Fluxes of nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) were followed at winter-grazed (WG) and ungrazed steppe (UG99) in Inner Mongolia during the winter-spring transition of 2006. Mean fluxes during the period March 12-May 11 were 8.2±0.5 (UG99) and 1.5±0.2 μg N 2 O-N m −2 h −1 (WG) for N 2 O, 7.2±0.2 (UG99) and 3.0± 0.1 mg CO 2 -C m −2 h −1 (WG) for CO 2 and −42.5±0.9 (UG99) and −14.1±0.3 μg CH 4 -C m −2 h −1 (WG) for CH 4 . Our data show that N 2 O emissions from semiarid steppe are strongly affected by freeze-thawing. N 2 O emissions reached values of up to 75 μg N 2 O-N m −2 h −1 at the UG99 site, but were considerably lower at the WG site. The observed differences in N 2 O, CH 4 and CO 2 fluxes between the ungrazed and grazed sites were ascribed to the reduced plant biomass at the grazed site, and-most important-to a reduction in soil moisture, due to reduced snow capturing during winter. Thus, winter-grazing significantly reduced N 2 O emission but on the other hand also reduced the uptake of atmospheric CH 4 . To finally evaluate which of the both effects is most important for the non-CO 2 greenhouse gas balance measurements covering an entire year are needed.
Abstract.Model and field studies generally posit that when the application rates of nitrogen fertilizer exceed crop needs, nitrous oxide (N 2 O) emissions will increase nonlinearly, though linear responses are also extensively reported by field studies. We conducted year-round measurements of crop yield, N 2 O and methane (CH 4 ) fluxes for treatments of six fertilizer nitrogen levels (0, 135, 270, 430, 650 and 850 kg N ha −1 yr −1 in the form of urea) in a typical irrigated wheat-maize rotation field in northern China. Linear models characterized the responses of cumulative N 2 O emissions to fertilizer rates well; therefore, the calculated N 2 O emission factors of 0.17 ± 0.02 %, 0.73 ± 0.05 % and 0.49 ± 0.02 % for the wheat season, maize season and annual scale, respectively, were appropriate for the different fertilizer rates. The cumulative CH 4 uptake by the soil tended to be enhanced at higher fertilizer rates (≥350 kg N ha −1 ) in the maize season whereas no effect was observed for the wheat season. When the annual fertilizer rates increased from 270 to 430, from 270 to 650, and from 270 to 850 kg N ha −1 yr −1 , the crop yields increased only 3 ∼ 15 % (0.5 ∼ 2.1 t ha −1 yr −1 ), but cumulative N 2 O emissions increased 35 ∼ 115 % (0.9 ∼ 3.0 kg N ha −1 yr −1 ). We recommend 270 kg N ha −1 yr −1 as the locally optimum fertilizer rate. Considering the nitrogen inputs by fertilization (270 kg N ha −1 yr −1 ), irrigation (4.3 ± 0.2 kg N ha −1 yr −1 ) and deposition (wet deposition: 30.5 ± 1.5 kg N ha −1 yr −1 ), the slightly positive soil nitrogen balance could maintain the current crop yield (∼13.8 t ha −1 yr −1 ) and reduce the present high N 2 O emissions (>3.51 kg N ha −1 yr −1 ) of the local farmers' practice (fertilizer rate > 430 kg N ha −1 yr −1 ).
The application of nitrification inhibitors together with ammonium-based fertilizers is proposed as a potent method to decrease nitrous oxide (N2O) emission while promoting crop yield and nitrogen use efficiency in fertilized agricultural fields. To evaluate the effects of nitrification inhibitors, we conducted year-round measurements of N2O fluxes, yield, aboveground biomass, plant carbon and nitrogen contents, soil inorganic nitrogen and dissolved organic carbon contents and the main environmental factors for urea (U), urea + dicyandiamide (DCD) and urea + 3,4-dimethylpyrazol phosphate (DMPP) treatments in a wheat–maize rotation field. The cumulative N2O emissions were calculated to be 4.49 ± 0.21, 2.93 ± 0.06 and 2.78 ± 0.16 kg N ha−1 yr−1 for the U, DCD and DMPP treatments, respectively. Therefore, the DCD and DMPP treatments significantly decreased the annual emissions by 35% and 38%, respectively (p < 0.01). The variations of soil temperature, moisture and inorganic nitrogen content regulated the seasonal fluctuation of N2O emissions. When the emissions presented clearly temporal variations, high-frequency measurements or optimized sampling schedule for intermittent measurements would likely provide more accurate estimations of annual cumulative emission and treatment effect. The application of nitrification inhibitors significantly increased the soil inorganic nitrogen content (p < 0.01); shifted the main soil inorganic nitrogen form from nitrate to ammonium; and tended to increase the dissolved organic carbon content, crop yield, aboveground biomass and nitrogen uptake by aboveground plant. The results demonstrate the roles the nitrification inhibitors play in enhancing yield and nitrogen use efficiency and reducing N2O emission from the wheat–maize cropping system
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.