Search

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. [ABSTRACT FROM AUTHOR]

Water-intensive systems of rice cultivation are facing major challenges to increase rice grain yield under conditions of water scarcity while also reducing greenhouse gas (GHG) emissions. The adoption of effective irrigation strategies in the paddy rice system is one of the most promising options for mitigating GHG emissions while maintaining high crop yields. To evaluate the effect of different alternate wetting and drying (AWD) irrigation strategies on GHG emissions from paddy rice in dry and wet seasons, a field experiment was conducted at the Tamil Nadu Rice Research Institute (TRRI), Aduthurai, Tamil Nadu, India. Four irrigation treatments were included: One-AWD (one early drying period), Two-AWD (two early drying periods), Full-AWD (wetting and drying cycles throughout the rice season), and CF (continuous flooding). Different rice varieties were also tested in the experiment. In this study, we emphasized one factor (irrigation effect) that affects the dependent variable. The results show that early AWD treatments reduced methane (CH4) emissions by 35.7 to 51.5% in dry season and 18.5 to 20.1% in wet season, while full-AWD practice reduced CH4 emissions by 52.8 to 61.4% compared with CF. Full-AWD in dry season not only significantly reduced CH4 emission during that season, it also resulted in the decline of the early season emission in the succeeding wet season. Global warming potential (GWP) and yield-scaled GWP were reduced by early or full season AWD in both rice seasons. The GWP value from nitrous oxide (N2O) was relatively low compared to that from CH4 in both rice seasons. Rice yield was not affected by irrigation treatments although varietal differences in grain and straw yields were observed in both rice seasons. This study demonstrated that early season water managements are also effective in reducing CH4 and total GHG emissions without affecting rice yield. [ABSTRACT FROM AUTHOR]

In paddy soils in the Mekong Delta, soil archaea emit substantial amounts of methane. Reproducing ground flux data using only satellite-observable explanatory variables is a highly transparent method for evaluating regional emissions. We hypothesized that PALSAR-2 (Phased Array type L-band Synthetic Aperture RADAR) can distinguish inundated soil from noninundated soil even if the soil is covered by rice plants. Then, we verified the reproducibility of the ground flux data with satellite-observable variables (soil inundation and cropping calendar) and with hierarchical Bayesian models. Furthermore, inundated/noninundated soils were classified with PALSAR-2. The model parameters were successfully converged using the Hamiltonian–Monte Carlo method. The cross-validation of PALSAR-2 land surface water coverage (LSWC) with several inundation indices of MODIS (Moderate Resolution Imaging Spectroradiometer) and AMSR-2 (Advanced Microwave Scanning Radiometer-2) data showed that (1) high PALSAR-2-LSWC values were detected even when MODIS and AMSR-2 inundation index values (MODIS-NDWI and AMSR-2-NDFI) were low and (2) low values of PALSAR-2-LSWC tended to be less frequently detected as the MODIS-NDWI and AMSR-2-NDFI increased. These findings indicate the potential of PALSAR-2 to detect inundated soils covered by rice plants even when MODIS and AMSR-2 cannot, and show the similarity between PALSAR-2-LSWC and the other two indices for nonvegetated areas. [ABSTRACT FROM AUTHOR]

Rice ( Oryza sativa L.) production is facing major challenges, including scarcity of irrigation water and ongoing climate change. Modifications of the current cropping techniques could increase yield, save water, and mitigate greenhouse gas emission. We investigated the effect of planting methods (young seedlings, wide spacing with alternate wetting and drying irrigation [YW-AWD], old seedlings, narrow spacing with continuous flooding [ON-CF], and in-between the two planting methods [IB-AWD]) and rice varieties on methane (CH 4 ) and (N 2 O) emissions during two crop seasons. The results show that CH 4 emission, averaged over rice varieties, reduced for YW-AWD by 41% and 24%, compared with ON-CF, while the reduction in emission for the IB-AWD method was 48% and 26% in summer (dry) and monsoon (wet) season, respectively. However, an increase in N 2 O emission was observed for YW-AWD and IB-AWD methods in both seasons. There was no significant difference in CH 4 and N 2 O emissions between the tested varieties. The total water saving under YW-AWD and IB-AWD was 47.5% and 49.3% in summer, and 79.4% and 79.8% in monsoon season, respectively, compared with ON-CF. The grain yields of YW-AWD and IB-AWD were comparable with the yield of ON-CF in both seasons. The CO 2 -eq emission and yield-scaled CO 2 -eq emission from YW-AWD and IB-AWD were significantly lower compared with ON CF due to low CH 4 emission, while maintaining similar rice yields. This study showed that the YW-AWD and IB-AWD methods are effective in reducing CO 2 -eq emission and saving irrigation water, while maintaining the rice yield. [ABSTRACT FROM AUTHOR]

A correction to the article "Media Optimization of Parietochloris Incisa for Arachidonic Acid Accumulation in an Outdoor Vertical Tubular Photobioreactor," by Hazel Tababa Guevarra and colleagues,published in the November 19, 2011 issue is presented.

This document is an editorial from the journal "Biology & Fertility of Soils" discussing recent advances in the study of biology and fertility in paddy field soil. Paddy fields are flooded during rice cultivation, which affects the activities of microorganisms and microbial community structures. The editorial highlights the importance of understanding the biology and fertility of paddy field soil for sustainable rice production. The special issue of the journal includes research papers on topics such as nutrient cycles, decomposition of organic matter, greenhouse gas production, and interactions between microbes and rice plants. The authors express gratitude to the contributors and hope that the contents of the special issue provide new insights into this field of study. [Extracted from the article]

The leaves of Cryptomeria japonica D. Don collected near an electrochemical plant (on Yakushima Island) had more wax (approximately 10% higher in 1-year leaves) and less chlorophyll (approximately 50 and 30% lower in 0- and 1-year leaves, respectively) than those from a reference area, although the trees showed no symptoms of decline. In the Kanto Plain around Tokyo (Saitama and Ibaraki), where C. japonica is declining (dieback and (or) defoliation), the amount of epicuticular wax in current-year leaves and the leaf chlorophyll content were almost equivalent to those of healthy plants in mountainous areas, but the wax eroded more rapidly (approximately 1.5 times faster). Although the C and O contents and the C/O ratio of epicuticular wax were approximately equivalent irrespective of the levels of decline, the cuticular transpiration rate, especially in 1-year leaves, was higher in Saitama (water loss: 0.92 1 0.21%/h) and to some extent in Ibaraki (0.66 1 0.08%/h) than in the mountainous area (0.60 1 0.12%/h). This excessive transpiration, probably resulting from a degraded wax layer andthe partial malfunctioning of stomata due to deposited aerosols, maybe a significant factor causing the decline of C. japonica. Dry atmospheric conditions (e.g., rain factor <100), which have prevailed since the 1950s due to urbanization, may have inflicted additional stress on the tree. [ABSTRACT FROM AUTHOR]

Biogas production generates digested slurry, as a byproduct, which can be used as fertilizer after its conversion into digested liquid and biochar. A microcosm-based study was conducted to evaluate the effects of chemical fertilizer (CF), digested liquid (DL) and varying concentrations of biogas digested slurry based-biochar along with DL on NO flux, CO flux, soil chemical properties and crop yield for three continuous cropping cycles of komatsuna ( Brassica rapa var. perviridis) from April to July 2013. Analyses revealed that DL-treated soils released almost equal cumulative amounts of NO and CO as soils treated with CF. The soil mineral-N contents were also similar for the DL- and CF-treated soils while DL application increased the soluble organic carbon (SOC) content of the soil compared to CF treatment. The application of slurry-based biochar increased NO and CO flux, which, in turn, appeared to depend upon biochar concentration. The application of biochar probably increased the nitrification rate as biochar-treated soils had higher values of NO-N and lower values of NH-N compared to soils not treated with biochar at most of the observations. The SOC content was also the highest in biochar-treated soils. The overall crop yield for three cropping cycles was the highest in DL and biochar at low application rate (BL), and it was lower in CF, biochar at medium (BM) and high (BH) application rate. This study indicates that the application of DL could be an effective strategy to minimize the use of CF, without affecting NO flux, CO flux, soil mineral N, and increasing crop productivity. The effects of slurry-based biochar on greenhouse gases flux and crop yield depends on the application rate of biochar. [ABSTRACT FROM AUTHOR]

Laboratory indices (KCl extraction, thermal fractionation, pepsin extraction, C:N ratio and N mineralization) of organic materials were compared with plant availability of mineral-N produced from organic-N in a greenhouse experiment. Six types of organic materials [farmyard manure (FYM), pig manure (PG), poultry manure (PL), sewage sludge (SS), pressmud (PM) and compost (CP)] were compared with urea as a chemical reference fertilizer. Relative effectiveness of organic N (REo) was used to compare the fraction of N extracted with different N availability laboratory indices. REovalues of organic materials ranged from 0.14 to 0.77 and decreased in the following order: PL > PG > SS > PM > CP > FYM. The KCl-extracted inorganic N, pepsin-extracted organic N and N mineralized during 42 days gave a positive relationship with REo, and the C:N ratio a negative relationship with REo. Among the different N availability laboratory indices, pepsin extraction of organic N, C:N ratio and N mineralization can be recommended for determining mineralizable organic N in organic materials. KCl-extracted inorganic N proved to be a useful index for organic materials having a low inorganic N fraction. Thermal fractionation did not provide a suitable index of plant-available N in organic materials. [ABSTRACT FROM PUBLISHER]

The green alga Parietochloris incisa contains a significant amount of the nutritionally valuable polyunsaturated fatty acid and arachidonic acid (AA) and is being considered for mass cultivation for commercial AA production. This study was primarily aimed to define a practical medium formulation that can be used in commercial mass cultivation that will contribute to a substantial increase in the AA productivity of P. incisa with concomitant reduction of nutritional cost. The effect of nutrient limitation on growth and AA content of this microalga was explored in a batch culture in outdoor conditions using a vertical tubular photobioreactor. The study was conducted in two parts: the first was primarily focused on the effect of different nitrogen concentration on growth and AA content and the second part compares nitrogen deprivation, combination of nitrogen and phosphorus deprivation, and combined overall nutrient limitations at different levels of deprivation under low and high population densities. Since complete nitrogen deprivation hampers lipid and AA accumulation of P. incisa, thus, a critical value of nitrogen supply that will activate AA accumulation must be elucidated under specific growth conditions. Under the present experimental conditions, 0.5 g sodium nitrate obtained a higher AA productivity and volumetric yield relative to the nitrogen-deprived culture corresponding to 36.32 mg L day and 523.19 mg L. The combined nitrogen and phosphorus limitation seemed to enhance AA productivity better than nitrogen deprivation alone. The effect of overall nutrient limitation indicates that acute nutrient deficiency can trigger rapid lipid and AA syntheses. The effect of light as a consequence of culture cell density was also discussed. This study therefore shows that the nutrient cost can be greatly reduced by adjusting the nutrient levels and culture density to induce AA accumulation in P. incisa. [ABSTRACT FROM AUTHOR]

Abstract: Three types of culture experiments using paddy rice (Oryza sativa L.) were performed to examine root-uptake of 14C in the form of acetic acid: double pot experiment (hydroponics), wet culture experiment (submerged sand medium), and chamber experiment (hydroponics and submerged sand medium). The 14C radioactivity in the plant, mediums, and atmospheric carbon dioxide (14CO2) in the chamber were determined, and the distribution of 14C in the plant was visualized using autoradiography. In the double pot experiment, the shoot of the plant and the lower root which was soaked in the culture solution had 14C radioactivity, but the upper root which did not have contact with the solution had none. There were also 14C radioactivity in the grains and roots in the wet culture experiment. Results of the chamber experiment showed that 14CO2 gas was released from the culture solution in both types of cultures. Results indicated that the 14C-acetic acid absorbed by rice plant through its root would be very small. Most of the 14C-acetic acid was transformed into gaseous forms either in the culture solution or rhizosphere. A relatively longer time would be needed to assimilate 14C derived from acetic acid to grain parts after it was once absorbed by the shoot through the root. Availability of 14C for the plant in sand culture was considered to be decreased compared with that for the plant in the hydroponics experiment. It was suggested that rice plant absorbed and assimilated 14C through the plant roots not because of uptake of 14C-acetic acid but because of uptake of 14C in gaseous forms such as 14CO2. [Copyright &y& Elsevier]

The effects of liquid residue derived from grass clipping after steam-treatment on the in vitro growth of Rhizoctonia solani SN-1, AG-4 were evaluated to verify the antifungal activities of the residue. The liquid residue inhibited R. solani growth, with increasing inhibition with higher concentrations and lower pH. Test of individual organic acids (acetic, formic and propionic acids) present in the residue indicate that the inhibitory effect may be attributed to the organic acids, and the effect of the organic acids seems to depend on pH, especially at lower concentrations. [ABSTRACT FROM AUTHOR]

The effect of mineral fertilization and its application pattern on microbial activity and the subsequent CO2 and CH4 emissions arising from soil organic matter (SOM) or added substrate remains unclear. We quantified the decomposition of 13C-labeled straw and the priming effect (PE) governed by the N and P fertilizer application pattern during a 100-day experiment in a flooded soil. Straw addition increased the total CO2 and CH4 emissions. Straw mineralization increased by 30% and decreased by 19% after full and split NP application, respectively, compared with only straw addition. However, application of NP fertilization (full or split) inhibited straw-derived CH4 emissions compared with only straw addition. SOM decomposition was increased by straw addition, yielding a positive PE for CO2 emission. The application of split NP fertilization along with straw addition improved microbial activity, yielding the highest positive PE for CO2 emission. In contrast, compared with the control (no addition), split NP application decreased the positive PE for CH4 emission. Therefore, the straw-C-derived total CO2 equivalent emission was decreased by split NP application. These results were mainly attributable to the increased Olsen P, microbial biomass, enzyme activity, and straw-derived C microbial use efficiency of split NP application, which negatively affected the PE for CH4 emission; this was supported by the results of standardized total effects determined from structural equation models. Overall, compared with full application, split NP fertilizer application significantly decreased the straw-C mineralization rate and PE for CH4 emission, thereby mitigating greenhouse gas emission and SOM storage in paddy soil. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH4, N2O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha−1combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH4emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N2O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO2-equivalents (CO2e) and yield-scaled CO2e (GHGI) of CH4and N2O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Aim: This study aims to improve our understanding of temporal variations and controlling factors of soil respiration (R) and its components (microbial respiration or R and root respiration or R) in an Asian tropical seasonal forest at diurnal, seasonal and annual timescales in relation to biotic and abiotic controls. Methods: R was studied by the trenching method in a seasonal dry diptercarp forest, western Thailand. An automated soil chamber system was used to produce hourly data of R during 2008-2011. Analysis of R in relation to both biotic and abiotic factors was carried out to understand its temporal variations at different timescales. Results: R was the main contributor to overall magnitude and variability of R. Soil temperature alone was the main driver of diurnal variation, while the combination of soil moisture and soil temperature determined the seasonal variations. The amount of R was also related to the fine root (<2 mm) and microbial biomass at seasonal timescales. Due to the small inter-annual variations in soil temperature and moisture, total soil respiration among the 4 years was not significantly different ( p < 0.05). The annual totals for R during 2008-2011 were 3.20, 3.89, 3.52, 4.14 kgCO m years, respectively. The 4-year average ratio of R (trenched) to R (untrenched) was 66 ± 4 %. Conclusion: R plays a crucial role in determining the magnitude (large ratio between R and R) and temporal variations of R. In this forest ecosystem, high seasonal variations in R were observed and were mainly attributed to the response of R to moisture. [ABSTRACT FROM AUTHOR]

For sustainable food production in the Mekong Delta, local information on irrigation status is essential for allocating water resources efficiently at the community level. ALOS-2 PALSAR-2 L-band SAR can be used to detect submerged and nonsubmerged soil covered by rice plants at a spatial resolution compatible with field observation but a low temporal resolution. In this study, a new multiscale data assimilation technique is developed to estimate the spatiotemporal dynamics of field water levels at a temporal resolution appropriate to inform decision-making on when to initiate irrigation. The method employs an irrigation model based on parameters representing farmers' irrigation practices. ALOS-2 PALSAR-2 data are used to derive the hydrological parameters of the model, including an irrigation parameter representing how deep the field water level dropped until the next round of irrigation was initiated. We developed observation operators for the soil submersion status under vegetation and spatial submersion percentages instead of assimilating soil moisture products. The study uses ALOS-2 PALSAR-2 data (25–100 m spatial resolution, approximately every 42 days) over the Mekong Delta and experimental data collected in situ for model initialization and validation. The estimated irrigation parameter controlling the maximum depth of field water level showed spatio-temporal consistency with the ground-observed value (RMSE = 4.24 cm). The values of the parameters also showed spatial consistency with respect to DEM data; he paddies with low irrigation model parameter values were prone to be located in low-elevation zones (<2 m), whereas high model parameters values tended to be located in paddies in the high-elevation zones (>3 m).The results show promising applications using L-band SAR observations for monitoring paddy field water level, for irrigation practices and for estimation of the water consumption and of methane emissions. • A technique to detect soil-submersion covered by rice plants were introduced. • Assimilation of fine-resolution SAR data based on spatio-temporal ergodicity. • A technique was implemented to adaptatively optimize states with different scales. • Stable assimilation even with sparse observation by using inundation probability. • The estimated irrigation parameters showed a consistency with ground observed values. [ABSTRACT FROM AUTHOR]

A microcosm-based study was conducted to evaluate the effects of varying concentrations of biogas digested slurry-based biochar on CH 4 flux, associated methanogenic archaeal community, soil chemical and microbial properties, and plant biomass in paddy soil. Our results showed that biochar application significantly increased the CH 4 flux compared to untreated soil, and it increased with the increase in biochar concentration. The NH 4 + -N concentration also increased significantly in biochar treated soils due to more reducible conditions in the soil which prevented NH 4 + -N conversion to NO 3 – -N. The application of biochar significantly increased soluble organic carbon, microbial biomass carbon and soluble total nitrogen content of the soils without affecting microbial biomass nitrogen contents. Paddy plant biomass such as shoot weight, panicle numbers and weight of panicles were also higher in biochar treated soils. Denaturing gradient gel electrophoresis revealed all methanogenic groups with the dominance of Methanosaetaceae and Methanocellales groups, whereas no differences were found in methanogenic archaeal diversity among biochar treated and non-treated soils. Thus, the increase in CH 4 flux with the application of varying biochar concentration is possibly due to the variation in the soil variables and plant biomass without affecting methanogenic archaeal diversity. [ABSTRACT FROM AUTHOR]

Soil characteristics regulate various belowground microbial processes including methanogenesis and, consequently, affect the structure and function of methanogenic archaeal communities due to change in soil type which in turn influences the CH production potential of soils. Thus, five different soil orders (Alfisol, Entisol, Inceptisol, Podzol and Vertisol) were studied to assess their CH production potential and also the methanogenic archaeal community structure in dryland irrigated Indian paddy soils. Soil incubation experiments revealed CH production to range from 178.4 to 431.2 μg CH g dws in all soil orders as: Vertisol

Biogas production generates digested slurry as a by-product. It can be used as fertilizer especially after its conversion into digested liquid. A microcosm-based study was conducted in order to compare the effects of single application of digested liquid or chemical fertilizer on NO flux and crop yield of komatsuna vegetable. Analysis revealed that digested liquid-treated soils released almost equal cumulative NO (0.43 g N m) compared to chemical fertilizer (0.39 g N m). The uncropped soils treated with the digested liquid and chemical fertilizer released more NO compared to corresponding cropped soils. The NO emission factor and soil mineral N contents were similar for the digested liquid and chemical fertilizer-treated soils. Plant biomass in the first crop after digested liquid application was significantly higher (5.59 g plant) than that after applied chemical fertilizer (4.78 g plant); but there was no significant difference for the second crop. Nitrogen agronomic efficiency was improved by the digested liquid compared to chemical fertilizer. This study indicates that cumulative NO flux was similar after application of the digested liquid and chemical fertilizer, while the overall yield from both croppings was increased in the digested liquid-treated soil compared to chemical fertilizer-treated soil. [ABSTRACT FROM AUTHOR]

Dry deposition fluxes (F L) of NO3 − and SO4 2− to leaf surfaces were measured for Japanese red pine (Pinus densiflora), Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa), and Japanese white oak (Quercus myrsinaefolia), together with atmospheric concentrations (C L) of NO x (NO+NO2), T-NO3 (gaseous HNO3 +particulate NO3 −) and SO x (gaseous SO2 +particulate SO4 2−) around the leaves in a suburban area of Japan, using a modified leaf-washing technique. F L of NO3 − and SO4 2− decreased as follows: pine>>cedar>cypress≥oak and pine>>cedar>oak≥cypress, respectively. F L of NO3 − for all tree species fluctuated synchronously with C L of T-NO3. F L of SO4 2− fluctuated with C L of SO x , but the dominant pollutant deposited (SO2 or SO4 2−) appeared to differ for different tree species. Dry deposition conductance (K L) of T-NO3 and SO x was derived as an F L/C L ratio. Seasonal variations of K L likely reflect the gas/particle ratios of T-NO3 and SO x , which were affected by meteorological conditions such as temperature. Dry deposition velocities (V d) of T-NO3 and SO x were obtained as the mathematical product of annual mean K L and the total leaf surface areas in the forests. The comparison of V d among tree species indicated that the loads of acidic air pollutants were higher to coniferous forests than broad-leaved forest because of the higher K L and/or larger leaf surface areas. [Copyright &y& Elsevier]

The author regret that the above article originally published with an error in the equation under "Calculation of GHG emission, PE, C-mineralization, microbial C use efficiency, and enzyme activity" section. The corrected equation is now presented in this article. [ABSTRACT FROM AUTHOR]

Field and incubation experiments were conducted to determine the emission rate of greenhouse gases, nitrogen change, populations of AOB, NOB, and fungi as well as growth of corn in response to amendment of urea granulated with and without nitrification inhibitors and zeolite. The application of urea with neem, urea with zeolite, urea with zeolite + neem, urea with zeolite + dicyandiamide, and urea with dicyandiamide (UD) decreased the N 2 O emissions by 16.3%, 59.6%, 66.8%, 81.9%, 16.3%, and 86.7%, respectively. Meanwhile, patterns of CH 4 fluxes were mostly determined by small emissions. Increase in corn height, weight of cobs, biomass, and chlorophyll leaf contents were not significantly different between urea alone and urea with NIs and zeolite. In the incubation experiment, the highest concentration of NH 4 + and N 2 O production was detected during the first week and it remained high up to the second week of incubation in the combination of urea with NIs and zeolite treatments, although there was no significant difference compared with urea. During NH 4 + decrease, the concentration of NO 3 - started to accumulate from the second to the third weeks. Production of CO 2 showed no significant differences among treatments. The static production of CO 2 could also explain that NIs and zeolite additions did not change AOB, NOB, and fungi activities after the fourth week of incubation.

The influence of organic and conventional farming and agroecology on the diversity and functioning of indigenous soil microbial communities was examined using a multifactorial analysis based on an extended minimum data set of classical status and functional tests. Main soil physicochemical properties and selected microbiological indicators, the quantity of heterotrophic or aerobic spore-forming bacteria, basal and substrate-induced respiration, catabolic activity with MicroResp ™ , and fluorescein diacetate enzyme activity were characterized. A pot experiment applying the most probable number method was designed with soil dilution series using Pisum sativum L. and Triticum spelta L. to assess the symbiotic infectivity and genetic diversity of key indicator groups of the plant microbiome, e.g. nitrogen-fixing bacteria (rhizobia) and arbuscular mycorrhizal fungi. Soil pH, humus content, CFU, enzyme activity, and soil respiration were significantly higher in organic soils. The activity of soil microorganisms was mainly related to clay, humus, calcium, and magnesium parameters. A redundancy analysis test of catabolic activities showed that samples were grouped according to different substrate utilization patterns and land uses were also clearly separated from each other. Farming practice influenced the abundance and diversity of microbial populations. Dark septate endophytic fungi were only found in conventional soils. In addition to confirming soil health improvements by organic management, our results highlight the importance of a complex evaluation including both classical status and functional parameters of soil microbiota, which may more reliably indicate a shift in the quality status of soils.

Red soils are the major land resource in subtropical and tropical areas and are characterized by low phosphorus (P) availability. To assess the availability of P for plants and the potential stability of P in soil, two pairs of subtropical red soil samples from a paddy field and an adjacent uncultivated upland were collected from Hunan Province, China. Analysis of total P and Olsen P and sequential extraction was used to determine the inorganic and organic P fractions in different aggregate size classes. Our results showed that the soil under paddy cultivation had lower proportions of small aggregates and higher proportions of large aggregates than those from the uncultivated upland soil. The portion of >2-mm-sized aggregates increased by 31 and 20 % at Taoyuan and Guiyang, respectively. The total P and Olsen P contents were 50-150 and 50-300 % higher, respectively, in the paddy soil than those in the upland soil. Higher inorganic and organic P fractions tended to be enriched in both the smallest and largest aggregate size classes compared to the middle size class (0.02-0.2 mm). Furthermore, the proportion of P fractions was higher in smaller aggregate sizes (<2 mm) than in the higher aggregate sizes (>2 mm). In conclusion, soils under paddy cultivation displayed improved soil aggregate structure, altered distribution patterns of P fractions in different aggregate size classes, and to some extent had enhanced labile P pools.

An anammox assay involving a ¹⁵N tracer and gas chromatography-mass spectrometry revealed that the potential anammox activity accounted for 1 to 5% of total N₂ production in a ravine paddy field, Japan. Among four 4-cm-deep layers, the top layer showed the highest activity. Clone libraries showed that the DNA in the top layer contained sequences related to those of Candidatus 'Brocadia fulgida', Ca. 'B. anammoxidans', and Ca. 'Kuenenia stuttgartiensis'. These results suggest that a specific population of anammox bacteria was present in paddy soils, although a small part of dinitrogen gas was emitted from the soil via anammox.