Assessing Field-Scale Effects of Controlled Tile Drainage On N Mass Balance From Corn and Soybean Fields In Eastern Ontario, Canada.

Nitrogen budgets help us to better understand N nutrient use efficiency, and ways to optimally mitigate water, air, and soil contamination. Controlled tile drainage is a management practice that regulates the amount of tile drainage water that can leave a field. This flexible practice can increase water table elevations and soil water contents in the field, thus allowing for crops to more readily access water and nutrients during critical crop growth stages especially when droughts occur. From 2005-09, we measured and estimated major N inputs and outputs for conventionally tiled, and controlled tile-drained fields during the growing season (typically April-October). The field conditions were wetter than the normal during 2006 and 2008 and drier than the normal during 2007 and 2009. Crop yields of CTD-managed fields were on average 4% higher than the UTD-managed fields. There was 3% higher plant N uptake in the CTD-managed fields compared to the UTD-managed fields. Tile discharge and associated N loss in the tile discharge from CTD-managed fields were always less than from UTD-managed fields. Compared to the UTD management practice, there was on average a 52% reduction in tile discharge and 47% reduction in tile drain N losses when CTD management practice was adopted. Predicted gaseous N emissions (nitrification + denitrification) from CTD-managed fields were generally higher than those from UTD-managed fields by, on average 42%. The lateral ground water discharge below surface and associated total N losses were generally lower for CTD-managed fields than those for UTD-managed fields, but losses were not great (0.0-4.6 kg N ha^-1). The N loss in vertical deep seepage ranged between 0.0 and 1.9 kg N ha^-1 with higher losses observed for CTD- compared to UTD-managed fields.