Emissions of Nitrous Oxide and Carbon Dioxide in Maize Under Production Systems of Different Intensification.

Agriculture is a major contributor to greenhouse gas emissions (GHG), which would be responsible for an estimated 14% of global anthropogenic emissions (IPCC, 2007). Carbon dioxide (CO₂) and nitrous oxide (N₂O) stand among the main GHGs associated to the agricultural sector. The objective of the study was to evaluate the effect of production systems with contrasting degrees of intensification on soil and crop management on the magnitude of CO₂ and N₂O fluxes during the growth of maize. The study was conducted at EEA INTA Balcarce-FCA/UNMdP (Balcarce, Argentina) (37 ° 45 'S, 58 º 18' W), in a long-term experiment under wheat/double cropped soybean-maize started in 2009. Treatments were 1) current management of the area average farmer (FP) where nitrogen (N) fertilization is applied at a fixed rate at planting, and 2) sustainable intensified management (SI) which includes higher plant population, reduced row distance, and N fertilization nitrogen according to soil analysis at two stages (planting and V6). The CO₂ and N₂O fluxes were measured during the 2011/12 using static cameras similar to those designed by Parkin et al. (2003).

CO₂ emissions varied between 35.8 and 227.5 mg CO₂ m^-2 h^-1, with significant differences between dates (p<0.05). The CO₂ flows increased from mid-spring to early summer, in conjunction with plant biomass increase, and then decline into the fall. A CO₂ peak (54 kg ha^-1 day^-1) was observed days at anthesis, in association with high soil temperatures (23.7^oC) but with low moisture content, 30% water-filled pore space. Trough physiological maturity, the average CO₂ flow was of 51.6 mg m^-2 h^-1; however, it increases to 113.2 mg CO₂ m^-2 h^-1 in April, because of an increase in soil temperature.

In general, N₂O emissions were low with maximum emissions ranging from 18.9 to 20.8 mg N₂O m^-2 h^-1 in November and December, representing a loss of 4.5 and 4.9 g N₂O ha^-1 day^- 1. 0.05) entre los muestreos de marzo y abril, y en general con">In the final stages of crop growth, N₂O flow was low, between 2.9 and 3.0 ug N₂O m^-2 h^-1, without significant differences between samplings in March and April, and in general those made in February (p> 0.05). These results could be due to the low moisture content which did not exceed 50% water-filled pore space. In most months, rainfalls were below the historical record, and the soil surface remained below field capacity even after a rainfall event. The N₂O emission peaks were observed in late spring and early summer, when rainfalls were more intense and frequent, 151 mm in 11 rainfall events in November. At this time, high nitrate levels also favored increased emissions of N₂O. Also, N₂O peaks were recorded in February as rainfalls totaled 105 mm, and temperatures were high, between 23^oC and 27^oC. Since soil moisture content was mostly below or close to the field capacity, with water-filled pore space between 13% and 51%, it is likely that the main contribution to the production of N₂O has been via nitrification.
0.05) emisiones acumuladas de CO2 y N2O durante 146 días que el sistema AP.">The SI treatment recorded similar (p> 0.05) cumulative emissions of CO₂ and N₂O during 146 days to the FP treatment. The cumulative CO₂ emission was of 2780 and 2596 kg CO₂ ha^-1 under SI and FP, respectively, and cumulative N₂O emission was of 273 g N₂O ha^-1 and 227 g N₂O ha^-1 for SI and FP, respectively. The lack of measurements of N₂O immediately after the application of N, especially for FP, may have led to the underestimation of N₂O losses. It is necessary to extend this type of research in the region, to contribute to the development of agronomic practices aimed at mitigating the effects of GHGs on the environment.

References
Parkin, T., A. Mosier, J. Smith, R. Venterea, J. Johnson, D. Reicosky, G. Doyle, G. McCarty, and J. Baker. 2003. Chamber-based trace gas flux measurement protocol. USDA-ARS GRACEnet. Available at http://www.usmarc.usda.gov/SP2UserFiles/person/31831/2003GRACEnetTraceGasProtocol.pdf, verified 10/5/13.