Relationship between Soil-Applied Pyrazon and Content in Soil Solution

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Abstract
The relationship between pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] in soil solution and dosage was examined in two soils under slurry equilibrium conditions and at field water capacity. In a sandy soil, the partition coefficient, calculated from a regression analysis of soil water content on dosage applied, was similar under slurry conditions and at field water capacity, but in a loamy sand, high in organic matter, the partition coefficient was somewhat higher at field water capacity than the estimated 4.71 measured in a great excess of water. In the sandy soil, neither the partition coefficients under slurry conditions nor at field water capacity were significantly different from Freundlich's k. Under slurry conditions in the loamy sand this difference was barely significant, whereas at field water capacity the estimated partition coefficient was significantly higher than Freundlich's k. Soil water sampling at field water capacity a fortnight after the start of the experiment showed a considerable increase in partition coefficient compared with the first sampling after 2 days, and the relationship in a sandy soil showed a slight non-linear trend, but that of the loamy sand still appeared to be linear. A desorption experiment indicated that the recovery of soil-adsorbed pyrazon was almost complete.