Features Drainage Management Systems
Adaptive design

Nitrate loss through tile drainage systems has been a water quality concern in the Midwest for many years. Reducing concentration from current values to a maximum level of 10 mg
N L-1 has been adopted as a goal in many nutrient reduction plans.

But, as changes in precipitation, temperature, and other climate components have been measured in Iowa, and changing CO2 concentration in the atmosphere is recorded, it’s unclear if these changes affect nitrate concentration in tile drainage. This uncertainty is due to the complicated water and nitrogen dynamics in a drained agricultural system.  

Because drainage experimental plots are relatively large, it is difficult to conduct field experiments at a plot scale under controlled climate variables, such as the Free-Air CO2 Enrichment (FACE) program. Agricultural systems models, equipped with newly updated scientific findings, can be used as a tool to mimic field situations under a changing climate. Therefore, by employing an agricultural system model emphasising water quality – known as the Root Zone Water Quality Model (RZWQM2) – I, along with my colleagues, Zhaozhi Wang, Lulin Xue, Melissa Bukovsky and Matthew J. Helmers, investigated climate change impacts on nitrate leaching and crop yield. Our work, which was published in the March edition of the journal Climatic Change studied a drainage site near Gilmore City, Iowa, as an example. The site is managed by Helmers, my PhD supervisor. RZWQM2 was used because the response of water and nitrogen dynamics, as well as crop growth, to key climate components are taken into account by the model. These include: atmospheric CO2 concentration; air temperature; rainfall amount and intensity; solar radiation; wind speed; and relative humidity.  

A successful calibration and validation of the model is the cornerstone of modeling work. In this study, calibration and validation of RZWQM2 in Iowa’s subsurface drained agricultural fields can be traced back many years. Based on the work of Allah Bakhsh et al. (2001 and 2004) and Kelly Thorp et al. (2007) who have conducted the RZWQM model test under the lead of Ramesh Kanwar, Dan Jaynes, and Robert Malone, I further calibrated and validated the RZWQM2 model in 2011 using five years of observed data at Gilmore City. The model was subsequently tested again in 2012 using 16 years of observed drainage flow and nitrate loss data at the same site. Ranvir Singh et al. (2006) calibrated and validated the DRAINMOD computer simulation model at this site and some verified parameters were adopted by my RZWQM2 simulation. Without those explorations by earlier researchers, this work (which was mainly conducted by Wang, a postdoctoral fellow on my team) would not have been possible. Although climate change is a sensitive topic, we are confident conducting climate change impact research using the RZWQM2 model because of these previous consolidate works.

To predict climate change impacts, we ran the RZWQM2 model under historical observed (1990-2009) and future predicted (2045-2064) climate data and subsequently compared the output of drainage flow, N loss in tile drainage, and crop yield under these two scenarios.  

The future climate data was created by superimposing the predicted monthly change to the observed 20-year historical weather data. The predicted climate change data was provided by Xue and Bukovsky at the National Center for Atmospheric Research in Boulder, Colo. They used six sets of different global and regional climate models to establish their prediction data.

 The projected climate change from 1990-2009 to 2045-2064 suggested more significant changes in air temperature and precipitation than other climate components. Compared to historical weather, mean annual air temperature is projected to increase by 2.2C (3.96F) (that’s 26.9 percent greater than the historical value of 8.1C (46.6F), and mean annual precipitation is projected to increase from a baseline value of 76.9 to 81.3 cm (30.3 to 32 inches) (suggesting an increase of 5.6 percent).   

The simulation showed that, compared to drainage flows under historical climate conditions, the annual drainage flow and annual NO3-N loss are projected to increase by 4.2 cm (1.7 inches) and 11.6 kg (25.6 pounds) N ha-1, respectively. The annual flow-weighted average annual nitrate-N concentration is also projected to increase by 2.0 mg N L-1 under forecasted future climate conditions. The percentages of those increases were 14.5 percent, 33.7 percent, and 16.4 percent, respectively. The yield of soybean increased by 28 percent mostly due to CO2 enrichment but increased temperature showed negligible effect. However, the yield of corn decreased by 15 percent because of fewer days to physiological maturity due to increased temperature and limited benefit of CO2 to corn yield and water conservation under a sub-humid climate.

What does all this mean for drainage contractors? In order to drain more water under future climate conditions, I think that drainage spacing will have to be narrower or the depth of tile installations will have to go deeper. Additionally, I think that under projected future climate conditions the drainage coefficient used to design drainage systems should be slightly higher to accommodate anticipated increases in drainage requirements. In other words, the frequency of flooding affecting drainage systems designed with the current drainage coefficient may increase under the future climate conditions. Moreover, nitrogen loss and its concentration, which is one of the major factors in eutrophication, will probably tend to be higher. Developing a more environment-friendly drainage design would allow contractors to capture a bigger share of the market.    

In terms of future work, my research team at McGill University is now applying this RZWQM2 model in Quebec and Ontario to simulate climate change impact on nitrate loss through tile drainage, through a collaboration with McGill professor Chandra Madramootoo, and Agriculture and Agri-Food Canada scientists Chin S. Tan and Tiequan Zhang. And, since phosphorus is another major concern on tile drained fields amended with manure, we are developing a phosphorus module for the RZWQM2 model through a close collaboration with Lajpat R. Ahuja and Liwang Ma, soil scientists with the United States Department of Agriculture Agricultural Research Service (USDA-ARS). Hopefully we can further evaluate climate change impact on the fate and transport of phosphorus after a P module is linked to RZWQM2. 

Dr. Zhiming Qi is an assistant professor with McGill University’s department of bioresource engineering. He holds a B.S. in irrigation and drainage engineering and an M.S. in soil and water engineering from China Agricultural University in Beijing. He earned his Ph.D. in agricultural engineering and environmental science from Iowa State University.