Saflufenacil, atrazine, and pyroxasulfone represent herbicides with a relative field persistence of low, medium, and high, respectively. Field studies were conducted over 2 yr when herbicides and rates were assembled in a factorial arrangement of treatments, and herbicides were applied at rates of 100, 1,000, and 10,000 g ai ha−1. Soil samples were collected over the course of 365 d and analyzed to detect dissipation of the herbicides. Regression analysis was used to quantify the dissipation of each herbicide. The initial herbicide concentration had no effect on the observed dissipation rates of atrazine or saflufenacil; however, pyroxasulfone dissipation was slower at the highest field dosage in both years. Soils from Georgia, Illinois, and Tennessee were fortified with known concentrations of the three herbicides dissolved in water and incubated at 22 C for 154 d. Laboratory studies generally demonstrated slower dissipation compared to field studies, which is plausible because the important loss mechanisms of volatilization or photodegradation do not occur in the laboratory test system. Pyroxasulfone and saflufenacil exhibited no effect of half-life from various initial concentrations, but atrazine exhibited slower degradation occurring at lower initial concentrations. Findings from these studies suggest that initial herbicide concentration has a limited effect on the dissipation of some herbicides: pyroxasulfone in the field and atrazine in the laboratory. This finding is important for researchers who use herbicide degradation rates in simulation modeling because herbicide degradation is often assumed to be independent of the rate applied. Another aspect of this research was the application of each herbicide alone and in combination with the others. Under field and laboratory conditions, there was no change in dissipation if the herbicides were applied alone or in combination.

Intermittency as it occurs in fast dynamos in the magnetohydrodynamics (MHD) framework is evaluated through the examination of relations between normalized moments at third order (skewness $S$) and fourth order (kurtosis $K$) for both the velocity and magnetic field, and for their local dissipations. As investigated by several authors in various physical contexts such as fusion plasmas (Krommes 2008 Phys. Plasmas 15, 030703), climate evolution (Sura & Sardeshmukh 2008 J. Phys. Oceano. 38, 639-647), fluid turbulence or rotating stratified flows (Pouquet et al. 2023 Atmosphere 14, 01375), approximate parabolic $K(S)\sim S^\alpha$ laws emerge whose origin may be related to the applicability of intermittency models to their dynamics. The results analyzed herein are obtained through direct numerical simulations of MHD flows for both Taylor–Green and Arnold–Beltrami–Childress forcing at moderate Reynolds numbers, and for up to $3.14 \times 10^5$ turn-over times. We observe for the dissipation $0.2 \lesssim \alpha \lesssim 3.0$, an evaluation that varies with the field, the forcing and when filtering for high-skewness intermittent structures. When using the She & Lévêque (1994) Phys. Rev. Lett. 72, 336-339 intermittency model, one can compute $\alpha$ analytically; we then find $\alpha \approx 2.5$, clearly differing from a (strict) parabolic scaling, a result consistent with the numerical data.

Dissipation of S-metolachlor, a soil-applied herbicide, on organic and mineral soils used for sugarcane production in Florida was evaluated using field studies in 2013 to 2016. S-metolachlor was applied PRE at 2,270 g ha−1 on organic and mineral soils with 75% and 1.6% organic matter, respectively. The rate of dissipation of S-metolachlor was rapid on mineral soils compared with organic soils. Dissipation of S-metolachlor on organic soils followed a negative linear trend resulting in half-lives (DT50) ranging from 50 to 126 d. S-metolachlor loss on organic soils was more rapid under high soil-moisture conditions than in corresponding low soil-moisture conditions. On mineral soils, dissipation of S-metolachlor followed an exponential decline. The DT50 of S-metolachlor on mineral soils ranged from 12 to 24 d. The short persistence of S-metolachlor on mineral soils was likely attributed to low organic matter content with limited adsorptive capability. The results indicate that organic matter content and soil moisture are important for persistence of S-metolachlor on organic and mineral soils used for sugarcane production in Florida.

Three field studies were conducted over a 2-yr period to evaluate the persistence of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl) aniline], and to determine whether DBCP (1,2-dibromo-3-chloropropane) affected persistence. Fluchloralin was applied to field plots at 1.1 kg/ha with and without DBCP at 20.5 kg/ha. In the first study, soil samples were taken periodically over a 1-yr period and assayed for fluchloralin by both gas chromatography (GC) and a sorghum (Sorghum bicolor L. Moench ‘AKS-516’) root-elongation bioassay. Both methods of analysis indicated that fluchloralin persistence was unaffected by DBCP. An oat (Avena sativa L. ‘Ora’) bioassay of soil from the field plots 41 weeks after treatment showed no residual herbicide activity. In the next two field studies, soil samples were taken periodically over a 32-week period and assayed by GC for fluchloralin. A greenhouse sorghum bioassay of soil samples taken from both tests 32 weeks after application showed residual activity of fluchloralin in one test, but differences were not attributable to DBCP. A two-phase process of fluchloralin dissipation in field soil was indicated from analysis of the data using a complex first-order regression, as opposed to a simple first-order regression. Half-life values describing fluchloralin persistence, using the complex first-order regression, ranged from 2.3 to 3.7 weeks for the first phase and 9.5 to 26.7 weeks for the second phase.

This study examined the response of corn to clomazone, chlorimuron, imazaquin, and imazethapyr the year following their application to soybeans. Herbicides were surface-applied from one-half to three times the labeled application rates. Soybeans were planted the year of application and crop tolerance was evaluated. Corn was planted in rotation the following season. Soybeans were tolerant of all four herbicides. The highest rates of clomazone, chlorimuron, and imazaquin injured the corn early in the season. Imazethapyr did not influence corn growth. Visual estimates of clomazone injury were as high as 39% chlorosis. Seedling dry weight reductions at the highest chlorimuron and imazaquin rates were 32% and 24%, respectively. Although corn was injured by higher rates of clomazone, imazaquin, and chlorimuron at the 3-leaf stage, none of the herbicides significantly reduced grain yield. This study suggests that these herbicides can carry over and injure corn, especially if labeled application rates are exceeded. However, low to moderate early season injury to corn may not affect grain yield.

One year after application under irrigated conditions, atrazine at 1.2 kg/ha injured oat but there was no effect after two years. On dryland, wheat and barley were injured for up to two years after atrazine was applied at 1.5 kg/ha. Atrazine concentrations in the soil were related to accumulated rainfall in an exponential equation. The equation predicted that, under the most severe drought conditions ever recorded for southern Alberta, injury to cereal crops could occur for at least three years after atrazine application at 1.2 to 1.5 kg/ha. Cyanazine did not injure subsequent crops under either irrigated or dryland conditions.

Field experiments were conducted to determine wheat injury following clomazone application in soybeans and fallow in North Dakota. Clomazone at recommended rates generally caused 10% or less visible chlorosis in spring wheat planted 11 to 12 mo after application or winter wheat planted 11 mo after application, although greater chlorosis was observed in two of seven location/year environments. Tillage preceding wheat planting increased chlorosis from clomazone residues in some environments. Clomazone residues reduced wheat grain yield only in three of seven location/year environments and usually at application rates of 1.4 kg ai ha-1 or greater. Severe drought prevailed during the study and probably increased clomazone persistence and wheat chlorosis. Drought also may have limited expression of grain yield reductions attributable to clomazone residues.

The overall degradation of chlorimuron was very similar at −0.1 and −1.5 MPa and slightly less in air-dry soil. Degradation rates increased with increasing temperature. The primary 14C-labeled compounds observed in moist-soil extracts were desmethyl chlorimuron and saccharin, while the primary 14C-labeled compound observed in air-dry soil extracts was saccharin. Saccharin is formed quantitatively from ethyl 2-(aminosulfonyl)benzoate (phenylsulfonamide) during extraction and therefore represents phenylsulfonamide formed in the soil as a result of chemical hydrolysis of the sulfonylurea bridge. These degradation products suggest that chemical hydrolysis of the sulfonylurea bridge is the primary mode of degradation in air-dry soil, while microbial degradation and chemical hydrolysis both occur in moist soil. These laboratory results demonstrate that chlorimuron will degrade in air-dry soil at a temperature-dependent rate by chemical hydrolysis.

Greenhouse experiments determined differences in imazaquin bioavailability over time under various soil moisture regimes. All soils were initially fortified with 63 ppb (w/w) of commercially formulated imazaquin. Treatments consisted of maintaining at field capacity for 15 wk (FC), maintaining air-dry for 15 wk (AD), soil that was maintained air-dry for 2 wk and then wet to field capacity at 2 wk intervals (2WAD), and soil that was wet to field capacity at the initiation of the experiment and at 2 wk intervals (2WFC). Little dissipation of imazaquin occurred in the AD soil over the 100 d of this study. Rapid dissipation over the first 35 d occurred for the other three treatments. Imazaquin half-life ranged from 17 to 18 d for the FC, 2WAD, and 2WFC soils. Imazaquin concentration increased or only slightly decreased in samples taken after the second watering in both the 2WAD and the 2WFC soils. Due to differences in adsorption/desorption of imazaquin with changing soil moisture levels, bioassays may not determine the dissipation of the actual concentration of imazaquin contained in soil.

Herbicides can persist in the soil and injure sensitive crops planted in the years following herbicide application. The response of sugarbeet to clomazone, imazaquin, imazethapyr, and chlorimuron residues in soil was examined. Clomazone at 1.1 or 2.2 kg ai ha-1 did not reduce yield of sugarbeet planted 1 or 2 yr after application. Imazaquin at 0.07 to 0.28 kg ai ha-1, and imazethapyr at 0.09 to 0.14 kg ai ha-1, can reduce yield of sugarbeet planted 1 yr after application. Imazaquin at 0.07 to 0.14 kg ha-1 caused 28 to 47% sugarbeet injury and imazethapyr at 0.09 kg ha-1 caused 54% injury 2 yr after application in soybean. A 25% yield loss occurred from the imazethapyr treatment. Sugarbeet injury 2 yr after application was greatest when sugarbeet also was planted the year following soybean. Chlorimuron at 0.02 to 0.08 kg ai ha-1 plus linuron at 0.4 to 0.9 kg ai ha-1 reduced yield of sugarbeet planted 1 yr after application when compared with linuron alone, regardless of soil pH. Visible sugarbeet injury of 38 to 66% was still evident from chlorimuron plus linuron treatments 2 yr after application. Sugarbeet should not be planted less than 25 mo following imazaquin, imazethapyr, or chlorimuron application.