Valid results from studies of adsorption of labile organic compounds in soil can be obtained only if microbial degradation of the compound is inhibited. This study investigated effectiveness of sterilization of three silt loams with dry heat, cobalt‐60 irradiation, propylene oxide, mercuric chloride, autoclaving, sodium azide, microwave, chloroform, and antibiotics. These treatments were begun after air‐dried, sieved soil was moistened to −30 kPa water potential and incubated for 48 h at 25 °C. Sterilization was effective and microorganisms were eliminated by cobalt‐60 irradiation, propylene oxide, mercuric chloride, and autoclaving 2 × or 3 × as evidenced by a lack of microbial growth on potato‐glucose agar, plate count agar, and nutrient broth. Soil physical and chemical properties were altered by most sterilization treatments. Measured surface areas of the three soils were significantly reduced by propylene oxide. Propylene oxide and sodium azide produced an average pH increase for the three soils of 0.7 and 0.3 units, respectively. All effective sterilization methods except mercuric chloride significantly increased extractable Mn levels in the three soils. None of the effective treatments significantly influenced cation exchange capacity or levels of extractable Ca, Mg, and K of the soils. Mercuric chloride resulted in effective sterilization with minimal changes in soil chemical and physical properties. Following proper safeguards, mercuric chloride could be used to prevent microbial degradation in studies to evaluate adsorption of labile organic chemicals by soil.

Flooding is often a problem in areas of the southern USA with high rainfall and impermeable soils. A field study was conducted on two poorly drained, slowly permeable soils, a Sharkey clay (veryfine, montmorillonitic, nonacid, thermic Vertic Haplaquept) and a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf), to determine the influence of prolonged flooding on the growth and seed yield of eight determinate soybean [Glycine max. (L.) Merr.] cultivars. Soybean was continuously flooded 3 cm above the soil surface at either the V4 or R2 growth stage for 2, 4, 7, or 14 d. Soil water pressures were monitored at four depths in the Sharkey profile. Flood duration effects on the soybean plant were manifested in yellowing and abscission of leaves at the lower nodes, stunting, and reduced dry weight and seed yield. Canopy height and dry weight decreased linearly with duration of the flood at both growth stages. The growth rates were 25 to 35% less when soybean was flooded at R2 than at V4. The additional 4 wk of vegetative growth after flooding allowed the soybean flooded at V4 to recover to a greater extent than the cultivars flooded at R2. A linear relation was found between seed yield and monthly average crop growth rates for the 4 wk following flooding. A linear decrease in seed yield with flood duration was also found. On the Sharkey clay, rates of yield reduction were 157 and 124 kg ha−1 d−1 of the flood for the soybean flooded at R2 and V4, respectively. On the Crowley silt loam, yield reduction rates were 101 and 53 kg ha−1 d−1 of the flood duration for the soybean flooded at R2 and V4, respectively. Crop susceptibility factors (CS) were determined by dividing the decline in yield by the unstressed control, where the 2‐d flooded soybean cultivars were considered the controls. Values of CS ranged from 0.0 to 0.6 and were linearly related to flood duration after 2 d. The slopes of the lines were 1.5 times greater for the flood applied at R2 than at V4, and 2.4 times greater with soybean grown on the Sharkey clay than on the Crowley silt loam. The determinate soybean cultivars were more susceptible to prolonged flooding during early reproductive growth than early vegetative growth and when grown on the clayey soil than on the silt loam.

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Field persistence of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} applied preemergence as high as 16 times the 0.14 kg ai/ha recommended rate was studied at two locations in Arkansas in 1984 and 1985. Rapid dissipation of these high rates occurred on the Taloka silt loam under hot, dry field conditions in 1984 when no rainfall occurred for 2 weeks after application. In 1985, when furrow irrigation was applied 7 days after application, imazaquin phytotoxicity was greater and dissipation was delayed. Imazaquin persistence and soil adsorption were greater on Sharkey silty clay than on Taloka silt loam. Following 3- and 8-cm irrigation, 84 and 78%, respectively, of the14C-labeled imazaquin remained in the surface 5 cm, but in plots covered between rainfalls and receiving 8 cm rain, 74% leached out of this top layer. Since nonincorporated imazaquin dissipated rapidly under hot, dry field conditions, carryover into the next growing season or leaching below the plow layer would not be expected. However, in cool, wet conditions immediately after application, the weakly adsorbed imazaquin molecule was readily bioavailable and mobile in the soil profile.

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