful tools for assessing the fate of hexachlorocyclohexanes (HCHs) in the environment. However, there is no systematic study on the CSIA and ESIA analysis test methods of the carbon isotopes of HCHs in water and soil environments, in particular the isotope fractionation in the pre-concentration process. We endeavored to test the compatibility of CSIA and ESIA with the liquid–liquid extraction method of HCHs in water. The results showed that there were negligible changes in the δ13C of HCHs after extraction, indicating that liquid–liquid extraction can be used as a pre-concentration method for the determination of δ13C of HCHs in water. The optimized method was validated and then applied to differentiate three HCHs from different manufacturers, to identify in situ degradation of HCHs of groundwater from a contaminated site and to resolve the carbon isotope fractionation occurring in the α-HCH oxidation by CaO2/Fe(II) Fenton system. The results showed that the same reagents from different manufacturers have different carbon isotope compositions, and different isomers from the same manufacturer also have different isotope compositions, showing useful evidence in identifying the source of HCHs. The more enriched δ13C in the down-gradient wells indicated that HCHs have undergone biodegradation or/and chemical reactions in the groundwater system of the site. Carbon isotopic enrichment factors (εC) of −1.90 ± 0.10‰ were obtained in the oxidation process. Hence, the method validated in this study has great potential as a method for identifying the degradation of HCHs in a water environment.

Hot water- and water-extracted organic matter was extracted from soil samples collected after a 31-year long-term experiment which aimed to assess the effect of different fertilization strategies (inorganic fertilizers and organic matters) commonly used for paddy rice cultivation in Yamagata, northeastern Japan. The ratio of soil to extracted water was 2:3. The amounts of hot water-extracted organic carbon and nitrogen (HWEOC and HWEN) at 80 oC and 16 hours, water-extracted organic carbon and nitrogen (WEOC and WEN) at room temperature, and their δ13C and δ15N were measured from the five fertilizer treatment plots as [1) PK, 2) NPK, 3) NPK + 6 Mg ha-1 rice straw (RS), 4) NPK + 10 Mg ha-1 rice straw compost (CM1), and 5) NPK + 30 Mg ha-1 rice straw compost (CM3)], for surface (0-15 cm) and subsurface (15-25 cm) layers. HWEOC and WEOC accounted for an average of about 1.51 and 0.66% of SOC, while HWEN and WEN accounted for an average of about 1.09 and 0.40% of soil TN, respectively. About 90% of the extracted N was organic form among all treatments. The values of δ13C for HWEOC and WEOC ranged from -28.2 to -26.5‰ and from -28.3 to -27.0‰, similar to the original rice straw and rice straw compost, and lower than the value of original soil at -22.5‰. The values of δ15N of HWEN, WEN and bulk soil ranged from 0.8 to 3.8‰, from 1.0to 4.0‰, and from 0.8 to 2.8‰, respectively. It was clear that δ15N decreased in RS but increased in CM3 treatments. Our results indicated that the amounts of hot water- and water-extracted organic matter were affected by long-term application of inorganic fertilizers and organic matters remarkably. However, the values of δ13C for HWEOC and WEOC were not different among 5 treatments, but values of δ15N of HWEN and WEN were affected by RS and CM3 applications clearly.

Different weeding frequencies (WFs)―0WF, 2WF, 4WF, 6WF, and 8WF―were adopted in an organic rice field to investigate their influence on weed types, rice and weed biomass, rice tiller and weed number, N concentration, and N uptake. The study field was located in Tsuruoka, Yamagata, Japan. Rice (cv. Sasanishiki) was planted from May to September 2019, and all weeding events were carried out until 49 days after transplantation (DAT) using a rotary weeder. Rice and weed samples were collected at 60, 88, and 110 DAT. Echinochloa crus-galli (E. crus-galli), Schoenoplectus juncoides, and Monochoria vaginalis (Burm. f.) were the most commonly found weeds. High weed diversity was observed at both 6WF and 8WF, E. crus-galli was the dominant weed at 0WF. Compared to 0WF, 2WF displayed a significantly decreased weed biomass. However, at 8WF, the weed biomass was reduced by 79.0%, the rice biomass was increased by 277%, and the rice tiller number was almost three times higher than that at 0WF and 110 DAT. Compared to 0WF, a significantly increased rice N uptake was observed at 4WF, and rice N uptakes achieved at 6WF and 8WF were two and four times higher than those at 0WF, respectively. Higher weeding frequencies provide notable benefits in suppressing weeds and supporting rice growth, especially in N uptake competition with weeds.

Abstract There are large amounts of dissolved organic matter (DOM) released into the soil during spring thaw, but its bioavailability and components are still unknown. The quantity, composition and stability of DOM in water extracts of forest soils during thaw were studied after two-month freezing with 9 levels of soil moisture ranging from 10% to 90% water-filled pore space (WFPS), by measuring soil carbon dioxide (CO2) flux, biodegradable dissolved organic carbon (BDOC) and nitrogen (BDON), ultraviolet absorbance and parallel factor analysis of fluorescence excitation-emission matrices. Concentrations of BDOC, BDON, DOC and DON were lowest around 30% WFPS and relatively higher and lower soil moisture both increased DOM and BDOM concentrations in thawing soil. With increasing WFPS, the dominant component of soil DOM changed from humic acid-like substances to fulvic acid-like substances and the biological origin of DOM increased gradually. The protein-like component accounted for 8–20% of soil DOM and was affected by vegetation type and WFPS singly and interactively. The results implied that forest soils with more than 50% WFPS before winter freezing could release large amounts of fulvic acid-like DOM, which would be easily biodegraded and emitted as CO2 or run off with ground water during spring snow thaw.

The objective of this study was to determine the changes in the basic soil chemical properties including pH, electrical conductivity (EC), available phosphorus (P), dissolved organic carbon (DOC) and inorganic Nitrogen (NH4+ -N and NO3- -N) after approximately 15-40 years land use change from rice paddy field to orchard, wetland and upland in northeast Japan. Five land use change fields were investigated, including, forest, rice paddy, orchard, wetland and upland near Kumagai shrine, Shonai-machi, Yamagata, Japan. Soil samples were collected from surface layer (0-15 cm) and subsurface layer (15-30 cm) in October 2015. Soil chemical properties of pH, EC, available P, DOC and inorganic N (NH4+ -N and NO3- -N) were analyzed on air-dried samples. The pH increased significantly in the upland after 15 years conversion from rice paddy in both layers, with other land use changes only increasing pH in subsurface layer. EC significantly decreased in the surface layer of orchard and upland fields and in subsurface layers of all the converted fields. Available P significantly decreased in the converted fields, except in the upland subsurface layer. DOC amounts were not significantly different after land use changes from paddy fields. The NH4+ -N decreased significantly only in the surface layer of upland, while NO3- -N increased significantly only in the surface layer of wetland. Significant changes in soil properties were observed after 15 years conversion to upland and 40 years conversion to orchard and wetland from former rice paddy field in this study.

To determine the difference in greenhouse gas emissions between two rice (Oryza sativa L.) varieties; Takanari (Tak) and Koshihikari (Kos), under organic rice cultivation with or without weeds management, a pot experiment was conducted at Tsuruoka, Yamagata, Japan. The Tak and Kos varieties were transplanted individually and interplanted as Tak+Kos, with the main treatments of weeding (w) and no-weeding (nw). Methane (CH4), nitrous oxide (N2O), and plant night respiration (CO2 emission) fluxes were measured once weekly or biweekly during the rice growth period. As the results, N2O fluxes were not detected but CH4 fluxes varied with the rice growth stage for all treatments. Compared with the Kos(w), Tak(w) and Tak+Kos(w) significantly decreased total seasonal CH4 emissions by 12.4% and 19.1%, respectively. This was attributed to higher rhizospheric CH4 oxidation and the offset of potential methanogenic activities because of the larger root biomass and a higher harvest index for both Tak(w) and Tak+Kos(w) compared with Kos(w). Conversely, Kos(nw) significantly reduced cumulative CH4 emissions by 31.7% and 48.6% compared with Tak(nw) and Tak+Kos(nw), respectively. This was ascribed to high rhizospheric CH4 oxidation promoted by the presence of significantly higher weed biomass for Kos(nw) at 65.0% and 44.0% compared with Tak(nw) and Tak+Kos(nw), respectively. On average, the no-weeding practice significantly decreased cumulative CH4 emissions by 50.5% compared with the weeding practice, with a significantly high (P<0.001) interaction between weed management and variety differences observed. The CH4 emissions and plant biomass under variety interplanting (Tak+Kos) were not significantly different to Tak individual planting, but were significantly different to Kos individual planting, which implied variety Tak had strong competition to variety Kos. More studies on appropriate variety choice and pairs, and the effect of aquatic weeds presence in no-weeding organic paddy fields are necessary to estimate CH4 emission and attenuation. [ABSTRACT FROM AUTHOR]

Organic farming uses alternatives to agricultural chemicals such as synthetic fertilizers and pesticides. The primary challenge in organic rice farming is controlling weeds without using herbicides and improving rice yield without chemical fertilizers. In our previous paper entitled as combined use of Azolla and loach suppressed weed Monochoria vaginalis and increased rice yield without agrochemicals, we reported the first year rice growth season results from an in situ container experiment. The experiment was designed with 4 treatments—control (with neither Azolla nor loach), Azolla (Azolla alone), loach (loach alone), and Az+Lo (combined Azolla and loach)—with 3 replications each. The first year results showed that combined use of Azolla and loach was successful in weed suppression and increase in rice yield in 2012. In this paper, we report the second year results from the continuous container experiment in 2013. M.vaginalis emergences were very low in second year rice growth season on all treatments. Compared first year, the rice yields decreased in second year on all treatments due to different weather condition and with or without organic soybean oil cake application between two rice growth seasons. The second year results also showed the raising loach had a stronger effect to increase tiller and panicle numbers, and spikelet number per panicle, then improve rice yields to 2.3 times than control. The Azolla residues left from first year have weaker effect on rice growth and yield, but increase soil organic matter accumulation at second year. The two years study indicated that combined use of Azolla and loach can meet two of the greatest challenges in organic rice production: providing effective weed control and improving rice nutrition without agrochemicals.