Increased simulated precipitation frequency promotes greenhouse gas fluxes from the soils of seasonal fallow croplands

Context Conversion of grasslands to croplands can usually result in the degradation of soils and increased greenhouse gas (GHG) emissions such as carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). However, little is known about the impacts of grassland conversion to recently tilled croplands on soils and GHG fluxes. Aims A field experiment was established in 2016 to evaluate the impacts of grassland conversion to tilled cropland under different landscape positions (upslope, backslope, and footslope) on select soil properties and soil GHG fluxes. Key results The findings showed that the grassland conversion significantly increased soil bulk density and electrical conductivity but reduced pH and total nitrogen (TN). The conversion impacted soil biome community grassland and tilled croplands. The landscape position significantly impacted soil pH (footslope < upslope) and TN (footslope > upslope). The grassland conversion significantly decreased soil CO2 fluxes, but increased soil CH4 and N2O fluxes. The landscape position significantly impacted soil CO2 (footslope > upslope and backslope) and CH4 (upslope > footslope and backslope) fluxes for some periods. Soil CO2 and N2O fluxes generally followed upward and downward trends over time, respectively. Conclusions These results indicate that grassland conversion was able to lose soil N, increase soil compaction, acidity, salts, and soil N2O and CH4 fluxes, and decrease the diversity of abundant genera and CO2 fluxes. Footslope increased TN, soil acidity, CO2, and CH4 fluxes, compared with upslope and backslope. CO2 fluxes under grassland and tilled cropland significantly increased over time, whereas N2O fluxes under grassland significantly reduced. Implications Conversion of grassland to tilled cropland significantly impacted on sol quality. It caused a loss in soil N and increased soil compaction, acidity and salts. Grassland conversion also decreased the abundance and diversity soil microbiome.

No-till farming and greenhouse gas fluxes: Insights from literature and experimental data

Atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are predicted to increase as a consequence of fossil fuel emissions and the impact on biosphere–atmosphere interactions. Forest ecosystems in general, and forest soils in particular, can be sinks or sources for CO2, CH4, and N2O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil greenhouse gas (GHG) flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation by soil biotic vs. abiotic factors on GHG emissions, particularly under predicted increase in global temperatures, and changes in intensity and frequency of precipitation events. Here we measured net CO2, CH4 and N2O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ≈45% summer rainfall reduction, in two forest sites in a boreal–temperate ecotone under different habitat conditions (closed or open canopy) in Minnesota, USA. We evaluated the importance of microbial gene abundance and climo‐edaphic factors (soil texture, canopy, seasonality, climate, and soil physicochemical properties) driving GHG emissions. We found that changes in CO2 fluxes were predominantly determined abiotically by temperature and moisture, after accounting for bacterial abundance. Methane fluxes on the other hand, were determined both abiotically, by gas diffusivity (via soil texture) and microbially, by methanotroph pmoA gene abundance, whereas, N2O emissions showed only a strong biotic regulation via ammonia‐oxidizing bacteria amoA gene abundance. Warming did not significantly alter CO2 and CH4 fluxes after 5 years of manipulation, while N2O emissions were greater with warming under open canopy. Our findings provide evidence that soil GHG emissions result from multiple direct and indirect interactions of microbial and abiotic drivers. Overall, this study highlights the need to include both microbial and climo‐edaphic properties in predictive models in order to provide improved mechanistic understanding for the development of future mitigation strategies. A plain language summary is available for this article.

Greenhouse gas (CO2, CH4, N2O) emissions from soils following afforestation in central China

The invasions of the alien species such as Spartina alterniflora along the northern Jiangsu coastlines have posed a threat to biodiversity and the ecosystem function. Yet, limited attention has been given to their potential influence on greenhouse gas (GHG) emissions, including the diurnal variations of GHG fluxes that are fundamental in estimating the carbon and nitrogen budget. In this study, we examined the diurnal variation in fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from a S. alterniflora intertidal flat in June, October, and December of 2013 and April of 2014 representing the summer, autumn, winter, and spring seasons, respectively. We found that the average CH4 fluxes on the diurnal scale were positive during the growing season while negative otherwise. The tidal flat of S. alterniflora acted as a source of CH4 in summer (June) and a combination of source and sink in other seasons. We observed higher diurnal variations in the CO2 and N2O fluxes during the growing season (1 536.5 mg CO2 m–2 h–1 and 25.6 μg N2O m–2 h–1) compared with those measured in the non-growing season (379.1 mg CO2 m–2 h–1 and 16.5 μg N2O m–2 h–1). The mean fluxes of CH4 were higher at night than that in the daytime during all the seasons but October. The diurnal variation in the fluxes of CO2 in June and N2O in December fluctuated more than that in October and April. However, two peak curves in October and April were observed for the diurnal changes in CO2 and N2O fluxes (prominent peaks were found in the morning of October and in the afternoon of April, respectively). The highest diurnal variation in the N2O fluxes took place at 15:00 (86.4 μg N2O m–2 h–1) in June with an unimodal distribution. Water logging in October increased the emission of CO2 (especially at nighttime), yet decreased N2O and CH4 emissions to a different degree on the daily scale because of the restrained diffusion rates of the gases. The seasonal and diurnal variations of CH4 and CO2 fluxes did not correlate to the air and soil temperatures, whereas the seasonal and diurnal variation of the fluxes of N2O in June exhibited a significant correlation with air temperature. When N2O and CH4 fluxes were converted to CO2-e equivalents, the emissions of N2O had a remarkable potential to impact the global warming. The mean daily flux (MF) and total daily flux (TDF) were higher in the growing season, nevertheless, the MF and TDF of CO2 were higher in October and those of CH4 and N2O were higher in June. In spite of the difference in the optimal sampling times throughout the observation period, our results obtained have implications for sampling and scaling strategies in estimating the GHG fluxes in coastal saline wetlands.

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63 –386.36 mg/(m•h), CH4 uptake fluxes of 0.113–0.023 mg/(m•h) and N2O fluxes of –1.68 –19.90 μg/(m•h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

Vol. 80 (2009) No. 2 (pp. 109–218 ) Original Papers Effect of surface application timing of crushed fibrous-bamboo and intertillage and ridging on N2 fixation and production of soybean (Glycine max L. Merr.) cv. Fukuyutaka Yuki NAKAGAWA*1, Takeo YAMAKAWA*2 and Yoshinori KAJIHARA*3 *1Grad. Sch. Bioresour. Bioenviron. Sci., Kyushu Univ., *2Dept. Plant Resour., Fac. Agric., Kyushu Univ., *3University Farm, School of Agric., Kyushu Univ. (Jpn. J. Soil Sci. Plant Nutr., 80, 109–115, 2009) Field experiments were performed on agricultural farm of Kyushu university to investigate the effect of surface application timing of crushed fibrous-bamboo (bamboo powder) and intertillage and ridging on N2 fixation and production of soybean (Glycine max L. Merr.) cv. Fukuyutaka in 2005 and 2006. Moso bamboo (Phyllostachys pubescens Mazel) of 3 to 4 age was crushed in fiber-shaped and used as a bamboo powder. Treatments in 2005 were non-multi, early stage mulching, and late stage mulching, which bamboo powder was not applied, applied just after sowing or applied just after the cultivating and ridging, respectively. Treatments without cultivating and ridging in 2006 were F0, F40 and F80, which 0, 40 and 80 kg 10a−1 of commercial chemical fertilizer (N; P2O5; K2O = 3.0; 10.0; 10.0%) without bamboo powder was applied on the surface of soil just after sowing, respectively and M0, M40 and M80, which 0, 40 and 80 kg 10a−1 of compound fertilizer was applied on the surface of bamboo powder spread on soil just after sowing, respectively. All treatments had three replicates. The results in 2005 indicated that the surface application of bamboo powder decreased the soybean yield regardless of the application timing. Therefore, it was concluded that the cultivation method with cultivating and ridging was not suitable for the soybean production under the application of bamboo powder. The results in 2006 indicated the surface application of bamboo powder without cultivating and ridging increased the soybean yield. Because, the surface application of bamboo powder improved the germination and facilitated the growth from late vegetative to flowering stage. Furthermore, this method increased N2 fixation (relative abundance of ureides). Key words: bamboo powder, N2 fixation, relative abundance of ureides, soybean, surface application. Phytoremediation of cadmium by rice in low-level of Cd contaminated paddy field Toshimitsu HONMA*1,2, Hirotomo OHBA*1, Ayako KANEKO*1, Takashi HOSHINO*1, Masaharu MURAKAMI*3 and Takuji OHYAMA*2,4 *1Niigata Agric. Res. Inst., *2Graduate School. Sci. and Tech., Niigata Univ., *3Natl. Inst. Agro-Environ. Sci., 4Facul. Agric. Niigata Univ. (Jpn. J. Soil Sci. Plant Nutr., 80, 116–122, 2009) Phytoremediation using hyperaccumulator wild plants has been proposed as a promising, environmentally-friendly, low-cost technology for decontaminating toxic metals from soil. However, it may be difficult to use hyperaccumulator wild plants for practical phytoremediation of Cd-contaminated paddy fields because of their several drawbacks. Several rice varieties that accumulate high-Cd in their shoots have been found. To select rice variety practicable for phytoremediation of low-Cd-contaminated paddy field, we examined the decrease effect of Cd concentration in soil and brown rice of food rice variety by phytoremediation using six rice varieties. Six rice varieties (Kusayutaka, LAC 23, Milyang 23, Habataki, Moretsu, and IR 8) were planted for 3 years in Andosol, in which plow layer contained 0.44–0.50 mg Cd kg−1 extracted with 0.1 mol L−1 HCl (1:5 w/v). The order of the shoot Cd uptakes by these rice varieties was as follows: Kusayutaka < LAC 23 < Milyang 23 < Habataki < Moretsu < IR 8. IR 8 absorbed 158 g Cd ha−1 in its shoot from soil by 3-year phytoremediation. Soil Cd concentration in the IR 8 plot has been decreased from 0.48 mg Cd kg−1 to 0.33 mg Cd kg−1. Cd concentrations in brown rice of food rice variety (Koshihikahi) grown after the phytoremediation by IR 8, Habataki and Moretsu were lower than those by Kusayutaka and LAC 23. Judging from these results, we conclude that IR 8 is the most promising in the six varieties for phytoremediation of Cd from paddy fields contaminated with relatively low Cd concentration. Key words: cadmium, paddy rice, phytoremediation. The influence of no-tilled direct seeding cultivation on greenhouse gas emissions from rice paddy fields in Okayama, Western Japan 5. Annual emission of CH4, N2O and CO2 from rice paddy fields under different cultivation methods and carbon sequestration into paddy soils Eiji ISHIBASHI*1, Syogo YAMAMOTO*1, Naohiko AKAI*1, Toru IWATA*2 and Haruo TSURUTA*3 *1Okayama Pref. Gen. Agric. Cent., *2Faculty of Environ. Sci. and Tecnol. , Okayama Univ., *3Natl. Inst. Agro-Environ. Sci., Present address: Cent. for Climate Sys. Res., Univ. of Tokyo (Jpn. J. Soil Sci. Plant Nutr., 80, 123–135, 2009) In order to clarify any difference in the emission of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2), from two rice paddy fields under the continuation of no-tilled direct seeding cultivation (ND), two rice paddy fields under the conventional tilled transplanting cultivation (TT), and one rice paddy field under the tilled direct seeding cultivation (TD), we measured CH4, N2O and CO2 fluxes from these fields with gray lowland paddy soils in Sanyoh of Okayama Prefectural General Agriculture Center, by using a closed chamber method for 2–5 years (1998–2002). We estimated the Net Ecosystem CO2 Exchange (NEE) during rice-growing seasons by using a model based on the eddy covariance flux measurement made at a rice paddy field in Hachihama of Okayama University, a 23 km-distance from Sanyoh. Consequently, the following results were obtained. 1) A clear trade-off relationship was shown between CH4 and N2O fluxes in all the rice paddy fields. 2) The sum of annual CO2 equivalent emission of CH4 and N2O was a little bit higher in ND than in TT but not significantly different between ND and TT, possibly due to the long-term continuation of ND, although the emission of CH4 was much lower in ND than in TT during a few or several years after TT was converted to ND. 3) The averaged annual emission ratio of N2O to the sum of CH4 and N2O on the CO2 equivalent basis was 9.0%, 7.3%, and 1.8% in ND, TD and TT, respectively. The highest ratio in ND was caused by sporadic enhancements of N2O flux in fallow seasons due to an organic matter layer only formed on the surface soil of ND. 4) As a result, the N fertilizer-induced emission factor of N2O in a three-year average was 0.48% and 2.5% in TT and ND, respectively. 5) During fallow and no-flooded seasons, the CO2 flux from the surface soil to the atmosphere was higher in ND than in TT. An annual NEE in TD was estimated to be -294 and -311 g CO2 m−2 y−1 in 1998 and 1999, respectively. 6) The organic matter layer formed on topsoil increased with the continuation of ND , and the carbon sequestration rate to the surface soil was 86.2 g C m−2 y−1, equal to about 30% of the total annual CO2 equivalent emission rate of CH4 and N2O. 7) According to the carbon neutral principle, the annual net CO2 emission in ND was -268 g CO2 m−2 y−1 by adding the CO2 emission through the slow decomposition of soil organic matter to the carbon sequestration rate. 8) Hence, the total CO2 equivalent greenhouse gas emission (the sum of CH4, N2O, and CO2) in ND was 811 and 648 g CO2 m−2 y−1 in 1998 and 1999, respectively, and which were lower by 20% than those in TT, mainly due to carbon sequestration to soils in ND. 9) The conversion to TD or TT from ND with the continuation for 8 years, by incorporating the surface organic matter into the plowed layer, did not show any increase in the emission of CH4 or N2O during the following two years. 10) A possible and effective option for mitigation of greenhouse gas emissions in ND is that ND fields should be converted to TT or TD fields after the continuation of ND for 4–5 years. Key words: paddy soil, no-tilled direct seeding, methane, nitrous oxide, rice straw. Effectiveness of silica application at the panicle formation stage on the rice production Shizuka MORI1 and Hiroshi FUJII2 1Yamagata General Agric. Res. Cent., Dept. of Agro-Prod. Sci., Shonai Branch. 2Yamagata Univ. (Jpn. J. Soil Sci. Plant Nutr., 80, 136–142, 2009) The effects of silica application on the yield and quality of rice were compared among the following plots: (A) a new silicate fertilizer A was applied at the panicle formation stage at 12 g m−2, (B) a new silicate fertilizer B was applied at the panicle formation stage at 12 g m−2, (C) a conventional silicate fertilizer was applied before transplanting as a basal fertilizer at 36 g m−2, and (N) no silicate fertilizer was applied. The results obtained were as follows: 1. The relative yields at the experimental plots A, B, C and N were 106, 104, 104, and 100, respectively. The effectiveness of applied silicate ((yield at A, B, or C - yield at N) / the amount of Si applied) for A, B, and C were 2.58, 2.17 and 0.67 g m−2, respectably. In addition, higher cost performances were achieved in A and B than in C. 2. The numbers of grains were as follows: 30,400 grains m−2 for C > 30,100 for A and B > 28,900 for N. On the other hand, no significant difference was found in the 1,000-grain weight and the percentage of ripened grains among those experimental plots. 3. The amounts of Si in the leaves plus stems were as follow: 65.0 for A and B (110) >63.0 g m−2 for C (107) > 59.3 for N(100). The amount of Si in the grains were as follows: 35.3 g m−2 for C (116) > 33.2 for A and B (109) > 30.4 for N (100). This fact indicates that the top-dressed Si was more effectively used by the rice plant than the basal Si. 4. Total amount of N acquisition and the recovery rate of top-dressed N by the rice plants were higher in Si-applied plots than in non-Si-applied plot. It is likely that the application of Si enhances the N acquisition, resulting in increase of the number of grains. Key words: nitrogen, rice yield, rice plant, silicic acid, panicle formation stage. Time course transition of soil solution composition and its cation balance during vegetable cultivation using salt-concentrated compost (1)— In the case of mini tomato cultivation - Munehiro EBATO1, 2 and Mitsue KURIBARA3 1National Institute of Livestock and Grassland Science, Nasu Research Station, 2Present address: National Institute of Livestock and Grassland Science, Miyota Research Station, 3Livestock Industry Research Center, Fukushima Agricultural Technology Center (Jpn. J. Soil Sci. Plant Nutr., 80, 143–151, 2009) Recently, Japan has placed a legal restriction on the stacking of livestock manure in the fields owned by livestock farmers. As a result, compost containing a large amount of sodium and potassium (salt-concentrated compost), has been made from the manure. Due to the high amount of salt, it is difficult to determine the suitable amount of salt-concentrated compost to use for vegetable cultivation in the field. This study aimed to clarify the effects of salt-concentrated compost on mini tomato (Solanum lycopersicum) growth and on soil by investigating the time course transition of soil solution composition and its cation balance. Mini tomatoes were cultivated in pots filled with an Andosol and a Brown lowland soil (Fluvisol) applied with chemical fertilizer, normal compost or salt-concentrated compost. The concentration of soil solution transited at a low level after normal compost application. However, the concentration of soil solutions increased in accordance with the amount of salt-concentrated compost applied, and was maintained at a high level during mini tomato cultivation. The application of salt-concentrated compost to the Andosol caused a blossom-end rot disease to the mini-tomato fruits. Blossom-end rot is known as a response to calcium deficiency. Since the application of the salt-concentrated compost drastically increased the concentration of potassium and sodium in the soil solution, it was suggested that the relative ratio of calcium to monovalent cations was a key factor causing the symptom. By introducing a new index for the activity ratio for potassium plus sodium, i.e. ARK+Na, composition of cations in the soil solution could be evaluated quantitatively. Based on the analyses using ARK+Na, it was found that blossom-end rot occurred when ARK+Na value became too low and exceeded some level (-0.1 in the present case) while mini tomato fruit was constituted at the first branch. In the case that the amount of salt-concentrated compost applied to the Andosol was reduced to be 20 Mg ha−1 or less, the values of ARK+Na were higher than the value when blossom-end rot had occurred, and the blossom-end rot did not occur. Key words: ARK+Na, blossom-end rot, mini tomato, salt-concentrated compost, soil solution composition. Notes Effect of combined application with 15N-labeled ammonium sulfate and swine or poultry manure compost on mineralization of compost nitrogen Masahiko KATOH*, Yasuhito HAYASHI* and Hiromasa MORIKUNI* *JA ZEN-NOH R&D Cent. (Jpn. J. Soil Sci. Plant Nutr., 80, 152–156, 2009) A new protocol to identify soil ciliates through movie data and DNA extracted from one soil ciliate Chikako SHIMAYA* and Tomoyoshi HASHIMOTO* *National Agricultural Research Center for Kyusyu Okinawa Region (Jpn. J. Soil Sci. Plant Nutr., 80, 157–160, 2009) Bacterial direct count with the wash-sonic method in water dispersed small soil particles Nobuyuki KOHNO*1,2 and Tomoyoshi HASHIMOTO*1 *1National Agricultural Research Center for Kyusyu Okinawa Region, *2Present address: Institute for Environmental Studies, Fukuyoshi Engineering Co. Ltd., Hiroshima 732–0045, Japan. (Jpn. J. Soil Sci. Plant Nutr., 80, 161–164, 2009) Characteristic of chicken manure compost produced in Mie Prefecture Keiichi MURAKAMI*1, Sachiko KOSAKA*1,2, Takayuki FUJIWARA*1,3 and Masayuki HARA*1 *1Mie Prefecture Agricultural Research Institute, Present addresses: *2Iga Agriculture Forestry Commerce Industry and Environment Office, *3Mie Prefecture Industrial Research Institute (Jpn. J. Soil Sci. Plant Nutr., 80, 165–167, 2009) Effect of composition of sewage sludge incinerated ash mixing rate of alkali on phosphate fertilizer efficiency of fused sludge ash compound fertilizers Shuko KUBOYAMA*1, Yoshiko KUBOTA*1, Takashi KOMATSU*2 and Itsuo GOTO*1 *1Tokyo University of Agriculture, *2SANKI (Jpn. J. Soil Sci. Plant Nutr., 80, 168–172, 2009) Current Topics Estimation of available nitrogen content in upland soil by a boiling decoction method Atsushi YAMAKI Chiba prefectural agriculture and forestry research center (Jpn. J. Soil Sci. Plant Nutr., 80, 173–176, 2009) Decision support system for application of manure and fertilizer to grassland and forage corn field based on nutrient recycling Teruo MATSUNAKA*1, Toshiya SAIGUSA*2, Hiroyuki SASAKI*3, Takehiko MATSUMOTO*4, Kazunori KOHYAMA*5, Akihiro FURUDATE*6 and Shu MIURA*7 *Rakuno Gakuen Univ., *2Hokkaido Konsen Agric. Exp. Stn., *3National Institute of Livestock and Grassland Science, *4Hokkaido Central Agric. Exp. Stn., *5National Institute of Livestock and Grassland Science (present, National Institute for Agro-Environmental Sciences), *6Hokkaido Kamikawa Agric. Exp. Stn. Tenpoku Branch, *7Hokkaido Kamikawa Agric. Exp. Stn. Tenpoku Branch (present, Hokkaido Kitami Agric. Exp. Stn.) (Jpn. J. Soil Sci. Plant Nutr., 80, 177–182, 2009) Lecture Recent development in the plant nutritional diagnosis by non-destructive methods: 3. Utilization of diagnosis of crop plant using a chlorophyll meter for forage crop productions Yoshihito SUNAGA National Institute of Livestock and Grassland Science (Jpn. J. Soil Sci. Plant Nutr., 80, 183–187, 2009) Nutritional diagnosis technique of apple tree using the image analysis Yoshinori TAKAHASHI*1,2 *1Iwate Agric. Res. Cent., *2Present address: Ministry of Agriculture, Forestry and Fisheries General Food Policy Bureau (Jpn. J. Soil Sci. Plant Nutr., 80, 188–191, 2009) Miscellaneous Food and Health: The necessity of minerals and fatty acids Toshihiro KATO*1, Harumi OKUYAMA*2, Sinkan TOKUDOME*3, Hisao ODA*4, Kazuhiko WATANABE*5, Makoto KIMURA*6 *1Aichi Agricultural Research Center, *2Kinjo Univ., *3Nagoya City University Graduate School of Medical Sciences and Medical School, *4Eisai Seikaken Co.,Ltd., *5Tokyo University of Agriculture, 6Nagoya University Graduate School of Bioagricultural Sciences (Jpn. J. Soil Sci. Plant Nutr., 80, 192–200, 2009) Studies of protozan and nematode dynamics and diversity for soil quality evaluation Tomoyoshi HASHIMOTO*1, Susumu ASAKAWA*2, Jun MURASE*2, Satoshi SHIMANO*3, Tadao TAKAHASHI*4, Hiroaki OKADA*5, Erika SATO*6, Koki TOYOTA*6 *1Natl. Agri. Res. Cent. Kyushu Okinawa Reg., *2Grad. Sch. Bioagric. Sci., Nagoya Univ., *3Miyagi Univ. Educ., *4Nishikyushu Univ., *5Natl. Inst. Agro-Environ. Sci., 6Tokyo Univ. Agri. Technol. (Jpn. J. Soil Sci. Plant Nutr., 80, 201–206, 2009) Challenges of soil sciences to climate change-international meetings in Beijing and Nanjing, China, October 2008 Kazuyuki INUBUSHI Graduate school of Horticulture, Chiba Univ. (Jpn. J. Soil Sci. Plant Nutr., 80, 207, 2009)

How do sand addition, soil moisture and nutrient status influence greenhouse gas fluxes from drained organic soils?

This study is to explore effects of nitrogen application and straw incorporation on abundance of relevant microbes and CH 4 and N2O fluxes in a midseason aerated rice paddy field. Fluxes of CH 4 and N2O were recorded, and abundance of relevant soil microbial functional genes was determined during rice-growing season in a 6-year-long fertilization experiment field in China. Results indicate that application of urea significantly changed the functional microbial composition, while the influence of straw incorporation was not significant. Application of urea significantly decreased the gene abundances of archaeal amoA and mcrA, but it significantly increased the gene abundances of bacterial amoA. CH 4 emission was significantly increased by fresh straw incorporation. Incorporation of burnt straw tended to increase CH 4 emission, while the urea application had no obvious effect on CH 4 emission. N2O emission was significantly increased by urea application, while fresh or burnt straw incorporation tended to decrease N2O emission. The functional microbial composition did not change significantly over time, although the abundances of pmoA, archaeal amoA, nirS, and nosZ genes changed significantly. The change of CH 4 emission showed an inverse trend with the one of the N2O emissions over time. To some extent, the abundance of some functional genes in this study can explain CH 4 and N2O emissions. However, the correlation between CH 4 and N2O emissions and the abundance of related functional genes was not significant. Environmental factors, such as soil Eh, may be more related to CH 4 and N2O emissions.

Responses of soil greenhouse gas fluxes to land management in forests and grasslands: A global meta-analysis.

Greenhouse gas (GHG) flux from wetland systems, both in their natural state and following drainage, has not been well accounted for in the carbon accounting process. We review GHG production from both natural and drained wetlands, and estimate the likely GHG emissions from these systems in Australia. Only a small number of studies have quantified GHG emissions from undisturbed Australian wetland environments. Consequently, in order to estimate GHG flux for Australia, it was necessary to collate data collected overseas from similar climatic zones. Using this approach, it appears that undisturbed, vegetated wetlands in Australia are likely to be net GHG sinks, with the greatest rates of sequestration occurring in mangrove ecosystems (–2669 g CO2-e/m2.year) where biomass production is high but CH4 emissions are limited by salinity. The uncertainty surrounding these values is high, however, due to (a) the low number of measurements from Australia, (b) the low number of measurements for CO2 flux, and (c) the low number of studies where all GHGs have been measured concurrently. It was estimated that the drainage of melaleuca and mangrove forest wetlands in Australia would turn them from carbon sinks into carbon sources, and that in the first 50 years since drainage, this has increased global warming potential by 1149 Tg CO2-e or 23 Tg CO2-e/year. This is significant given that GHG emissions due to land-use change in 2007 totalled 77.1 Tg CO2-e. However, data surrounding the area of wetlands drained, carbon stocks in drained wetlands, and the effect of drainage on CH4 and N2O flux are limited, making the uncertainty surrounding these estimates high. Further study is clearly required if Australia wishes to accurately incorporate wetland systems into national carbon and greenhouse gas accounting budgets.

Emission factors and global warming potential as influenced by fertilizer management for the cultivation of rice under varied growing seasons

In the climate change scenario, studying greenhouse gases (GHG) emissions and measures of mitigation in the Caatinga biome are strategic and may provide a basis for mitigation plans. This study aimed to evaluate the soil CO2, CH4 and N2O fluxes, as well as determining an annual baseline for GHG emissions, in a reference site of silvopastoral production system in the Brazilian semiarid region, in order to provide subsidies for future studies on GHG emissions mitigation. The GHG fluxes were monitored over one year, in a buffel grass pasture and in grazed and native Caatinga areas, which are components of a long-term silvopastoral system. The CO2 fluxes ranged from -19.98 to 179.12 mg m-2 h-1 of CO2-C, CH4 fluxes from -76.21 to 113.87 µg m-2 h-1 of CH4-C, N2O fluxes from -1,043.12 to 471.37 µg m-2 h-1 of N2O-N and the soil moisture was the main factor limiting the GHG fluxes. The total emissions converted to CO2-equivalent in the anthropized areas were lower than in the native area (65 % for the buffel grass pasture and 741 % for the grazed Caatinga). Therefore, it is possible to afrm that the GHG soil emissions from grazed areas in the Caatinga biome are not as high as in the native Caatinga, what is an important indication of the environmental sustainability of the evaluated silvopastoral system.

Rivers play an important role in greenhouse gas emissions. Over the past decade, because of global urbanization trends, rapid land use changes have led to changes in river ecosystems that have had a stimulating effect on the greenhouse gas production and emissions. Presently, there is an urgent need for assessments of the greenhouse gas concentrations and emissions in watersheds. Therefore, this study was designed to evaluate river-based greenhouse gas emissions and their spatial-temporal features as well as possible impact factors in a rapidly urbanizing area. The specific objectives were to investigate how river greenhouse gas concentrations and emission fluxes are responding to urbanization in the Liangtan River, which is not only the largest sub-basin but also the most polluted one in Chongqing City. The thin layer diffusion model method was used to monitor year-round concentrations of pCO2, CH4, and N2O in September and December 2014, and March and June 2015. The pCO2 range was (23.38±34.89)-(1395.33±55.45) Pa, and the concentration ranges of CH4 and N2O were (65.09±28.09)-(6021.36±94.36) nmol·L-1 and (29.47±5.16)-(510.28±18.34) nmol·L-1, respectively. The emission fluxes of CO2, CH4, and N2O, which were calculated based on the method of wind speed model estimations, were -6.1-786.9, 0.31-27.62, and 0.06-1.08 mmol·(m2·d)-1, respectively. Moreover, the CO2 and CH4 emissions displayed significant spatial differences, and these were roughly consistent with the pollution load gradient. The greenhouse gas concentrations and fluxes of trunk streams increased and then decreased from upstream to downstream, and the highest value was detected at the middle reaches where the urbanization rate is higher than in other areas and the river is seriously polluted. As for branches, the greenhouse gas concentrations and fluxes increased significantly from the upstream agricultural areas to the downstream urban areas. The CO2 fluxes followed a seasonal pattern, with the highest CO2 emission values observed in autumn, then successively winter, summer, and spring. The CH4 fluxes were the highest in spring and the lowest in summer, while N2O flux seasonal patterns were not significant. Because of the high carbon and nitrogen loads in the basin, the CO2 products and emissions were not restricted by biogenic elements, but levels were found to be related to important biological metabolic factors such as the water temperature, pH, DO, and chlorophyll a. The carbon, nitrogen, and phosphorus content of the water combined with sewage input influenced the CH4 products and emissions. Meanwhile, N2O production and emissions were mainly found to be driven by urban sewage discharge with high N2O concentrations. Rapid urbanization accelerated greenhouse gas emissions from the urban rivers, so that in the urban reaches, CO2/CH4 fluxes were twice those of the non-urban reaches, and all over the basin N2O fluxes were at a high level. These findings illustrate how river basin urbanization can change aquatic environments and aggravate allochthonous pollution inputs such as carbon, nitrogen, and phosphorus, which in turn can dramatically stimulate river-based greenhouse gas production and emissions; meanwhile, spatial and temporal differences in greenhouse gas emissions in rivers can lead to the formation of emission hotspots.

Soil greenhouse gas emission during non-growing season plays an important role in ecosystem carbon and nitrogen cycling in mid and high latitude regions. However, the effects of harvest on greenhouse gas emission during non-growing remain unclear. We measured the fluxes of CO2, CH4 and N2O and environmental factors (soil temperature, moisture, soil organic carbon and total nitrogen etc.) during non-growing season from four kinds of forested swamps (Alnus sibirica swamp, Betula platyphylla swamp, Larix gmelinii-Carex schmidti swamp, L. gmelinii-moss swamp) under different harvest disturbances for 10 years, including control (no cutting), 45% selective cutting, clear cutting, by using static chamber technique and gas chromatography in Xiaoxing'an Mountains, Northeast China. The aim of this study was to reveal the effects of harvest on greenhouse gas emission from temperate forested swamp during non-growing season and the main controlling factors. The results showed that the average fluxes of CO2, CH4 and N2O from four kinds of swamps distributed in 53.08-81.31 mg·m-2·h-1, 0.09-3.07 mg·m-2·h-1 and 4.07-8.83 μg·m-2·h-1, respectively. Clear cutting significantly increased the fluxes of CO2, CH4, and N2O from A. sibirica swamp and L. gmelinii-moss swamp. Selective cutting significantly increased CO2 fluxes from B. platyphylla swamp and L. gmelinii-moss swamp and decreased CO2 flux from A. sibirica swamp. Selective cutting significantly decreased CH4 fluxes from all the four forested swamps and N2O flux from Larix gmelinii-Carex schmidti swamp. The CO2 fluxes from natural forested swamps were strongly influenced by soil temperature, soil organic carbon and C/N. CH4 fluxes were influenced by soil temperature, soil organic carbon. N2O fluxes were affected by air temperature and soil pH. Harvesting increased the correlation between soil CO2 flux and air temperature, soil moisture and snow depth, the correlation between soil CH4 flux and air temperature, soil moisture and C/N, as well as the correlation between soil N2O flux and soil total nitrogen and C/N. The annual cumulative contribution of CO2, CH4 and N2O emission from natural forested swamp during non-growing season were 33.2%-46.5%, 6.3%-9.1% and 61.5%-68.3%, respectively. The clear cutting increased the annual cumulative contribution of CO2 from B. platyphylla swamp and L. gmelinii-moss swamp and that of N2O from other swamps except L. gmelinii-moss swamp. The selective cutting increased the annual cumulative contribution of CO2, CH4 and N2O from L. gmelinii-C. schmidti swamp and L. gmelinii-moss swamp, but decreased that from B. platyphylla swamp. The annual cumulative contributions of N2O and CO2 during non-growing season were relatively high from temperate natural forested swamps, and clear cutting further increased their contribution, while the selective cutting just increased that of CH4 during non-growing season.