Effect of imazaquin applications on the growth,leaf chlorophyll and yield of soybean in the Guinea Savanna of Nigeria

Abstract

Field trials were conducted during the wet seasons of 1989, 1991, 1994 and 1995 to evaluate the effects of pre‐emergence and post‐emergence applications of four rates of imazaquin (0.00; 0.15; 0.30 and 0.45kg a.i/ha) on the growth, leaf chlorophyll types and grain yield of soybean c.v. SAMSOY 2. Imazaquin applications had no significant effect on the growth of soybean roots on most of the sampling dates, but pre‐and post‐emergence applications of imazaquin at 0.30 and 0.45kg a.i/ha reduced soybean root nodules at 5 and 7 weeks after planting (WAP). Soybean shoot growth was generally reduced at 5WAP by the pre‐emergence and at 7WAP by the higher rates (0.30 & 0.45kg a.i/ha) of post‐emergence application of imazaquin. Pre‐and post‐emergence applications of imazaquin showed a strong tendency to reduce the concentration of chlorophyll a and total chlorophyll at at 3 and 5WAP respectively. The concentrations of chlorophyll types in soybean leaves at 9WAP was generally comparable among most treatments especially in 1991. Whole plant fresh weight of soybean at 7WAP was reduced by all rates of post‐emergence application of imazaquin. However, there was no significant difference in the whole plant dry weight of soybean at 3 to 7 WAP in 1989 and at 3, 5 and 9WAP in 1991. In each trial, pre‐and post‐emergence applications of soybean significantly increased the grain yield of soybean compared with the control treatment. This study showed that, inhibition of soybean shoot growth and leaf chlorophyll concentration was transient and that soybean plants require about 6 weeks for complete recovery from imazaquin phytotoxicity.     

Biodegradation of triazine herbicide metribuzin by the strain Bacillus sp. N1

By enrichment culturing of soil contaminated with metribuzin, a highly efficient metribuzin degrading bacterium, Bacillus sp. N1, was isolated. This strain grows using metribuzin at 5.0% (v/v) as the sole nitrogen source in a liquid medium. Optimal metribuzin degradation occurred at a temperature of 30ºC and at pH 7.0. With an initial concentration of 20 mg L^?1, the degradation rate was 73.5% in 120 h. If the initial concentrations were higher than 50 mg L^?1, the biodegradation rates decreased as the metribuzin concentrations increased. When the concentration was 100 mg L^?1, the degradation rate was only 45%. Degradation followed the pesticide degradation kinetic equation at initial concentrations between 5 mg L^?1 and 50 mg L^?1. When the metribuzin contaminated soil was mixed with strain N1 (with the concentration of metribuzin being 20 mg L^?1 and the inoculation rate of 10¹¹ g^?1 dry soil), the degradation rate of the metribuzin was 66.4% in 30 days, while the degradation rate of metribuzin was only 19.4% in the control soil without the strain N1. These results indicate that the strain N1 can significantly increase the degradation rate of metribuzin in contaminated soil.     

Polynomial response of 2,4-D mineralization to temperature in soils at varying soil moisture contents,slope positions and depths

The herbicide 2,4-D [2,4-(dichlorophenoxy) acetic acid] is a widely used broadleaf control agent in cereal production systems. Although 2,4-D soil-residual activity (half-lives) are typicaly less than 10 days, this herbicide also has as a short-term leaching potential due to its relatively weak retention by soil constituents. Herbicide residual effects and leaching are influenced by environmental variables such as soil moisture and temperature. The objective of this study was to determine impacts of these environmental variables on the magnitude and extent of 2,4-D mineralization in a cultivated undulating Manitoba prairie landscape. Microcosm incubation experiments were utilized to assess 2,4-D half-lives and total mineralization using a 4 × 4 × 3 × 2 factorial design (with soil temperature at 4 levels: 5, 10, 20 and 40°C; soil moisture at 4 levels: 60, 85, 110, 135 % of field capacity; slope position at 3 levels: upper-, mid- and lower-slopes; and soil depth at 2 levels: 0–5 cm and 5–15 cm). Half-lives (t_1/2) varied from 3 days to 51 days with the total 2,4-D mineralization (M _T ) ranging from 5.8 to 50.9 %. The four-way interaction (temperature × moisture × slope × depth) significantly (p< 0.001) influenced both t_1/2 and M _T. Second-order polynomial equations best described the relations of temperature with t_1/2 and M_T as was expected from a biological system. However, the interaction and variability of t_1/2 and M_T among different temperatures, soil moistures, slope positions, and soil depth combinations indicates that the complex nature of these interacting factors should be considered when applying 2,4-D in agricultural fields and in utilizing these parameters in pesticide fate models.     

除草剂对土壤氮素循环的影响

土壤微生物参与土壤氮素循环的生物学与生物化学过程,对氮素形态转化与去向产生很大影响。在现代农作物生产上农田普遍施用除草剂,除草剂进入土壤生态环境中影响土壤微生物种群数量、活性和土壤氮素循环过程,在一定程度上改变氮素各去向的比例。因此,除草剂的施用对植物氮素吸收利用和土壤氮的环境释放具有一定效应。文章综述了除草剂对生物固氮、土壤氮矿化与转化、氨挥发、硝化反硝化、温室气体N2O排放、植物的氮吸收利用、土壤氮损失等方面的影响,并提出了今后进一步研究的方向,为减少氮素损失和温室气体排放以及除草剂使用的安全性评价提供参考。     

Photodegradation of the herbicide goal

Photodegradation products of the herbicide Goal active ingredient were obtained with a xenon lamp and analyzed using direct inlet mass spectrometry, MS/MS and GC/MS. A number of products were identified and their generation pathways were established to be mainly Ar—O bond cleavage, dechlorination and photocyclisation. The latter process gives chlorinated and unchlorinated dibenzofurans some of which may be toxic.     

Techniques to Reduce the Impact of Asulam Drift from Helicopter Sprayers on Native Vegetation

Asulam is often applied from the air to control bracken. This herbicide affects other ferns and spray drift could affect their survival. This paper discusses the use of bioassays to assess drift (a) spatially around a single bracken patch, (b) downwind from sprayed areas, and (c) spatially in undulating terrain and with different vegetation cover types. The aims were to develop policies to protect sensitive habitats. It is suggested that “no-spray” buffer zones in excess of 160–180 m are needed to minimise risk. Protection of rare ferns from overstorey vegetation or from steep slopes did not occur. Although less drift was found upwind there was significant damage at the end of the helicopter runs because of errors in switching the sprayer on and off.     

EFFECT OF SULFOMETURON METHYL ON GROUND WATER AND STREAM QUALITY IN COASTAL PLAIN FOREST WATERSHEDS1

ABSTRACT: Sulfometuron methyl [methyl 2-[[[[4,6-dimethly 2-(pyrimidinyl) a-mino] carbony l]amino] sulfonyl] benzoate] was applied by a ground sprayer at a maximum labeled rate of 0.42 kg ha^-1 a.i. to a 4 ha Coastal Plain flatwoods watershed as site preparation for tree planting. Herbicide residues were detected in Streamflow for only seven days after treatment and did not exceed 7 mg m^-3. Sulfometuron methyl was not detected in any stormflow and was not found in any sediment (both bedload and suspended). Sampling of a shallow ground water aquifer, > 1.5 m below ground surface, did not detect any sulfometuron methyl residues for 203 days after herbicide application. Lack of herbicide residue movement was attributed to low application rates, rapid hydrolysis in acidic soils and water and dilution in streamflow.     

Determination of glyphosate residue in maize and rice using a fast and easy method involving liquid chromatography–mass spectrometry (LC/MS/MS)

A fast and easy method was developed for the determination of glyphosate in maize and rice by using liquid chromatography triple quadrupole mass spectrometry with a Dionex Ion Pack column and phosphate buffer mobile phase. Samples were extracted with an acidified methanol solution. An isotope-labeled internal standard was added to the sample before extraction to ensure accurate tracking and quantification. The method’s performance was evaluated through a series of assessments to determine the accuracy, precision, linearity, matrix effect, limit of detection (LOD), and limit of quantification (LOQ). The mean recoveries for both matrices were within 70–105% at three fortification levels, including the LOQ. The precision for replicates was <20% (RSD%) for both matrices. Good linearity (R²=0.9982) was obtained over the concentration range of 0.01–1.5?mg kg^?1. The LOD was determined to be 0.002?mg kg^?1 for rice and 0.004?mg kg^?1 for maize. The LOQ was 0.01?mg kg^?1 for both maize and rice. Due to its versatility, the proposed method could be considered useful for the determination of glyphosate in cereals in routine analysis.     

Rice and wheat straw ashes: Characterization and modeling of pretilachlor sorption kinetics and adsorption isotherm

The rice straw ash (RSA) and wheat straw ash (WSA) were explored as low cost adsorbent for pretilachlor removal from water. The ashes were characterized and sorption behavior of pretilachlor was evaluated. Kinetics study suggested that the modified Elovich model best explained the pretilachlor sorption on both the ashes. The adsorption data were analyzed using 2-, 3- and 4-parameter models and nine error functions were used to compute the best fit isotherm by nonlinear regression analysis. The pretilachlor was more sorbed onto the RSA (22.0–92.2%) than the WSA (11.4–61.4%) and percent adsorption decreased with increase in the herbicide concentration in solution. Isotherm model optimization analysis suggested that the Freundlich and the Temkin isotherms were the best models to predict the pretilachlor adsorption onto the RSA and the WSA. The error analysis suggested that the reciprocal of the observed squared (ROS) and the reciprocal of the predicted squared (RPS) error functions provided the best determination of the adsorption constants for the Freundlich and the Temkin isotherms, respectively. The RSA, which exhibited higher pretilachlor sorption potential, can be utilized as low cost adsorbent for pesticide removal from contaminated water.     

Vegetative Buffer Strips for Reducing Herbicide Transport in Runoff: Effects of Buffer Width,Vegetation, and Season

The effectiveness of vegetative buffer strips (VBS) for reducing herbicide transport has not been well documented for runoff prone soils. A multi‐year plot‐scale study was conducted on an eroded claypan soil with the following objectives: (1) assess the effects of buffer width, vegetation, and season on runoff transport of atrazine (ATR), metolachlor (MET), and glyphosate; (2) develop VBS design criteria for herbicides; and (3) compare differences in soil quality among vegetation treatments. Rainfall simulation was used to create uniform antecedent soil water content and to generate runoff. Vegetation treatment and buffer width impacted herbicide loads much more than season. Grass treatments reduced herbicide loads by 19‐28% and sediment loads by 67% compared to the control. Grass treatments increased retention of dissolved‐phase herbicides by both infiltration and adsorption, but adsorption accounted for the greatest proportion of retained herbicide load. This latter finding indicated VBS can be effective on poorly drained soils or when the source to buffer area ratio is high. Grass treatments modestly improved surface soil quality 8‐13 years after establishment, with significant increases in organic C, total N, and ATR and MET sorption compared to continuously tilled control. Herbicide loads as a function of buffer width were well described by first‐order decay models which indicated VBS can provide significant load reductions under anticipated field conditions.