Location: Agroecosystems Management ResearchTitle: Effects of subsurface drainage systems on water and nitrogen footprints simulated with RZWQM2
|CRAFT, KRISTINA - Iowa State University|
|HELMERS, MATT - Iowa State University|
|Malone, Robert - Rob|
|PEDERSON, CARL - Iowa State University|
|SCHOTT, LINDA - Iowa State University|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2017
Publication Date: 1/1/2018
Publication URL: http://handle.nal.usda.gov/10113/6472256
Citation: Craft, K., Helmers, M.J., Malone, R.W., Pederson, C.H., Schott, L.R. 2018. Effects of subsurface drainage systems on water and nitrogen footprints simulated with RZWQM2. Transactions of the ASABE. 61(1):245-261. https://doi.org/10.13031/trans.12300.
Interpretive Summary: Developing conservation systems in the Midwest to reduce nitrogen (N) transport to the Northern Gulf of Mexico Hypoxic Zone requires understanding the long term performance of these systems. A cost effective and efficient way to do this is to use field tested computer models. Model testing against Midwest field data for simulation of controlled drainage (CD) and shallow drainage (SD) is limited. Controlled drainage (CD) has an outlet control structure to limit drainage when it is unnecessary for improved production, and shallow drainage (SD) has drain lines installed closer to the ground surface to maintain a higher water table. We tested the Root Zone Water Quality Model (RZWQM) using nine years (2007 to 2015) of field data from Southeast Iowa for CD, SD, undrained systems (ND), and conventionally drained systems (DD), and simulated the long-term (1971-2015) impacts. RZWQM accurately simulated N loss in subsurface drainage and the simulations agreed with field data that CD and SD substantially reduced N loss to drainage. As indicated in the field data, the SD nitrogen concentration was predicted to be greater than DD and CD, likely due to a reduced time of travel to shallower drains. The long term simulations show that CD and SD reduced annual N lost via tile drainage by 26% and 40%, respectively. For the purpose of addressing hypoxia in the Gulf of Mexico, spring N loading to drains under CD was found to be less effective than SD and in many years CD exported more N in the spring than DD. Spring N-loading, April through June, was indicated by the EPA Science Advisory Board to have the greatest impact on hypoxia in the Northern Gulf of Mexico. Therefore, improvement of CD systems within the months of April-June to reduce N loss in drainage across the upper Midwest landscape may be required. Limited research in the upper Midwest has addressed spring N-loading under controlled drainage systems (CD). This research will help model developers, model users, and agricultural scientists more clearly understand N transport in subsurface drainage under different management including CD, SD, and ND, which will help in the design of more effective systems to reduce N transport from tile drained agriculture to streams and rivers.
Technical Abstract: When considering the use of drainage water management (DWM) in the Midwest to reduce nutrient contributions to the Northern Gulf of Mexico Hypoxic Zone, it is essential to understand the long-term performance of these systems. Few studies have evaluated long-term impacts of DWM and the simulation of controlled drainage (CD) with the Root Zone Water Quality Model (RZWQM) is limited while shallow drainage (SD) has not been examined. Using nine years (2007-2015) of field data from Southeast Iowa, we calibrated RZWQM with conventional drainage (DD), tested for controlled drainage (CD), shallow drainage (SD) and undrained (ND) systems and simulated long-term (1971-2015) impacts. RZWQM performed well in the simulation of CD, SD and ND, based on model performance criteria. Simulated average annual N-load from DD, CD and SD was 25, 17 and 18 kg-N ha-1 yr-1, respectfully, while the related observed values were 32, 16 and 17 kg-N ha-1 yr-1. The simulated nine-year average percent-reduction in NO3-N load for CD (31%) and SD (28%), compared to DD, was underestimated compared to measured values for CD (48%) and SD (44%), due to a slight under-prediction in drainage and N-load in the DD system. As was found in the field, the SD system flow-weighted annual nitrogen (N) concentration (FWANC) (mg L-1) prediction was significantly higher than DD and CD, likely due to a reduced time of travel to shallower drains. Yield loss due to a shallower water table in CD, SD and ND, compared to DD, was simulated as a 3% yield loss for all three systems, while field measurements were 5%, 4% and 8% yield loss, respectfully. The soybean crop model was unable to simulate this yield loss, indicating a need for excess moisture stress development. Long-term, CD reduced annual tile drainage by 18% compared to DD, while SD reduced drainage by 48%; associated NO3-N lost via tile drainage was reduced by 26% with CD and by 40% with SD. The annual percent reduction in NO3-N lost via tile drainage ranged from 28% in the driest years to 22% in the wettest years for CD and from 56% in the driest years to 35% in the wettest years for SD. Considering spring NO3-N loading for the purpose of addressing hypoxia in the Gulf of Mexico, long-term simulations of CD suggest it is less effective at limiting nutrient contributions than SD and in many years CD exported more NO3-N in the spring than DD.