Relationship between Soil-Applied Pyrazon and Content in Soil Solution

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'sk.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'sk.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.

Study of diuron in soil solution by means of a novel simple technique using glass microfibre filters

“…Adsorption was initially substantial and rapid, more than 90% of the applied herbicide being adsorbed in less than 1 day. Subsequent adsorption was slower, and involved only a small fraction of the applied diuron, but this was sufficient to decrease further and significantly the herbicide concentration in soil solution (by up to 50% at the low dose between 1 and 6 days), A similar decrease has been observed with pyrazon (Streibig, 1982) and imazaquin (Wolt et al, 1989), Moreover, it seems that herbicide adsorbed during this later phase was not released into diluted soil solution, as shown by the similar decrease in diuron percentage (c, 4%) in both soil solution and diluted soil solution. It may be supposed (Hance, 1976) that herbicide moved, by mass flow and diffusion, into small pores of soil particles that offered new adsorption sites and/or that herbicide molecules could gradually reach hidden sites on soil surfaces.…”

“…Many reviews have addressed these different aspects (see, for example, Calvet et al, 1980a,b,c,d;Moyer, 1987;NichoUs, 1988), Several techniques have been developed for the extraction of soil solution for determination of dissolved herbicide. They include (i) centrifugation for diuron (Moyer et al, 1972) and fluometuron (Patterson etal., 1982), (ii) suction for atrazine (Green & Obien, 1%9) and pyrazon (Streibig, 1982), (iii) pressure for atrazine and linuron (Walker, 1973), simazine, metribuzin and linuron (Hance & Embling, 1979) and imazaquin (Goetz et al, 1986), and (iv) displacement for imazaquin (Wolt et al, 1989), Most of these techniques require relatively large soil samples and high soil moisture, and are time consuming. Some of them also affect soil structure.…”

Chlorsulfuron Adsorption by Selected Soil Samples

“…1. The soil : solution ratio (1 : 5) and the background electrolyte (0.01 hl CaC12) are the same, as those used in investigations of other herbicide-soil systems (Streibig, 1980(Streibig, , 1982. The various soils exhibit highly different capacities to adsorb chlorsulfuron.…”

“…Another possibility could be alterations of humic acid, compared to natural organic matter, by the extraction and purification procedure. Differences in the solid : solution ratios, being 1 : 5 for the soil but I :50 for humic acid, may also contribute, since the soil: solution ratio has been shown sometimes to affect adsorption of other herbicides (Streibig, 1982) and of phosphate (Barrow & Shaw, 1979). The regression coefficients ( Table 4) corresponding to amorphous and poorly crystalline iron oxides (Fe(EDTA)) are 2.601 or 0.067 per m2 at pH 4.2 and 0.101 (not significant) or 0.003 per m2 at pH 7, and those corresponding to crystalline iron oxides (Fe(DElFe(EDTA)) are, on average, 0.40 or 0.030 per m2 at pH 4.2 and 0.06 or 0.0035 per m2 at pH 7.…”

“…Scand. 39 (1989) Practical curisideratioris Numerous factors affect herbicide behaviour in soils (Stevenson, 1972;Adams, 1973;Streibig, 1980Streibig, , 1982Graham-Bryce, 1981; Gish et al, 1986;Hance, 1987). Soil adsorption is one of these factors, especially important for herbicide mobility but it may also influence degradability and phytotoxicity.…”