Nitrogen Loss From Field-Scale Managed and Unmanaged Artificial Subsurface Drainage Systems.

Nitrogen (N) loss from agricultural land means economic loss for producers and may also contribute to water quality impairments. Research was initiated to investigate controlled drainage (CD) as a possible strategy to minimize N loss through artificial subsurface drainage systems to surface water. Controlled drainage, as opposed to conventional free drainage (FD), creates an opportunity to manage drainage systems according to seasonal needs. The objective of this research was to quantify the effectiveness of CD to reduce N loads in Minnesota, USA. A field study was conducted from 2006-2010 on an artificially drained Havelock clay loam soil (mesic Cumulic Endoaquolls). The field site consisted of two independently drained management zones, 15 and 22 ha, respectively. Each zone was outleted into a water table management structure equipped with a stilling well to measure drain outflow volume and P yield and flow weighted mean N concentration (FWMNC). A combination of grab and storm activated discrete samples were collected from each management zone. Samples were analyzed for total nitrogen (TN), nitrate-N (NO3-N) and ammonium (NH4-N). The experimental approach consisted of an unreplicated, paired-design experiment. The experimental approach consisted of an unreplicated, paired-design experiment. Treatment effects were evaluated between the paired sites using ANOVA after fitting a beta distribution on the daily ratio between treatments of interest, e.g. CD/FD for TN yield. Statistical analysis showed CD effectively reduced drainage water outflow and annual TN, NO3-N and NH4-N yields compared to a FD system. Results from this experiment demonstrated that CD was an effective method for reducing N losses from subsurface drainage in relatively flat landscapes favorable to its installation.