Effects of tillage and application rate on atrazine transport to subsurface drainage: Evaluation of RZWQM using a six-year field study

Authors: Malone, Robert - Rob; NOLAN, BERNARD - Us Geological Survey (USGS); Ma, Liwang; KANWAR, RAMESH - Iowa State University; PETERSON, CARL - Iowa State University; Heilman, Philip - Phil

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2013
Publication Date: 10/30/2013
Publication URL: http://handle.nal.usda.gov/10113/59436
Citation: Malone, R.W., Nolan, B.T., Ma, L., Kanwar, R., Peterson, C., Heilman, P. 2013. Tillage and application rate affects atrazine transport to subsurface drainage with macropore flow: Evaluation of RZWQM using a long-term field study. Agricultural Water Management. 132:10-22.

Interpretive Summary: Well-tested agricultural system models can improve our understanding of the water quality effects of management practices under different conditions. The Root Zone Water Quality Model (RZWQM) has been tested under a variety of conditions. However, the current model’s ability to simulate pesticide transport to subsurface drain flow under different tillage and application rates is not clear. Our results show that RZWQM accurately simulates pesticide transport in subsurface drainage under different tillage and application rates compared to field data. The field and model results show that pesticide transport was greater in the no-till soil, partly because of flow through worm and root channels. The results suggest that 1) RZWQM is a promising tool to study pesticide transport to subsurface drain flow under different tillage and application rates, 2) pesticide transport in drain flow can be greater with no-till compared to tilled soil, and 3) pesticide transport in drain flow is driven by features of water movement through worm and root channels during large storms. This research will help model developers, model users, and agricultural scientists more clearly understand pesticide transport in subsurface drainage under different tillage and application rates, which will help in the design of more effective management to reduce pesticide transport from tile drained agriculture to streams and rivers.

Technical Abstract: Well-tested agricultural system models can improve our understanding of the water quality effects of management practices under different conditions. The Root Zone Water Quality Model (RZWQM) has been tested under a variety of conditions. However, the current model’s ability to simulate pesticide transport to subsurface drain flow over a long-term period under different tillage and application rates is not clear. Therefore, we calibrated and tested RZWQM using six years of data from Nashua, Iowa, where atrazine was spring applied at 2.8 kg/ha (1990-1992) and 0.6 kg/ha (1993-1995) to two plots with different tillage (till and no-till). Observed and simulated average annual flow weighted atrazine concentration (FWAC) in subsurface drain flows from the no-till plot were 3.7 and 3.2 µg/L for the years with high atrazine application rates (1990-1992). The observed and simulated values were lower for the years with low application rates (0.8 and 0.9 µg/L for 1993-1995). Observed and simulated average annual FWAC differences between the no-till and tilled plots were 2.4 and 2.1 µg/L (1990-1992) and 0.1 and 0.1 µg/L (1993-1995). The Nash-Sutcliffe model performance statistic for cumulative atrazine flux to subsurface drain flow was 0.93 for the no-till plot testing years (1993-1995), which is comparable to other recent model tests. The order of selected parameter sensitivity for RZWQM simulation of atrazine concentration in drain flow is: atrazine partition coefficient > number of macropores > atrazine half life in soil > soil saturated hydraulic conductivity. Simulations from 1990-1995 with four different atrazine application rates show that the atrazine concentration in drain flow for the no-till plot was twice that of tilled over the simulation period and that the difference is more pronounced in the early simulation period partly because of the characteristics of macropore flow during large storms. The results suggest that RZWQM is a promising tool to study pesticide transport to subsurface drain flow under different tillage and application rates over several years, the concentrations of atrazine in drain flow can be higher with no-till compared to tilled conditions over a range of atrazine application rates, and atrazine concentrations in drain flow are sensitive to the macropore flow characteristics of different tillage and storms.