Controlled release of the herbicide,fluometuron, from matrix granules based on fractionated organosolv lignins

An organosolv lignin and several of its fractions were used to prepare controlled release matrix granules with fluometuron using a melt process. Release profiles of fluometuron from these granules and a commercial granular formulation were studied in vitro. The release rates of fluometuron were considerably reduced from all lignin-based granules as compared to the commercial formulation. The release rates markedly varied with the lignin fraction used in the fluometuron-lignin matrix systems with the corresponding times for 50% release (T(50)) values ranging from 2.37 to 11.2 days. The variation in release rate of fluometuron was related to the high proportion of low molecular weight lignin and its associated water soluble lignin in the lignin-based granules, in terms of the hydrophobicity of matrix, the content, and release rate of soluble lignin. The release kinetics were fitted to the generalized model for up to 60% release of fluometuron; the kinetics of fluometuron were of the anomalous type for all matrixes in which release rates increased following a delay.     

Controlled release of herbicide acetochlor from clay/carboxylmethylcellulose gel formulations

Controlled-release formulations of the herbicide acetochlor were prepared by using carboxylmethylcellulose (CMC) gel and different types of clay, which were obtained by acid activation, pillared with metal hydroxides, or saturated with organic cations. The effect of formulation parameters (amount and type of clay used, cross-linking time, and drying of the hydrogel formulations) on the acetochlor release rate from different formulations was evaluated by water-release studies. The time taken for 50% of acetochlor to be released, t 50, showed a wide variation (151-522 h) for dried gel formulations, the largest value corresponding to the formulation incorporating aluminum hydroxide pillared clay into CMC gels. The release rate of acetochlor from clay/CMC hydrogel formulations decreased with the increase of the hydrogels' cross-linking time (t50 values ranged from 2.18 to 14.0 h for cross-linking times ranging from 2.0 to 120 min). The performance of inorganic clays in dried gel formulations on slowing the release of acetochlor is related to their sorption capacities, but the addition of organic clay did not lead to the slowest release despite its highest sorption capacity. According to the parameters of an empirical equation used to fit herbicide-release data, the release of acetochlor from clay/CMC gel formulations is controlled by diffusion mechanism.     

Controlled release of the herbicide norflurazon into water from ethylcellulose formulations

The herbicide norflurazon was encapsulated in ethylcellulose (EC(40)) microspheres by the solvent evaporation technique to obtain controlled release formulations. The kinetics of release of the active ingredient into the aqueous solution from different preparations was determined. It was found that the percentage release of the incorporated herbicide was a function of the composition and formation conditions of the formulations (amount of emulsifying agent, EC(40)/herbicide ratio, stirring speed, and percentage of pore-forming agent). The percentage of the herbicide release was related to the properties of the different microspheres obtained, such as particle size distribution, herbicide loading, or surface morphology. The release percentage depended inversely on the particle size of the microspheres and directly on the content of active ingredient and emulsifying and pore-forming agents. An empirical equation was used to fit the herbicide release data, indicating that the release of norflurazon from the various formulations is controlled by a diffusion mechanism. The time taken for 50% of the active ingredient to be released into water (T(50)) was calculated, showing a wide variation among the different preparations (0.95-16.4 days).     

Controlled release of tebuconazole from a polymer matrix microparticle: release kinetics and length of efficacy

Preparation and characterization of microencapsulated tebuconazole, its release kinetics in water, and the bioefficacy of these formulations in controlling wheat rust in spring wheat is described herein. Controlled-release (CR) formulations based on matrix microparticles were prepared by the oil-in-water emulsion process. Polymer-based matrix was prepared from poly(methyl methacrylate) (PMMA) and poly(styrene-co-maleic anhydride) (PSMA). Modification of the matrix was achieved by the use of different low molecular weight or polymeric additives. These additives were found to lower the glass transition temperature of the matrix and enhance the release rate of tebuconazole in water, under infinite sink conditions. Release of tebuconazole from matrix microparticles was found to be diffusion controlled. CR formulations were found to be very efficacious in controlling wheat rust. Soil-applied CR formulations prepared from a PMMA or PSMA matrix, modified with poly(vinyl acetate), were as effective in controlling wheat rust (Puccinia recondita) as foliar-applied tebuconazole, Raxil, from Bayer AG. Results suggest that CR formulations with a systemic fungicide, such as tebuconazole, applied as either a soil or seed treatment, may provide control of foliar diseases, possibly eliminating or reducing the need for traditional foliar applications.     

Ethylcellulose formulations for controlled release of the herbicide alachlor in a sandy soil

The development of controlled-release formulations of alachlor to diminish its leaching in sandy soils, avoiding groundwater contamination and maintaining its efficacy, was studied. For this purpose, ethylcellulose (EC) microencapsulated formulations (MEFs) of alachlor were prepared under different conditions and applied to soil columns to study their mobility. The results show that in all cases the release into water of alachlor from MEFs was retarded when compared with commercial formulation. Total leaching losses in soil columns were reduced to 59% from 98%. The mobility of alachlor from EC microspheres into soil columns has been greatly diminished in comparison with its current commercial formulation (CF), above all with increasing EC/herbicide ratios. Distribution of alachlor applied as MEFs at different depths in the soil was higher in the soil surface (66.3-81.3% of herbicide applied at the first 12 cm). In contrast, the residues from CF along the complete soil column were only 20.4%. From the results of bioassays, MEFs showed a higher efficacy than CF at 30 days after the treatment. The use of ME formulations could provide an advantage in minimizing the risk of groundwater contamination by alachlor and reducing the application rates, as a result of maintaining the desired concentration of the herbicide in the top soil layer, obtaining longer periods of weed control.     

Controlled release of carbofuran from an alginate-bentonite formulation: water release kinetics and soil mobility

The insecticide-nematicide carbofuran was incorporated in alginate-based granules to obtain controlled-release (CR) properties. The basic formulation [sodium alginate (1.61%)-carbofuran (0. 59%)-water] was modified by addition of sorbents. The effect on carbofuran release rate, caused by the incorporation of natural and acid-treated bentonite (0.5 and 1.0 M H(2)SO(4)) in alginate formulation, was studied by immersion of the granules in water under shaking. The time taken for 50% of the active ingredient to be released into water, t(50), was longer for those formulations containing natural bentonite (6.1 h) or acid-treated bentonite (9.0 and 11.7 h for 0.5 and 1.0 M H(2)SO(4) treatments, respectively) than for the preparation without bentonite (4.7 h). It appears from the results that the release of carbofuran from the various formulations is controlled by a diffusion mechanism according to the n values obtained, which were close to 0.5 in all cases. The mobility of carbofuran from alginate-based CR formulations was investigated by using soil columns packed with a clay soil (53% clay and 0.08% organic matter). Two alginate-based CR formulations containing natural bentonite or acid-treated bentonite (0.5 M H(2)SO(4)) were compared to technical grade carbofuran. The use of alginate-based CR formulations resulted in a reduction of the leached amount of carbofuran compared with the total amount of pesticide leached using the technical product (50 and 75% for CR granules containing natural and acid-treated bentonite, respectively). Alginate-bentonite CR formulations might be efficient systems for reducing carbofuran leaching in clay soils, which would reduce the risk of groundwater pollution.     

A laboratory investigation of the release of a conservative tracer and herbicide from topsoil aggregates under varying rainfall intensities

Abstract. This paper describes the results of laboratory-based research which investigated the losses of the herbicide, isoproturon, and a non-adsorbing solute, bromide, from topsoil aggregates under high (7 mm h⁻¹ and low 2.7 mm h⁻¹) intensity simulated rainfall. The structures of the micro- and macro-aggregates from a clay soil of the Denchworth Series (from Wytham, Oxfordshire, UK) were observed using a scanning electron microscope, and the slaking of the topsoil aggregates was also investigated in order to provide a context for interpreting the experimental results. The topsoil at Wytham was found to have a bimodal structure with small microaggregates of 0.71 to 1 mm diameter clustered together to form larger macroaggregates of up to several centimetres diameter. Selected aggregates were air dried and then repacked in Buchner funnels to several centimetres depth in order to remove variability in the experimental results due to the effects of surface microrelief. Under saturated surface conditions high intensity simulated rainfall was less efficient at removing both non-adsorbing and adsorbing solutes from the repacked topsoil aggregates than low intensity rainfall. The observed decrease in the concentration of isoproturon and bromide in the leachate with time could be explained by a transport non-equilibrium effect.     

Controlled release of diuron from an alginate-bentonite formulation: water release kinetics and soil mobility study

The herbicide diuron was incorporated in alginate-based granules to obtain controlled release (CR) properties. The standard formulation (alginate-herbicide-water) was modified by the addition of different sorbents. The effect on diuron release rate caused by incorporation of natural and acid-treated bentonites in alginate formulation was studied by immersion of the granules in water under static conditions. The release of diuron was diffusion-controlled. The time taken for 50% release of active ingredient to be released into water, T(50), was calculated for the comparison of formulations. The addition of bentonite to the alginate-based formulation produced the higher T(50) values, indicating slower release of the diuron. The mobility of technical and formulated diuron was compared by using soil columns. The use of alginate-based CR formulations containing bentonite produced a less vertical distribution of the active ingredient as compared to the technical product and commercial formulation. Sorption capacities of the various soil constituents for diuron were also determined using batch experiments.     

Controlled release of manganese into water from coated experimental fertilizers: laboratory characterization

The release of manganese into water from controlled-release formulations containing manganese EDTA or manganese lignosulfonate was studied. These fertilizers were obtained in the laboratory by adhering the source of manganese over urea pellets and by adding a coating. The materials used as adhesives and coatings were mixtures of rosins plus tricalcium phosphate. With regard to the chemical composition, these formulations conformed to national and international standards for commercial fertilizers. The rate of release of manganese was a function of both the source of manganese used and the coating thickness. Under the same conditions the release of manganese was greater for formulations with manganese EDTA than with manganese lignosulfonate. To predict the kinetic behaviors of the two series of formulations, mathematical equations were established. The manganese source plus rosin coatings improved the handling and storage characteristics of the commercial urea pellets. The study of the rosin coatings using scanning electron microscopy showed that they were compact and homogeneous.     

Controlled release of isoproturon, imidacloprid, and cyromazine from alginate-bentonite-activated carbon formulations

Different alginate-based systems of isoproturon, imidacloprid, and cyromazine have been investigated in order to obtain controlled release (CR) properties. The basic formulation [sodium alginate (1.50%), pesticide (0.30%), and water] was modified using different amounts of bentonite and activated carbon. The higher values of encapsulation efficiency corresponded to those formulations prepared with higher percentages of activated carbon, showing higher encapsulation efficiency values for isoproturon and imidacloprid than for cyromazine, which has a higher water solubility. The kinetic experiments of imidacloprid/isoproturon release in water have shown us that the release rate is higher in imidacloprid systems than in those prepared with isoproturon. Moreover, it can be deduced that the use of bentonite and/or activated carbon sorbents reduces the release rate of the isoproturon and imidacloprid in comparison with the technical product and with alginate formulation without modifying agents. The highest decrease in release rate corresponds to the formulations prepared with the highest percentage of activated carbon. The water uptake, permeability, and time taken for 50% of the active ingredient to be released into water, T50, were calculated to compare the formulations. On the basis of a parameter of an empirical equation used to fit the pesticide release data, the release of isoproturon and imidacloprid from the various formulations into water is controlled by a diffusion mechanism. The sorption capacity of the sorbents and the permeability of the formulations were the most important factors modulating pesticide release. Finally, a linear correlation of the T50 values and the content of activated carbon in formulations were obtained.     

Effects of a sulfonylurea herbicide on soil microarthropods

 The short-term effects on soil microarthropods of the herbicide triasulfuron, belonging to the chemical class of sulfonylureas, were evaluated in two fields which had never been treated with sulfonylureas, and were cultivated with winter wheat. In particular, the effects of single applications at rates corresponding to two- (rate 2) and sixfold (rate 6) the recommended agricultural rate (7.5 g active ingredient ha^–1) were analysed and compared with controls. The changes in the populations of the main groups of microarthropods were evaluated. Rate 2 had very low effects, whereas rate 6 produced a significant decrease in the number of microarthropods, Acarina and Collembola in the surface soil layer (0–7.5 cm). The Collembola were analysed at the species level. Statistical analysis revealed significant differences only for a few species, and only after treatment with the highest rate of triasulfuron. Finally, the results of the field tests were compared to those of laboratory tests carried out previously, which examined the effects of the same herbicide on a collembolan species. Received: 11 November 1998     

Inorganic and organic clays as carriers for controlled release of the herbicide hexazinone

The risk of ground water contamination resulting from rapid leaching of highly soluble pesticides can be minimized through the application of the pesticide adsorbed on a matrix or carrier, which limits the amount of pesticide immediately available for undesirable losses. The use of natural materials for this purpose is of special interest in terms of economy and sustainability. In this work the adsorption of the herbicide hexazinone by two montmorillonites saturated with various inorganic and organic cations was determined and the ability of the two clays displaying the highest adsorption capacities [Fe(3+)-saturated Wyoming montmorillonite, (Fe-SW) and hexadecyltrimethylammonium-saturated Arizona montmorillonite (HDTMA-SA)] to act as carriers for slow release of hexazinone and to reduce herbicide leaching losses was evaluated. Hexazinone formulations based on Fe-SW and HDTMA-SA displayed slow release properties in water and soil/water suspensions, reduced herbicide leaching in soil columns, and maintained herbicidal activity, as compared with the currently available commercial hexazinone formulation (wettable powder). Loosely bound hexazinone-HDTMASA formulations, which led to the slowest breakthrough of hexazinone in soil columns along with the greatest amounts of herbicide released from the clay particles, displayed the most interesting characteristics for their use as slow release formulations and to prevent ground water contamination.     

Fertilizer technology based on optimized nitrogen release from urea-loaded natural superabsorbent carriers

There is a pressing need for advanced fertilizer application technologies that enhance crop yields, maintain soil health and reduce the environmental impact from agriculture. Here, we report on the optimization of nitrogen release profiles of urea-loaded polysaccharide (starch) superabsorbent carriers, employing analytical techniques including UV–VIS, FTIR, EDX, SEM and GC-FID for structural and phospholipid fatty acids PLFA analyses. We fitted existing kinetic models to the uptake and release profiles, providing a link between nitrogen release kinetics and carrier structural variables. The inclusion of zeolite microparticles in the starch-based carriers accelerated the rate of nitrogen release and increasing the maximum amount released. Field tests of the technology on maize crops demonstrated improved plant parameters and enhanced the soil microbial population. These findings highlight the promise of urea-loaded natural superabsorbent carriers as a sustainable alternative to core-shell CRF fertilizers and urease inhibitors.     

NMR characterization of lignins isolated from fruit and vegetable insoluble dietary fiber

Compositional information for lignins in food is rare and concentrated on cereal grains and brans. As lignins are suspected to have important health roles in the dietary fiber complex, the confusing current information derived from nonspecific lignin determination methods needs to be augmented by diagnostic structural studies. For this study, lignin fractions were isolated from kiwi, pear, rhubarb, and, for comparison, wheat bran insoluble dietary fiber. Clean pear and kiwi lignin isolates allowed for substantive structural profiling, but it is suggested that the significance of lignin in wheat has been overestimated by reliance on nonspecific analytical methods. Volume integration of NMR contours in two-dimensional (13)C-(1)H correlation spectra shows that pear and wheat lignins have comparable guaiacyl and syringyl contributions and that kiwi lignins are particularly guaiacyl-rich (approximately 94% guaiacyl) and suggest that rhubarb lignins, which could not be isolated from contaminating materials, are as syringyl-rich (approximately 96% syringyl) as lignins from any known natural or transgenic fiber source. Typical lignin structures, including those newly NMR-validated (glycerols, spirodienones, and dibenzodioxocins), and resinols implicated as possible mammalian lignan precursors in the gut are demonstrated via their NMR correlation spectra in the fruit and vegetable samples. A novel putative benzodioxane structure appears to be associated with the kiwi lignin. It is concluded that the fruits and vegetables examined contain authentic lignins and that the detailed structural analysis exposes limitations of currently accepted analytical methods.     

Characterization of dietary fiber lignins from fruits and vegetables using the DFRC method

Insoluble fiber fractions from 11 fruits and vegetables were investigated for their lignin composition using the derivatization followed by reductive cleavage (DFRC) methodology. To enrich lignin contents and to minimize polysaccharide excess that led to nonanalyzable DFRC chromatograms, the insoluble fibers were degraded by a carbohydrolases mixture. The residues that were found to be representative for the insoluble fiber lignins were analyzed. The investigated fibers differ considerably in their lignin contents and also in their lignin compositions. With the exception of radish fiber, only trace amounts (or none) of the products resulting from p-hydroxyphenyl units were detected. Lignins noticeably differed in the ratio of the DFRC products resulting from syringyl units (S) and guaiacyl (G) units (G/S ratios ranged from approximately 39 to 0.2). The insoluble fiber lignins were classified as G-rich lignins (G/S ratio > 3; carrot, spinach, kiwi, curly kale, radish, and asparagus), S-rich lignins (S/G ratio > 3; rhubarb), or balanced lignins (0.3 < G/S ratio < 3; pear, apple, small radish, and kohlrabi). Information about further structural characteristics, for example, cinnamyl endgroups, was obtained from the analysis of DFRC minor products.     

Low molecular weight polylactic acid as a matrix for the delayed release of pesticides

Low molecular weight polylactic acid (LMW PLA) was used as a matrix to formulate biodegradable matrix granules and films with bromacil using a melt process. The compatibility of the PLA with bromacil was evaluated. The release characteristics of the formulations were investigated in vitro. The degradation and erosion of the formulations were monitored by pH and gravimetric analysis during the course of release. Various granules and films had similar biphasic release patterns, a delayed release followed by an explosive release. The release rates were independent of bromacil content in the matrix, but varied with the geometry of matrices. The mechanisms of diffusion and erosion were involved in the release. The delayed release of the formulations was dominantly governed by the degradation and erosion of PLA. LMW PLA underwent bulk erosion. LMW PLA-based matrix formulations could thus be useful for the application of pesticides to sensitive targets such as seed treatment.     

Effect of the herbicide butachlor on methane emission and ebullition flux from a direct-seeded flooded rice field

 Application of a commercial formulation of the herbicide butachlor (N-butoxymethyl-2-chloro-2′,6′-diethyl acetanilide) at 1 kg a.i. ha^–1 to an alluvial soil planted with direct-seeded flooded rice (cv. Annada), significantly inhibited both crop-mediated emission and ebullition fluxes of methane (CH₄). Over a cropping period of 110 days, the crop-mediated cumulative emission flux of CH₄ was lowered by ∼20% in butachlor-treated field plots compared with that of an untreated control. Concurrently, ebollition flux of CH₄ was also retarded in butachlor-treated field plots by about 81% compared with that of control plots. Significant relationships existed between CH₄ emission and redox potential (E _h) and Fe²⁺ content of the flooded soil. Application of butachlor retarded a drop in soil redox potential as well as accumulation of Fe²⁺ in treated field plots. Methanogenic bacterial population, counted at the maturity stage of the crop, was also low in butachlor-treated plots, indicating both direct and indirect inhibitory effects of butachlor on methanogenic bacterial populations and their activity. Results indicate that butachlor, even at field-application level, can effectively abate CH₄ emission and ebollition from flooded soils planted to rice whilst maintaining grain yield. Received: 15 March 2000     

天然载体控释氮肥研究初探

The Wangdonggou Watershed on the Loess Plateau in China was selected as the study area to develop a model for soil erosion assessments. Using the data collected at 20 sampling sites all tentatively selected indicators were assessed against their corresponding erosion intensity through a correlation analysis. Eight highly correlated indicators were then chosen for the soil erosion assessment. In addition, threshold limits to delineate the class size for these indicators and weights to rank them were determined. Next, a grading model incorporating the selected indicators class rating and their associated weights was developed and verified by an on site evaluation of the soil erosion intensity in the study area. Results of the verification showed that the overall accuracy of the indicator system for assessing soil erosion in the Loess Plateau gully regions could reach 85%.     

Partitioning of penoxsulam, a new sulfonamide herbicide

Penoxsulam (trade name Granite) is a new acetolactate synthase (ALS) inhibitor herbicide for postemergence control of annual grasses, sedges, and broadleaf weeds in rice culture. This study was done to understand the equilibrium phase partitioning of penoxsulam to soil and air under conditions simulating California rice field conditions. Partitioning of penoxsulam was determined between soil and water (Kd) by the batch equilibrium method and between air and water (K(H)) by the gas-purge method. In four representative soils from the Sacramento Valley, the Kd values ranged from 0.14 to 5.05 and displayed a modest increase with soil pH. In soil amended with manure compost, soil sorption increased 4-fold with increasing soil organic matter content, but was still low with a Kd of 0.4 in samples with high organic carbon contents of 15%. Penoxsulam was confirmed to be extremely nonvolatile and did not partition into air at any measurable rate at 20 or 40 degrees C. K(H) (pH 7) was estimated at 4.6 x 10(-15) Pa x L x mol(-1) on the basis of available water solubility and vapor pressure data. The results imply that soil and air partitioning of penoxsulam do not significantly affect its potential for degradation or offsite movement in water.     

Effects of the herbicide glyphosate on nitrification in four soils from Atlantic Canada

The herbicide glyphosate, supplied as Roundup (Monsanto Canada Inc.), was tested for effects on nitrification in four soils from Atlantic Canada. These included a sandy loam (pH 6.8), two silt loam (pH 6.4 and 5.8) agricultural soils and a clay loam forest soil (pH 3.5). Glyphosate was tested at normal field exposure rates (FR) and levels up to 200 times higher. FR values ranged from 19.83 to 29.26 ppm (jig glyphosate g^?1 soil). Glyphosate had no deleterious effects on nitrification in any soil when tested at FR concentrations. In the sandy loam soil nitrification was significantly stimulated at a glyphosate level 50 times higher than FR. With this soil and one of the silt loam soils (pH 6.4) glyphosate levels of 100 times FR and higher were required for a significant inhibition of nitrification. With the other silt loam soil (pH 5.8) glyphosate significantly inhibited nitrification at concentrations 10 times FR and higher. Nitrification in the acidic forest soil was very low and accurate toxicity data could not be obtained. The EC₅₀ of glyphosate towards nitrification in soil ranged from 1435 to 2920 ppm, which corresponds to exposure levels from 67 to 150 times higher than recommended field application rates. The use of glyphosate in agriculture and forestry should have no toxic effects on nitrification in soil.