|WANG, XIUYING - Blackland Research And Extension Center|
|WILLIAMS, CANDIS - Natural Resources Conservation Service (NRCS, USDA)|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2014
Publication Date: 7/31/2014
Citation: Francesconi, W., Smith, D.R., Heathman, G.C., Wang, X., Williams, C. 2014. Monitoring and APEX modeling of no-till and reduced-till in tile drained agricultural landscapes for water quality. Transactions of the ASABE. 57(3):777-789.
Interpretive Summary: The National Soil Erosion Research Laboratory (NSERL) has been monitoring the St. Joseph River Watershed as part of the Conservation Effects Assessment Project (CEAP). Water quality data for two agricultural field sites managed under different conservation tillage practices (No-till and Reduced-till) was described and compared statistically. The results showed that No-till practices significantly reduced the amount of sediments lost in runoff and soluble nitrogen in tile flow. The monitored data was also use to calibrate and validate the Agricultural Policy/ Environmental eXtender (APEX) model. The modeling results indicate that APEX was able to predict in a satisfactory manner the sediment and nutrients transport values at the outlet. The present study confirms the effectiveness of No-till practices at reducing erosion and water pollution in surface water bodies, supports the application of the APEX model as a tool for simulating conservation practices in the absence of experimental data, and demonstrates the need for monitoring and modeling data required by CEAP.
Technical Abstract: The evaluation of agricultural practices through monitoring and modeling is necessary for the development of more effective conservation programs and policies. No-till and reduced-till are both agricultural conservation practices widely promoted for their proven ability to conserve water and reduce soil erosion. The Agricultural Policy/Environmental eXtender (APEX) Model was used to simulate these conservation practices in order to evaluate the model’s performance in predicting sediment and nutrient transport in tile drained agricultural fields. Data from two corn-soybean rotation sites located within the St. Joseph River Watershed was collected and compared. The observed daily surface and subsurface tile flow, sediment load and nutrient variables (soluble phosphorus (SP), total phosphorus (TP), soluble nitrogen (SN) and soluble nitrogen in tile (SN-Tile)), were described and analyzed using a Wilcoxon signed-rank test. The monitored results agree with previous findings identifying lower sediment and nutrient transport values in No-till compared to reduced-till (except for SP during the corn planting year). Significantly lower values however, were only observed for sediment and SN-Tile losses at the No-till system. The monitored variables were also used for the calibration/validation of the APEX model. APEX calibration/validation evaluation scores were good for surface runoff for both tillage management simulations (R2= 0.87/0.76 NSE= 0.65/0.76, PBIAS= 9.79/-2.47, RSR=0.50/0.56, and R2= 0.76/0.74 NSE= 0.74/0.74, PBIAS= -11.53/-45.68, RSR=0.52/0.62 for No-till and reduced-till respectively). Model performance simulating sediment load, nutrient variables and tile flow were lower, yet overall satisfactory. APEX was an efficient tool in simulating most of the variables examined. However, the model presents limitations in simulating tile flow, and consequently nitrogen loss from tile drained systems.