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Title:   Author  item
                                            FANG, Q - Qingdao Agricultural Universityitem
                                            Malone, Robert

                                                         - *Rob*item
                                            Ma, Liwangitem
                                            Jaynes, Danitem
                                            Thorp, Kellyitem
                                            Green, Timothyitem
                                            Ahuja, Lajpat
  Submitted to: Agricultural Water Management
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/7/2011
                                    Publication  Date: 1/3/2012
                                    Citation: Fang, Q.X., Malone, R.W., Ma, L., Jaynes, D.B., Thorp, K.R., Green, T.R., Ahuja, L.R. 2012. Modeling the effects of controlled drainage, N rate and weather on nitrate loss to subsurface drainage. Agricultural Water Management. 103:150-161.Interpretive Summary: Controlled subsurface drainage can reduce nitrate loss to tile flow, but the effects may vary with different nitrogen (N) application rates and weather conditions. Interactions between these factors can be understood better via combinations of field experiments and modeling. Therefore, the Root Zone Water Quality Model (RZWQM2) was tested for its response to controlled drainage (CD) management and the tested model was used to investigate the long term effects of controlled drainage. Changing from free drainage (FD) to CD reduced the annual N loss in tile flow by 22% and 32% based on measured and RZWQM2 simulated results, respectively. The model over-predicted the CD effect, possibly because of the slope of the field, which reduces the effect of CD but is not simulated by the model. Long-term RZWQM2 simulations (1996-2008) suggest that N loss can be reduced by about 40% in both FD and CD by decreasing N rate from 245 to 140 N ha-1 with little effect on corn yield. A further reduction in N loss of 39% (9 kg N ha-1) was simulated by implementing CD at the reduced N rate, and the reduced N loss to tile flow was mainly associated with increased N loss to seepage and crop N uptake. The CD effects on N loss were magnified with increased rainfall, but showed only a slight decrease with increased N rates. The results indicate that RZWQM2 accurately responds to CD compared to field measurements, and CD management in combination with reduced N application rates can substantially reduce N loss to the environment with little negative effect on corn yield. This research will help model developers, model users, and agricultural scientists more clearly understand the benefits, limitations, and effects of controlled drainage, and more effectively design management that reduce N loss from tile drained agriculture to streams and rivers.
                                Technical Abstract: Controlled subsurface drainage can reduce nitrate loss to tile flow, but the effects may vary with different N application rates and weather conditions. Interactions between these factors can be understood better via combinations of field experiments and modeling. Using an automated parameter estimation method (PEST), the Root Zone Water Quality Model (RZWQM2) was calibrated with measured monthly tile flow, N loss and flow weighted nitrate-N concentration (FWNC) from 2006 to 2008 in a corn and soybean rotation system with free drainage (FD) management. Similar data from 2006 to 2008 with controlled drainage (CD) management were used to evaluate the model. Changing from FD to CD reduced the annual N loss in tile flow by 22% and 32% based on measured and RZWQM2 simulated results, respectively. The model over-predicted the CD effect, possibly because of the slope of the field, which reduces the effect of CD but is not simulated by the model. Long-term RZWQM2 simulations (1996-2008) suggest that N loss can be reduced by about 40% in both FD and CD by decreasing N rate from 245 to 140 N ha-1 with little effect on corn yield. A further reduction in N loss of 39% (9 kg N ha-1) was simulated by implementing CD at the reduced N rate, and the reduced N loss to tile flow was mainly associated with increased N loss to seepage and crop N uptake. The CD effects on N loss were magnified with increased rainfall, but showed only a slight decrease with increased N rates. The results indicate that RZWQM2 accurately responds to CD compared to field measurements, and CD management in combination with reduced N application rates can substantially reduce N loss to the environment with little negative effect on corn yield.


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