Dissipation of nicosulfuron and rimsulfuron in surface soil

Adsorption and degradation of the herbicide nicosulfuron in a stagnic Luvisol and Vermic Umbrisol cultivated under conventional or conservation agriculture

The main goals of conservation agriculture are to enhance soil fertility and reduce soil degradation, especially through erosion. However, conservation agriculture practices can increase the risk of contamination by pesticides, mainly through vertical transfer via water flow. Better understanding of their sorption and degradation processes is thus needed in conservation agriculture as they control the amount of pesticide available for vertical transfer. The purpose of our study was to investigate the sorption and degradation processes of nicosulfuron in soil profiles (up to 90 cm deep) of a Vermic Umbrisol and a Stagnic Luvisol managed either in conventional or in conservation agriculture. Two laboratory sorption and incubation experiments were performed. Low sorption was observed regardless of the soil type, agricultural management or depth, with a maximum value of 1.3 ± 2.0 L kg^-1. By the end of the experiment (91 days), nicosulfuron mineralisation in the Vermic Umbrisol was similar for the two types of agricultural management and rather depended on soil depth (29.0 ± 2.3% in the 0-60-cm layers against 7.5 ± 1.4% in the 60-90 cm). In the Stagnic Luvisol, nicosulfuron mineralisation reached similar value in every layer of the conservation agriculture plot (26.5% ± 0.7%). On the conventional tillage plot, mineralisation decreased in the deepest layer (25-60 cm) reaching only 18.4 ± 6.9% of the applied nicosulfuron. Regardless of the soil type or agricultural management, non-extractable residue formation was identified as the main dissipation process of nicosulfuron (45.1 ± 8.5% and 50.2 ± 7.0% under conventional and conservation agriculture respectively after 91 days). In our study, nicosulfuron behaved similarly in the Vermic Umbrisol regardless of the agricultural management, whereas the risk of transfer to groundwater seemed lower in the Stagnic Luvisol under conservation agriculture.

Generation of herbicide tolerance traits and a new selectable marker in wheat using base editing

Developing herbicide-tolerant varieties by genome editing holds great promise for addressing the worsening weed problems in wheat cultivation¹. Here, we generated transgene-free wheat germplasms harbouring herbicide tolerance mutations that confer tolerance to sulfonylurea-, imidazolinone- and aryloxyphenoxy propionate-type herbicides by base editing the acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase genes. These stackable herbicide tolerance traits provide a potentially powerful tool for weed management. In addition, we found that base editing at the wheat ALS Pro-174 codon (TaALS-P174) endowed wheat with sufficient resistance to nicosulfuron herbicide in MS growth medium to allow selection. When the TaALS-P174 editor was coupled with editors for other targets of interest, co-editing occurred in the nicosulfuron-resistant plants, and selection for resistance in growth medium enriched the frequency of coupled targets by several-fold. This selectable co-editing system has the potential to greatly bolster adoption of base editing for crop improvement applications.

Tree uptake of excess nutrients and herbicides in a maize-olive tree cultivation system

Due to the extent of non-point source agricultural pollution, protective measures to control agrochemicals from entering aquatic systems are necessary. Measures may include, among others, vegetated buffer strips (VFS), no spray buffer zones, alley crops and agroforestry systems (AFS). The scope of the present work is to examine the pollution abatement potential of a maize-olive (MO) AFS. The efficiency of a combined MO trees system in reducing nutrients and herbicides is tested through soil monitoring in an experimental plot, located in Koropi, Eastern Attica, Greece, in the period May 2015 to November 2015. The monitored pollutants were nitrogen and phosphorus, as well as two herbicides: pendimethalin and nicosulfuron. Soil samples were collected every 3-5 weeks at various soil horizons and distances from the tree row. Pollutant concentrations were determined using liquid chromatography tandem mass spectrometry (LC-MS/MS), ion chromatography (IC) and spectrophotometry techniques. The studied MO tree system exhibited the potential to reduce pollutant migration, with removals ranging 36.8-78.9% for [Formula: see text], 79.3-100% for [Formula: see text], 76.7-100% for [Formula: see text], 79.4-100% for [Formula: see text] and 70-100% for the examined herbicides. The higher removal percentages were observed in the upper soil layers (5-35 cm, below the crops), and where the finer tree roots extend. Thus, the results indicate that planting of trees in cultivated fields can contribute to the reduction of agrochemical pollution of the subsurface soil and in extension of groundwater.

A novel carbon quantum dot-based fluorescent nanosensor for selective detection of flumioxazin in real samples

Herein, a carbon quantum dot-based highly selective luminescent probe has been designed for the detection of the pesticide flumioxazinviathe alkyne azide click reaction.

Dissipation and residues of rimsulfuron in potato and soil under field conditions

The analytical method for the residue analysis of a sulfonylurea herbicide, rimsulfuron, and its dissipation in soil and potato plants under field conditions were studied. Rimsulfuron residues were determined by Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method and ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Mean recoveries ranged from 74.6 % to 106.2 % with relative standard deviations (RSDs) of 2.0 %-13.8 % at three different spiking levels for each different matrix. The limits of detection (LOD) of rimsulfuron were ranged from 0.3 to 1.4 μg/kg, while the limits of quantification (LOQ) ranged from 0.9 to 4.3 μg/kg in different matrixes. The dissipation dynamics of rimsulfuron in the field trials in Shandong and Zhejiang Province were investigated. The half-lives in potato seedlings were 4.1 days in Shandong and 4.3 days in Zhejiang, both with a dissipation rate of 90 % about 7 days after application. The half-lives in soil were 6.0 days in Shandong and 6.6 days in Zhejiang, and with a dissipation rate of 90 % over 28 days. The terminal residues in potato and soil were not detectable. The fact that all the terminal residues were below the maximum residue level (0.1 mg/kg) set by Japan and 0.05 mg/kg set by EU. Hence it was safe for the use of this pesticide and the results also could give a reference for maximum residue limits setting of rimsulfuron in potato in China.

Biodegradation of nicosulfuron by the bacterium Serratia marcescens N80

By enrichment culturing of the sludge collected from the industrial wastewater treatment pond, we isolated a highly efficient nicosulfuron degrading bacterium Serratia marcescens N80. In liquid medium, Serratia marcescens N80 grows using nicosulfuron as the sole nitrogen source, and the optimal temperature, pH values, and inoculation for degradation are 30-35°C, 6.0-7.0, and 3.0% (v/v), respectively. With the initial concentration of 10 mg L⁻¹, the degradation rate is 93.6% in 96 hours; as the initial concentrations are higher than 10 mg L⁻¹, the biodegradation rates decrease as the nicosulfuron concentrations increase; when the concentration is 400 mg L⁻¹, the degradation rate is only 53.1%. Degradation follows the pesticide degradation kinetic equation at concentrations between 5 mg L⁻¹ and 50 mg L⁻¹. Identification of the metabolites by the liquid chromatography/mass spectrometry (LC/MS) indicates that the degradation of nicosulfuron is achieved by breaking the sulfonylurea bridge. The strain N80 also degraded some other sulfonylurea herbicides, including ethametsulfuron, tribenuron-methyl, metsulfuron-methyl, chlorimuron-ethyl,and rimsulfuron.

Dissipation and residues of nicosulfuron in corn and soil under field conditions

A simple, sensitive method for the analysis of nicosulfuron in corn and soil was developed. Samples were extracted with acetonitrile: water (2:3, V/V) mixture and partitioned with dichloromethane. After concentration, the soil sample extracts were detected using high performance liquid chromatography-ultraviolet detector (HPLC-UVD), and the corn sample extracts were detected using high performance liquid chromatography-mass spectrometry detector (HPLC-MSD). The fortified recoveries at 0.05-1.0 mg/kg were 79.7%-115.8%, with the relative standard deviation of 1.40%-13.8%. The limit of detection of the analytical method was 0.05 ng at a signal-to-noise ratio of 3, and the limit of quantification was 0.05 mg/kg for both corn and soil. The dissipation dynamics of nicosulfuron in the field trials in Beijing and Changchun were investigated. The half-lives of nicosulfuron in corn plants were 0.73 days in Beijing and 0.53 days in Changchun, both with a dissipation rate of 90% over 7 days after application. The half-lives in soil were 13.64 days both in Beijing and in Changchun with a dissipation rate of 90% over 21 days. Low residues and short half-life in corn suggested that nicosulfuron could be safely used in corn crops with the suitable dosage and application.

Characterization of nicosulfuron availability in aged soils

Sorption-desorption interactions of pesticides with soil determine their availability for transport, plant uptake, and microbial degradation. These interactions are affected by the physical-chemical properties of the pesticide and soil, and for some pesticides, their residence time in the soil. This research evaluated changes in sorption/availability of nicosulfuron (2-[[[[(4,6-dimethoxy-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide) herbicide with aging in different soils, using a radiolabeled ((14)C) tracer. Aging significantly increased sorption. For instance, after the 41-day incubation, calculated K d,app increased by a factor of 2 to 3 in Mollisols from the Midwestern United States and by a factor of 5 to 9 in Oxisols from Brazil and Hawaii, as compared to freshly treated soils. In view of this outcome, potential transport of nicosulfuron would be overpredicted if freshly treated soil K d values were used to predict transport. The fact that the nicosulfuron solution concentration decreased faster than the soil concentration with time suggested that the increase in sorption was because the rate of degradation in solution and on labile sites was faster than the rate of desorption of the neutral species from the soil particles. It may have also been due to nicosulfuron anion diffusion to less accessible sites with time, leaving the more strongly bound neutral molecules for the sorption characterization. Regardless of the mechanism, these results are further evidence that increases in sorption during pesticide aging should be taken into account during the characterization of the sorption process for mathematical models of pesticide degradation and transport.