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item MA, Q
item HOOK, J
item Wauchope, Robert - Don
item Sumner, Harold
item Johnson, Alva
item DAVIS, J
item GASCHO, G
item Truman, Clinton
item Dowler, Clyde
item Chandler, Laurence - Larry

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2000
Publication Date: 8/1/2000
Citation: MA, Q.L., HOOK, J.E., WAUCHOPE, R.D., SUMNER, H.R., JOHNSON, A.W., DAVIS, J.G., GASCHO, G.J., TRUMAN, C.C., DOWLER, C.C., CHANDLER, L.D. Surface transport of atrazine under conventional tillage corn: observations versus GLEAMS, Opus, PRZM2B and PRZM3 model simulations. Soil Sciu. Soc. Amer. J. 64:2070-2070. 2000.

Interpretive Summary: GLEAMS and PRZM are well-known computer models used to predict pollution of groundwater and surface water by agricultural chemicals and sediment. These models calculate the losses of pesticides, fertilizers and sediment from fields when data describing weather, soil properties and agricultural operations are fed in. Regulators and others worldwide concerned with agricultural pollution are increasingly relying on these models to answer "what if" questions regarding the potential pollution of some agricultural practice or chemical application. But how good are these models? This is not a simple question to answer, because the data sets fed in are complicated, output is complicated, and there are few good field data sets which are complete enough to adequately test these models. This paper describes the use of an exceptionally complete field data set, generated by a large multidisciplinary project at Tifton, GA to test two versions of PRZM, GLEAMS, and a newer model called OPUS. In this paper (one of a series) we examined prediction of atrazine herbicide runoff, a major pollution issue in the U.S. The results are encouraging: the models were able to predict atrazine concentrations in runoff within about a factor of two--considered good accuracy given all the variability that is observed in the system.

Technical Abstract: High intensity storms that often occur shortly after chemical application to cropland have the greatest potential for chemical runoff. We examined how effectively current chemical transport models GLEAMS, Opus, PRZM2B and PRZM3 could predict water runoff and runoff losses of atrazine [6-chloro-N- ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine) under such conditions, ,as compared with observations from a controlled runoff experiment. The experiment was a large-scale rainfall simulation on 14.6 x 42.7 m plots within a corn (Zea mays L.) field on a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) under conventional tillage practices. Atrazine was applied as surface spray immediately after planting and followed by a 50-mm, 2 h simulated rainfall 24 h later. A similar pre-application rainfall and four subsequent rainfalls during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly tilled soil or under full canopy cover; more runoff occurred when nearly bare soil had crusted. Total seasonal atrazine runoff averaged 2.7% of that applied, with the first post-treatment event runoff averaging 89% of the total. GLEAMS, Opus, PRZM2B and PRZM3 adequately (using a factor-of-2 criterion) simulated water runoff amounts, with normalized root mean square errors of 29%, 29%, 31% and 31%, respectively. GLEAMS and PRZM3 predicted atrazine concentrations within a factor of two of observed concentrations. PRZM2B overpredicted atrazine concentrations. Opus adequately simulated atrazine concentrations in runoff when it was run with an equilibrium adsorption model but significantly underestimated atrazine concentrations when it was