Modeling the Effect of Precision Agriculture: Pesticide Losses to

Chapter 20

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on November 1, 2016 | http://pubs.acs.org Publication Date: December 15, 2002 | doi: 10.1021/bk-2002-0842.ch020

Modeling the Effect of Precision Agriculture: Pesticide Losses to Surface Waters 1

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D. J. Mulla , P. Gowda , W. C. Koskinen , B. R. Khakural , G. Johnson , and P. C. Robert 3

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Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108 2Agricultural Research Service, U.S. Department of Agriculture, University of Minnesota, St. Paul, MN 55108 Southern Research and Outreach Center, University of Minnesota, Waseca, MN 56093

In this study we evaluated the environmental impacts of spatially variable versus uniform applications of acetochlor. Spatially varying rates of acetochlor ranging from 2.0 to 2.7 kg ha were applied to a 32 ha bare field planted to corn during the spring of 1998. These rates were varied in accordance with measured soil surface organic matter contents, sorption K values, and grassy weed populations. Surface runoff and tile drain leaching losses of acetochlor were measured using automated sampling systems. The Agricultural Drainage and Pesticide Transport ( A D A P T ) model was calibrated to measured water fluxes, and losses of sediment, nitrate, and acetochlor to surface waters. There was good agreement between measured and modeled water fluxes, sediment losses, nitrate losses, and acetochlor losses. Simulated acetochlor losses for the variable rate strategy were 11 - 33% lower than losses for a uniform application of 2.7 kg ha . -1

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© 2003 American Chemical Society

Arthur et al.; Terrestrial Field Dissipation Studies ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

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Introduction Precision agriculture is an approach that allows the rate of pesticide applied to a field to be varied in response to spatial patterns in weed populations, soil organic matter content, and pesticide sorption or dissipation characteristics. It is hypothesized that this approach allows effective weed control, maintains crop productivity (1), reduces the environmental impacts of pesticides (2), and increases farm profitability (3). This hypothesis has not been fully tested. Stafford and Miller (4) developed a method for spraying specific patches of weeds in cereal crops. This method reduced herbicide inputs from 40-60%. Khakural et al. (5) found that variable rate applications of alachlor in small steep hillslope plots resulted in runoff losses that were as much as 24% smaller than losses from uniform applications. The objective of this research was to evaluate long-term average edge-of-field losses of acetochlor on a commercial corn field using variable rate applications (precision agriculture) of acetochlor. These losses were compared with simulated losses of acetochlor from the same field receiving a uniform application rate of acetochlor.

Methods A commercial corn field in Blue Earth county of southern Minnesota was selected for variable rate applications of acetochlor. Applications varied from 2.0 to 2.7 kg ha (2). Application rates ranged from low to high label rates. Application rates were determined using information about the spatial variability in grass weed densities and sorption partition coefficients of alachlor. A rate of 1.96 kg ha" was used with K values * Southern Monitoring Location • 72.9

71.2

0.73

0.58

31.77

140.0

Sediment (kg)

1.7

1.5

0.81

0.91

0.29

4.2

Nitrate (kg)

1.0

1.0

0.57

1.26

-0.27

1.7

0.01 0.01 0.57 (g>* * Acetochlor losses are for tile drainage only.

0.46

0.00

0.01

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Flow (m )

Acetochlor



DISTANCE (m) ure 1. Spatial Pattern in Surface Organic Carbon (%).



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DISTANCE (m) Figure 2. Cokriged Acetochlor Kd Values (ug/rnL).



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DISTANCE (m) Figure 3. Spatial Patterns in Grassy Weeds (Number per 0.304 m χ 0.304 m)



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Figure 4. Site-specific Acetochlor Management Map.


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Table I V . Mean Annual Acetochlor Losses (kg ha" ) in Runoff, Eroded Sediment, and Drainage Water Using a 3 Year A D A P T Simulation.


Acetochlor Loss Pathways

Runoff Sediment Drainage Total Runoff Sediment Drainage Total

Uniform Application Losses (kg ha' ) 1

Variable Application Losses (kg ha" )

Northern Part of Field0.03 0.00002 0.00003 0.03 Southern Part of F i e l d 0.09 0.00005 0.00006 0.09

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0.02 0.00001 0.00002 0.02 0.08 0.00004 0.00004 0.08

Conclusions This is the first study to provide comparisons between field-scale losses with a variable rate versus a uniform rate application of herbicide. Modeled losses of acetochlor were roughly 1-3% of the amount applied. Losses occurred primarily through surface runoff. In the flat portion of the field, acetochlor losses were 33% smaller with the variable rate than with the uniform rate application strategy. In the steep portion of the field, losses were 11% smaller with the variable rate than the uniform rate strategy. These results indicate that measurable reductions in off-site losses of acetochlor could occur on similar sites using a variable rate application strategy in comparison to a uniform application rate strategy.

Acknowledgment Research presented in this paper was funded by U S D A - C S R E E S grant #9537102-2174 entitled: "Impact of soil-specific herbicide application on water quality."


317 References 1. Larson,W.E.,Lamb,J.Α.,Khakural,B.R.,Ferguson,R.B.,and Rehm, G. W. In The State of Site-Specific Management for Agriculture; Pierce,F.J.and Sadler,E.J.,Eds.;Soil Sci. Soc. Am.: Madison, WI, 1997, pp 337-367. 2. Khakural,B.R.,Robert,P.C.,Mulla,D.J.,Oliveira,R.S.,Johnson,G.Α., and Koskinen,W.C.InProc.4 Int'l. Conf. Precision Agriculture; Robert,P.C., Larson, W. E., and Rust, R., Eds.; Soil Sci. Soc. A m . : Madison, WI, 1999, pp 1719-1731. 3. Clay,S.Α.,Lems,G.J.,Clay,D.E.,Ellsbury,M.M.,and Forcella, F. In Proc. 4 Int'l. Conf. Precision Agriculture; Robert,P.C.,Larson,W.E.,and Rust, R., Eds.; Soil Sci. Soc. A m . : Madison, WI, 1999, pp 1699-1707. 4. Stafford, J. V., and Miller, P. C. H. In Proc.3 Int'l.Conf. Precision Agriculture; Robert,P.C.,Larson,W.E.,and Rust,R.,Eds.;Soil Sci. Soc. A m . : Madison, WI, 1996, pp 465-474. 5. Khakural, B. R., Robert, P. C., and Koskinen, W. C. Soil Use Manage -ment. 1995, 10, 158-164. 6. Nelson,D.W.,and Sommers, L. E. In Methods of Soil Analysis Part 2.; Page,A.L.,Ed.;Agronomy Monograph No. 9; Soil Sci. Soc. Am.: Madison, WI, 1986, pp 539-579. 7. Leonard, R. Α., Knisel, W. G., and Still, D. A. Trans. Am. Soc. Ag. Eng. 1987, 30, 1403-1408. 8. Chung, S. O., Ward, A. D., and Shalk, C. W. Trans. Am. Soc. Ag. Eng. 1992, 35, 571-579. 9. Davis, D., Gowda, P., Mulla, D. J., and Randall, G. J. Environ. Qual. 2000, 29:1568-1581.


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Modeling the Effect of Precision Agriculture: Pesticide Losses to

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