Feng Cui

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 aimsKnowledge 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.MethodsMeasurements 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.ResultsDuring 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) kgxa0Nu2009ha−1, respectively, in the rice-wheat field, and 20.81 and 47.13xa0kgxa0N 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) kgxa0Nu2009ha−1, respectively, in the rice−wheat rotation, and 2.98 and 0.80xa0kgxa0N 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 0.56xa0% in the rice-wheat field, while the seasonal EFd of NO was 0.34xa0% during the non-rice period of the rotation cycle. In the vegetable field, the seasonal EFds of N2O and NO varied from 0.15xa0% to 14.50xa0% and 0.80xa0% to 28.21xa0%, respectively, among different crop seasons; and the annual EFds were 1.38xa0% and 3.59xa0%, respectively.ConclusionsThis 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.

Influences of free-air CO2 enrichment (FACE), nitrogen fertilizer and crop residue incorporation on CH4 emissions from irrigated rice fields

To investigate the response of methane (CH4) emissions to an elevated atmospheric carbon dioxide (CO2) concentration (200xa0±xa040xa0μmolxa0mol−1 higher than the ambient atmosphere), we performed a 4-year multi-factorial experiment at a subtropical rice paddy that contained sandy loam soil in the Yangtze River Delta from 2004 to 2007 using free-air CO2 enrichment (FACE) technology. Our results revealed that the elevated atmospheric CO2 increased the seasonal cumulative CH4 emissions by 15xa0% on average during the 4-year period. The increase was insignificant and much weaker than the previous studies, which might be primarily attributed to the absence of a significant difference in the rice biomass between the two CO2 levels in half of the field treatments. Crop residue incorporation hindered the stimulatory effects induced by the elevated CO2, which were 37, 14 and 6xa0% for the fields that were incorporated with none, half or all of the wheat straws that were harvested in the preceding winter wheat season, respectively. Nitrogen fertilizers application also hindered the stimulatory effects of the elevated CO2 on the CH4 emissions. The CO2 stimulatory effect was 39xa0% for the field without nitrogen fertilizers, and reduced to 17, 7 and 5xa0% for the field with nitrogen fertilization of 125, 250 and 350xa0kgxa0Nxa0ha−1, respectively. The regulation of nitrogen fertilizers on the CO2 effects in this experiment does not well agree with the previous studies, which might because the soil type was different from those of the previous studies. Thus, further studies are necessary to evaluate the role of soil properties in regulating the effects of elevated atmospheric CO2 on CH4 emissions from managed and natural wetlands. There were no significant interactions between the atmospheric CO2 and the incorporations of nitrogen fertilizer and crop residue. Appropriate experiments are necessary for better understanding of the interact influences of the elevated CO2 and farm managements.

Nitrous oxide emissions from black soils under a continuous soybean cropping system in northeast China

A large number of natural wetlands in northeast China have been reclaimed as farmland in the last few decades, and soybean is the main rain-fed crop here. For the depth understanding of nitrous oxide (N2O) emission from reclaimed soybean fields, using static opaque chamber method, we conducted a four-year N2O flux measurement at two adjacent soybean fields cultivated after wetland drainage in 1987 and 1993, respectively, in the Sanjiang Plain of northeast China Using static opaque chamber method,. Both sites had two treatments including soybean cropped and bare soils (i.e., SF87, BS87, SF93 and BS93). The results showed that soil N2O emission from all of the plots was severely inhibited by the low temperature in winter (November to March), while a N2O emission pulse occurred during the spring thaw (April and May). Temporal variation of the N2O fluxes during the growing season varied over all the four years but was mainly affected by soil water-filled pore space (WFPS). Intense rainfall events increased the intensity and duration of N2O pulses during the growing season, and most high fluxes were occurred at WFPS > 45%. The mean annual N2O emission from all treatments over four years was 4.8 ± 1.2 kg N ha-1 (ranges: 1.9-19.8), and one third of the emission originated from the spring-thaw. In addition, soybean growth did not increase N2O emissions during the growing season, which support the cancellation of N2O emission calculations from nitrogen fixed by legumes in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.