Long-term results of management practices aimed at reducing nitrous oxide emissions from agricultural fields

Agriculture contributes approximately 70% of Canada’s nitrous oxide (N2O) emissions. Nitrous oxide is a potent greenhouse gas, having a global warming potential 310 times greater than that of carbon dioxide. A large part of the agricultural N2O is emitted from soils, through the processes of nitrification and denitrification. There are two episodes that account for the bulk of the annual nitrous oxide emissions:

(i) Emissions occurring shortly after fertilizer application. (ii) Emissions occurring at the spring thaw.

Due to this, the production and emission of N2O is a very complex process since environmental factors, such as soil moisture and other soil characteristics, can change the annual amount of N2O emitted just by affecting these two episodes. The purpose of this study is to evaluate the management practices and factors that govern the emissions of nitrous oxide from agricultural fields.

A study was initiated in 2000 to analyze N2O emissions from two different management systems applied to a corn-soybean-wheat rotation. One management system, the “Conventional” treatment, consisted of applying the standard amount of inorganic N-based fertilizer (150 kg N/ha), tilling the fields and using no cover crop. The other management system, the “Best Management” treatment, consisted of applying the amount of fertilizer determined by a soil nitrogen test, no-tilling the fields and using cover crops when possible. The flux-gradient method was used to measure the N2O fluxes and concentrations of N2O were quantified using a Tunable Diode Laser Trace Gas Analyzer (TDLTGA).

Data obtained from 2000 - 2002 found that the Best Management treatment reduced the annual amount of nitrous oxide emitted by an average of 40%. It was also found that in 2000, when corn was planted, the Best Management treatment reduced the amount of nitrous oxide emitted by approximately 40%. In 2003, corn was planted again with the same treatments as 2000. This setup presents a unique opportunity to study the effect that environmental factors can have on nitrous oxide emissions. While this type of inter-annual study could be done on data from previous years (ie. data from 2000 and 2001), it would be difficult since both the crops and management practices would differ. Thus, to achieve the purpose of this study the variability in N2O emissions caused by the Best Management treatment will be determined, given that environmental conditions can strongly affect N2O emissions. As well, any variations found will be related to environmental variables.