Measuring the Effects of Water Table Management On Soil Greenhouse Gas Emissions From Corn and Soybean Fields In Eastern Canada.

Controlled tile drainage (CTD) is a management practice that regulates the amount of tile drainage water that can leave a field thus allowing for crops to more readily access water and nutrients during critical crop growth stages. As a result soils are generally wetter under CTD which may influence GHG emissions. The objective of this study was to compare field emissions of soil CH₄, N₂O, and CO₂ for fields under conventional (UTD) and controlled tile drainage (CTD) for corn/soybean cropping system in eastern Ontario, Canada. From 2005-09, soil GHG measurements were made from two field pairs with fields within each pair being of comparable size, soil types, and agronomic-cropping practices but differing only in how tile drainage was managed. The field conditions were wetter than the normal during 2006 and 2008 and drier than the normal during 2007 and 2009. There was no statistical difference (p>0.05) in log-transformed soil CH₄ emissions between CTD and UTD for all years and all field pairs examined. The median CH₄ emissions for the yearly monitoring periods ranged between 0.000 and 0.001 kg ha^-1 day^-1. Median yearly study season soil CO₂ emissions ranged between 20 (CTD, corn, 2007) and 39 (CTD, soybeans, 2006) kg ha^-1 day^-1. Yearly log-transformed soil CO₂ emissions differed statistically (p≤0.05) among the tile management practices during 2006 and 2007 (CTD>UTD emissions). The most important independent criteria delineating CO₂ emission was soil temperature (positively) and N fertilizer rates (negatively). The yearly study season median soil N₂O emissions ranged from 0.003 (UTD, corn, 2008) to 0.028 (CTD, corn, 2006) kg ha^-1 day^-1. For each year, the study season log-transformed soil N₂O emissions did not differ statistically among CTD and UTD fields. N₂O was most strongly linked (positively) to both soil NO₃^- concentrations and N fertilizer application rate and not the physical factors (e.g., soil-water content, water table depth) deemed to be most directly influenced by CTD practices.