Effects of subsurface drain depth on nitrogen losses from drained lands

A simulation study was conducted to determine effects of drain depth on nitrogen (N) loss in drainage water Simulations were conducted for drain depths of 0.75, 1.0, 1.25, and 1.5 m for a Portsmouth sandy loam at Plymouth, North Carolina. A wide range of drain spacing was considered for each depth. Corn yields were predicted and an economic analysis was conducted to determine the drain spacing giving maximum predicted profit for each depth. Results showed that nitrogen losses from subsurface drains can be reduced by placing the drains at shallow depths. In order to satisfy agricultural production requirements, shallow drains must be placed closer together than deeper drains. While predicted agricultural profits for the shallow drains are reduced somewhat compared to the deeper drains, overall profits are substantially increased when the cost of removing N from drainage water is considered.