Influence of cultivars and nitrogen rates on the residual effects of potassium applications to preceding cotton on maize

The long-term residual effects of K application rates and cultivars for preceding cotton (Gossypium hirsutum L.) on subsequent maize (Zea mays L.) and the influence of N rates applied to preceding cotton and to maize on the residual K effects were examined on maize under no-tillage in the United States. Two field experiments were conducted on a no-till Loring silt loam at Jackson, TN during 1995–2008 with N rates (90 and 179 kg ha^?1) × K rates (28, 56, and 84 kg ha^?1) and cotton cultivars (determinate and indeterminate) × K rates (56 and 112 kg ha^?1) as the treatments, respectively, in the preceding cotton seasons. Maize was planted under no-tillage on the preceding cotton experiments without any K application during 2009 through 2011. The residual effects of K rates applied to preceding cotton on soil K levels were significantly influenced by the N rates applied to preceding cotton and to maize when the data were combined from 2008 to 2011. Relative to the standard N management practices of 168 kg N ha^?1 for maize and 90 kg N ha^?1 for preceding cotton, the higher N application rate 269 kg N ha^?1 to maize and 179 kg N ha^?1 to preceding cotton reduced the residual effects of K rates on soil K. However, cultivar for preceding cotton did not affect the residual effects of K fertilizer on soil K fertility, leaf K nutrition, plant growth, or grain yield of subsequent maize on a high K field.     

Accumulation and apparent recovery of N,P and K after the incorporation of gliricidia and manure in intercropping during the cultivation of corn–cowpea–cotton

Fertilization with manure is widely adopted by farmers in the semiarid region of northeastern Brazil, although the quantity of available manure is limited. Thus, among other alternatives, gliricidia has been used as an additional source of organic fertilizer. The objective of this study was to evaluate the accumulation and apparent recovery of N, P and K after using different forms of gliricidia and manure application in the intercropping of corn, cowpea and cotton in three crop cycles in the semi-arid northeast region of Brazil. The following treatments were used: gliricidia incorporated into the soil before planting; gliricidia spread on the surface of the soil at 45 days after planting; manure and gliricidia incorporated into the soil before planting; manure incorporated into the soil before planting and gliricidia spread on the surface of the soil at 45 days after planting; manure incorporated into the soil before planting; and no addition of organic fertilizer (control). Accumulations followed the same pattern as biomass production but differed greatly from the concentrations. Low apparent recoveries were obtained in the first and second cycles, and high apparent recoveries were obtained in the third cycle. The nutrient balances indicated that the incorporation of gliricidia before planting or spread on the surface does not meet crop needs. The incorporation of manure as well as manure and gliricidia when applied on the surface, were able to meet growth needs and maintain soil fertility.     

Relationship of cotton nitrogen and yield with Normalized Difference Vegetation Index and plant height

The strength of the associations of cotton (Gossypium hirsutum L.) yield and N nutrition with integrated Normalized Difference Vegetation Index (NDVI) and plant height measurements has been scarcely documented. The objective of this investigation was to compare the strength in terms of determination coefficient (R²) among the associations of cotton yield and leaf N concentration with integrated and respective NDVI and plant height measurements taken at key growth stages. A field experiment was carried out on no-till cotton at Jackson and Milan in Tennessee during 2008–2010. Six N treatments of 0, 45, 90, 135, 179, and 224 kg N ha^?1 were implemented in a randomized complete block design with four replicates for all site years. Regressions of lint yield with NDVI × plant height and NDVI + plant height were sometimes stronger than those of lint yield with NDVI alone. Associations of leaf N concentration with NDVI × plant height and NDVI + plant height were similar to or variably stronger than those of leaf N with NDVI alone. Regressions of lint yield and leaf N with NDVI × plant height or NDVI + plant height were generally similar to those of lint yield and leaf N with plant height alone. Utilization of integrated NDVI and plant height measurements to predict cotton yield and/or assess N nutrition has variable advantages over the use of NDVI alone. Both integrated and respective NDVI and plant height measurements are more appropriate to be used to predict cotton yield than to assess N nutrition.     

Crop response to manure and fertilizer in Burkina Faso and Niger

Farmyard manure (FYM) is valuable for soil management, especially for soils with <?10 g kg^?1 organic C in semi-arid West Africa. This study determined short-term FYM effects on yield and on response to N, P and K fertilizer for 20 trials in Niger and 28 trials in Burkina Faso involving six crops. The comparisons were of 0 and 2.5 Mg ha^?1 yr^?1 FYM applied in Niger, and of 0 and 5 Mg ha^?1 FYM applied once in 2 years in Burkina Faso. Fertilizer and FYM application alone had little effect on yield in Niger but there was a synergistic effect of fertilizer P with FYM which included increased mean responses to P of, respectively: 0.22 and 0.43 Mg ha^?1 for sorghum grain and fodder (Sorghum bicolor L.); 0.15 and 0.27 Mg ha^?1 for cowpea grain and fodder; 0.16 Mg ha^?1 grain for pearl millet (Pennisetum glaucum L.) when intercropped with cowpea (Vigna unguiculata L.); and 0.39 Mg ha^?1 for groundnut fodder (Arachis hypogea L.). Application of FYM increased pearl millet response to N but decreased legume response to K fertilizer. In Burkina Faso, there was a mean grain yield increase of 0.29 Mg ha^?1 yr^?1 due to FYM and the effect of applying both FYM and fertilizer was additive except for a synergy of N fertilizer plus manure application for maize (Zea mays L.). Therefore, farmers should apply FYM and fertilizer together in Niger but these can be applied alone or together in Burkina Faso with mostly similar effects.     

Nitrogen dynamics in maize-based agroforestry systems as affected by landscape position in southern Malawi

In Malawi, agroforestry is very promising for N replenishment; however, there are still large variations in the performance of these agroforestry technologies on farmers’ fields. A study was conducted on-farm to determine the influence of three landscape positions on N dynamics in maize (Zea mays L.)-based agroforestry systems. The agroforestry systems were relay fallow using Sesbania sesban (L.) Merr or Tephrosia vogelii (Hook F.), simultaneous fallow using Gliricidia sepium(Jacq.) Walp., and maize without trees as a control. Sesbania was superior to other systems in the bottom slope, producing the highest tree biomass (1,861 kg ha⁻¹), whereas, gliricidia gave the highest tree biomass production in the mid-slope (2,147 kg ha⁻¹) and upper slope (1,690 kg ha⁻¹). Preseason inorganic N, maize flag leaf N concentration, maize total N uptake and maize yields followed a similar trend to tree biomass production with tree-based cropping systems exhibiting higher productivity (P < 0.05) than the cropping systems without trees. Nitrogen leaching from gliricidia agroforestry systems was lower than in the other agroforestry systems across all landscape positions as evidenced by 17% lower amounts (P < 0.05) of inorganic N adsorbed to ionic exchange resin membranes at 60 cm soil depth most likely due to the permanent root system of gliricidia. The difference between δ¹⁵N values of the trees and the soil did not change between landscape positions suggesting that if the leguminous trees fixed atmospheric N₂, the proportion of total N uptake was identical at all locations. We concluded that landscape positions have a significant effect on tree performance with sesbania remarkably adapted to the bottom slope, gliricidia to the mid-slopes and tephrosia fairing similar in both the bottom slope and mid-slopes.     

Assessment of maize yield gap and major determinant factors between smallholder farmers in the Dedza district of Malawi

This study explored the effect of soil nutrient status, agronomic practices and socio-economic factors on maize yield attained by smallholder farmers in the Dedza District of Malawi. Results show that maize yield ranged between 0.4 and 12 t ha^?1 with a mean value of 4.1 t ha^?1. Observed high yields (>8.0 t ha^?1) were associated with households using improved varieties combined with improved management practices such as NPK, urea and animal manure. With regards to soil factors, boron (B) and nitrogen (N) which are critically deficient in the area were significantly (β = 21.1, p < 0.01) associated with maize yield increase. From agronomic factors, weeds, seed spacing, plant density and fertilizer application played significant role in maize yield. Weed rating inversely impacted yield (β = ?0.5; p < 0.001) where fields with the lowest weed rating had the highest yield (4.6 t ha^?1) than those with the highest rating (2.3 t ha^?1). Socio-economic factors such as household wealth, household members with off-farm employment, number of years the household head has been involved in farming decision making, access to agricultural advice and group membership also influenced agronomic practices and resulted in yield gap. Household wealth and off-farm employment contributed to increased yield while household head experience in farming had negative impact. Extension service impacted yield negatively which can be attributed to the low extension worker to farmer ratio. The study demonstrated that closing yield gap in maize mixed farming systems requires integrated approach to addressing agronomic, biophysical and socio-economic constraints.     

Ovipositional response of threeHeliothis species (Lepidoptera: Noctuidae) to allelochemicals from cultivated and wild host plants

The role of plant allelochemicals on the oviposition behavior ofHeliothis virescens (F.),H. subflexa (Guenee), andH. zea (Boddie) was investigated in the laboratory using a “choice” bioassay system. Fresh young leaves of tobacco,Desmodium tortuosum (Swartz) de Candolle, groundcherry (Physalis angulata L.), and cotton (Gossypium hirsutum L.) squares (flower buds) were washed in methylene chloride or methanol, concentrated to 1 g equivalent of washed material, and applied to a cloth oviposition substrate. Each of the extracts—including groundcherry, a nonhost—stimulated oviposition byH. virescens. H. subflexa were stimulated to oviposit by groundcherry extract, its normal host, and extract from cotton squares, a nonhost. None of the extracts stimulated oviposition byH. zea, although all except groundcherry were from reported hosts. The sensitivity of the bioassay was confirmed by givingH. virescens andH. subflexa an opportunity to choose between extracts that showed stimulant qualities when tested independently versus only solvent-treated controls. In these tests, tobacco showed the highest level of stimulant activity forH. virescens; groundcherry exhibited the highest level of stimulation forH. subflexa.     

Synthesis,characterization and in vitro antibacterial assessments of a novel modified poly[maleic anhydride-alt-acrylic acid]/acriflavine conjugate

Water-soluble maleic anhydride-containing poly[maleic anhydride-alt-acrylic acid] (poly(MA-alt-AA) or MAAA) copolymer was synthesized by free-radical chain polymerization reaction, in 1,4-dioxane in the presence of benzoyl peroxide, 0.1 %, as the radical initiator at 70 °C under a nitrogen atmosphere. The purified copolymer was then modified with an anti-external fungal and anti-cancer active agent, acriflavine (AF). The modification reaction was performed 48 h at 70 °C in dimethylformamide organic media, using triethylamine (TEA or Et₃N) as the catalyst. The modified or conjugated copolymer/drug couple was named as MAAA/AF. Detailed structural characterization of the copolymer (MAAA) and modified product (MAAA/AF) was carried out by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (¹H-NMR and ¹³C-NMR). The obtained FTIR, ¹H-NMR, and ¹³C-NMR spectra confirmed that AF was successfully bound to the MAAA copolymer backbone by ring-opening reaction. Antimicrobial susceptibility of the MAAA, AF, and MAAA/AF was evaluated by Kirby Bauer Disc Diffusion method on Mueller–Hinton Agar using Enterecoccus faecium, Enterohaemorrhagic Escherichia coli (EHEC), Staphylococcus aureus and Listeria monocytogenes. Results obtained indicated that MAAA/AF had antibacterial activity on EHEC and S. aureus at 50, 40, and 30 µg. A mechanism for MAAA and AF was then also suggested for the conjugation reaction.     

Nitrogen balances in farmers fields under alternative uses of a cover crop legume: a case study from Nicaragua

Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N₂ fixation was assessed using the ¹⁵N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha^?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha^?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.     

Composition and pH dependence on aggregation of SiO2–PVA suspension for the synthesis of porous SiO2–PVA nanocomposite

Porous monolithic SiO₂–poly(vinyl alcohol) (PVA) nanocomposites were fabricated by drying an SiO₂–PVA suspension. Depending on the amount of added PVA and pH value of the suspension, the Brunauer–Emmett–Teller surface areas, total pore volumes, and mean pore radii of the (100 ? x)SiO₂–xPVA (x = 0, 10, 20, 30 wt%) nanocomposites were 102–313 m² g^?1, 0.61–1.42 cm³ g^?1, and 8.1–14.7 nm, respectively. Some cracks were observed in the monolithic SiO₂–PVA nanocomposite, affected by the pore size. To elucidate crack generation, the correlation between the dispersion/aggregation in the SiO₂–PVA suspension and the pore size distribution of the nanocomposite was evaluated in terms of the added PVA amount and pH value. At x = 20 and pH 3, the SiO₂ particles and PVA aggregated in the suspension. The preparation of crack-free monolithic SiO₂–PVA nanocomposites was possible using the aggregated suspension owing to the low capillary force during drying because of the relatively large pores.     

Historical role of manure application and its influence on soil nutrients and maize productivity in the semi-arid Ethiopian Rift Valley

Maize yield dynamics generally involve temporal changes, because increasing soil organic matter through manure application influences maize yields over the longer term, while inorganic nutrient application controls shorter term yields. These temporal soil properties and yield changes have been measured with long-term experiments. In sub-Saharan Africa (SSA), long-term experiments (more than 20 years) are rare due mainly to lack of funds. Farmers in the semi-arid northern Ethiopian Rift Valley (NERV) apply manure to maize fields in the long term. The relationships between the manure application levels, nutrient supply, soil nutrient levels, maize grain yields, and above-ground plant nutrient uptake levels were investigated by field measurement, interviews with farmers, laboratory analyses, and 2-years’ yield trials. The farmers applied on average 6.0 Mg ha^?1 yr^?1 of manure over 16.8 years on average. Significant linear or curve-linear correlations were found (1) between the annual nutrient supply and soil nutrient levels and (2) between the soil nutrient levels and maize productivities with minor exceptions. The regression equations determined from the yield trials proved 3.0 and 4.0 Mg ha^?1 of maize yields can be expected when soil available N contents were 3.9 and 5.1 mg kg^?1 in an ordinary rainfall year in NERV. For the farmers who apply 6.0 Mg ha^?1 yr^?1 manure, they are recommended to use 30 kg ha^?1 yr^?1 additional Urea to attain 3.0 Mg ha^?1 maize yields. These types of assessment methods do not require much cost, and yet it can provide long-term scientific information in SSA.     

Plastic-film mulch and fertilization rate affect the fate of urea-<Superscript>15</Superscript>N in maize production

We investigated the effects of interaction between plastic-film mulch and nitrogen (N) fertilization rate on the fate of fertilizer N in a ridge–furrow maize (Zea mays L.) cropping system. Three N levels (0, 138 and 207 kg ha^?1, abbreviated as N0, N1 and N2) were combined with plastic-film-mulching and no-mulching, successively in 2015 and 2016, at a cold semiarid site. Within each treated plot, a micro-plot was established to trace the fate of urea-N (only ¹⁵N-labeled in 2015). Averaging 2 years, increasing fertilization from N1 to N2 increased maize grain yield and total N uptake only in mulched soils. Mulch increased both maize grain yield and total N uptake more at N2 than at N1. In 2015, mulch increased the in-season fertilizer N uptake in maize by 53% at N1 but by 75% at N2; increasing N application from N1 to N2 enhanced the fertilizer N acquisition by 26% in non-mulched but by 45% in mulched plots. In 2016, similar effects of interaction existed between mulch and fertilization rate on the residual fertilizer N uptake by maize. Mulch enhanced fertilizer N availability in the topsoil relative to no mulch, responsible for the increased maize fertilizer N uptake in mulched treatments. Decreased in-season fertilizer N loss and transformation of urea N to the organic N in mulched soils were contributors to the increased fertilizer N availability, compared to non-mulched soils. We concluded that the effects of fertilization on maize total N uptake and fertilizer N recovery benefited from plastic-film mulch.     

Assessing agronomic and environmental implications of different N fertilisation strategies in subtropical grain cropping systems on Oxisols

A multi-season ¹⁵N tracer recovery experiment was conducted on an Oxisol cropped with wheat, maize and sorghum to compare crop N recoveries of different fertilisation strategies and determine the main pathways of N losses that limit N recovery in these agroecosystems. In the wheat and maize seasons, ¹⁵N-labelled fertiliser was applied as conventional urea (CONV) and urea coated with a nitrification inhibitor (DMPP). In sorghum, the fate of ¹⁵N-labelled urea was monitored in this crop following a legume ley pasture (L70) or a grass ley pasture (G100). The fertiliser N applied to sorghum in the legume-cereal rotation was reduced (70 kg N ha^?1) compared to the grass-cereal (100 kg N ha^?1) to assess the availability of the N residual from the legume ley pasture. Average crop N recoveries were 73 % (CONV) and 77 % (DMPP) in wheat and 50 % (CONV) and 51 % (DMPP) in maize, while in sorghum were 71 % (L70) and 53 % (G100). Data gathered in this study indicate that the intrinsic physical and chemical conditions of Oxisols can be extremely effective in limiting N losses via deep leaching or denitrification. Elevated crop ¹⁵N recoveries can be therefore obtained in subtropical Oxisols using conventional urea while in these agroecosystems DMPP urea has no significant scope to increase fertiliser N recovery in the crop. Overall, introducing a legume phase to limit the fertiliser N requirements of the following cereal crop proved to be the most effective strategy to reduce N losses and increase fertiliser N recovery.     

Fate of labeled urea-15N as basal and topdressing applications in an irrigated wheat-maize rotation system in North China plain: II summer maize

A field micro-plot experiment for summer maize was conducted in an irrigated winter wheat (Triticum aestivum)-summer maize (Zea mays L.) rotation system in Mazhuang, Xinji of Hebei province in the North China Plain, using the ¹⁵N isotope method to determine the effects of N application (rates and timing) on urea-¹⁵N fate, residual N effects and N recovery efficiency (NRE) by maize. The experiment included three N rates (90, 180, and 270 kg ha^?1), divided by two ¹⁵N-labeled groups of basal-¹⁵N (30, 60, and 90 kg ha^?1, respectively) and topdress-¹⁵N (60, 120, and 180 kg N ha^?1, respectively). All of the treatments were irrigated two times, once at seeding time and once at topdressing time. The absorbed N in the maize plant derived from basal-N (6.8?C13%) and topdress-N (17?C30%) was identified. The residual N in the 0?C150-cm soil depth ranged from 45 to 60% at the first maize harvest, mainly retained in the top 20-cm layers. Both NRE in grain and total N recovery in plant in the first maize crop were higher from topdress-¹⁵N (26?C31 or 41?C51%, respectively) than from basal-¹⁵N (18?C23 or 34?C43%, respectively). The residual N in the 0?C150-cm soil layer was lower from topdress-¹⁵N (45?C47%) than from basal-¹⁵N (55?C60%) after the first maize harvest. Residual N recovery was 6?C11% in the second and 1.5?C3.5% in the third crop. Cumulative N recovery in the maize-wheat-maize rotations was higher from the topdress-¹⁵N (49?C59%) than from basal-¹⁵N and (45?C55%). The unaccounted N loss was 14?C24% from the basal-¹⁵N and 20?C33% from the topdress-¹⁵N, with a double dose of basal-¹⁵N application. An N rate of approximately 180 kg ha^?1 appears to be an effective application rate to optimum maize yield and NRE on North China Plain, depending on the residual N and the crop yield potential.     

Olfaction in the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae): Electroantennogram studies

Electroantennogram (EAG) techniques were utilized to measure the antennal olfactory responsiveness of adult boll weevils,Anthonomus grandis Boh. (Coleoptera: Curculionidae), to 38 odorants, including both insect and host plant (Gossypium hirsutum L.) volatiles. EAGs of both sexes were indicative of at least two receptor populations: one receptor population primarily responsive to pheromone components and related compounds, the other receptor population primarily responsive to plant odors. Similar responses to male aggregation pheromone components (i.e., compounds I, II, and III + IV) were obtained from both sexes, but females were slightly more sensitive to I. Both sexes were highly responsive to components of the “green leaf volatile complex,” especially the six-carbon saturated and monounsaturated primary alcohols. Heptanal was the most active aldehyde tested. More acceptors responded to oxygenated monoterpenes than to monoterpene hydrocarbons. β-Bisabolol, the major volatile of cotton, was the most active sesquiterpene. In general, males, which are responsible for host selection and pheromone production, were more sensitive to plant odors than were females. In fact, males were as sensitive to β-bisabolol and heptanal as to aggregation pheromone components. Electrophysiological data are discussed with regard to the role of insect and host plant volatiles in host selection and aggregation behavior of the boll weevil.     

Impacts of conservation agriculture on soil aggregation and aggregate-associated N under an irrigated agroecosystem of the Indo-Gangetic Plains

We evaluated impacts of conservation agriculture (zero tillage, bed planting and residue retention) on changes in total soil N (TSN) and aggregate-associated N storage in a sandy loam soil of the Indo-Gangetic Plains. Cotton (Gossypium hirsutum) and wheat (Triticum aestivum) crops were grown during the first 3 years (2008–2011) and in the last year, maize (Zea mays) and wheat were cultivated. Results indicate that after 4 years the plots under zero tillage with bed planting (ZT-B) and zero tillage with flat planting (ZT-F) had 15 % higher TSN concentrations than conventional tillage and bed planting plots (CT-B) (0.63 g kg^?1 soil) in the 0–5 cm soil layer. CT-B plots had lower soil bulk density that ZT plots in that layer. Plots under ZT-B (0.57 Mg ha^?1) contained 20 % higher TSN stock in the 0–5 cm soil layer than CT-B plots (0.48 Mg ha^?1). However, tillage had no impact on TSN concentration or stock in the sub-surface (5–15 and 15–30 cm) soil layers. Thus, in the 0–30 cm soil layer, ZT-B plots contained 6 and 5 % higher (P > 0.05) TSN stock compared with CT-B (2.15 Mg N ha^?1) and CT-F (2.19 Mg N ha^?1) plots respectively after 4 years. Plots that received cotton/maize + wheat residue (C/M + W RES) contained 16 % higher TSN concentration than plots with residues removed (N RES; 0.62 g kg^?1 soil) in the surface (0–5 cm) layer. Plots with only cotton/maize residue (C/M RES) or only wheat residue (W RES) retention/incorporation had similar TSN concentrations and stocks in the subsurface layer. Plots under ZT-B also had more macroaggregates (0.25–8 mm) and greater mean weight diameter with lower silt + clay sized particles than CT-B plots in that layer. A greater proportion of large macroaggregates (2–8 mm) in the plots under C/M + W RES compared with N RES were observed. In the 5–15 cm soil layer ZT-B and C/M + W RES treated plots had more macroaggregates and greater mean weight diameter than CT-B and N RES treated plots, respectively. Because of the greater amount of large aggregates, plots under ZT-B and C/M + W RES had 49 and 35 % higher large macroaggregate-associated N stocks than CT-B (38 kg TSN ha^?1) and N RES (40 kg TSN ha^?1) plots, respectively, in the 0–5 cm soil layer, although aggregates had similar TSN concentrations in all plots. Both tillage and residue retention had greater effects on aggregate-associated N stocks in the 5–15 cm layers. In addition to N content within large macroaggregates, small macroaggregate-associated N contents were also positively affected by ZT-B and C/M + W RES. Tillage and residue retention interaction effects were not significant for all parameters. Thus, the adoption of ZT in permanent beds with crop residue addition is a better management option for improvement of soil N (and thus possibly a reduced dose of fertilizer N can be adopted in the long run), as the management practice has the potential to improve soil aggregation with greater accumulation of TSN within macroaggregates, and this trend would likely have additive effects with advancing years of the same management practices in this region.     

Photo-induced controlled/living copolymerization of styrene and acrylic acid and determination of reactivity ratios

A controlled/living photopolymerization of styrene (St) and acrylic acid (AA) mediated by FeCl₃·6H₂O/tetramethylethylenediamine (TMEDA) was performed in N,N-dimethylformamide using 4-bromomethylbenzophenon (4-BMBP) as photoinitiator at room temperature under UV irradiation. 4-BMBP was first used as ATRP initiator and photoinitiator. A well-defined poly(styrene-co-acrylic acid) with predetermined molecular weight and narrow molecular weight distribution was obtained. The kinetic rule of controlled free radical photopolymerization of St and AA was studied. The kinetic results showed that the obtained random poly(St-co-AA) copolymers produced narrow polydispersity (PDI) within the range of 1.25–1.32 when the conversion was beyond 16.5 %, which was characterized by GPC. The plots of number average molecular weight versus conversion and ln([M]₀/[M]) versus time were linear, indicating a controlled/living photopolymerization process. The system proceeded under mild and environmentally friendly conditions. The effects of initiator, catalyst, ligand, and vitamin C(VC) concentrations on polymerization process were investigated. The copolymers were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR). The methods of Mayo-Lewis (ML), Kelen-Tudos (KT), and Yzrielev-Brokhina Roskin (YBR) were used to calculate the monomer reactivity ratios of controlled/living photopolymerization of St and AA at low conversions under selected conditions. The monomer reactivity ratios of St and AA were calculated to be r _St = 0.82 and r _AA = 0.30, respectively in this system. The living characteristics were demonstrated by chain extension experiment.     

Synthesis and properties of novel X-type polyurethane containing dicyanovinylnitrocatechol of enhanced SHG thermal stability for electro-optic applications

Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass-transition temperature obtained from differential scanning calorimetry thermogram of around 113 °C. The second harmonic generation (SHG) coefficient (d ₃₃) of poled polymer film at 1,064 nm fundamental wavelength is around 5.72 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 7 °C higher than glass-transition temperature, and there was no SHG decay below 120 °C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications.     

Complete mineralization of the antibiotic amoxicillin by electro-Fenton with a BDD anode

On April 30, 2014, the World Health Organization’s first global report on the presence of antibiotics in waters focused on their negative consequences, which may include the growth of microorganisms with antimicrobial resistance. The β-lactam antibiotic amoxicillin (AMX) is widely used in human and veterinary medicine, and it has been recently detected in sewage treatment plants and effluents. In this paper, the degradation of acidic aqueous solutions of AMX by electro-Fenton process has been studied at constant current. Experiments have been performed in an undivided cell equipped with a carbon-felt cathode and a Pt or boron-doped diamond (BDD) anode. In such systems, the organic molecules are mainly oxidized by hydroxyl radical (^?OH) simultaneously formed on the anode surface from water oxidation as well as in the bulk from Fenton’s reaction between Fe²⁺ catalyst and electrogenerated H₂O₂. The decay and mineralization of AMX was monitored by means of high performance liquid chromatography (HPLC) and TOC measurements. The evolution of the concentration of the final aliphatic carboxylic acids and inorganic ions like ammonium, nitrate and sulfate was assessed by HPLC and ion chromatography, respectively. The effect of the anode material, initial AMX concentration and current density was thoroughly studied. The AMX decay always followed a pseudo-first-order kinetics using either Pt or BDD, and the apparent rate constant increased with applied current. A quicker mineralization was reached with BDD because of the larger production of active ^?OH. The absolute rate constant between hydroxyl radical and AMX determined by the competition kinetics method using p-hydroxybenzoic acid as the reference compound was found to be (2.02 ± 0.01) × 10⁹ M^?1 s^?1.     

Isotopic discrimination associated with symbiotic nitrogen fixation in stylo (Stylosanthes hamata L.) and cowpea (Vigna unguiculata L.)

A glasshouse study was carried out to determine the isotopicdiscrimination (B values) and the isotopic fractionation factors ()associated with symbiotic nitrogen fixation in stylo (Stylosantheshamata L.) and cowpea (Vigna unguiculata L.Walp). The B values are required to improve the accuracy of estimates ofnitrogen fixation based on the differences in the natural abundance of¹⁵N between nitrogen fixing and non-fixing plants. The B values ofplants grown in nitrogen free media for stylo were –1.60, 82 days after planting (DAP) and –1.86, 98 DAP and –1.48, 49DAP and –1.51 for cowpea shoots 73 DAP. Theisotopic fractionation factors for stylo and cowpea were 1.0016, 82DAP and 1.0019, 98 DAP and 1.0018, 49 DAPand 1.0015, 73 DAP, respectively.