Guanxiong Chen

Mitigating nitrous oxide emissions from a maize-cropping black soil in northeast China by a combination of reducing chemical N fertilizer application and applying manure in autumn

Abstract Nitrous oxide (N2O) emissions from agricultural soils, mainly caused by chemical nitrogen (N) fertilizer inputs, are major sources of N2O in Chinese terrestrial ecosystems. Thus, attempts to reduce N2O emissions from agricultural soils by optimizing N applications are receiving increasing attention. Further, organic fertilizers are being increasingly used in China to improve crop production/quality and prevent or reduce soil degradation. However, organic and chemical fertilizers are often both applied in spring in northeast China, which promotes N2O emissions and may be sub-optimal. Therefore, we hypothesized that reducing applications of chemical fertilizer N and applying manure in autumn could be an effective strategy for mitigating N2O emissions from cropped soils in the region. To test this hypothesis, we established a field trial to investigate the effects of different combinations of chemical N fertilizer applications and animal manure in autumn on both N2O emissions and maize (Zea mays L.) grain yields in northeast China. The treatments, expressed as NxMy (where Nx and My denote the total amounts of chemical fertilizer nitrogen (N) and manure (M) applied in kg N ha−1 and m3 M ha−1, respectively), were N0M0, N230M0, N270M12, N230M15, N320M18 in 2010 and N0M0, N230M0, N200M12, N200M15, N280M18 in 2011. Measurements of the resulting N2O emissions showed that pulse fluxes occurred after each chemical N fertilizer application, but not after manure inputs in autumn or during soil-thawing periods in the following spring. Emission factors for the chemical fertilizer N were on average 1.07% (1.00˜1.10%) and 1.14% (0.49˜1.83%) in 2010 and 2011, respectively. Furthermore, by comparing the nine pairs of fertilization treatments, the relative increase in cumulative nitrous oxide-nitrogen (N2O-N) emissions was found to be proportional to the relative increase in urea application, but independent of the amount of autumn-applied manure. These findings imply that N2O emissions from fertilized agricultural soils in northeast China could be mitigated by supplying manure in the autumn and reducing the total amount of chemical N fertilizer applied in the following year. Although no significant difference in maize grain yield was found among the fertilization treatments, the grain yield-scaled N2O emissions for the treatments with a lower chemical N application (e.g., N230M15 and N200M15 treatments) were significantly lower than those with a higher chemical N application (e.g., N320M18 and N280M18 treatments). Meanwhile, under the condition of the same application amount of chemical fertilizer N, the grain yield-scaled N2O emission decreased with the increase of manure application rate. Thus, the results support the hypothesis that combining reductions in chemical N fertilizer and applying manure in autumn could be an effective strategy for mitigating N2O emissions from N-fertilized soils in northeast China.

Study of microbial community structures in UASB sludge treating municipal wastewater by denaturing gradient gel electrophoresis of 16S rDNA

The structures of microbial communities in lab-scale upflow anaerobic sludge blanket (UASB) reactors for treating municipal wastewater with different ratios of CODsoluble/ CODtotal were studied using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes. The microbial structure of the inoculum sludge obtained from a full-scale UASB reactor of treating potato processing wastewater was compared with the structures of sludges collected from three lab-scale UASB reactors after eight months feeding with raw municipal wastewater, with CEPS (chemically enhanced primary sedimentation) pretreated municipal wastewater, and with a synthetic municipal sewage, respectively. Computer-aided numerical analysis of the DGGE fingerprints showed that the bacterial community underwent major changes. The sludges for treating raw and CEPS pretreated wastewater had very similar bacterial and archaeal communities (82% and 96% similarity) but were different from that for treating the synthetic sewage. Hence, despite similar % COD in the particulate form in the synthetic and the real wastewater, the two wastewaters were selected for different microbial communities. Prominent DGGE bands of Bacteria and Archaea were purified and sequenced. The 16S rRNA gene sequences of the dominant archaeal bands found in the inoculum, and UASB sludge fed with raw sewage, CEPS pretreated wastewater, and synthetic sewage were closely associated withMethanosaeta concilii. In the UASB sludge fed with synthetic sewage, another dominant band associated with an uncultured archaeon 39-2 was found together withM. concilii.

N2O and N2 production potential in various chinese agricultural soils by denitrification

Abstract Eleven agricultural soils were collected from Chinese uplands and paddy fields to compare their denitrification activities under identical laboratory conditions. Before starting the assays, all air-dried soils were pre-incubated for 4 weeks at 25°C and 40% WFPS (waterfilled pore space). N2O and N2 production potentials in various Chinese agricultural soils by denitrification were determined by acetylene inhibition method at 25°C and 80% MTPS for 2 d incubation, with or without KNO3 (200 mg N kg-1 soil) addition. The N2O and N2 productions by denitrification from soils with KNO3 addition were 0.17 and 0.35 μg N kg-1 d-1 on average, ranging between 0.04–0.55 and 0.10–1.33 μg N kg-1 d-1, respectively. The denitrified N increased by 200 mg N kg-1 KNO3-N addition was 0.22 μg N kg-1 d-1 on average and ranged between 0.01–1.40 μg N kg-1 d-1. No relationships were found between gases productions (N2O, N2, and CO2) from 3 kinds of denitrification assays and soil properties such as bulk density, total C, total N, soluble C, microbial biomass C, and NO3 --N concentration. However the denitrified N from soils without KNO3 addition had significantly negative correlation with the pH of soils (p < 0.05). Among 11 soils, the Ultisols acid paddy soil had the strongest denitrification activity. There was significant correlation between CO2 production and N2O and N2 productions from 3 kinds of denitrification assays.

Stimulation of methanogenesis in a laboratory scale UASB reactor treating domestic sewage by Fe(0) application.

The effects of application of zero valence Fe (Fe(0)) on the anaerobic digestion of sewage was investigated using two laboratory scale UASB reactors. One reactor had Fe(0) addition in a container found midway along the recycling loop. The other one was a control reactor. In a test run period of 76 days, the Fe(0) application significantly increased the CH 4 yield by 8.7% and decreased the effluent COD concentration by 21.0% relative to the control reactor. A decrease of the H2 concentration of biogas and the CODs/CODt ratio in effluent by Fe(0) application were observed. The obtained results imply that the methanogenesis and COD removal efficiency of the UASB reactor were stimulated by Fe(0) application. The higher performance of the reactor with Fe(0) application arises from the integrated functions of Fe(0) or its ionic state as donor of H2, macronutrient, and flocculant. This study showed that the supply of Fe(0) to a UASB can improve the methanogenesis and the overall COD removal of a UASB reactor treating low-strength domestic waste water.