Search

Determining a precise nitrogen fertilizer requirement for maize in a particular field and year has proven to be a challenge due to the complexity of the nitrogen inputs, transformations and outputs in the nitrogen cycle. Remote sensing of maize nitrogen deficiency may be one way to move nitrogen fertilizer applications closer to the specific nitrogen requirement. Six vegetation indices [normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), red-edge normalized difference vegetation index (RENDVI), triangle greenness index (TGI), normalized area vegetation index (NAVI) and chlorophyll index-green (CIgreen)] were evaluated for their ability to detect nitrogen deficiency and predict grain maize grain yield. Strip trials were established at two locations in Arkansas, USA, with nitrogen rate as the primary treatment. Remote sensing data was collected weekly with an unmanned aerial system (UAS) equipped with a multispectral and thermal sensor. Relationships among index value, nitrogen fertilizer rate and maize growth stage were evaluated. Green NDVI, RENDVI and CIgreen had the strongest relationship with nitrogen fertilizer treatment. Chlorophyll Index-green and GNDVI were the best predictors of maize grain yield early in the growing season when the application of additional nitrogen was still agronomically feasible. However, the logistics of late season nitrogen application must be considered.

HighlightsBetween 1950 and 2017, there was a 12-fold increase in irrigated area in Arkansas and a doubling in Louisiana.Groundwater provides over 90% of the irrigation water applied to the 4 Mha of cropland in the LMRB.Ongoing efforts to address aquifer declines have been multi-faceted and include those of producers, public (local, state, and federal) institutions, and private organizations.Irrigation water management innovations include precision grading, reduced-flood or no-flood rice irrigation, pump automation, computerized hole selection, flowmeter requirements, and permit-based water use limitations.Abstract. The Lower Mississippi River Basin (LMRB) is an agricultural region of national and international significance. The basin relies heavily on the Mississippi River Valley alluvial aquifer to provide over 90% of the irrigation water applied to over four million hectares of cropland, with Arkansas using approximately 70% of the water and Mississippi and Missouri using approximately 15% each. Surface methods predominate, especially furrow irrigation using plastic lay-flat tubing in corn, cotton, peanut, and soybean and flood methods in rice. Irrigation extent has steadily increased by approximately 2% per year, such that irrigation withdrawals, combined with the region’s geology, have led to considerable aquifer declines in portions of Arkansas and Mississippi. Attempts to address these declines have been multi-faceted and include innovations in crop management and source water management, and programs in water resources management. Crop management innovations are focused on soybean and rice production and include precision grading, reduced-flood or no-flood rice irrigation, pump automation, and computerized hole selection. Adoption of these practices remains heavily reliant on field demonstrations and extension outreach. Source water management innovations include on-farm reservoirs, managed aquifer recharge, and regional-scale river diversions. Due to the concerted efforts of producers participating in regional and state programs, progress has been made in making surface irrigation more efficient and less reliant on groundwater. However, aquifer decline remains a challenge to the LMRB’s economy, ecology, and culture. Keywords: Aquifer decline, Irrigation, Lower Mississippi River Basin, Mississippi River Valley alluvial aquifer, Surface water.

Improved irrigation management is identified as a potential mitigation option for methane (CH4) emissions from rice (Oryza sativa). Furrow-irrigated rice (FR), an alternative method to grow rice, is increasingly adopted in the Mid-South U.S. However, FR may provide a potential risk to yield performance and higher emissions of nitrous oxide (N2O). This study quantified the grain yields, CH4 and N2O emissions from three different water management practices in rice: multiple-inlet rice irrigation (MIRI), FR, and FR with cereal rye (Secale cereale) and barley (Hordeum vulgare) as preceding winter cover crops (FRCC). CH4 and N2O fluxes were measured from May to September 2019 using a static chamber technique. Grain yield from FR (11.8 Mg ha−1) and MIRI (12.0 Mg ha−1) was similar, and significantly higher than FRCC (8.5 Mg ha−1). FR and FRCC drastically reduced CH4 emissions compared to MIRI. Total seasonal CH4 emissions decreased in the order of 44 &gt, 11 &gt, 3 kg CH4-C ha−1 from MIRI, FR, and FRCC, respectively. Cumulative seasonal N2O emissions were low from MIRI (0.1 kg N2O-N ha−1) but significantly higher from FR (4.4 kg N2O-N ha−1) and FRCC (3.0 kg N2O-N ha−1). However, there was no net difference in global warming potential among FR, FRCC and MIRI. These results suggest that the increased N2O flux from furrow-irrigated rice may not greatly detract from the potential benefits that furrow-irrigation offers rice producers.

As part of conjunctive water resource management, on-farm reservoirs have been constructed to address declines in the Mississippi River Valley Alluvial aquifer, the primary source of irrigation for most of the row crops grown in eastern Arkansas. These reservoirs and their associated infrastructure represent significant investments in financial and natural resources, and may cause producers to incur costs associated with foregone crop production and long-term maintenance. A better understanding of past trends in reservoir construction can allow for more efficient resource allocation towards future adoption of this practice. Thus, an analysis of reservoir construction trends in the Grand Prairie (GP) Critical Groundwater Area and Cache River (CR) Critical Groundwater Area was conducted. Between 1996 and 2015, on average, 16 ± 5 and 4 ± 1 reservoirs were constructed per year, corresponding to cumulative new reservoir surface areas of 161 ± 49 and 60 ± 18 ha yr−1, for GP and CR, respectively. In terms of reservoir locations relative to aquifer status, after 1996, 84.5% of 309 reservoirs constructed in GP and 91.0% of 78 in CR were located in areas with remaining saturated aquifer thicknesses of 50% or less. The majority of new reservoirs (74% in GP and 63% in CR) were constructed on previously productive cropland. The next most common land use, representing 11% and 15% of new reservoirs constructed in GP and CR, respectively, was the combination of a field edge and a ditch, stream, or other low-lying area. Less than 10% of post-1996 reservoirs were constructed on predominately low-lying land, and the use of this land cover decreased in both critical groundwater areas during the past 20 years. A reservoir footprint analysis indicated that 85% of the typical reservoir system consists of the reservoir pond itself with the remaining 15% of land area consisting of tailwater recovery ditches, and other associated features. The disparities in reservoir construction rates, locations, and prior land uses between the two critical groundwater areas is likely due to groundwater declines being first observed in GP as well as the existence of two large-scale river diversion projects under construction in GP that feature on-farm storage as a means to offset groundwater use. Results of this analysis can be used in the development of targeted resource allocation initiatives and conservation efforts in critical groundwater areas and other similarly water-scarce regions.

With over 4 million ha irrigated cropland, the Lower Mississippi River Valley is a highly productive agricultural region where irrigation practices are similar and the Mississippi River Valley alluvial aquifer (MRVA) serves as a primary source of on-demand irrigation. The power conversion coefficient method was used to measure season-long irrigation applied by producers to cotton, maize, rice, and soybean grown in the Mississippi Delta over a 12-year period that spanned a range of weather and cropping conditions. Averaged across all years and irrigation methods, irrigation rates were 9200, 3100, 2800, and 1800 m3 ha−1 for rice, maize, soybean, and cotton, respectively. Pivot and flood methods resulted in the lowest application rates when compared to furrow irrigation of row crops. In terms of rice, zero-grade fields received the least irrigation while multiple-inlet rice irrigation reduced irrigation by 19% relative to cascade flooding. No differences were measured between contour- and straight-levee rice fields. Irrigation rates for cotton and rice remained unchanged over time. Maize-soybean rates increased by approximately 200 m3 ha−1 y−1 and correlated (r > 0.67) with cumulative moisture deficit at Stoneville. Study results provide irrigation rates necessary to calculate detailed water budgets for the MRVA. These data may also serve as benchmarks for irrigation performance evaluations.

The objective of this work was to evaluate the effect of raised seedbeds associated with irrigation on the yield of soybean (Glycine max) rotated with rice (Oryza sativa) in lowland conditions in Southern Brazil. Field experiments were conducted in two crop seasons (2014/2015 and 2015/2016), with two planting systems (raised seedbed and flat planting) and two irrigation managements (irrigated and nonirrigated). Water use, biological nitrogen fixation, and yield were evaluated. The water used for raised seedbeds was 14% (151 m3 ha-1) and 27% (163 m3 ha-1) lower than that for flat planting in the first and second crop seasons, respectively. Irrigation increased nodule number per plant, nodule dry weight, and biological nitrogen fixation. The average grain yield of the raised seedbed system was 10% (529 kg ha-1) and 9% (362 kg ha-1) higher than that of flat planting in 2014/2015 and 2015/2016, respectively. Irrigation improved yield by 5% (203 kg ha-1) and 7% (265 kg ha-1) in each crop year. The use of raised seedbeds associated with irrigation improves the yield of soybean grown in rotation with rice in lowland in Southern Brazil.

Research was conducted to help rice (Oryza sativa L.) farmers increase rainfall capture to offset groundwater use in the Lower Mississippi River Valley (LMRV). The LMRV is where a majority ...

(1) Background: Elevated atmospheric CO2 concentration affects the growth and development of the rice crop. In Southern Brazil, rice is traditionally produced with continuous irrigation, implying a significant amount of water used. Besides, continuous flooding favors the uptake of toxic elements such as arsenic (As) and cadmium (Cd). In this work, one Brazilian rice cultivar (IRGA 424) was tested for the effects of elevated CO2 concentration and different water regimes on rice yield, and As and Cd accumulation in grain. (2) Methods: Rice was grown in two CO2 concentrations (400 and 700 µmol mol−1) and two irrigation regimes (continuous and intermittent). It was evaluated the number of tillers, plant height, aboveground dry weight (ADW), water use efficiency (WUE), rice yield components, and As and Cd concentration in rice grain. (3) Results: Rice plants were taller and had a higher WUE when cultivated at e[CO2]. The ADW and the rice yield component were not affected by CO2 levels nor water regimes. Intermittent flood regimes had a lower average As concentration. The Cd concentration in the samples in both growing seasons and all treatments was below the limit of quantitation (8.76 μg kg−1). (4) Conclusions: Enhanced CO2 concentration did not affect rice yield, increased the WUE, and reduced As concentration in grains. Regarding water management, the intermittent regime enhanced WUE and promoted a reduction in As concentration in grains.

Arkansas, which ranks third in the nation in terms of irrigated cropland, relies heavily on the Mississippi River Valley alluvial aquifer for irrigation. Two critical groundwater areas have been identified, with one in the Grand Prairie in central Arkansas and the other along the Cache River in northeast Arkansas. Thus, there has been a call to develop surface water resources for irrigation, and as a result, on-farm irrigation reservoirs have been constructed to capture and store surface water. To assess the current state of surface water development, a remote-sensing survey using National Agricultural Imagery Program data was conducted to provide an inventory of the locations and surface area of on-farm reservoirs in the two critical groundwater areas. Expert consultation and on-site inspections were used to confirm the remote sensing results. In the larger Grand Prairie area, where aquifer decline was recognized earlier, 632 reservoirs were identified for a total surface area of 9,300 ha. In the Cache River area, 143 reservoirs were identified for a total surface area of 2,000 ha. Average reservoir size in both regions was 14.6 ± 20 ha and ranged from 1 to 265 ha. Reservoir area comprised approximately 3% and 1% of the areas of potentially-irrigated cropland in Grand Prairie and Cache River regions, respectively. Keywords: Aquifer depletion, Irrigation, On-farm reservoirs, Surface water.

Multiple-inlet rice irrigation (MIRI) decreased irrigation applications by an average of 24% over an 86-day flood when compared to single-inlet (SI) rice flood distribution. Even in the abs...

Use of furrow irrigation in row crop production is a common practice through much of the Midsouth US and yet, nutrients can be transported off-site through surface runoff. A field study with cotton (Gossypium hirsutum, L.) was conducted to understand the impact of furrow tillage practices and nitrogen (N) fertilizer placement on characteristics of runoff water quality during the growing season. The experiment was designed as a randomized complete block design with conventional (CT) and conservation furrow tillage (FT) in combination with either urea (URN) broadcast or 32% urea ammonium nitrate (UAN) injected, each applied at 101 kg N ha− 1. Concentrations of ammonium (NH4-N), nitrate (NO3-N), nitrite (NO2-N), and dissolved phosphorus (P) in irrigation runoff water and lint yields were measured in all treatments. The intensity and chemical form of nutrient losses were primarily controlled by water runoff volume and agronomic practice. Across tillage and fertilizer N treatments, median N concentrations in the runoff were

Although intermittent flooding of rice (Oryza sativa L.) has been shown to significantly reduce irrigation demand, farmer adoption is limited in the United States where continuous flooding remains standard practice. This limited extent of adoption stems in part from a number of scalability and agronomic concerns. This study used replicated trials established in farmer-managed fields to determine if intermittent flooding can be successfully adapted to commercial-scale rice production in Mississippi. When intermittent flooding was coupled with multiple-inlet rice irrigation (MIRI), the quantities and qualities of yields were maintained or increased for five commercial rice varieties and one hybrid, relative to continuously-flooded controls. Only CL151 exhibited a decrease in total head rice when milled, this after being subjected to five or more wetting and drying cycles over ≈80 day flood periods. Water use over three years averaged 32% less than comparable MIRI systems not using intermittent flooding. These results demonstrate that intermittent flooding can be successfully adapted by producers to commercial-scale and that 600 mm irrigation is an achievable goal for rice grown on clay soils in Mississippi. The positive yield responses of CL162 to intermittent flooding and pre-flood urea-nitrogen support research showing that rice benefits from carefully managed wetting- and drying-periods when used in conjunction with effective pest management. The success of these producers at adapting intermittent rice flooding to commercial scale can be attributed in part to their having comprehensive weed and disease management programs, proficiency in using MIRI, and reliable irrigation systems with ample well capacities that allowed rapid flood establishment. Even partial adoption of intermittent rice flooding can increase rainfall capture and reduce demand for irrigation. In turn, this could help to alleviate overdraft of the Mississippi River Valley Alluvial aquifer, a resource of national and international significance.

In the Brazilian state of Rio Grande do Sul, rice (Oryza sativa) is predominantly grown using a continuous flood, which can cause herbicide runoff when fields are over-irrigated or heavy rainfall occurs. Proper irrigation and drainage management can reduce herbicide transport to the environment. The objective of this study was to evaluate the effect of different irrigation practices on water runoff and the transport and dissipation of the herbicides imazethapyr and imazapic. The experiments were conducted in the 2007/08 and 2008/09 growing seasons at the experimental area of the Universidade Federal de Santa Maria. The treatments comprised two irrigation management systems: continuous flooding of an approximate 10-cm flood depth and intermittent flooding where the flood was allowed to fully subside before being reestablished to a 10-cm height. The amount of water runoff and the rates of herbicide dissipation and transport were evaluated. Owing to increased storage of rainwater, intermittent flooding reduced water runoff by 47% and runoff of imazethapyr and imazapic by 89 and 77%, respectively, relative to the continuously flooded control. Imazapic was significantly more persistent than imazethapyr, but there was no effect of irrigation management on herbicide persistence in water.

Information on the dissipation of clomazone, imazapyr, and imazapic in paddy water under different irrigation system is not available in the literature. The objective of this study was to investigate the effect of two irrigation systems (intermittent (IF) and continuous (CF) flood) on the dissipation of clomazone, imazapyr, and imazapic in paddy water. Imazapic was the least persistent herbicide in paddy water, with DT50-values of approximately 3 and 5d under CF and IF, respectively. Imazapyr required a two-fold increase in time to reach its half-life in water in contrast to imazapic, with DT50-values of approximately 6 and 11d under CF and IF, respectively. Clomazone showed the highest DT50-values, varying between 7 to 21d under CF and IF, respectively. Imazapyr and imazapic dissipation was faster under CF, while clomazone was not affected. This investigation found that the dissipation behaviors of herbicides vary under different rice irrigation regimes. Thus changes in irrigation management, as will be required to produce more rice grain with less water to avoid future scarcity, should consider impacts of flood management on herbicide persistence and environmental behavior.

Inconsistent control of barnyardgrass with bispyribac may be alleviated through adjuvant technology. Experiments were conducted to determine the effect of adjuvant and urea ammonium nitrate (UAN) on absorption and translocation of bispyribac in barnyardgrass. Additional experiments were conducted to determine when maximum absorption and translocation occurred with the use of a methylated seed oil/organosilicone adjuvant (MSO/OSL) plus UAN (0.37 L ha−1and 2% v/v). In the initial experiment,14C-bispyribac–treated leaves, nontreated leaves, and roots were collected 6 and 24 h after application. Absorption was greatest with tank-mixed MSO/OSL (0.37 L ha−1) plus UAN (2% v/v) and the proprietary blend of MSO/OSL/UAN (2% v/v) at 80 and 74% of applied14C-bispyribac, respectively. Translocation to nontreated leaves and roots was also highest with these treatments. Increased translocation appeared to be due to greater herbicide absorption, not an increase in translocation rate. The addition of 32% UAN to MSO/OSL and nonionic organosilicone (OSL/NIS) adjuvant systems resulted in a four to fivefold increase in absorption compared with treatments without UAN. Recovery of14C-bispyribac in additional experiments generally decreased as time after application increased; however, recovery was 86% or greater for all time intervals. By 12 h after application, 68% of applied14C-bispyribac was absorbed. At this time,14C-bispyribac was partitioned within the plant in the following manner: 48% in the treated area, 10% in leaf tissue from treated area to tip of the treated leaf, 1.9% in leaf tissue from treated area to collar region of the treated leaf, 1.6% in remaining leaves from collar of treated leaf upward, 5.3% in remaining leaves from collar of treated leaf downward to soil line, and 0.7% in the roots. These data indicate that maximum absorption was achieved within 12 h with a tank mix of MSO/OSL and UAN or the MSO/OSL/UAN blend.

Field studies were conducted in 2001 through 2003 to determine if shikimic acid accumulation could be used to accurately predict yield reductions in field corn exposed to sublethal rates of glyphosate. Glyphosate (0-0.32 kg ae/ha) was applied to corn at the V6 to V8 growth stage. Corn whorls were randomly collected up to 14 days after application (DAA), and shikimic acid accumulation in the whorls was determined using HPLC-UV. Maximum shikimic acid accumulation occurred 3-7 DAA in corn receiving 0.16 and 0.32 kg/ha. Shikimic acid accumulation 3, 5, and 7 DAA did correlate (r = 0.80-0.86) to yield losses from a sublethal application of glyphosate. Shikimic acid accumulation 3, 5, and 7 DAA was better correlated to visual injury at 14 DAA than to yield reductions. Visual injury ratings 14 DAA were a slightly better indicator of potential yield losses (r = 0.93) than shikimic acid accumulation in field-grown corn whorls (r = 0.8-0.86).

Rice irrigation-water use was estimated in Mississippi (MS) and Arkansas (AR) in 2003 and 2004. Irrigation inputs were compared on naturally sloping (i.e. contour-levee system) and mechanically graded fields. In MS, rice production consumed, on average, 895 mm water, but irrigation inputs were greatly affected by production system. Contour-levee systems accounted for 35% of the production area and consumed 1,034 mm irrigation. Fields mechanically graded to a consistent slope of approximately 0.1% (i.e. straight-levee systems) consumed 856 mm irrigation and accounted for 60% of the production area. Fields devoid of slope (i.e. zero-grade system) accounted for 5% of the production area and consumed 382 mm irrigation. In AR, contour-levee rice production consumed 789 mm compared to 653 mm with a straight-levee system. Using low pressure, thin wall (9–10 mil) disposable irrigation tubing to deliver water to each paddy independently reduced irrigation inputs by 28% in MS and 11% in AR when compared to a single-point (levee-gate) distribution system.

The recent introduction of imidazolinone-tolerant rice varieties allow imazethapyr to be used in commercial rice. Little is known about imazethapyr photodegradation in the rice field. Laboratory studies were conducted to determine the direct and indirect photolysis rates for imazethapyr and to evaluate the photolysis of imazethapyr in three rice paddy waters. The reaction quantum yield (phi I) for imazethapyr was determined to be 0.023 +/- 0.002, while the hydroxyl radical rate constant (K(I)*OH) was 2.8 x 10(13) M(-1) h(-1). These results show that imazethapyr is susceptible to both direct and indirect photolysis reactions in water. The results also show that imazethapyr photolysis in paddy water will be affected by turbidity because of its impact on the availability of sunlight to drive direct and indirect photolysis reactions.

Discoloration of bermudagrass often results from application of MSMA herbicide used to control southern crabgrass and other weeds. However, when products containing iron sulfate (FeSO4) are tank-mixed with MSMA, this discoloration is reduced. Experiments investigated the effect of tank-mixing organic arsenical herbicides with FeSO4or a chelated iron source (Sprint 330) in terms of southern crabgrass control and injury to bermudagrass. Tank-mixing MSMA with FeSO4reduced bermudagrass injury. However, southern crabgrass control was also reduced by at least 50% with the addition of ≥0.38 kg Fe2+ha−1. Neither antagonism nor safening of bermudagrass was observed when the chelated Fe2+source was used. Applying FeSO4as a separate treatment 1 to 4 d before or after MSMA application did not reduce visual burmudagrass injury 1 wk after treatment. Solution pH and FeSO4concentration controlled the extent of complexation and level of antagonism observed in the field; inorganic Fe2+reacted with MSMA to form a complex having reduced herbicidal activity. Potentiometric and spectrophotometric investigations found that methylarsonate, the parent acid of MSMA and other organic arsenical herbicides, reacts with inorganic Fe2+to form a stable 1:1 Fe2+-methylarsonic acid chelate having two points of metal coordination and a stability constant log10(β) = 2.77 ± 0.04. Tank-mixing MSMA with FeSO4to protect against bermudagrass injury negates the benefit of applying the herbicide for weed control, and therefore is not a recommendable practice for turf managers.

An interlaboratory study was conducted to compare pesticide recovery from Empore C(18) and Speedisks C(18)XF solid phase extraction disks after shipping. Four pesticides were used for the comparison of the two disk extraction materials: atrazine, diazinon, metolachlor, and tebuconazole. These pesticides were chosen to provide a range of physiochemical properties. Water samples were extracted onto the disk types and shipped to a cooperating laboratory for elution and analysis. The mean recoveries from Empore disks were atrazine, 95%; diazinon, 91%; metolachlor, 92%; and tebuconazole, 83%. The recoveries from Speedisks C(18)XF were atrazine, 89%; diazinon, 87%; metolachlor, 86%; and tebuconazole, 79%. Means for each of the pesticides using the different disk types were not statistically different (alpha = 0.05), but results were more variable when using Speedisks C(18)XF as compared to Empore disks. Reasons for the increased variability are discussed, but overall results indicate that Speedisks C(18)XF could be used as an alternative to Empore disks. Speedisks C(18)XF are enclosed in a plastic housing, so they can be used more easily in remote sampling sites without the possibility of glassware breakage, no prefiltration of samples is needed, and there are realignment problems that can be associated with the Empore disks.

Because organic sorption in soil may never reach equilibrium, a thin-disc flow nonequilibrium method may be helpful in understanding herbicide-soil interactions. This research was conducted to (i) determine the influence of incubation time on imazaquin [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid] desorption from soil, (ii) examine the influence of solution flow velocities on desorption, and (iii) elucidate the most appropriate kinetic model to describe imazaquin leaching. Soil at 7.5% moisture w/w was treated with imazaquin and incubated for 24, 72, and 168 h. Treated soil was sealed in an in-line filter apparatus and rinsed with 5.0 mM CaCl 2 at 0.33, 0.67, or 1.0 mL min -1 . Effluent was collected as 1.0-mL fractions for a total of 50 mL. Flow was stopped for 24 h. When flow resumed, fractions were collected for an additional 15 mL. After the initial desorption, 79% of the imazaquin incubated for 24 h was leached. Increasing incubation time beyond 24 h reduced imazaquin leaching. After both desorption events, 13% of the initially applied imazaquin remained in the soil incubated for 168 h, compared with 7% with soil incubated for 24 h. Elovich and Freundlich kinetics accounted for 98% of the variance observed in the imazaquin desorption curves. First-order and diffusion kinetics accounted for 91% of the variance. Incubating soil for 72 h before desorption reduced the rate of imazaquin desorption by approximately 12%, compared with the 24-h incubation treatment. Imazaquin desorption was not affected by wash solution flow rate. These data suggest that the kinetics of desorption in prolonged desorption events are limited by transport phenomena (i.e., particle and film diffusion).

The inositol isomer composition of phosphoinositides, polyphosphoinositols, phosphatidylinositol-linked glycans, and glycosyl phosphatidylinositol-anchored proteins of logarithmic phase Tetrahymena vorax was determined by GC-MS analysis of trimethylsilylimadazole derivatives. The most abundant inositol found was the myo-isomer; however, appreciable percentages of scylloinositol were present in the free inositol pool, phosphatidylinositol-linked glycan fraction, and glycosyl phosphatidylinositol-anchored protein fraction. Trace quantities of chiro- and neo-inositols also were present.

Research on best management practices, including vegetative filter strips, is needed to evaluate the potential for reducing herbicides in surface runoff. Laboratory studies were conducted to determine the influence of different filter strip components on fluometuron adsorption. Samples were taken from a switchgrass filter strip (1-m wide) established on a Brooksville silty clay. Sampled components included switchgrass stems clipped to 4 cm, plant residue on the soil surface, and topsoil

S-metolachlor is a preemergent herbicide used for the control of annual grasses and small-seeded broadleaf weeds in more than 70 agricultural crops worldwide. Recently, Smetolachlor has been used to control imidazolinone-resistant red rice in rice-soybean rotation in lowland environments of the Southern Brazil. However, limited information concerning the environmental fate of S-metolachlor in lowland soil is available in the literature. Thus, this review was designed to describe the major transport and dissipation processes of Smetolachlor in attempting to improve weed management programs used in rice-soybean rotation and mitigate environmental contamination of lowland areas.

Studies were conducted to determine the ability of ozonation catalyzed by hydrogen peroxide (H2O2) to degrade solutions of Scepter herbicide (imazaquin). Scepter herbicide solutions were rapidly degraded using a range of solution temperatures (1−35 °C) and H2O2 concentrations (0−69 mM). The most rapid degradation occurred when the [H2O2] was 0.2 mM; imazaquin was also rapidly degraded in the absence of H2O2. The ozonation times required for 90% removal of the herbicide were typically < 15 min. Approximately 10.5 ± 4.4% (quinoline ring) to 17.1 ± 7.8% (carboxylic acid) of [14C]imazaquin was oxidized to 14CO2 when solutions with pH values ranging from 5.5 to 8.5 were ozonated for 0.5 h at 20 °C. Resulting ozonation products, which included nitrate, exhibited rapid biomineralization when added to two soils. The ozonation products of Scepter herbicide were not phytotoxic when applied to cotton, corn, and soybean seedlings at application rates equivalent to 34 g a.i./ha. Keywords: Imazaquin; ozonation; pestici...

Surface water samples were collected from May 2002 through May 2003 at seven locations within the Upper Pearl River Basin (UPRB) in east-central Mississippi to assess levels of pesticide impairment in the watershed. Depth-integrated samples were collected at three sites from September 2001 through January 2003 for total dissolved solid (TDS) analysis. Samples were extracted via Solid Phase Extraction (SPE) and analyzed for fifteen pesticides: triclopyr, 2,4-D, tebuthiuron, simazine, atrazine, metribuzin, alachlor, metolachlor, cyanazine, norflurazon, hexazinone, pendimethalin, diuron, fluometuron, and the dichlorodiphenyltrichloroethane (DDT) degradation product p,p'-DDE. Of the analyzed compounds, hexazinone was detected in 94% of the samples, followed by metolachlor (76%), tebuthiuron (48%), and atrazine (47%). Metribuzin was detected in 6% of the samples and was the least detected compound of those analyzed. Sediment concentrations ranged from 20.64 mg/L at Burnside to 42.20mg/L at Carthage, which also had the highest cumulative total sediment concentration at 4,009 mg/L.

Only limited information exists concerning the fate of aged herbicide residues in subsurface soils. To assess the importance of degradation and leaching in the persistence of aged herbicide residues in subsoils, formulations of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one), metolachlor (2-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide), pidoram (4-amino-3,5, 6-trichloropyridine-2-carboxylic acid), 2,4-D (2,4-dichlorophenoxyacetic acid), and alachlor (2-chloro-2',6'-diethyl-N-methoxyethylacetanilide) were applied separately to two moist Arkansas subsoils and buried for up to 3 yr. The treated subsoils were placed in one of two storage container types, buried in situ at 30, 90, or 150 cm within the soil profile, and retrieved at 6-mo intervals. Amounts of herbicide remaining in the subsoils at two study locations were determined chromatographically. Use of two different types of storage containers allowed for comparison of the relative degradation and leaching that occurred with time. Statistical evaluation of these data found that significant early (less than 6 mo after treatment) degradation occurred in 80% of 36 possible herbicide x soil depth x location combinations. Early leaching occurred between 30 and 50% of the time. Long-term degradation (greater than 6 mo after treatment) occurred in 23 of 28 cases, while long-term leaching occurred in 7 cases. Slow degradation and notable leaching of picloram occurred at 90 and 150 cm at the loamy fine sand location. In addition, prolonged persistence of alachlor relative to metoachlor was observed in subsoils at both study locations.

PREFACE 1. Research on the Fate of Pesticides Applied to Turfgrass: A Perspective by a Scientist, Administrator and Emeritus - Al Smith 2. Aesthetics and Practice of Maintaining the Ideal Lawn in Peachtree City, GA - Ted L. Gragson, Andrew G. Keeler 3. Effects of Turf Pesticides on Aquatic Invertebrates - Jay P. Overmyer 4. Determination of Transferable Residues of Carbaryl from Turf - Michael E. Krolski, Joseph R. Hudson, Vicky Standart, Curt Lunchick, James K. Campbell 5. Surface Drinking Water Assessment and Monitoring for Oxadiazon Herbicide on Golf Courses - Ujjana B. Nandihalli, Russell L. Jones, Richard Allen, Tharacad S. Ramanarayanan, George J. Sabbagh 6. Comparison of Regulatory Method Estimated Drinking Water Exposure Concentrations with Monitoring Results from Surface Water Drinking Supplies - Scott H. Jackson, John J. Jones, John Hanzas 7. . Turfgrass Dissipation of Cyazofamid - Jerome L. Wiedmann 8. Field Design and Quality Control Considerations for Turfgrass Runoff Studies Conducted for Modeling Purposes - Joseph H. Massey, Peter A. Y. Ampim, Barry R. Stewart, Mark J. Carroll, M. Cade Smith 9. Modeling Approach for Regulatory Assessment of Turf and Golf Course Pesticide Runoff - James N. Carleton, Cheryl Sutton, James Lin, Mark Corbin 10. The Development of a Standard Turf Scenario:Notes of an External Review of the USEPA Turf Scenario - Adrian M. Wadley, Mary T. Nett 11. Modeling 2,4-D Transport in Turfgrass, Thatch and Soil - S. Raturi, R.L. Hill, M.J. Carroll 12. Regional Analyses of Pesticide Runoff from Turf - Douglas A. Haith, Matthew W. Duffany, Antoni Magri 13. Development and Testing of a Comprehensive Model of Pesticide Losses from Turf - Antoni Magri, Douglas A. Haith, A. Martin Petrovic, Laosheng Wu, Robert L. Green

Nonequilibrium disc-flow techniques may better reproduce dynamic soil-pesticide interactions than traditional batch sorption studies. Batch kinetic and equilibrium experiments and dual-label thin-disc flow experiments were conducted with atrazine (6-chloro-N-ethyl-N'-isopropyl-1,3,5-triazine-2,4-diamine) and imazaquin [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid] using a Demopolis silt loam (loamy-skeletal, carbonatic, thermic, shallow Typic Udorthent; 8% clay, 62 g kg(-1) organic matter, 7.6 pH). Batch kinetic studies with both herbicides revealed an almost instantaneous rapid phase and a much slower gradual phase. The rapid phase was complete after 5 min and equilibrium was reached at 24 h. The rapid phase accounted for 74% and 12 to 30% of the total amounts adsorbed for atrazine and imazaquin, respectively. The sorption of both the rapid and 24-h isotherms for each herbicide best fit the Freundlich equation. The rapid and 24-h K(f) values of atrazine were 1.38 and 2.41, respectively, and the N value of both phases was approximately 0.93. For imazaquin, the rapid and 24-h K(f) values were 0.056 and 035, respectively, and the N value for the rapid phase of imazaquin was 0.71, compared with 0.86 for the 24-h isotherm. In the dual-label thin-disc flow experiments, the average partition coefficient for atrazine at the peak soil concentration point was 1.54. This value closely agreed with the observed rapid-phase K(f) value of 1.38. In contrast, the thin-disc flow experiments failed to detect any imazaquin retention. The thin-disc flow method can allow for a greater resolution of rapid sorption kinetics, which is impractical with batch studies. Along with dynamic partitioning data, the thin-disc flow method may provide kinetics data that may better complement environmental models than coefficients generated with batch techniques.

Horseweed (Conyza canadensis) is a cosmopolitan weed that commonly grows throughout North America. Horseweed that is not completely controlled by normal applications of glyphosate has been reported in western Tennessee. This research had three objectives: (1) to develop and validate an analytical procedure for the quantitative determination of shikimate, an important indicator of glyphosate activity in plants; (2) to confirm resistance to glyphosate in a horseweed population; and (3) to examine the accumulation of shikimate in both glyphosate-resistant and glyphosate-susceptible horseweed plants. The analytical procedure to determine shikimate used extraction with 1 M HCl for 24 h, followed by liquid chromatography using photodiode array detection, and shikimate recoveries wereor=82%. Glyphosate applications of both 0.84 kg ae/ha (the standard application rate) and 3.8 kg ae/ha to susceptible plants caused complete plant death. The same glyphosate applications to putative resistant populations caused less than 15% growth reduction as determined by visual evaluations, and fresh weights of these resistant plants 17 days after glyphosate treatment (DAT) were reduced an average of 45% in one population and were not affected in a different population. This direct comparison conclusively confirms that horseweed plants collected in western Tennessee in 2002 are resistant to 4 times the normal application dosage of glyphosate. The glyphosate-resistant horseweed biotypes still exhibited some herbicidal effects from the glyphosate, such as yellowing in the most actively growing, apical shoot meristems. The yellowing in the shoot apexes was transitory, and the plants recovered from this damage. Shikimate concentrations in all untreated horseweed plants were less than 100 microg/g, which was significantly less than that in all plants which had been treated with 0.84 kg ae/ha of glyphosate. Unexpectedly, shikimate accumulated (1000 microg/g) in both resistant populations and the susceptible population. However, there were differences in shikimate accumulation patterns between resistant and susceptible horseweed biotypes. Shikimate concentrations in resistant populations declined about 40% from 2 to 4 DAT, while shikimate concentrations in the susceptible horseweed plants increased about 35% from 2 to 4 DAT. The confirmed resistance of a widespread weed implies that alternative control strategies for glyphosate-resistant horseweed will be needed in those no-tillage production systems where it commonly occurs.

A year-long nurseryworker pesticide exposure study was designed to measure and evaluate the exposure occurring to workers who had the potential for simultaneous exposure to multiple pesticides. This four-State study was conducted in five nurseries (four USDA Forest Service and one State) involved in conifer seedling production. Primary comparisons were made among nursery workers in the Pacific northwest and south central United States. Worker exposure was assessed by using patches attached to clothing, handrinse samples and urine excreted from potentially exposed workers. In addition, dislodgeable residue in rinsate from a water wash of pesticide-treated seedlings was also evaluated. Four different groups of field workers, designated as applicators, weeders, scouts and packers, were included. The pesticide absorbed dose, assessed by urine analysis of pesticide metabolites and the deposition of pesticide on patches attached to the clothing of field workers, was monitored as they performed their duties under normal conditions (e.g., typical clothing, pesticide application). Monitoring was performed for the 14 different pesticides which were used in these nurseries. Seven pesticides were studied in more detail using biological monitoring. For these compounds, metabolites known to be excreted in the urine of exposed humans or other mammals were used to estimate the dose of pesticide absorbed by the exposed workers. The highest percentage of positive samples came from dislodgeable residue samples (8.3%) followed by patch samples (3.2%), handrinse (2.9%), and urine samples (1.3%). To summarize the conclusions from the urinary excretion data, 12 of the 73 nursery workers in the study received a low absorbed dose of pesticide. Biological monitoring revealed that three pesticides (benomyl, bifenox and carbaryl) were found in the urine of some of the workers. Of the 3,134 urine samples analyzed there were 42 positive; 11 urine samples were positive for benomyl, while bifenox was responsible for 13 positives and carbaryl accounted for the remaining 18. The 12-week continuous monitoring of urine showed that metabolites of these materials were rapidly excreted; thus, no build-up in the body is anticipated. Margins of Safety (MOS) calculations were made to provide an assessment of the significance of the exposure. Based on the low frequency of positive urine samples in the study, the low levels of metabolites when they were found, their apparent rapid excretion rate and the No Observed Effect Level (NOEL) data, furnished from other sources, nursery worker exposure to pesticides in these conifer nurseries is below health threatening levels.