Monitoring and APEX Modeling of No-Till and Reduced-Till in Tile-Drained Agricultural Landscapes for Water Quality

Abstract

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. These conservation practices were used to evaluate the APEX (Agricultural Policy/Environmental Extender) model. Data from two tile-drained corn-soybean rotation fields located within the St. Joseph River watershed in northeast Indiana were collected and compared. Observed daily surface and subsurface tile flow, sediment load, and nutrient transport values were described and analyzed using a Wilcoxon signed-rank test. Among the nutrient variables examined, we compared soluble phosphorus (SP), total phosphorus (TP), soluble nitrogen (SN), and soluble nitrogen in tile (SN-tile). The 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 year). However, significantly lower values were only observed for sediment and SN-tile losses in the no-till system. The monitored variables were also used for calibration and validation of the APEX model. APEX calibration/validation evaluation scores were satisfactory for surface runoff for both tillage management simulations (R 2 = 0.87/0.76 and NSE = 0.65/0.76 for no-till, and R 2 = 0.76/0.74 and NSE = 0.74/0.74 for reduced-till, in addition to other statistical analyses). Model performances in simulating sediment load, nutrient variables, and tile flow were relatively lower, yet satisfactory overall. APEX was an efficient tool for simulating most of the variables examined. However, the model presents limitations in simulating tile flow, and consequently nitrogen loss, from tile-drained systems.