[Effect of Organic Fertilizer and Inorganic Fertilizer Application on N2O Emissions from Fluvo-aquic Soil in the North China Plain].

The North China Plain is an important grain production area in China. Due to the low content of soil organic carbon, increasing the application rate of nitrogen fertilizer would not lead to a continuous increase of maize yield at present. The combined application of organic fertilizer and inorganic fertilizer is widely regarded as a measure to simultaneously increase grain yield and soil organic carbon; however, the effect of organic fertilizer and inorganic fertilizer application on N2O emissions from farmland in the North China Plain is unclear. Here, N2O emissions and crop yields in cropland under the combined application of different types and rates of organic fertilizers plus inorganic N fertilizer were measured in the North China Plain. The field experiment included eight treatments:no N fertilizer (CK), inorganic fertilizer (NPK), 40% cow manure N plus 60% inorganic fertilizer N (CM), 40% chicken manure N plus 60% inorganic fertilizer N (FC), 40% pig manure N plus 60% inorganic fertilizer N (FP), 20% cow manure N plus 80% inorganic fertilizer N (1/2CM), 20% chicken manure N plus 80% inorganic fertilizer N (1/2FC), and 20% pig manure N plus 80% inorganic fertilizer N (1/2FP). The N2O fluxes were significantly correlated with soil water-filled pore space during the maize season (P<0.05). There was a significant linear relationship between N2O fluxes and soil dissolved organic carbon content during the maize season in all treatments except the NPK treatment. In the maize season, N2O emission was 0.50 kg·hm-2 under CK treatment, and increased to 2.28 kg·hm-2 under NPK treatment. However, when the proportion of manure N to total N applied was reduced from 40% to 20%, N2O emissions were significantly reduced by 33.6%, 43.7%, and 12.1% under 1/2CM, 1/2FC, and 1/2FP treatments, respectively. The difference in application rate of organic manure N did not significantly affect maize yield. The reduction of N2O emission at the low manure application rate compared with the high manure application rate was likely due to the decrease in dissolved organic carbon in soils.

[Effects of Controlled-Release Urea Application on N2O Emission in Maize-Cultivated Sandy Loam Soil].

A field experiment was conducted in maize-cultivated sandy loam soil in the old flooded area of the Yellow River to evaluate the responses of N2O emissions to application of different type of controlled-release urea. An inorganic N fertilizer was applied at 270 kg·hm-2 during the maize season. Urea was applied alone and in combination with sulfur-coated urea (SCU) or polyurethane-coated urea (PCU) at N ratios of 30%:70%, 50%:50%, and 70%:30%, respectively. Cumulative N2O emission under urea treatment alone (CN) was 1.78 kg·hm-2 with a N2O emission factor of 0.38%. In comparison to CN, 70% urea+30% SCU, 50% urea+50% SCU, and 30% urea+70% SCU treatments reduced N2O emission by 1.12%, 22.5%, and 11.2%, respectively. In contrast, application of urea in combination with PCU (with the proportion varied from 30%-70%) increased N2O emission by 0.02-0.41 kg·hm-2 compared with the CN, while 30% urea+70% PCU treatment showed a 23.0% increase. Regression analysis showed that N2O flux was significantly (P<0.01) correlated with soil temperature at 10 cm depth and concentrations of soil NH4+-N and NO3--N in all the treatments, but not with soil moisture or dissolved organic carbon concentration. Compared with the CN, the 50% urea+50% SCU and 50% urea+50% PCU treatments slightly, but not significantly, increased the maize yield, whereas the 30% urea+70% SCU treatment showed a reduction effect. Overall, the mitigation effect of controlled-release urea on N2O emission may primarily depend on its coating material and application rate.

[Research progresses on methanogenesis pathway and methanogens in coastal wetlands]. / æ»¨æµ·æ¹¿åœ°ç”²çƒ·äº§ç”Ÿé€”å¾„å’Œäº§ç”²çƒ·èŒç ”ç©¶è¿›å±•.

Coastal wetlands contribute about 75% to the global oceanic CH4 emissions, thus play a vital role in global C cycles. In this paper, we provided a perspective on researches on metabolic, phylogenetic, and ecological diversity of the methanogenic archaea and the regulating environmental factors in coastal wetlands. Because of the presence of more favorable electron acceptors such as sulfate, methanogenesis via CO2 reduction and acetate fermentation are limited by availability of substrates, and hydrogenotrophic and acetotrophic methanogens generally express low relative abundance. In contrast, "non-competitive" substrates such as methanol and methylated compounds have been shown to contribute substantially to methane formation in coastal wetlands, and the facultative methanogens are predominant in those environments. Salinity regulates vegetation zonation and is related to SO42- concentration, by regulating types of methanogenic substrates and contents of compe-titive electron acceptors, indirectly affects the structure and function of methanogens. Major uncertainties in the current studies include the following: methanogen community structure, the key environmental factors regulating methane pathway, and their effects on methane emissions in coastal wetlands.

[Effects of nitrogen fertilization on soil respiration during maize growth season].

In order to understand how nitrogen (N) fertilization affects soil respiration, a pot experiment with splitting-root compartment and by root-cutting was conducted in a greenhouse. The experiment had four treatments, i. e., unplanted and N-unfertilized (CKO), unplanted but fertilized with 150 mg N x kg(-1) CKN), planted maize (Zea mays L.) but N-unfertilized (MO), and planted maize and fertilized with 150 mg N x kg(-1) (MN). Soil respiration, soil basal respiration, root respiration, and rhizospheric microbial respiration were measured simultaneously. In unplanted soils (treatments CKO and CKN), soil respiration rate (soil basal respiration) ranged from 13.41 to 77.27 mg C x m(-2) x h(-1), and N fertilization had less effect; while in planted soils, the averaged soil respiration rate in treatment MN amounted to 138.54 mg C x m(-2) x h(-1), and was 17.7% higher (P < 0.05) than that in treatment MO. This increment mainly occurred at tasselling and flowering stages. During maize growth season, the contribution of soil basal respiration, root respiration, and rhizospheric microbial respiration to soil respiration in treatments MN and MO was 36.2%, 45.9%, and 17.9%, and 35.5%, 36.9%, and 37.6%, respectively.

[Simulation of methane emissions from rice fields in the Taihu Lake region, China by using different unit of soil database with the DNDC model].

Application of a biogeochemical model, DeNitrification and DeComposition or DNDC, was discussed to assess the impact of CH4 emissions on different soil database from rice fields in Taihu Lake region of China. The results showed that CH4 emissions of the polygon-based soil database of 1:50000, which contained 52034 polygons of paddy soils representing 1107 paddy soil profiles extracted from the latest national soil map (1:50000), were located within the ranges produced by the county-based soil database of 1:50000. However, total emissions of the whole area differed by about 1680 Gg CH4-C. Moreover, CH4 emissions of the polygon-based soil database of 1:50000 and the county-based soil database of 14,000,000, which was the most popular data source when DNDC model was applied in China, have a big estimation discrepancy among each county-based unit in spite of total emissions of the whole area by a difference of 180 Gg CH4-C. This indicated that the more precise soil database was necessary to better simulate CH4 emissions from rice fields in Taihu Lake region using the DNDC model.

Effects of long-term amendment of organic manure and nitrogen fertilizer on nitrous oxide emission in a sandy loam soil.

To understand the effects of long-term amendment of organic manure and N fertilizer on N2O emission in the North China Plain, a laboratory incubation at different temperatures and soil moistures were carried out using soils treated with organic manure (OM), half organic manure plus half fertilizer N (HOM), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (NK) and control (CK) since 1989. Cumulative N2O emission in OM soil during the 17 d incubation period was slightly higher than in NPK soil under optimum nitrification conditions (25 degrees C and 60% water-filled pore space, WFPS), but more than twice under the optimum denitrification conditions (35 degrees C and 90% WFPS). N2O produced by denitrification was 2.1-2.3 times greater than that by nitrification in OM and HOM soils, but only 1.5 times greater in NPK and NP soils. These results implied that the long-term amendment of organic manure could significantly increase the N2O emission via denitrification in OM soil as compared to NPK soil. This is quite different from field measurement between OM soil and NPK soil. Substantial inhibition of the formation of anaerobic environment for denitrification in field might result in no marked difference in N2O emission between OM and NPK soils. This is due in part to more rapid oxygen diffusion in coarse textured soils than consumption by aerobic microbes until WFPS was 75% and to low easily decomposed organic C of organic manure. This finding suggested that addition of organic manure in the tested sandy loam might be a good management option since it seldom caused a burst of N2O emission but sequestered atmospheric C and maintained efficiently applied N in soil.