Modeling nitrogen loadings from agricultural soils in southwest China with modified DNDC

Degradation of water quality has been widely observed in China, and loadings of nitrogen (N) and other nutrients from agricultural systems play a key role in the water contamination. Process‐based biogeochemical models have been applied to quantify nutrient loading from nonpoint sources at the watershed scale. However, this effort is often hindered by the fact that few existing biogeochemical models of nutrient cycling are able to simulate the two‐dimensional soil hydrology. To overcome this challenge, we launched a new attempt to incorporate two fundamental hydrologic features, the Soil Conservation Service curve and the Modified Universal Soil Loss Equation functions, into a biogeochemistry model, Denitrification‐Decomposition (DNDC). These two features have been widely utilized to quantify surface runoff and soil erosion in a suite of hydrologic models. We incorporated these features in the DNDC model to allow the biogeochemical and hydrologic processes to exchange data at a daily time step. By including the new features, DNDC gained the additional ability to simulate both horizontal and vertical movements of water and nutrients. The revised DNDC was tested against data sets observed in a small watershed dominated by farmlands in a mountainous area of southwest China. The modeled surface runoff flow, subsurface drainage flow, sediment yield, and N loading were in agreement with observations. To further observe the behaviors of the new model, we conducted a sensitivity test with varied climate, soil, and management conditions. The results indicated that precipitation was the most sensitive factor determining the rate of N loading from the tested site. A Monte Carlo test was conducted to quantify the potential uncertainty derived by variations in four selected input parameters. This study demonstrates that it is feasible and effective to use enhanced biogeochemical models such as DNDC for quantifying N loadings by incorporating basic hydrological features into the model framework

Modeling nitrogen loading in a small watershed in southwest China using a DNDC model with hydrological enhancements

The degradation of water quality has been observed worldwide, and inputs of nitrogen (N), along with other nutrients, play a key role in the process of contamination. The quantification of N loading from non-point sources at a watershed scale has long been a challenge. Process-based models have been developed to address this problem. Because N loading from non-point sources result from interactions between biogeochemical and hydrological processes, a model framework must include both types of processes if it is to be useful. This paper reports the results of a study in which we integrated two fundamental hydrologic features, the SCS (Soil Conservation Service) curve function and the MUSLE (Modified Universal Soil Loss), into a biogeochemical model, the DNDC. The SCS curve equation and the MUSLE are widely used in hydrological models for calculating surface runoff and soil erosion. Equipped with the new added hydrologic features, DNDC was substantially enhanced with the new capacity of simulating both vertical and horizontal movements of water and N at a watershed scale. A long-term experimental watershed in Southwest China was selected to test the new version of the DNDC. The target watershed\u27s 35.1 ha of territory encompass 19.3 ha of croplands, 11.0 ha of forest lands, 1.1 ha of grassplots, and 3.7 ha of residential areas. An input database containing topographic data, meteorological conditions, soil properties, vegetation information, and management applications was established and linked to the enhanced DNDC. Driven by the input database, the DNDC simulated the surface runoff flow, the subsurface leaching flow, the soil erosion, and the N loadings from the target watershed. The modeled water flow, sediment yield, and N loading from the entire watershed were compared with observations from the watershed and yielded encouraging results. The sources of N loading were identified by using the results of the model. In 2008, the modeled runoff-induced loss of total N from the watershed was 904 kg N yr−1, of which approximately 67 % came from the croplands. The enhanced DNDC model also estimated the watershed-scale N losses (1391 kg N yr−1) from the emissions of the N-containing gases (ammonia, nitrous oxide, nitric oxide, and dinitrogen). Ammonia volatilization (1299 kg N yr−1) dominated the gaseous N losses. The study indicated that process-based biogeochemical models such as the DNDC could contribute more effectively to watershed N loading studies if the hydrological components of the models were appropriately enhanced

Characteristics of multiple‐year nitrous oxide emissions from conventional vegetable fields in southeastern China

The annual and interannual characteristics of nitrous oxide (N2O) emissions from conventional vegetable fields are poorly understood. We carried out 4 year measurements of N2O fluxes from a conventional vegetable cultivation area in the Yangtze River delta. Under fertilized conditions subject to farming practices, approximately 86% of the annual total N2O release occurred following fertilization events. The direct emission factors (EFd) of the 12 individual vegetable seasons investigated ranged from 0.06 to 14.20%, with a mean of 3.09% and a coefficient of variation (CV) of 142%. The annual EFd varied from 0.59 to 4.98%, with a mean of 2.88% and an interannual CV of 74%. The mean value is much larger than the latest default value (1.00%) of the Intergovernmental Panel on Climate Change. Occasional application of lagoon‐stored manure slurry coupled with other nitrogen fertilizers, or basal nitrogen addition immediately followed by heavy rainfall, accounted for a substantial portion of the large EFds observed in warm seasons. The large CVs suggest that the emission factors obtained from short‐term observations that poorly represent seasonality and/or interannual variability will inevitably yield large uncertainties in inventory estimation. The results of this study indicate that conventional vegetable fields associated with intensive nitrogen addition, as well as occasional applications of manure slurry, may substantially account for regional N2O emissions. However, this conclusion needs to be further confirmed through studies at multiple field sites. Moreover, further experimental studies are needed to test the mitigation options suggested by this study for N2O emissions from open vegetable fields

Diversity of classic and novel human astrovirus in outpatient children with acute gastroenteritis in Shanghai, China

IntroductionHuman astrovirus (HAstV) is an important pathogen of acute gastroenteritis (AGE) in children. This study was aimed at investigating the diversity and epidemiology of classic and novel HAstV in outpatient children aged 0–16 years old with AGE in Shanghai.MethodsFrom May 2020 to December 2022, a total of 1,482 stool samples were collected from children diagnosed as AGE from the Children’s Hospital of Fudan University. HAstV was identified using pan-astrovirus consensus primers by Reverse transcription PCR.ResultsDuring the study period, 3.3% (49/1,482) of specimens were identified as HAstV, with a detection rate of 2.5% (37/1,482) for classic HAstV and 0.8% (12/1,482) for novel HAstV. Among the 12 novel HAstV strains, 11 (91.7%) belonged to the HAstV-MLB and 1 (8.3%) was HAstV-VA. Genotyping revealed six circulating genotypes. Strain HAstV-1 was predominant in the study population with a detection rate of 1.8% (26/1,482) followed by HAstV-MLB1 (0.7%, 10/1,482) and HAstV-4 (0.6%, 9/1,482). Of note, all the HAstV-4 strains detected in this study were close to one astrovirus strain isolated from Bactrian camels with 99.0-100.0% amino acid sequences identity. In this study, HAstV was detected in all age groups with the highest detection rate of HAstV-positive specimens observed in children older than 73 months (5.7%, 12/209).DiscussionThis study provided useful information and contributed to the molecular epidemiology of both classic and novel HAstV, which were simultaneously characterized and reported for the first time in Shanghai

Nitrous oxide emissions during the non-rice growing seasons of two subtropical rice-based rotation systems in southwest China

Background and aims High nitrous oxide (N2O) emissions may occur during the non-rice growing season of Chinese rice-upland crop rotation systems. However, our understanding of N2O emission during this season is poor due to a scarcity of available field N2O measurements. Methods Using the static manual chamber-GC technique, seasonal N2O emissions during the non-rice growing season were simultaneously measured at two adjacent rice-wheat and rice-rapeseed fields in southwest China for three consecutive annual rotation cycles (May 2005 to May 2008). Results Compared to the control, N fertilizer applications significantly enhanced soil N2O emissions from both wheat and rapeseed systems. Seasonal cumulative N2O fluxes from wheat systems were on average 2.6 kg N ha−1 for the recommended practice (RP [150 kg N ha−1]) and 5.0 kg N ha−1 for the conventional practice (CP [250 kg N ha−1]). Lower N2O emissions were observed from the adjacent rapeseed systems. Average cumulative seasonal N2O fluxes from rapeseed were 1.5 and 2.2 kg N ha−1 for the RP and CP treatments, respectively. The first 3 weeks after N fertilization were the “hot moment” of N2O emissions for both the wheat and rapeseed systems. The lowest yield-scaled N2O fluxes for wheat were obtained at the RP treatment (mean: 0.81 kg N Mg−1) while for rapeseed the CP treatment produced the lowest yield-scaled fluxes (mean: 0.79 kg N Mg−1). On average, the direct N2O emission factors (EFd) for the wheat system (1.76 %) were over two times higher than for the rapeseed system (0.73 %). Conclusions Intercropping of rapeseed tends to result in lower N2O emissions than wheat for rice-upland crop rotation systems of southwest China, indicating that either the N fertilization or the cropping system need to be considered not only for improving the estimate of regional and/or national N2O fluxes but also for proposing the climate-smart agricultural management practice to reduce N2O emissions from agricultural soils

Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

Aims A 3-year field experiment (October 2004–October 2007) was conducted to quantify N2O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China. Methods Static chamber-GC techniques were used to measure soil N2O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha−1 yr−1 or 150 kg Nha−1 per crop); N250 (500 kg N fertilizer ha−1 yr−1 kg or 250 kg Nha−1 per crop). Nitrate (NO3−) leaching losses were measured at nearby sites using free-drained lysimeters. Results The annual N2O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg Nha−1 yr−1corresponding to an N2O emission factor ranging from 0.12%to 1.06%(mean value: 0.61%). The relationship between monthly soil N2O fluxes and NO3- leaching losses can be described by a significant exponential decaying function. Conclusions The N2O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO3−, is an underrated regulating factor of soil N2O fluxes from cropland, especially in the regions where high NO3- leaching losses occur

Nitrous oxide and methane emissions from a subtropical rice–rapeseed rotation system in China: A 3-year field case study

Fertilizer nitrogen (N) application has been shown to impact both methane (CH4) and nitrous oxide (N2O) emissions from rice-based crop systems, yet the responses of CH4 and N2O fluxes to N fertilizer applications in subtropical rice–rapeseed rotation systems are not well documented. A three-year field experiment was conducted to simultaneously measure the fluxes of CH4 and N2O from a subtropical rice–rapeseed rotation system under three N fertilization treatments (control with no N fertilizer addition [CK], optimized N fertilizer management practice in accordance with the recommended N fertilizer application rate of 150 kg N ha−1 season−1 [OP], local farmers common N fertilizer management practice with 250 kg N ha−1 season−1 [CP]) in southwestern China. Results showed great intra- and inter-annual variations in CH4 and N2O emissions along with the temporal variations of environmental conditions, emphasizing the necessity of multi-year measurements to achieve representative estimates. Nitrogen fertilization tended to increase N2O emissions and to inhibit CH4 emissions. The direct N2O emission factors (EFd) for the rice systems (mean: 0.99%) were higher than those for the rapeseed systems (mean: 0.71%). In addition, the rice-growing season dominated annual CH4 emissions (>97%), which on average represented 87% of the annual total global warming potential (GWP) of CH4 and N2O emissions across experimental treatments and years. Linking total GWP of CH4 and N2O emissions with grain yields, the average annual yield-scaled GWP for the control (1467 kg CO2-eq Mg−1 grain) was significantly higher than for the OP (700 kg CO2-eq Mg−1 grain) and CP (682 kg CO2-eq Mg−1 grain) treatments (P < 0.05). Given the comparable area- and yield-scaled GWP between the CP and OP treatments, the OP treatment reduced local farmers’ common N fertilizer application rate by 40% and tended to maintain crop grain yields, however it also reduced N surplus and off-site N losses in the subtropical rice–rapeseed rotation systems of southwestern China

Annual emissions of nitrous oxide and nitric oxide from rice-wheat rotation and vegetable fields: a case study in the Tai-Lake region, China

Background and aims: Knowledge on nitrous oxide (N2O) and nitric oxide (NO) emissions from typical cropping systems in the Tai-Lake region is important for estimating regional inventory and proposing effective N2O and NO mitigation options. This study aimed at a) characterizing the seasonal and annual emissions of both gases from the major cropping systems, and b) determining their direct emission factors (EFds) as the key parameters for inventory compilation. Methods: Measurements of N2O and NO emissions were conducted year-round in the Tai-Lake region using a static opaque chamber method. The measurements involved a typical rice-wheat rotation ecosystem and a vegetable field. The two types of croplands were subjected to both a fertilized treatment and a control treatment without nitrogen addition. In the rice-wheat ecosystem, N2O emissions were measured throughout an entire year-round rotation spanning from June 2003 to June 2004, whereas NO emissions were measured only during the non-rice period. In the vegetable field, both N2O and NO emissions were measured from November 2003 to November 2004. Results: During the investigation period, the average cumulative N2O and NO emissions under the fertilized conditions amounted to 3.80 and 0.80 (during the non-rice period for NO) kg N ha−1, respectively, in the rice-wheat field, and 20.81 and 47.13 kg N ha−1, respectively, in the vegetable field. The average total N2O and NO emissions under the control conditions were 1.39 and 0.29 (during the non-rice period for NO) kg N ha−1, respectively, in the rice−wheat rotation, and 2.98 and 0.80 kg N ha−1, respectively, in the vegetable field. The direct emission factor (EFd, which is defined as the loss rate of applied nitrogen via N2O or NO emissions in the current season or year) of N2O was annually determined to be 0.56 % in the rice-wheat field, while the seasonal EFd of NO was 0.34 % during the non-rice period of the rotation cycle. In the vegetable field, the seasonal EFds of N2O and NO varied from 0.15 % to 14.50 % and 0.80 % to 28.21 %, respectively, among different crop seasons; and the annual EFds were 1.38 % and 3.59 %, respectively. Conclusions: This study suggests that conventional vegetable fields associated with intensive synthetic nitrogen application, as well as addition of manure slurry, may substantially contribute to the regional N2O and NO emissions though they account for a relatively small portion of the farmlands in the Tai-Lake region. However, further studies to be conducted at multiple field sites with conventional vegetable and rice-based fields are needed to test this conclusion

Effect of ammonium-based, non-sulfate fertilizers on CH4 emissions from a paddy field with a typical Chinese water management regime

The effects of ammonium-based, non-sulfate fertilizers, such as urea and/or ammonium phosphate (NH4H2PO4), on methane (CH4) emissions from paddy rice fields deserve attention, as they are being used increasingly for rice cultivation. A four-year field campaign was conducted in the Yangtze River Delta from 2004 to 2007 to assess the effects of different application rates of urea plus NH4H2PO4 on the CH4 emissions from a paddy rice field. The experimental field was under a typical Chinese water regime that follows a flooding-midseason drainage-reflooding-moist irrigation mode. Over the course of four years, the mean cumulative CH4 emissions during the rice seasons were 221, 136 and 112 kg C ha−1 for nitrogen addition rates of 0, 150 and 250 kg N ha−1, respectively. Compared to the treatment without nitrogen amendments, the 150 kg N ha−1 decreased the CH4 emissions by 6–59% (P \u3c 0.01 in one year, but not statistically significant in the others). When the addition rate was further increased to 250 kg N ha−1, the CH4 emissions were significantly reduced by 35–53% (P \u3c 0.01) compared to the no-nitrogen treatment. Thus, an addition rate of 250 kg N ha−1, which has been commonly adopted in the delta region in the past two decades, can be regarded as an effective management measure as regards increasing rice yields while reducing CH4 emissions. Considering that doses of ammonium-based, non-sulfate fertilizers higher than 250 kg N ha−1 currently are, and most likely will continue to be, commonly applied for paddy rice cultivation in the Yangtze River Delta and other parts of China, the inhibitory effects on CH4 emissions from rice production are expected to be pronounced at the regional scale. However, further studies are required to provide more concrete evidence about this issue. Moreover, further research is needed to determine whether N management measures are also effective in view of net greenhouse gas fluxes (including CH4, nitrous oxide, ammonia emissions, nitrate leaching and N loss from denitrification)