N_2O emissions from agricultural soils in the North China Plain: the effect of chemical nitrogen fertilizer and organic manure

An enclosed chamber technique was used to measure N 2O emissions from intensively agricultural soils of the North China Plain during the periods of 1995—1996 and 1997—1998, to reflect distinct components of winter wheat and summer maize growing seasons. The results showed that the continuous application of fertilizer in agricultural soils increased N\-2O emissions by a factor of 24.1—28.1, the calculated annual chemical N fertilizer\|transformed N\-2O\|N emissions was 0.67%. Our results indicated that the application of organic manure also had a significant influence on soil N 2O emissions, which combined with the use of chemical N increased about 20% in a year. It was calculated that there were about 0.11% N of organic manure transformed as N 2O N. Annual mean N 2O emission from our study area of fertilized soils was estimated to be 57.1 μgN 2O/(m 2·h). A weak correlation was also found between N 2O emissions and soil available nitrogen content NH + 4.

Progress and Yield Bottleneck of Aerobic Rice in the North China Plain: A Case Study of Varieties Handao 297 and Handao 502

Aerobic rice has been considered a promising rice cultivation system as water scarcity is increasing in the world. This article summarizes the advances in aerobic rice management researches in the North China Plain, focusing on yield formation and its bottleneck. High-yielding and good-quality aerobic rice varieties adapted to aerobic soil conditions have been released officially and adopted by farmers in North China. The varieties Handao 502 and Handao 297 have been recognized as the most promising varieties reaching a yield level ranging 3.5-5.0 t ha-1 with 450-650 mm water input. Compared with lowland rice, water input in aerobic rice was more than 50% lower, and water productivity was 60% higher. Researches on responses of rice cultivars to nitrate nitrogen （N） and ammonium N supplied at early growth stages provided the first evidence for a preference of aerobic rice HD297 for nitrate N supply, compared with the lowland rice variety. Zinc uptake studies demonstrated that introduction of aerobic rice system on calcareous soils may increase zinc deficiency problems. Sink size was identified as the limitation of aerobic rice yield, because its spikelet number m-2 was too low （20000-24 000） compared with the lowland rice. For future research, more attention is suggested to be paid to yield formation focusing on effects of water regimes on tiller dynamics. Understanding of nutrient uptake and response to fertilization effects are also urgently required to establish optimized crop management technology. Additionally, alternative cropping systems based on aerobic rice should be established, and key sustainability and environmental impact issues in the systems need to be identified.

Palaeorunoff estimations achieved from palaeoclimatic information for the southwest part of the North China Plain: an attempt to apply a climatological approach to palaeohydrology

Palaeoclimatic scenario projecting annual temperature and annual precipitation is firstly formalized with data available and speculations for the southwest part of the North China Plain (35— 37°N, 115—119°E) during the last 25000 years. Then, with three regression equations relating annual runoff to annual precipitation and derived with data of modern hydrological and meteorological records, values of annual runoff are calculated in terms of the corresponding values of annual precipitation from this palaeoclimatic scenario for this region during this temporal interval. These results indicate that runoff is the most during 8000—3000 a B.P. and the least during 25000—12000 a B.P.; runoff occurring during 12000—8000 a B.P. and during 3000—0 a B.P. is less than the one occurring during 8000—3000 a B.P. and more than the one occurring during 25000—12000 a B.P.; and the runoff occurring during 25000—12000 a B.P., 12000—8000 a B.P., and 3000—0 a B.P. is respectively 43, 46 and 66 percent of the one occurring during 8000—3000 a B.P. Values of bankfull discharge for palaeochannels of the Yellow River flowing in this region during the same interval are calculated from available estimates of slope of stream bed of these palaeochannels with a regression equation relating bankfull discharge to slope of stream bed and ratios of bankfull discharge are further calculated from these values for different groups of palaeochannel formed during different time spans embraced in this interval. To conduct a cross check, these values and ratios of bankfull discharge are compared to the corresponding values and ratios of runoff occurring during roughly the same time spans. The same direction and similar relative magnitude of changes of the surface water occurring in this region during the last 25000 years are indicated by these comparisons.

Seasonal characteristics and provenance of organic aerosols in the urban atmosphere of Liaocheng in the North China Plain:Significant effect of biomass burning

To better understand the seasonal characteristics of urban organic aerosol(OA)in the North China Plain(NCP),PM2.5 samples in the urban atmosphere of Liaocheng were collected and analyzed.The molecular distribution of the organic markers in the urban atmosphere of Liaocheng reveals that n-alkanes(39.3%)was the most abundant species all year round,followed by saccharides(28.2%),phthalic acids(Ph,20.8%),biogenic secondary organic aerosol(BSOA)tracers(9.4%),and polycyclic aromatic hydrocarbon(PAHs,2.3%).PM2.5,organic carbon(OC),elemental carbon(EC),and primary organic markers exhibit the highest concentrations in winter,due largely to the increased biomass burning and coal combustion for house heating in local and surrounding regions.However,the concentration and relative abundance of BSOA are significantly higher in summer than other seasons,induced by the more favorable meteoro-logical conditions that would promote the emissions of biogenic volatile organic compounds(BVOCs)and the secondary production of BSOA.The ratios of OC/EC and 3-methyl-1,2,3-butanetricarboxylic acid to cis-pinic acid plus cis-pinonic acid(MBTCA/(PA+PNA)are higher in the warm seasons than those in the cold seasons,indicating that the oxidation of OA is sensitive to air temperature.Compared to 2017,the concentration level of PAHs during wintertime decreased by 40.8%,confirming that the stringent regulation of coal burning is effective.The highest concentration of high molecular weight(HMW)n-alkanes and three anhydrosugars in winter,and the close correlation of levoglucosan with HMW n-al-kanes suggests that the impact of biomass burning was more significant in winter.The same seasonal characteristic of the ratios of high-/low-NO_(x) products with NO_(x) and the strong correlation of high-/low-NO_(x) products with levoglucosan indicate that the formation of isoprene SOA(SOA1)tracers was signif-icantly influenced by anthropogenic emissions.The molecular compositions,the distributions of fire spots,backward trajectories of air masses,and correlation analysis suggest that air pollution events in spring were primarily resulted from biomass burning and secondary oxidation,while pollution events in winter were largely driven by the increased combustion sources,and promoted aqueous secondary formation.Our results suggest that the reduction of biomass and coal combustion should be taken into account to improve the urban air quality in the NCP.

Variability of SO_2 in an intensive fog in North China Plain:Evidence of high solubility of SO_2

A field experiment was conducted in an intensive fog event between November 5 and November 8, 2009, in a heavily SO2-polluted area in North China Plain （NCP）, to measure SO2 and other air pollutants, liquid water content （LWC） of fog droplets, and other basic meteorological parameters. During the fog period, the concentrations of SO2 showed large variability, which was closely related to the LWC in the fog droplets. The averaged concentration of SO2 during non-fog periods was about 25 ppbv, while during the fog period, it rapidly reduced to about 4-7 ppbv. Such large reduction of SO2 suggested that a majority of SO2 （about 70%-80%） had reverted from gas to aqueous phase on account of the high solubility of SO2 in water in the fog droplets. However, the calculated gas to aqueous phase conversion was largely underestimated by merely using the Henry＇s Law constant of SO2, thus suggesting that aqueous reaction of SO2 in fog droplets might play some important role in enhancing the solubility of SO2. To simplify the phenomenon, an ＂effective solubility coefficient＂ is proposed in this study. This variability of SO2 measurement during the extensive fog event provides direct evidence of oxidation of SO2 in fog droplets, thus providing important implications for better understanding of the acidity in clouds, precipitation, and fogs in NCP, now a central environmental focus in China due to its rapid economic development.