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Pesticides not reaching the intended target may have negative effects on the environment and the ®eld ecosystem. To estimate the potential ground water pollution and risk for soil-dwelling organisms it is necessary to estimate the amount of pesticide reaching the soil in different spraying situations. Literature shows that ground deposition may vary even within equal growth stages due to variations in canopy density. This paper discusses the feasibility of estimating the ground deposition of pesticides from canopy density in cereal ®elds. Spray experiments were carried out in wheat and barley with¯at-fan nozzles of two sizes. Differences of ground deposition between the two nozzle sizes were insigni®cant. Adding surfactant to the spray solution signi®cantly reduced the soil deposition in barley and in wheat cv Sleipner but not in cv Haven. A signi®cant effect of Leaf Area Index (LAI) on ground deposition was obtained. A simple exponential model based on the LAI with an extinction coef®cient of 0.48±0.50 may for many occasions satisfactorily describe the soil deposition of pesticides in cereals. Using non-destructive LAI-measurements combined with the deposition model may be useful in pesticide risk assessment on ®eld, farm and larger regional scale and is optimising the application rate in site-speci®c farming.

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Deposition variability from a conventional field sprayer, and effects of wind and travel speed were measured by collecting on small artificial targets in the swath. Whilst deposition on 0.1-m2 plots varied by a factor of 3, deposition on single vertical targets typically varied by a factor of 10 and on horizontal targets by a factor of 6. Distinct transversal deposition patterns appeared according to wind direction. The quantity and structure of variability was compared with wind speed and turbulence intensity, but few significant trends were found. Deposition on vertical targets was enhanced by increasing wind speed or increasing travel speed, whilst effects on horizontal targets were inconsistent.