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Simultaneous losses of nitrogen via water and air from agricultural cropping systems

Smith, E. L., Vosman, A., Rodd, V., Kellman, L., Fuller, K., Nyiraneza, J., McDonald, B., Henry, R. Nov. 4-7, 2018. Simultaneous losses of nitrogen via water and air from agricultural cropping systems. American Society of Agronomy/Crop Science Society of America/Soil Science Society of America (ASA-CSSA-SSSA) International Annual Meeting: Enhancing Productivity in a Changing Climate. Baltimore, Maryland.

Abstract

Nitrogen losses via water and air from agricultural production systems can at times be significant if not managed properly and may result in eutrophication and stratospheric ozone depletion. Two agriculture field studies were designed in Nova Scotia and Prince Edward Island, Canada to quantify simultaneous nitrogen (N) losses via air (nitrous oxide: N2O) and water (nitrate-N: NO3--N ) based on various land management practices. Few studies have simultaneously measured these N losses from tile drained fields using various drainage types and plowing practices. Study 1 investigated losses from conventional (DD), shallow (SD) and controlled drainage (CD) systems under corn and alfalfa production. Study 2 investigated how plow timing impacts N losses when conducted in spring (S), early fall (EF) and late fall (LF) under a 3 yr potato rotation. In both studies, water samples were obtained from tile drains during flow periods and gas samples were obtained following field activities, as well as throughout the monitoring period using static chambers. In study 1, CD was found to reduce loadings by 42.3-58.2% in 2 yrs of the study compared to DD. Whereas, SD presented a reduced NO3--N loading of 54.9-73.1% in all yrs of the study compared to the DD. Despite raising the water table, CD was not found to increase gaseous N2O emissions compared to SD and DD in all 3 yrs of the study, resulting in no trade-off effect. In study 2, NO3--N loads over the 3 yrs were found to be reduced at 16.4 and 12.6 kg ha-1 for spring (S), and late fall (LF) respectively, when compared to the early fall (EF) plow at 21.5 kg ha-1. This suggests EF should be avoided to reduce NO3--N loading under similar climatic, soil and cropping conditions. Nitrous oxide losses over the study period were low and variable in magnitude, with only 1 yr producing a significant loss under S tillage (included incorporation of the legume crop). Minimal losses of N2O (approx. 1%: applied N) under both studies emphasized that higher importance should be placed on NO3--N losses under these field conditions, rather than gaseous losses. Results are promising to Atlantic Canadian farmers interested in reducing N losses to further improve management practices. Future studies are needed to further explore other N loss pathways such as dissolved N2O in drainage water, ammonium and dinitrogen gases to fully support CD as a climate adaptation option in the Atlantic region.

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