Laboratory Incubation Conditions Research Articles

Transformation of biochar into extracted humic substances under short-term laboratory incubation conditions: Evidence from stable carbon isotopes

Agricultural waste can be made into biochar, which serves to raise soil fertility and fix carbon (C). When biochar is added to soil, a small part of biochar could be transformed into soil organic C in a short time to promote soil fertility. However, it is still unknown how much biochar can be stored in the soil as stable C and whether it plays a role in C sequestration. In this study, a 540-day incubation experiment was conducted to evaluate the transformation of maize straw biochar into humus fractions using a 13C isotopic labelling technique. The treatments were CK (no biochar applied) and AB (21.3 g kg-1 of biochar + CK). The results showed that: 1) Compared with those in the CK treatment, the concentrations of organic and humus C in the bulk soil were significantly higher under the AB treatment. 2) The δ13C values of soil humus C were higher (ranging between 0% and 23.45%) in the AB treatment than those in the CK treatment. 3) The proportions of biochar transformed into humic acid (HA), fulvic acid (FA), water-soluble substances (WSS), and water floating substances (WFS) were 2.66–4.30%, 1.11–1.57%, 0.49–0.88%, and 0.68–1.40%, respectively. The remaining biochar (59.44–98.00%) remained in the crude humin form, retaining the inert nature of the biochar itself. Although biochar is relatively stable, approximately 4.22–5.40% of biochar was transformed into extracted humic substances (HA+FA). We concluded that a relatively small amount of biochar could be transformed into soil organic matter under short-term (540 days) incubation conditions.

Nitrogen Mineralization from Organic Amendments Predicted by Laboratory and Field Incubations

ABSTRACTReliable methods to estimate nitrogen (N) mineralization from organic amendments are needed to improve the fertilization recommendations for organic horticultural crops. With this aim, N mineralization from farmyard manure compost (FYMC), commercial organic fertilizer (COF) based on materials that are prompt to rapid N mineralization and green manure was determined in field situation where environmental factors affect mineralization rates and under controlled laboratory conditions that may not reflect conditions in the field. The ability of field and laboratory incubations to predict N mineralization was estimated during a field organic crop rotation set up with a cover crop of rye and vetch, followed by Portuguese cabbage and carrot. The relationship between mineralized N in field incubation and crop N accumulation suggests that field incubation is effective to predict N mineralization from FYMC, COF and green manure. However, the pattern of N mineralization from FYMC and green manure was different in field and laboratory incubation conditions as opposed to N mineralization from COF that was similar in both incubations.

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Effects of simulated Cd deposition on soil Cd availability, microbial response, and crop Cd uptake in the passivation-remediation process of Cd-contaminated purple soil

Atmospheric deposition of heavy metals such as Cd is a threat to ecosystems and food safety. Our knowledge is still limited about the effectiveness of remediation process for Cd-contaminated agro-soils under atmospheric Cd deposition. In this study, eight soil amendments were used in a Cd-contaminated purple soil to investigate their impacts on soil Cd availability, microbial response, and Cd uptake by mustard and corn plants via simulating the atmospheric Cd deposition under laboratory incubation and greenhouse conditions. Results showed that the simulated atmospheric Cd deposition increased the soil high-risk Cd (HR, exchangeable and carbonate Cd) and decreased soil medium-risk Cd fraction (MR, bound to Fe/Mn oxide and organic Cd), and the largest direct effects on crop Cd uptakes were 0.94 and 0.66 for mustard and corn based on the path-coefficient analysis, respectively. Generally, Cd deposition led to decreasing soil microbial biomass carbon, populations of bacteria, fungi and actinomycetes, and enzyme activities of urease, catalase, sucrase, and acid phosphatase whereas increasing soil microbial biomass nitrogen. Compared with control and lime treatments, an organic-inorganic combined preparation (OCP) appeared to be effective for remediation of the Cd-contaminated purple soil due to its potential to increase the HR-Cd and reduce both MR-Cd and crop Cd uptake, as accompanied by its neutral effects on soil bacterial alpha diversity and community structure. Results also indicated that application of nitrogen fertilizers should be considered for remediation of the Cd-contaminated soils as nitrogen inputs were demonstrated to promote soil health under elevated Cd condition.

Effects of the nitrification inhibitor acetylene on nitrous oxide emissions and ammonia-oxidizing microorganisms of different agricultural soils under laboratory incubation conditions

Acetylene (C2H2) is an effective nitrification inhibitor targeting autotrophic ammonia oxidizers, and has shown promise for improving nitrogen use efficiency by mitigating greenhouse gas nitrous oxide (N2O) emissions and reducing nitrate leaching. Its efficacy, however, varies considerably with edaphic and environmental conditions and remains largely less studied in dryland agricultural soils. Here we conducted two laboratory microcosm incubations to explore the efficacy of C2H2 across various agricultural soils and under different conditions. The first incubation was with four agricultural soils at 25°C and 60% water-filled pore space (WFPS), and the second incubation included one cropping soil under a range of conditions (15°C, 25°C, 35°C and 50%, 70% WFPS). Our results showed that incubation of soil with 1% v/v C2H2 resulted in complete or partial inhibition of nitrification, N2O emission, and AOA or AOB growth under the experimental conditions. Acetylene can totally inhibit nitrification in acidic cropping and dairy pasture soils through retarding both AOA and AOB growth, while C2H2 partly inhibited nitrification and N2O emission in the alkaline vegetable soil through impeding only AOB growth. The highest inhibition effect of C2H2 was achieved at 25°C and 50% WFPS, while there was no inhibitory effect of C2H2 when soil was incubated at 15°C and 50% WFPS suggesting soil temperature may have a significant influence on C2H2 effectiveness. The inhibition of C2H2 on cumulative N2O emission increased with increasing temperature at 50% WFPS. In contrast, at 70% WFPS, the inhibition of C2H2 on cumulative N2O emission decreased with increasing temperature. Since the effect of C2H2 varied with soils and environmental conditions, this highlights the assumption that N2O production and nitrification can be affected by low concentrations of C2H2 may be not appropriate in some occasions.

Snapshot of methanogen sensitivity to temperature in Zoige wetland from Tibetan plateau.

Zoige wetland in Tibetan plateau represents a cold environment at high altitude where significant methane emission has been observed. However, it remains unknown how the production and emission of CH4 from Zoige wetland will respond to a warming climate. Here we investigated the temperature sensitivity of methanogen community in a Zoige wetland soil under the laboratory incubation conditions. One soil sample was collected and the temperature sensitivity of the methanogenic activity, the structure of methanogen community and the methanogenic pathways were determined. We found that the response of methanogenesis to temperature could be separated into two phases, a high sensitivity in the low temperature range and a modest sensitivity under mesophilic conditions, respectively. The aceticlastic methanogens Methanosarcinaceae were the main methanogens at low temperatures, while hydrogenotrophic Methanobacteriales, Methanomicrobiales, and Methanocellales were more abundant at higher temperatures. The total abundance of mcrA genes increased with temperature indicating that the growth of methanogens was stimulated. The growth of hydrogenotrophic methanogens, however, was faster than aceticlastic ones resulting in the shift of methanogen community. Determination of carbon isotopic signatures indicated that methanogenic pathway was also shifted from mainly aceticlastic methanogenesis to a mixture of hydrogenotrophic and aceticlastic methanogenesis with the increase of temperature. Collectively, the shift of temperature responses of methanogenesis was in accordance with the changes in methanogen composition and methanogenic pathway in this wetland sample. It appears that the aceticlastic methanogenesis dominating at low temperatures is more sensitive than the hydrogenotrophic one at higher temperatures.

Field and Laboratory Evaluation of Dynamics in Soil Properties of Selected Land Use Types in Owerri, Southeastern, Nigeria

Dynamics in properties of soils of three land use types (Fallow, Pineapple and Cassava) in Owerri, Southeastern Nigeria were evaluated under field and laboratory incubation conditions. Soil properties varied with time within land use types, with chemical more significantly than physical properties under both conditions. Averaged over time, concentration in soil properties was a decreasing order of fallow > cassava > pineapple. Concentrations and correlation between soil properties were more significant (P = < 0.05) under laboratory than field conditions. More than 80% of the relationship between soil properties under field and laboratory conditions was estimated by a regression model. Generally, Knowledge of the dynamics in properties of soils of land use types could be useful for efficient environmental monitoring and control. Also relationship between soil properties under field and laboratory conditions could be extrapolated for addressing management problems on other soils under similar land use.

Interactive effect of dissolved organic matter and phenanthrene on soil enzymatic activities

The investigation of dissolved organic matter (DOM) on urease, catalase and polyphenol oxidase activity in a phenanthrene (Phe)-contaminated soil was conducted under laboratory incubation conditions. Values of soil enzymatic activity depended mainly on incubation time. In the initial 16 days, urease activity increased, and was followed by a decrease. In the initial 8 days, catalase activity decreased and then increased. Variation of polyphenol oxidase activity was just the reverse of catalase activity. After 30 days of incubation, no pronounced difference among treatments with Phe, Phe and DOM, and control were detected in urease, catalase and polyphenol oxidase activity. Phe might inhibit urease and catalase, and stimulate polyphenol oxidase. DOM could improve inhibition of Phe in soil urease and catalase activity during the initial period of applying DOM. Nevertheless, DOM had no significant effect on polyphenol oxidase activity in the Phe contaminated soil. There was a negative correlation between catalase and polyphenol oxidase ( r = −0.761***), and catalase and urease ( r = −0.554**). Additionally, a positive correlation between polyphenol oxidase and urease was also detected ( r = 0.701***). It is implied that the formed DOM after application of organic wastes into soils may counteract the inhibition of polycyclic aromatic hydrocarbons in soil enzyme activities.

Effects of goat manure and inorganic phosphate addition on soil inorganic and microbial biomass phosphorus fractions under laboratory incubation conditions

Changes in inorganic phosphorus (P) and soil microbial biomass P following the addition of goat manure and different amounts of inorganic P to an Umbric Ferralsol were assessed over 12 weeks under laboratory incubation conditions using a sequential fractionation procedure. Triple superphosphate was added at rates equivalent to 0, 45, 90, 135 and 180 mg P kg−1, with or without goat manure at a rate of 10 g kg−1soil on a dry-weight basis and incubated moist. Resin P, 0.5 mol L−1 NaHCO3 extractable inorganic P (NaHCO3-Pi), 0.1 mol L−1 NaOH extractable inorganic P (NaOH Pi) and soil microbial biomass P concentrations were determined on days 7, 14, 28, 56 and 84. The magnitudes of the inorganic P fractions extracted were: NaOH Pi > Resin P > NaHCO3 Pi. Thus, NaOH Pi was the major sink for the applied P. The dynamics of the three labile P fractions (resin P, NaHCO3 Pi and microbial biomass P) varied considerably during the incubation period. The resin P fraction consistently declined with time in all treatments, whereas the NaHCO3 Pi fraction changed little with time in the control and goat manure amended soil, but increased rapidly with time when inorganic P was applied alone or in combination with goat manure. Microbial biomass P increased with time in all treatments, peaking on day 28 and declining thereafter. The co-application of inorganic P with goat manure produced up to twofold more microbial biomass P than either inorganic P or goat manure applied alone. Therefore, the combined application of manure with low rates of P fertilizers may be a cost effective strategy for increasing the efficiency of fertilizer P use through enhanced biological cycling of P in small-holder farms in South Africa.

Structural Analysis of Biofilm Formation by Rapidly and Slowly Growing Nontuberculous Mycobacteria

Mycobacterium avium complex (MAC) and rapidly growing mycobacteria (RGM) such as M. abscessus, M. mucogenicum, M. chelonae, and M. fortuitum, implicated in health care-associated infections, are often isolated from potable water supplies as part of the microbial flora. To understand factors that influence growth in their environmental source, clinical RGM and slowly growing MAC isolates were grown as biofilm in a laboratory batch system. High and low nutrient levels were compared, as well as stainless steel and polycarbonate surfaces. Biofilm growth was measured after 72 h of incubation by enumeration of bacteria from disrupted biofilms and by direct quantitative image analysis of biofilm microcolony structure. RGM biofilm development was influenced more by nutrient level than by substrate material, though both affected biofilm growth for most of the isolates tested. Microcolony structure revealed that RGM develop several different biofilm structures under high-nutrient growth conditions, including pillars of various shapes (M. abscessus and M. fortuitum) and extensive cording (M. abscessus and M. chelonae). Although it is a slowly growing species in the laboratory, a clinical isolate of M. avium developed more culturable biofilm in potable water in 72 h than any of the 10 RGM examined. This indicates that M. avium is better adapted for growth in potable water systems than in laboratory incubation conditions and suggests some advantage that MAC has over RGM in low-nutrient environments.

Spatial Variability of Atrazine and Metolachlor Dissipation on Dryland No‐tillage Crop Fields in Colorado

An area of interest in precision farming is variable-rate application of herbicides to optimize herbicide use efficiency and minimize negative off-site and non-target effects. Site-specific weed management based on field scale management zones derived from soil characteristics known to affect soil-applied herbicide efficacy could alleviate challenges posed by post-emergence precision weed management. Two commonly used soil-applied herbicides in dryland corn (Zea mays L.) production are atrazine and metolachlor. Accelerated dissipation of atrazine has been discovered recently in irrigated corn fields in eastern Colorado. The objectives of this study were (i) to compare the rates of dissipation of atrazine and metolachlor across different soil zones from three dryland no-tillage fields under laboratory incubation conditions and (ii) to determine if rapid dissipation of atrazine and/or metolachlor occurred in dryland soils. Herbicide dissipation was evaluated at time points between 0 and 35 d after soil treatment using a toluene extraction procedure with GC/MS analysis. Differential rates of atrazine and metolachlor dissipation occurred between two soil zones on two of three fields evaluated. Accelerated atrazine dissipation occurred in soil from all fields of this study, with half-lives ranging from 1.8 to 3.2 d in the laboratory. The rapid atrazine dissipation rates were likely attributed to the history of atrazine use on all fields investigated in this study. Metolachlor dissipation was not considered accelerated and exhibited half-lives ranging from 9.0 to 10.7 d in the laboratory.

Differences of Soil Microbial Biomass and Nitrogen Transformation under Two Forest Types in Central Germany

In order to observe the tree species effect on soil N status, soil microbial biomass C and N (Cmic, Nmic), potential N mineralization and potential nitrification (under laboratory incubation conditions, 22 °C) in different subhorizons (LOf1, Of2, Oh and mineral soil at 0–10 cm depth) were determined at three forest sites in central Germany. At each site, two contrasting stands (Beech, Norway spruce or Scots pine) were selected, where the initial soil conditions were similar. Three sampling dates that represented different stages of tree growth were selected: growing season - August, dormant season - November, after budbreak – April. In organic layers, Cmic-to-total C (Ct) ratios under beech and under conifer were 0.72–4.74% and 0.34–2.11%, respectively. Nmic-to-total N (Nt) ratios were 2.47–11.61% and 0.71–5.77%, respectively. Both concentrations of Cmic and Nmic were significantly affected by the stand type and sampling time. Potential N mineralization rates, ranging from 3.7 to 19.7 mg N kg−1 d−1, showed no clear pattern in relation to stand type. However, potential nitrification rates were mostly significantly higher under beech than under contrasting conifer. In mineral soils, concentrations of Cmic and Nmic showed a clear temporal pattern in the order: August>November>April. The average Nmic and Nmic-to-Nt were higher in soils from beech than conifer, while Cmic and Cmic-to-Ct ratios were similar between the two forest types. In organic layers, the highest values of Cmic-to-Nmic ratio and Cmic were found in November samples, especially under beech. By contrast, in mineral soils the highest value of Cmic-to-Nmic ratios were found in April samples, and at that time the Cmic concentrations were the lowest, especially under conifer. These results revealed the differences in microbial growth form and survival strategy associated with different tree species and soil layers.

Soil P availability as affected by the chemical composition of plant materials: implications for P-limiting agriculture in tropical Africa

Plant materials that can replace costly inorganic fertilizers as phosphorus (P) sources are needed in smallholder farming systems in tropical Africa, where P is often yield-limiting. The objective of this study was to determine the relationship between the biochemical composition (quality) of plant materials, described in terms of total P, total nitrogen (N), lignin (LIG), and soluble phenolics (Pp), and soil P availability ( P av) under laboratory incubation conditions. The materials were ground and added to the soil at a rate equivalent to 10 Mg ha −1 (DM) and the samples (including a control soil) were kept at 50% field moisture capacity and 25 °C. The anion exchange resin method was used to extract solution P periodically. Because P added was not balanced among the treatments, P av was expressed as percentage of total P of plant material (i.e. P av =100×[(P av amended soil −P av control soil )/ total P added ] . Some treatments showed net P release and others showed net P uptake. The pattern of P av was viewed in three phases: (i) an initial rapid P release from the sparingly soluble inorganic P fraction of the plant materials, (ii) a subsequent phase when P in solution comes from both soluble P and mineralization of plant materials, and (iii) a last phase when P in solution is influenced by its equilibrium with P sorption processes. Total P was the best predictor of P av with r 2 ( P≤0.05) ranging from 0.50 to 0.77. Predictive functions were developed to determine the critical quality levels for net P release and net P uptake. The critical quality levels ranged from 2.0 to 2.7 g kg −1 for total P; 156:1 to 252:1 for C/P ratio; and 7:1 to 14:1 for N/P ratio. Among the materials tested, Tithonia diversifolia and Croton megalocarpus which contained total P >3.0 g kg −1 of total dry weight were identified as having the potential to release adequate P to replenish solution P for crop uptake.

Elevated atmospheric CO2 in open top chambers increases net nitrification and potential denitrification

AbstractThe control of soil nitrogen (N) availability under elevated atmospheric CO2 is central to predicting changes in ecosystem carbon (C) storage and primary productivity. The effects of elevated CO2 on belowground processes have so far attracted limited research and they are assumed to be controlled by indirect effects through changes in plant physiology and chemistry. In this study, we investigated the effects of a 4‐year exposure to elevated CO2 (ambient + 400 µmol mol−1) in open top chambers under Scots pine (Pinus sylvestris L) seedlings on soil microbial processes of nitrification and denitrification. Potential denitrification (DP) and potential N2O emissions were significantly higher in soils from the elevated CO2 treatment, probably regulated indirectly by the changes in soil conditions (increased pH, C availability and NO3– production). Net N mineralization was mainly accounted for by nitrate production. Nitrate production was significantly larger for soil from the elevated CO2 treatment in the field when incubated in the laboratory under elevated CO2 (increase of 100%), but there was no effect when incubated under ambient CO2. Net nitrate production of the soil originating from the ambient CO2 treatment in the field was not influenced by laboratory incubation conditions. These results indicate that a direct effect of elevated atmospheric CO2 on soil microbial processes might take place. We hypothesize that physiological adaptation or selection of nitrifiers could occur under elevated CO2 through higher soil CO2 concentrations. Alternatively, lower microbial NH4 assimilation under elevated CO2 might explain the higher net nitrification. We conclude that elevated atmospheric CO2 has a major direct effect on the soil microbial processes of nitrification and denitrification despite generally higher soil CO2 concentrations compared to atmospheric concentrations.

Tryptophan Catabolism in Brevibacterium linens as a Potential Cheese Flavor Adjunct

Attempts to develop a desirable reduced fat Cheddar cheese are impeded by a propensity for flavor defects such as meaty-brothy, putrid, fecal, and unclean off-flavors in these products. Recent studies suggest aromatic amino acid catabolism of starter, adjunct, and nonstarter lactic acid bacteria significantly impact off-flavor development. The objective of this study was to delineate pathways for catabolism of tryptophan (Trp) in Brevibacterium linens, a cheese flavor adjunct, and to determine the potential for this organism to contribute to this defect. Growth and production of aromatic compounds from Trp by B. linens BL2 were compared in two incubated conditions (laboratory and a cheese-like environment). A chemically defined medium was used to determine the cellular enzymes and metabolites involved in Trp catabolism. Trp was converted to kynurenine, anthranilic acid, and three unknown compounds in laboratory conditions. The accumulation of other unknown compounds in the culture supernatant in laboratory conditions indicated that B. linens BL2 degraded Trp by various routes. Up to 65% of Trp was converted to anthranilic acid via the anthranilic acid pathway. To assess this potential before cheese making, the cells were incubated in cheese-like conditions (15°C, pH 5.2, no sugar source, 4% NaCl). Trp was not utilized by BL2 incubated in this condition. Enzyme studies using cell-free extracts of cells incubated in laboratory conditions and assayed at optimal and nonoptimal enzyme assay conditions revealed Trp transaminase (EC 2.6.1.27) was active before enzymes of the anthranilic acid pathway were detected. The products of Trp transaminase activity were not, however, found in the culture supernatant, indicating these intermediates were not exported nor accumulated by the cells. Enzymes assayed in nonoptimal conditions had considerably lower enzyme activities than found in laboratory incubation conditions. Based on these results, we hypothesize that these enzymes are not likely to be involved in the formation of compounds associated with off-flavors in Cheddar cheese.

Quality of Particulate Matter and Its Potential Sinking Rates in Pelagic Samples of Inshore and Bodden Waters of the Southern Baltic Sea

In situ measurements of vertical particle transport are strongly influenced by water currents and resuspension. For mass balances, especially for calculations of POM im- and export in certain areas, or for estimating the significance of aggregate formation in the context of organisms' removal from the euphotic zone, a potential sedimentation of organic particles preferably in combination with particle quality parameters influencing sinking velocity is needed. Sedimentation of POM can be measured by small scale laboratory experiments in settling tubes. We used different parameters that describe the quantity and quality of POM in combination with the SETCOL method, Sinking rates of POC from 3 different nearshore and inner coastal waters of the Southern Baltic Sea were low with 1-32 cm d -1 , but comparable to rates obtained from several phytoplankton species, e.g. diatoms, which are important parts of POM and have a similar size range compared to the particles investigated in this study. We did not find any correlation between the sinking rate and the quantity or quality of particulate organic matter. Obviously, the differences in organic matter composition of particles smaller than 200 μm, investigated with this miniscale experimental method, did not affect the sinking rates considerably. Calculated from sinking rates and POC concentrations 19-1,430 mg C could sediment per squaremetre and day, if horizontal matter transfer and resuspension were ignored as it was done during the settling procedure. Concerning the application of the SETCOL method to plankton samples we must stress the importance of appropriate laboratory incubation conditions. Special attention has to be paid to an equal light climate and oxygen supply for the reference and settling vessels.

Nitrous oxide release from spruce forest soil: Relationships with nitrification, methane uptake, temperature, moisture and fertilization

The spatial variability in a homogeneous 63 yr old spruce forest stand was investigated with respect to potential release of N 2O in relation to nitrification rate, N mineralization rate, CH 4 uptake, organic C, total N and pH in soil under standardized laboratory incubation conditions. Soil samples were taken at random within a 100 m 2 forest stand, and gas fluxes at three temperatures (3, 10 and 15°C) and two soil moisture contents (35 and 45% v/v) were measured. In addition, a number of other relevant factors was measured in each soil sample. There was large spatial variation in N 2O release [coefficient of variation (CV)=up to 152%], nitrification rate (CV=65%) and N-mineralization rate (CV = 137%). Comparatively low spatial variations in organic C (CV=31%), total N (CV =29%), CO 2 evolution (CV = 38%), CH 4 uptake (CV = 37%) and pH (CV = 4.4%) were observed. The rate of N 2O release was positively correlated with nitrification rate and negatively correlated with pH. The rate of CH 4 uptake was negatively correlated (r = − 0.61) with nitrification rate. No significant correlation was observed between the N-mineralization rate and any of the variables measured. N 2O fluxes measured at 10 and 3°C were 76% (±14%) and 17% (±4%) of that measured at 15°C, respectively. We found a significant increase in N 2O accumulation by increasing the moisture content from 35 to 45%. Ammonium sulphate additions stimulated N 2O release but not the nitrification. The investigation demonstrated large spatial variation in the rates of nitrification, N 2O release, but it was difficult to identify regulating factors for this spatial variability.

Urea hydrolysis in a brown soil: Effect of hydroquinone

The inhibition of urea hydrolysis in a brown soil by hydroquinone lasted for < 10 days under laboratory incubation conditions. Soil ammonium-N content in the hydroquinone treatments was higher than that of the control during the middle and later stages of incubation and the increased amounts were positively related to the concentrations of hydroquinone. A pot trial with N-labelled urea showed that in the presence of the applied hydroquinone, wheat plants absorbed more soil-N and urea-N during the early and later growth stages respectively, and also, the rate of hydroquinone application was a key factor affecting wheat yield.

Phytotoxicity and Soil Activity of HOE 23408

Greenhouse and field studies were conducted to compare the phytotoxicity of HOE 23408 {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} to several crops and annual grass weeds, and to determine the herbicides's soil mobility and persistence. In general, the order of susceptibility of 13 seedling grassy weeds remained constant, whether the herbicide was applied preplant incorporated, pre-emergence, or postemergence. The herbicide was most phytotoxic when it was applied either preplant incorporated or early postemergence. Grain sorghum [Sorghum bicolor(L.) Moench ‘BR-54′] and oats (Avena sativaL. ‘Cimarron’) were moderately susceptible to HOE 23408, whereas barley (Hordeum vulgareL. ‘Will’) exhibited marginal tolerance. Wheat (Triticum aestivumL. ‘Triumph 64′) and cotton (Gossypium hirsutumL. ‘Westburn 70′) showed tolerance to HOE 23408 at rates up to 6 ppmw, and soybean [Glycine max(L.) Merr. ‘Bragg’] and peanut (Arachis hypogaeaL. ‘Spanhoma’) demonstrated tolerance to concentrations as high as 24 ppmw. The soil mobility of HOE 23408 was similar to that of trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). No soil phytotoxicity was found 8 weeks after herbicide application in the field or under laboratory incubation conditions of 5 or 10% soil moisture at 21 C. Dissipation was much slower at a temperature of 4.4 C, regardless of the soil moisture level.