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Modeling losses of copper-based fungicide foliar sprays in wash-off under simulated rain
Pérez-Rodríguez, P.; Paradelo, M.; Soto-Gómez, D.; Fernández-Calviño, D. & López-Periago, J.E.
Abstract
Wash-off experiments of three Cu-based fungicides
were conducted with a single raindrop simulator
with known drop size and fall height. Losses were quantified
as total Cu (CuT), in solution (CuL), and particulate
(CuP). Cu wash-off time course was modeled for two different
drop sizes using a stochastic model based on the
cumulative detachment by random scattered raindrop
impacts. In other set of experiments, the influence of
raindrop size, fall height, and fungicide dose was analyzed
statistically by means of a full factorial design. Most Cu
was lost as particles sized from 0.3 to 1 μm. The stochastic
model gave good estimations with two detachment performance
levels. The best-fitting model parameters were as
follows: the single element area covered by one impact (1.7
and 0.38 cm2 for the large and small raindrop, respectively),
the average number of repeated drop impacts on
one single element area that exhaust non-rainfast fungicide
(4.2 ± 3.0 small drops and 2.5 ± 0.5 large drops for the
high performance level, low performance level needed
30 ± 10 large drops and 40 ± 88 small drops), and the
mass washed-off by a single-drop impact (from
1.27 ± 0.2 μg Cu to 3 ± 1 ng Cu per impact). Factorial
design showed the dosage was the most influential factor in
the three fungicide formulations. The model can help to
estimate fungicide losses in field from rainfall and canopy
properties. However, the particulate/soluble loss ratio
cannot be predicted by the model since both the particle
detachment and solubilization were not clearly related with
the raindrop energy.
Keywords
Non-point source pollution; Copper fungicides; Rain fastness; Pesticide wash-off; Soil pollution
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