Zur statistischen Interpretation und graphischen Darstellung des Abbauverhaltens von Pflanzenschutzmittel-Rueckstaenden. 4. Physikalisch begruendete Modelle.
1993
Quest S. | Walter H. F. | Frehse H. | Timme G.
In the previous articles, empirical models were reported with which the degradation of residues can be described mathematically. This article reports attempts to replace these purely formal approaches by physically based models. Two lines of thought were followed. By linking growth laws, describing the increase in plant mass, with time laws of arbitrary order describing the biological and/or chemical degradation of residues, curve-fitting functions were obtained which in many cases gave a better fit to the measured residue data than did the purely formal approaches. In connection with this work it emerged that the growth of some typical fruits and plants over relevant periods of time can be represented by two simple types of mathematical functions. This opened up the possibility of considering separately two aspects of the degradation of residues in/on plants: the component due entirely to 'dilution' by the increase in plant mass and the component representing 'true' degradation. These physically based models are often unsatisfactory, however, if the decrease in residue concentration is much quicker shortly after application of the pesticide than at later stages. In the formal approaches reported previously, such cases are often described well by root functions. In the present article a physically based two-zone model provides the remedy. It assumes that a plant part such as a fruit can be divided into an inner and an outer zone. The active ingredient applied to the exterior penetrates gradually from the outer into the inner zone. The degradation in the two zones obeys different laws.
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