Degradation Of Herbicides In Soil Research Articles

Glyphosate and terbuthylazine effects on soil functions, microbiome composition and crop performance

Herbicides are widely used for weed control in agriculture, though their fate and impact on non-target organisms like soil microbes and their function remain relatively unknown. A further complication is that herbicide effects vary depending on how they are applied and due to varying soil moisture conditions. In this study we tested the hypothesis that spraying glyphosate or terbuthylazine directly onto bare soil and when soil moisture is high would impact the soil microbial communities and their function most strongly. We measured similar amounts of glyphosate and terbuthylazine in soil whether the herbicides were directly applied to soil or first sprayed on the weed Chenopodium album and we found evidence for more rapid metabolization at high soil moisture. We found that the soil bacterial rather than the fungal community was mainly affected by a single application of the two tested herbicides. The identified shifts in community composition were independent of the modes of herbicide application but strongly dependent on soil moisture. We further found that herbicide applications only had a small impact on soil microbial function, which was approximated with analyses of the activities of N-β-acetylglucosaminidase, acid phosphatase and β-glucosidase enzymes in soil. Finally, we also assessed the post-application performance of the subsequent crop and found that the herbicides did not affect maize height, chlorophyll content and biomass. Overall, our study revealed that a single application of herbicides in recommended doses had minor effects on the soil microbiome with a temporal and soil moisture dependency. The latter finding points out that to avoid repercussions on non-target organisms and soil function, key research needs to solve the context-dependency of rapid herbicide degradation in soil.

Evaluating phytochemical and microbial contributions to atrazine degradation

The inclusion of warm-season grasses, such as switchgrass (Panicum virgatum) and eastern gamagrass (EG) (Tripsacum dactyloides), in vegetated buffer strips has been shown to mitigate herbicide contamination in runoff and increase herbicide degradation in soil. The mode of action by which buffer strip rhizospheres enhance herbicide degradation remains unclear, but microorganisms and phytochemicals are believed to facilitate degradation processes. The objectives of this study were to: 1) screen root extracts from seven switchgrass cultivars for the ability to degrade the herbicide atrazine (ATZ) in solution; 2) determine sorption coefficients (Kd) of the ATZ-degrading phytochemical 2-β-D-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one (DBG) to soil and Ca-montmorillonite, and investigate if DBG or ATZ sorption alters degradation processes; and 3) quantify ATZ degradation rates and soil microbial response to ATZ application in mesocosms containing soil and select warm-season grasses. Phytochemicals extracted from the roots of switchgrass cultivars degraded 44–85% of ATZ in 16-h laboratory assays, demonstrating that some switchgrass cultivars could rapidly degrade ATZ under laboratory conditions. However, attempts to isolate ATZ-degrading phytochemicals from plant roots were unsuccessful. Sorption studies revealed that DBG was strongly sorbed to soil (Kd = 87.2 L kg−1) and Ca-montmorillonite (Kd = 31.7 L kg−1), and DBG driven hydrolysis of ATZ was entirely inhibited when either ATZ or DBG were sorbed to Ca-montmorillonite. Atrazine degradation rates in mesocosm soils were rapid (t0.5 = 8.2–11.2 d), but not significantly different between soils collected from the two switchgrass cultivar mesocosms, the eastern gamagrass cultivar mesocosm, and the unvegetated mesocosm (control). Significant changes in three phospholipid fatty acid biomarkers were observed among the treatments. These changes indicated that different ATZ-degrading microbial consortia resulted in equivalent ATZ degradation rates between treatments. Results demonstrated that soil microbial response was the dominant mechanism controlling ATZ degradation in the soil studied, rather than root phytochemicals.

Response of Mungbean to the Residual Toxicity of Herbicides Used in Wheat under Strip Tillage System

The residual effect of eight herbicides (Pendimethalin, Pretilachlor, Triasulfuron Ethoxysulfuron, Pyrazosulfuron Ethyl, Carfentrazone – ethyl, Carfentrazone – ethyl+ Isoproteuron, 2, 4 –D) used in wheat of Agronomy Field Laboratory during March to June 2014 was evaluated for mungbean. The eighteen herbicide treatment combinations of the eight herbicides were used in wheat. The experiment was conducted in Random Complete Block Design (RCBD) with three replications. The effect of herbicide residues on the mungbean was evaluated in term of germination, seedling root and shoot length, leaf chlorophyll content and seeding dry matter. The result showed that seedling establishment of mungbean was not adversely affected by the herbicides applied the previous wheat crop. Also, the residue of herbicides applied in strip-tilled wheat did not show any adverse effect on germination, shoot length and seedling dry matter of mungbean and even shoot growth of mungbean was not inhibited by the residue of those herbicides. The reason might be related to the half-life and rate of degradation of herbicides in soil. In addition, farmers can easily grow mungbean in a cropping pattern as a subsequent crop of wheat because the study ensures that tested herbicides did not show any adverse residual effect on the establishment of this succeeding crop. However, continuous use of same herbicide or different herbicides with same mode of action in the same land year after year is strictly prohibited. Also, the prudent use of chemical/herbicide is essential to fulfill the goals of conservation agriculture by having reducing detrimental environmental impact as well as reducing herbicide resistance development in crops.

Herbicides degradation kinetics in soil under different herbigation systems at field scale

Application of pesticides in agriculture is one of the main sources of soil and water contamination. Herbicides used by herbigation increases the possibility of water and soil contamination by these toxins. Thus, knowledge on degradation of herbicides in soil for selecting more efficient management strategies is necessary. The objective of this study was to quantitatively describe herbicides degradation in soil under different herbigation and conventional spraying systems in actual field conditions. Consequently, Metribuzin was applied to soil by herbigation and conventional spraying via four methods. The degradation kinetics of herbicide was determined by soil sampling of four layers over a period of 70 days. Results indicated that the herbicide degradation kinetics depends on application method and studying scale. Based on these results, at each of soil layer, degradation rate remained constant due to no changes in soil physical and chemical properties and soil moisture conditions during the experiment. In these conditions, degradation trends followed a single first order kinetics model. However, herbicide degradation kinetics at entire soil profile was different depending on application method. Once the herbicide was applied via the first irrigation, large portion of herbicide was leached out to the second, third and fourth soil layers. Owing to roughly similar clay, organic matter, moisture content along with microbial activity and population in these three layers, the degradation rate was constant, during the experiment, and degradation trend followed the single first order kinetics model. However, in other application methods, the degradation rate was inconstant as a result of remaining a large portion of herbicide in the first soil layer, as well as different soil physical, chemical and biological properties of this layer compared to other layers. This contributed to a deviation from first order kinetics. The degradation kinetics was described much better by bi-exponential model.

Methods Related to Herbicide Dissipation or Degradation under Field or Laboratory Conditions

Herbicide degradation in soil is a major research issue, as evidenced by the number of refereed articles on the subject (Figure 1). The approximate number of total citations per year has increased from about 70 in the mid-1990s to approximately 170 per year in the last few years (Figure 1a). From a weed science perspective, publications in the journalsWeed ScienceandWeed Technologyhave tended to decline from an average of eight per year in the 1995 to 2005 interval to about three per year in the last 10 yr (Figure 1b). This discrepancy of total citations vs. Weed Science Society of America journals may be due to funding availability and other more immediate research needs in weed science. Other reasons might be a lack of reader interest (indicating low potential impact in this specific topic area) or the perception thatWeed ScienceandWeed Technologyare light venues for such papers and therefore not the first choice for publication. The authors believe this research topic to be important and relevant to the discipline of weed science, even more so as herbicide use patterns become more complicated because of glyphosate-resistant (GR) weeds.

Influence of sugar cane vinasse on the sorption and degradation of herbicides in soil under controlled conditions

This study reports the influence of sugar cane vinasse on the persistence, sorption and leaching potential of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4-dione) and tebuthiuron (1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea) in both a clay and sandy soil from a tropical area of Brazil. The experiments were conducted out under controlled laboratory conditions. The addition of sugarcane vinasse to soil influenced the persistence and sorption of the herbicides in both the studied clay and sandy soils, with a considerable decrease in the diuron DT50 values in clay soil. The Ground Water Ubiquity Score (GUS) Index classifies the herbicides as leachers in both soils and treatments, with the exception of diuron, which is classified as a non-leacher in clay soil-vinasse and as a transient herbicide in sandy soil. These results suggest that special attention should be given to areas such as those where the sandy soil was collected in this study, which is a recharge area of the Guarani Aquifer and is likely to experience groundwater contamination due to the high leaching potential of the applied pesticides.

Biostimulation for the Enhanced Degradation of Herbicides in Soil

Cleanup of herbicide-contaminated soils has been a dire environmental concern since the advent of industrial era. Although microorganisms are excellent degraders of herbicide compounds in the soil, some reparation may need to be brought about, in order to stimulate them to degrade the herbicide at a faster rate in a confined time frame. “Biostimulation” through the appropriate utilization of organic amendments and nutrients can accelerate the degradation of herbicides in the soil. However, effective use of biostimulants requires thorough comprehension of the global redox cycle during the microbial degradation of the herbicide molecules in the soil. In this paper, we present the prospects of using biostimulation as a powerful remediation strategy for the rapid cleanup of herbicide-polluted soils.

Factors influencing the loss of pesticides in drainage from a cracking clay soil

An experiment was established on plot lysimeters in autumn 1989 to examine the loss of pesticides from a cracking clay soil. Emphasis was placed on the movement of two autumn/spring-applied herbicides with contrasting properties — isoproturon and mecoprop. The first major drainflows in autumn/winter were important for the transport of these herbicides. During the dry autumns of 1989 and 1990, the development of substantial subsoil cracks led to rapid vertical movement of water, through the soil-cracks to the drainage system, before field capacity was reached. Isoproturon was detected in the resultant drainflow at concentrations of up to 50 μg 1 −1, well above the EC Directive for potable waters. Mecoprop was not detected. Measurements of herbicide degradation in soil indicated that isoproturon was rather persistent and hence available over many months for transport to the drainage system. In contrast, the long delay between application and the onset of drainflow, combined with the much faster degradation of mecoprop, resulted in this herbicide not occurring in drainflow. Although the site was some distance from a supply point for potable water, the loss of such concentrations of isoproturon in the early drainage flush could have undesirable consequences for water supplies and for the ecology of adjacent water courses.

Studies on microbial degradation of herbicides in soil.

Studies on microbial degradation of herbicides in soil.