Simazine application inhibits nitrification and changes the ammonia-oxidizing bacterial communities in a fertilized agricultural soil

s-Triazine herbicides are widely used for weed control, and are persistent in soils. Nitrification is an essential process in the global nitrogen cycle in soil, and involves ammonia-oxidizing Bacteria (AOB) and ammonia-oxidizing Archaea (AOA). In this study, we evaluated the effect of the s-triazine herbicide simazine on the nitrification and on the structure of ammonia-oxidizing microbial communities in a fertilized agricultural soil. The effect of simazine on AOB and AOA were studied by PCR-amplification of amoA genes of nitrifying Bacteria and Archaea in soil microcosms and denaturing gradient gel electrophoresis (DGGE) analyses. Simazine [50?μg g(-1) dry weight soil (d.w.s)] completely inhibited the nitrification processes in the fertilized agricultural soil. The inhibition by simazine of ammonia oxidation observed was similar to the reduction of ammonia oxidation by the nitrification inhibitor acetylene. The application of simazine-affected AOB community DGGE patterns in the agricultural soil amended with ammonium, whereas no significant changes in the AOA community were observed. The DGGE analyses strongly suggest that simazine inhibited Nitrosobacteria and specifically Nitrosospira species. In conclusion, our results suggest that the s-triazine herbicide not only inhibits the target susceptible plants but also inhibits the ammonia oxidation and the AOB in fertilized soils.     

Effects of the herbicides Lindex and Simazine on chloroplast and nodule development,nodule activity,and grain yield inLupinus albus L.

Field and laboratory investigations were carried out to determine the influence of two commercial herbicides Lindex and Simazine on symbiotic N₂ fixation, the photosynthetic apparatus, percentage of proteins, and grain yield of lupins (Lupinus albus L. cv. Multolupa). The herbicides were added (3 kg commercial product in 9001 per ha) two weeks after sowing. The nodulated roots were tested for nitrogenase activity by the acetylene reduction assay (ARA) at the first and second flowering. The ARA values decreased with herbicide application. The decrease was smaller in the Simazine treatments with inoculated seeds. The ARA for plants treated with Lindex did not increase with inoculation. Nitrogenase activity was greater in the non-inoculated plants growing together with weeds. The effect of Simazine on the photosynthetic apparatus proved to be more toxic than that of Lindex, not only considerably reducing the size of the chloroplasts but also affecting the grana structure. The latter appeared as an electron-dense compact mass. There were no visible alterations in the photosynthetic apparatus of plants treated with Lindex. However starch, which was not present in the control leaves, accumulated. No ultrastructural changes were observed in the nodule cells treated with Lindex. Simazine altered nodule cells by causing vesicle formation, degeneration of bacteria, and by decreasing the number of N₂-fixing bacteroids. The grain yield decreased with both herbicide treatments, the decrease being lower in the inoculated plants, especially in the Simazine treatment. Our results suggest that each herbicide had a different effect on N₂ fixation, the photosynthetic apparatus and grain yield. Laboratory studies indicated that cyanazine and simazine did not adversely affect the growth of Bradyrhizobium.     

Study of soil algae

Summary Algal techniques were used to study the soil factors affecting the toxicity of herbicides. It was found that the organic matter adsorbed 18 times more herbicide than clay. The inherent phytotoxicity of different herbicides was tested by these methods and the results obtained compared favourably to those of higher plants. The order of toxicity as tested by algae was: diuron >neburon>monuron>atrazine>simazine>atratone. The prediction of application rates of diuron and simazine by algal methods was tested in the field with wheat as cereal crop. The data obtained testified that the predictions were correct and better than the commercial recommendation. Good chemical control of weeds was achieved by herbicide at the early stage of crop growth. At later stages of crop development the toxicity of the chemical was reduced to insignificance and the crop plants were then capable to compete successfully against the emerging weeds. Thus a biological weed control was obtained. Such combined chemical-biological weed control technique should be regarded as the most desirable practice in agriculture.     

Circadian response of annual weeds to glyphosate and glufosinate

Five field experiments were conducted in 1998 and 1999 in Minnesota to examine the influence of time of day efficacy of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [2-amino-4-(hydroxymethyl-phosphinyl)butanoic acid] applications on the control of annual weeds. Each experiment was designed to be a randomized complete block with four replications using plot sizes of 3×9 m. Glyphosate and glufosinate were applied at rates of 0.421 kg ae/ha and 0.292 kg ai/ha, respectively, with and without an additional adjuvant that consisted of 20% nonionic surfactant and 80% ammonium sulfate. All treatments were applied with water at 94 L/ha. Times of day for the application of herbicide were 06:00h, 09:00h, 12:00h, 15:00h, 18:00h, 21:00h, and 24:00h. Efficacy was evaluated 14 d after application by visual ratings. At 14 d, a circadian response to each herbicide was found, with greatest annual weed control observed with an application occurring between 09:00h and 18:00h and significantly less weed control observed with an application at 06:00h, 21:00h, or 24:00h. The addition of an adjuvant to both herbicides increased overall efficacy, but did not overcome the rhythmic time of day effect. Results of the multiple regression analysis showed that after environmental temperature, time of day was the second most important predictor of percent weed kill. Thus, circadian timing of herbicide application significantly influenced weed control with both glyphosate and glufosinate.     

Circadian response of annual weeds to glyphosate and glufosinate

Five field experiments were conducted in 1998 and 1999 in Minnesota to examine the influence of time of day efficacy of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [2-amino-4-(hydroxymethyl-phosphinyl)butanoic acid] applications on the control of annual weeds. Each experiment was designed to be a randomized complete block with four replications using plot sizes of 3×9 m. Glyphosate and glufosinate were applied at rates of 0.421 kg ae/ha and 0.292 kg ai/ha, respectively, with and without an additional adjuvant that consisted of 20% nonionic surfactant and 80% ammonium sulfate. All treatments were applied with water at 94 L/ha. Times of day for the application of herbicide were 06:00h, 09:00h, 12:00h, 15:00h, 18:00h, 21:00h, and 24:00h. Efficacy was evaluated 14 d after application by visual ratings. At 14 d, a circadian response to each herbicide was found, with greatest annual weed control observed with an application occurring between 09:00h and 18:00h and significantly less weed control observed with an application at 06:00h, 21:00h, or 24:00h. The addition of an adjuvant to both herbicides increased overall efficacy, but did not overcome the rhythmic time of day effect. Results of the multiple regression analysis showed that after environmental temperature, time of day was the second most important predictor of percent weed kill. Thus, circadian timing of herbicide application significantly influenced weed control with both glyphosate and glufosinate.     

Weed control and persistence of two oxyfluorfen formulations in olive groves under non tillage conditions

To obtain profitable yields in olive groves, residual preemergence herbicides are applied in October or November before the winter rains, and before the winter annual weeds germinate. Simazine, one of the herbicides most used for weed control in olive groves, has recently been banned. Oxyfluorfen is presented as a good alternative to simazine in olive fields. Experiments were carried out in 2002 and 2003 to evaluate the behaviour of two oxyfluorfen formulations, 2XL and G4F, at 480 g a.i. ha(-1) for three different soil management systems with three replications (1. bare soil; 2. bare soil and grassed buffer strips, chemically controlled and 3. bare soil and grassed buffer strips with controlled mowing; under non tillage conditions in all three cases). The most important species that survived 2XL and G4F treatments was Sagina apetala ARD. Oxyfluorfen residues were evaluated throughout 158 days after the applications. Three soil samples from each plot were collected, mixed and air dried. The herbicide extractions were made with methanol and the residues were analyzed by HPLC. We found no differences between the two formulations, but results showed that recoveries of oxyfluorfen were higher in plots with chemically controlled buffer grassed strips than in the other soil management types.     

Effect of simazine and atrazine on the mineralization of fertilizer and manure nitrogen

Summary Laboratory experiments were carried out with alluvial sandy loam soil to study the effect of simazine and atrazine herbicides at four levels (0.5, 1.0, 1.5 and 2.0 kg/ha) on the mineralization of nitrogen (ammoniacal and nitrate production) from fertilizer urea and sludge sources. The herbicides stimulated nitrate production. No specific trend in total mineralized nitrogen, ammoniacal and nitrate nitrogen was observed by varying the levels of herbicides. Mineralization of total nitrogen (ammoniacal and nitrate nitrogen) in presence of simazine and atrazine from the different sources in the descending order was:Urea > Sludge + Urea > Sludge > No Nitrogen.     

Growth and yield of groundnut (Arachis hypogaea L.) as influenced by weed management practices and Rhizobium inoculation

Groundnut (Arachis hypogaea L.) productivity in India is low, because of many problems beset in its cultivation. One of the serious problems are weeds. Groundnut yield losses due to weeds have been estimated as high as 24 to 70 percent. This has created a scope for using herbicides in groundnut crop. A field investigation was carried out during kharif (rainy) season of 2001-2002 on a sandy loam soil at College Agronomy Farm, B.A. College of Agriculture, Gujarat Agricultural University, Anand, India to study the effect of weed management practices and Rhizobium inoculation on growth and yield of groundnut (Arachis hypogaea L.). Ten weed control treatments, comprising four treatments of sole application of fluchloralin, pendimethalin, butachlor and metolachlor, respectively each applied at 1.0 kg ha(-1); four treatments comprising of an application of the same herbicides at the same levels coupled with one hand weeding at 30 DAS; one weed-free treatment (hand weedings at 15, 30, 45 DAS); and one unweeded control. All 10 treatmets were combined with and without Rhizobium inoculation (i.e. a total of 20 treatment combinations) under a factorial randomized complete block design (FRBD) with four replications. Minimum weed dry matter accumulation (70 kg/ha) with higher weed control efficiency (90.70%) was recorded under an integrated method i.e. pendimethalin at 1.0 kg ha(-1) + hand weeding at 30 DAS, which also resulted in maximum pod yield (1773.50 kg ha(-1)). This treatment was comparable to fluchloralin applied at 1.0 kg ha(-1) combined with hand- weeding at 30 DAS. Weedy conditions in the unweeded control treatment reduced pod yield by 29.90-35.95% as compared to integrated method. Significantly higher pod yield was obtained with Rhizobium inoculation than the mean value of all treatments without inoculation. For most agronomical parameters examined, Rhizobium inoculation and weed control treatments were independent in their effect.     

Chemical weed management in wheat at higher altitudes

To evaluate the effect of different herbicides for controlling weeds in wheat (variety Fakhr-i-Sarhad),at higher attitude, an experiment was conducted at Agriculture Research Station, Chitral during Rabi season 2003-04, using Randomized Complete Block Design, keeping four replications. The experiment, sown in November comprised of eight treatments, viz; seven herbicides and a weedy check. Each treatment consisted of 5 rows each 30 cm apart and 5 m long thus giving a total size of 5 m x 1.5 m. The herbicides used included; terbutryn + triasulfuron at 0.16 kg, 2,4-D at 0.7 kg, fenoxaprop-P-ethyl at 0.93 kg, clodinafop at 0.05 kg, bromoxynil + MCPA at 0.49 kg, carfentrazon-ethyl at 0.02 kg and isoproturon at 1.0 kg a.i ha(-1). The data were recorded on weed kill efficiency (%), fresh weed biomass (kg ha(-1)), plant height (cm), spike length (cm), number of tillers m(-2), number of grains spike(-1), thousand grains weight (g), biological yield (kg ha(-1)), grain yield (kg ha(-1)) and harvest index (%). The data recorded on weed kill efficiency, weed biomass (kg ha1), grains yield (kg ha(-1)) and harvest index (%) were significantly affected by the different herbicidal treatments. Statistically isoproturon treatment exhibited the best performance, with maximum weed kill efficiency (48.26%) and minimum fresh weed biomass (433.3 kg ha(-1)) as compared to weedy check (6 %) and (1102 kg ha(-1)), respectively. Similarly, the spike length (8.34 cm), number of tillers (427 m(-2)), number of grains spike(-1) (38.0), thousand grains weight (39.85 g), biological yield (8475 kg ha(-1)), grain yield (2530 kg ha(-1)) and harvest index (31.3%) were the highest in isoproturon treatments as compared to weedy check having (7.64 cm), (356 m(-2)), (34.1), (37.12 g), (6858 kg), (1913 kg ha(-1)) and (27%), respectively.     

Cellulose xanthate as a soil conditioner: implications for weed control with some soil-applied herbicides

Applications of cellulose xanthate equivalent to 50 kg cellulose/ha to fresh seedbeds preserved surface microtopography and prevented capping after rainfall. Numbers of weed seedlings were up to 50% greater than on untreated soil where capping occurred. The efficiency of nine soil-acting herbicides was not impaired when applied at normal rates either before or after cellulose xanthate. There was no evidence of interaction and the numbers of surviving weeds were proportional to the numbers where no herbicide had been applied. With propachlor, however, weed control was consistently less when applied shortly before or after cellulose xanthate, and analyses showed that in the presence of the soil conditioner the rate of herbicide loss was enhanced. This effect decreased the longer propachlor application was delayed, but was still evident with an interval of 96 h.     

Efficacy of triapenthenol as a safener against metribuzin injury in soybean (Glycine max) cultivars

Triapenthenol or RSW 0411 (B(-cyclohexalmethylene)-gamma-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), a triazole plant growth regulator, applied preemergence as a separate broadcast application, protected tolerant and midtolerant soybean cultivars from metribuzin (4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one)-induced necrotic injury, and stabilized seedling fresh weight and dry weight loss to herbicide treatment. Soybean yields were not significantly reduced by triapenthenol treatment alone, but 1.12 kg ai/ha metribuzin and a 0.56 kg ai/ha triapenthenol plus 1.12 kg ai/ha metribuzin combination reduced crop yield averaged across cultivars.     

Influence of Environmental Factors,Cultural Practices,and Herbicide Application on Seed Germination and Emergence Ecology of Ischaemum rugosum Salisb

Ischaemum rugosum Salisb. (Saramolla grass) is a noxious weed of rice that is difficult to control by chemical or mechanical means once established. A study was conducted to determine the effect of light, temperature, salt, drought, flooding, rice residue mulch, burial depth, and pre-emergence herbicides on seed germination and emergence of I. rugosum. Germination was stimulated by light and inhibited under complete darkness. Optimum temperature for germination was 30/20°C (97.5% germination). Germination reduced from 31 to 3.5% when the osmotic potential of the growing medium decreased from -0.1 to -0.6 MPa and no germination occurred at -0.8 MPa. Germination was 18 and 0.5% at 50 and 100 mM NaCl concentrations, respectively, but was completely inhibited at 150 mM or higher. Residue application at 1–6 t ha^-1 reduced weed emergence by 35–88% and shoot biomass by 55–95%. The efficacy of pre-emergence herbicides increased with increasing application rates and decreased with increasing rice residue mulching. The efficacy of herbicides was in the order of oxadiazon> pendimethalin> pretilachlor. At 6 t ha^-1, all herbicides, regardless of rates, did not differ from the control treatment. I. rugosum seeds buried at 2 cm or deeper did not emerge; however, they emerged by 4.5 and 0.5% at 0.5 and 1 cm depths, respectively, compared to the 39% germination for soil surface seeding. Flooding at 4 DAS or earlier reduced seedling emergence and shoot biomass while flooding at 8 DAS reduced only seedling emergence. The depth and timing of flooding independently reduced root biomass. Flooding at 4 and 6 cm depths reduced the root biomass. Relative to flooding on the day of sowing, flooding at 8 DAS increased root biomass by 89%. Similarly, flooding on the day of sowing and at 2 DAS reduced the root–shoot biomass ratio. Under the no-flood treatment, increasing rates of pretilachlor from 0.075 to 0.3 kg ai ha^-1 reduced weed emergence by 61–79%. At the flooding depth of 2–4 cm, pretilachlor reduced weed emergence and shoot and root biomass, but the differences across rates were non-significant. Information generated in this study will be helpful in developing integrated weed management strategies for managing this weed.     

Longleaf Pine (Pinus palustris P. Mill.) Restoration Using Herbicides: Overstory and Understory Vegetation Responses on a Coastal Plain Flatwoods Site in Florida,U.S.A.

A study was conducted on a Coastal Plain flatwoods site in Florida to determine the effects of common forestry herbicides on Longleaf pine seedling survival and growth and on the understory vegetation. Following removal of the overstory slash pine, five low‐rate herbicide treatments were applied over the top of planted Longleaf pine seedlings to provide short‐term understory vegetation control and accelerate seedling growth. The objective was to increase Longleaf pine growth by reducing the shrub competition while increasing the herbaceous ground cover. Despite causing reduction in seedling survival over the control treatment, imazapyr (0.21 ae kg/ha) resulted in the highest seedling growth (height and volume). The significant reduction of shrub cover, density, and height by imazapyr was believed to be responsible for the improved seedling growth in this treatment. Both hexazinone (0.56 ai kg/ha) and sulfometuron methyl (0.26 ai kg/ha) + hexazinone (0.56 ai kg/ha) treatments also reduced cover of Runner oak, a major shrub species, but the response was evident only 8 months after treatment. Although sulfometuron methyl (0.26 ai kg/ha) and sulfometuron methyl + hexazinone treatments did not result in any significant change in overall grass, forb, and shrub cover, both treatments resulted in greater Longleaf pine growth compared to the control. None of the herbicides significantly affected the major understory grasses and forbs. Overall, imazapyr provided the best desired results with significant increase in seedling growth and better control of shrub species with no significant effects on grass and other herbaceous species cover.     

Effect of four common herbicides on the population of microorganisms in Red Sandy soil

Summary A study was conducted to know the effect of four common herbicidesviz, Lasso, Nitrofen, Propinol, and Simazine on soil microorganisms in Red Sandy soil. In general the application of different herbicides did not adversely affect the microbial population. The bacterial population was decreased by the application of propinol and nitrofen. Simazine and lasso stimulated the fungal population. The stimulation in Azotobacter population was observed in lasso, nitrofen and simazine treated soil.     

Simazine treatment history determines a significant herbicide degradation potential in soils that is not improved by bioaugmentation with Pseudomonas sp. ADP

AIMS: To study biological removal of the herbicide simazine in soils with different history of herbicide treatment and to test bioaugmentation with a simazine-degrading bacterial strain. METHODS AND RESULTS: Simazine removal was studied in microcosms prepared with soils that had been differentially exposed to this herbicide. Simazine removal was much higher in previously exposed soils than in unexposed ones. Terminal restriction fragment length polymorphism analysis and multivariate analysis showed that soils previously exposed to simazine contained bacterial communities that were significantly impacted by simazine but also had an increased resilience. The biodegradation potential was also related to the presence of high levels of the atz-like gene sequences involved in simazine degradation. Bioaugmentation with Pseudomonas sp. ADP resulted in an increased initial rate of simazine removal, but this strain scarcely survived. After 28 days, residual simazine removals were the same in bioaugmented and not bioaugmented microcosms. CONCLUSIONS: In soils with a history of simazine treatment bacterial communities were able to overcome subsequent impacts with the herbicide. The success of bioaugmentation was limited by the low survival of the introduced strain. SIGNIFICANCE AND IMPACT OF THE STUDY: Conclusions from this work provided insights on simazine biodegradation potential of soils and the convenience of bioaugmentation.     

The effect of cultivation system and soil factors on the performance of herbicides against Alopecurus myosuroides

Aspects of chemical and cultural control of Alopecurus myosuroides (blackgrass) in winter wheat were studied on a naturally-occurring infestation over a 3-yr period. In two experiments a comparison was made between ploughing and direct drilling, whilst in the third experiment direct drilling alone was used. Straw was spread and burnt in each year. Herbicide treatments were: chlortoluron and isoproturon in all three experiments; diclofop-methyl and pendimethalin in two experiments; metoxuron, terbutryne, tri-allate, carbetamide, propyzamide, chlorsulfuron + methabenthiazuron and trifluralin + linuron in one experiment. Herbicides were applied either pre-emergence, early post-emergence or late postemergence to separate sub-plots. Surface soil (0–2.5 cm) samples were collected each year from unsprayed areas and used for soil analyses and for herbicide activity studies in pot experiments. Ploughing resulted in much lower populations of A. myosuroides than direct drilling. Most herbicides gave much better control of A. myosuroides in ploughed than in direct drilled soil in field and pot experiments, regardless of application time. Diclofop-methyl, applied early post-emergence at 1.13 kg a.i./ha, was the only herbicide treatment in field experiments to achieve over 90% weed control in direct drilled soil. Differences in adsorption between soils given different cultivations, determined as Kd values for chlortoluron and isoproturon, were much greater than differences in organic matter. The much greater adsorptive capacity of direct drilled soil, and consequently the poorer performance of all soil-acting herbicides, was attributed to the concentration of burnt straw residues near the soil surface.     

Influence of the soil conditioner cellulose xanthate on the activity and persistence of nine acetanilide herbicides

Applications of cellulose xanthate equivalent to 25 kg cellulose/ha increased the numbers of weed seedlings by up to 23% compared with untreated controls. With propachlor and prynachlor, weed control was poorer in the presence of cellulose xanthate and analyses of soil samples demonstrated that the rate of herbicide loss from the soil was enhanced. Although the soil conditioner increased the rate of loss of some other acetanilide herbicides, weed control was not greatly affected. The results suggest that interactions between cellulose xanthate and acetanilide herbicides are only important with those compounds which are normally of very short persistence.     

The Effects of Simazine, Applied for Weed Control, on the Mycorrhizal Development of Pinus Seedlings

The herbicide Simazine is widely used in forestry nurseries.Its effect on the incidence of ectomycorrhizae on pine seedlingroot systems was investigated. Under field (nursery) conditions,at routine rates of application, Simazine does not inhibit mycorrhizaldevelopment in Pinus sylvestris and P. nigra, and it may, undersome conditions, actually enhance mycorrhizal formation. Sucha stimulatory effect was also obtained with pot-grown seedlingstreated with the herbicide. It is suggested that soil type andclimatic factors might be involved in determining the responseto Simazine. The mode of stimulation of mycorrhizal developmentby this herbicide is not understood, but it is not via suppressionof weed growth. Pinus sylvestris, Pinus nigra, pine seedlings, ectomycorrhizae, Simazine     

A biosensor for the detection of triazine and phenylurea herbicides designed using Photosystem II coupled to a screen-printed electrode

A biosensor for the detection of triazine- and phenylurea-type herbicides was constructed using isolated Photosystem II (PS II) complexes as a biosensing element. PSII isolated from the thermophilic cyanobacterium Synechococcus elongatus was immobilized on the surface of a screen-printed sensor composed of a graphite working electrode and Ag/AgCl reference electrode deposited on a polymeric substrate. The biosensor was mounted in a flow microcell with illumination. The principle of the detection was based on the fact that herbicides selectively block PSII electron transport activity in a concentration-dependent manner. Changes of the activity were registered amperometrically as the rate of photoreduction of an artificial electron acceptor. The setup resulted in a reusable herbicide biosensor with a good stability (half-life of 24 h) and limit of detection of approximately 10(-9) M for diuron, atrazine and simazine.     

Ethylene in plant growth and development, storage, soil microbiology and plant pathology

In field experiments on a sandy loam at Wellesbourne, England in 1972 and on a silt loam at Agassiz, British Columbia in 1973, combinations of herbicides and insecticides were applied at sowing to determine their effects on weeds and invertebrate populations and on the growth and yield of cauliflowers grown at high density There was good agreement between the results from the two locations. The two combinations of herbicides, 0.6 kg trifluralin/ha incorporated pre-drilling plus 2.2 kg propachlor/ha pre-emergence and 2.2 kg nitrofen/ha plus 2.2 kg propachlor/ha both applied pre-emergence, gave good weed control, their relative effectiveness depending on the species composition of the weed population. The insecticides isophenphos, carbofuran, chlorfenvinphos and fensulfothion were applied as bow-wave treatments. None of them, whether in combination with herbicides or not, adversely affected crop stand or yield. Yield was reduced when either weeds or root-fly maggots (Hylemya brassicae (Bouché)) were not controlled. Only in one experiment was there any evidence of any herbicide-insecticide interactions. Where trifluralin and carbofuran were applied together at Agassiz, the control of both weeds and maggots was less than that with the other combinations. None of the treatments affected the populations of predatory beetles, but the numbers of earthworms were greatly reduced by carbofuran and to a lesser extent by chlorfenvinphos. Except for carbofuran in one experiment, the treatments had no effects on the numbers of aphids, lepidopterous larvae or leaf miners present at harvest.