Adaptive nitrogen and integrated weed management in conservation agriculture: impacts on agronomic productivity,greenhouse gas emissions,and herbicide residues

Increasing nitrogen (N) immobilization and weed interference in the early phase of implementation of conservation agriculture (CA) affects crop yields. Yet, higher fertilizer and herbicide use to improve productivity influences greenhouse gase emissions and herbicide residues. These tradeoffs precipitated a need for adaptive N and integrated weed management in CA-based maize (Zea mays L.)—wheat [Triticum aestivum (L.) emend Fiori & Paol] cropping system in the Indo-Gangetic Plains (IGP) to optimize N availability and reduce weed proliferation. Adaptive N fertilization was based on soil test value and normalized difference vegetation index measurement (NDVM) by GreenSeeker? technology, while integrated weed management included brown manuring (Sesbania aculeata L. co-culture, killed at 25 days after sowing), herbicide mixture, and weedy check (control, i.e., without weed management). Results indicated that the ‘best-adaptive N rate’ (i.e., 50% basal + 25% broadcast at 25 days after sowing + supplementary N guided by NDVM) increased maize and wheat grain yields by 20 and 14% (averaged for 2 years), respectively, compared with whole recommended N applied at sowing. Weed management by brown manuring (during maize) and herbicide mixture (during wheat) resulted in 10 and 21% higher grain yields (averaged for 2 years), respectively, over the weedy check. The NDVM in-season N fertilization and brown manuring affected N₂O and CO₂ emissions, but resulted in improved carbon storage efficiency, while herbicide residuals in soil were significantly lower in the maize season than in wheat cropping. This study concludes that adaptive N and integrated weed management enhance synergy between agronomic productivity, fertilizer and herbicide efficiency, and greenhouse gas mitigation.     

Ecological monitoring of wetlands in semi-arid region of Konya closed Basin, Turkey

Wetland ecosystems are of global significance having productive, regulatory and informative function. These wetlands are crucial for the long-term protection of water sources, as well as the survival of its unique biodiversity. Most of the wetlands of Turkey are now facing serious threat from the anthropogenic sources and now near to the verge of extinction. This study has been carried out to monitor vegetation dynamics and ecological status of wetlands of Koyna basin at spatial and temporal scale. This study has involved MODerate-resolution Imaging Spectroradiometer (MODIS) images of the year 2000, 2004 and 2008 on daily basis with spatial resolution of 1 km. The MODIS 16 days composite NDVI time series products of 250-m spatial resolution from year 2000 to 2008 has been utilized to monitor the ecological status of the wetlands. The European Nature Information System habitat classification map, meteorological data (precipitation, temperature) coupled with field data has been utilized to validate NDVI values of nine habitats in the wetlands. The time series analyses of NDVI data values have been correlated with the groundwater level depth from 1996 to 2004. The overall analysis has shown a declining trend of NDVI over the year 2000 to 2008, indicated a degraded wetland condition in span of 9 years.     

Synthesis and pesticidal activity of new N-alkyl-N-[1-(2-hydroxyphenyl) ethyl]amines

A series of novel N-alkyl-N-[1-(2-hydroxyphenyl) ethyl]amines were synthesized as potential new agents to control pests. Their structures were confirmed on the basis of IR, NMR and elemental analyses. Six new N-alkyl-N-[1-(2-hydroxyphenyl) ethyl]amines were prepared by reduction of corresponding Schiff bases using sodium borohydride in 80–87 % yields. These compounds were tested for their antifungal activity against two pathogenic fungi viz., Rhizoctonia bataticola ITCC 0482 and Sclerotium rolfsii ITCC 5226 and for insecticidal activity against insects of stored grain pest Callosobruchus analis. Fungicidal bioassay revealed that compound N-Decyl-N-[1-(2-hydroxyphenyl)ethyl]amine, was highly effective against R. bataticola (ED₅₀ 6.86 mg L^?1) which was comparable with that of commercial fungicide hexaconazole (ED₅₀ 6.35 mg L^?1). Also compounds N-Heptyl-N-[1-(2-hydroxyphenyl)ethyl]amine, N-Octyl-N-[1-(2-hydroxyphenyl)ethyl]amine and N-Nonyl-N-[1-(2-hydroxyphenyl)ethyl]amine displayed promising fungitoxicity against same pathogen. However, compound N-Heptyl-N-[1-(2-hydroxyphenyl)ethyl]amine was also found to be effective against S. rolfsii (ED₅₀ 4.92 mg L^?1 as against 1.27 mg L^?1 for hexaconazole). Compound N-Hexyl-N-[1-(2-hydroxyphenyl)ethyl]amine was most effective as insecticide followed by compound N-Octyl-N-[1-(2-hydroxyphenyl)ethyl]amine. LC₅₀ values for these compounds were 155.0 and 275.0 mg L^?1 respectively as against 36.70 mg L^?1 for commercial insecticide dichlorovos. The results obtained from bioassays indicate that this class of compounds can be utilized for the design of new substances endowed with pesticidal activities.     

Molecular characterization of soil bacteria antagonistic to Rhizoctonia solani,sheath blight of rice

Bacillus pumillus MTCC7615 has been identified as a potent isolate against Rhizocotonia solani, the fungal pathogen causing sheath blight in rice. The study aimed at probing the role of a 23kb size plasmid pJCP07 of Bacillus pumillus MTCC7615 in its fungal antagonism towards Rhizocotonia solani. Plasmid pJCP07 was found to be involved in production of a fungal antagonistic compound as demonstrated by plasmid curing and conjugational transfer experiments. Tn5 insertional studies further confirmed that the plasmid pJCP07 of Bacillus pumillus MTCC7615 carries some of the gene(s) involved in production of compound antagonistic to Rhizocotonia solani. The plasmid pJCP07 is thus a mobilizable medium-sized plasmid carrying genes responsible for antagonism of Bacillus pumillus MTCC7615 towards Rhizocotonia solani.     

Estimation of β-cyfluthrin and imidacloprid in okra fruits and soil by chromatography techniques

Dissipation of β-cyfluthrin and imidacloprid in okra was studied following three applications of a combination formulation of Solomon 300 OD (β-cyfluthrin 9 % + imidacloprid 21 %) @ 60 and 120 g a.i. ha^?1 at 7 days interval. Residues of β-cyfluthrin and imidacloprid in okra were estimated by gas liquid chromatography (GLC) and high performance liquid chromatography (HPLC), respectively. Residues of β-cyfluthrin were confirmed by gas chromatograph–mass spectrometry (GC-MS) and that of imidacloprid by high performance thin layer chromatography (HPTLC). Half-life periods for β-cyfluthrin were found to be 0.91 and 0.68 days whereas for imidacloprid these values were observed to be 0.85 and 0.96 days at single and double the application rates, respectively. Residues of β-cyfluthrin dissipated below its limit of quantification (LOQ) of 0.01 mg kg^?1 after 3 and 5 days at single and double the application dosage, respectively. Similarly, residues of imidacloprid took 5 and 7 days to reach LOQ of 0.01 mg kg^?1, at single and double dosages respectively. Soil samples collected after 15 days of the last application did not show the presence of β-cyfluthrin and imidacloprid at their detection limit of 0.01 mg kg^?1.     

Evaluation of the Potential of Laser-Induced Breakdown Spectroscopy for Detection of Trace Element in Liquid

Abstract

The analytical figure of merit of the potential of laser-induced breakdown spectroscopy (LIBS) has been evaluated for detection of trace element in liquid. LIBS data of Mg, Cr, Mn, and Re were studied. Various optical geometries, which produce the laser spark in and at the liquid sample, were tested. The calibration curves for Mg, Cr, Mn, and Re were obtained at the optimized experimental conditions with bulk liquid and in liquid jet. It was found that measurements using a liquid jet provide better detection limits than bulk liquid measurements. The limits of detection (LOD) of Mg, Cr, Mn, and Re in the present liquid jet measurement are found to be 0.1, 0.4, 0.7, and 8 ppm, respectively. The LOD of Mg using Mg 279.55 nm was compared with the values found in other liquid work.     

Effect of fly ash on sorption behavior of metribuzin in agricultural soils

This investigation was undertaken to determine the effect of two different fly ashes [Kota and Inderprastha (IP)] amendment on the sorption behavior of metribuzin in three Indian soil types. The IP fly ash was very effective in increasing the metribuzin sorption in the soils. The sorption with IP amendment was increased by 15–92%, whereas with the Kota fly ash an increase in sorption by 13–38% was noted. The adsorption isotherms fitted very well to the Freundlich adsorption equation and, in general, slope (1/n) values less then unity were observed. Although both the fly ashes significantly decreased metribuzin desorption, the IP fly ash was comparatively more effective in retaining metribuzin in the soils. Metribuzin sorption in the IP fly ash-amended soils showed strong correlation with the fly ash content and compared to K_f/K_d values, K_FA values (sorption normalized to fly ash content) showed less variation. Metribuzin sorption-desorption did not correlate to the organic carbon content of the soil-fly ash mixture. The study demonstrates that all coal fly ashes may not be effective in enhancing the sorption of metribuzin in soils to the same extent. However, among the fly ashes used in this study, the IP fly ash was observed to be significantly effective in enhancing the sorption of metribuzin in soils. This may play an important role in reducing the run off and leaching losses of the herbicide by retaining it in the soil.     

Bio-efficacy evaluation of nanoformulations of β-cyfluthrin against Callosobruchus maculatus (Coleoptera: Bruchidae)

In the present investigation, bioefficacy of developed β-cyfluthrin formulations, utilizing laboratory synthesized poly(ethylene glycols) based amphiphilic copolymers, were evaluated against Callosobruchus maculatus (Coleoptera: Bruchidae). The bioefficacy data indicated that the formulations developed by utilizing polymers having PEG – 1500 (3c) and PEG – 2000 (3d) as the hydrophilic segment showed greater efficacy after 14 days as evident from EC₅₀ values (2.2 and 1.58 mg L^?1 respectively). Also, release from the commercial SC formulation was faster than developed formulations as the commercial formulation had the lowest EC₅₀ value on the first day (0.51 mg L^?1). The mean EC₅₀ of the commercial formulation against C. maculatus was quite high as compared to those of developed formulations. The results suggest that depending upon the polymer matrix used, the application rate of β-cyfluthrin can be optimized to achieve insect control at the desired level and period. The results described in this paper are promising and provide a comparison of developed formulations with the commercial one showing an earlier degradation of β-cyfluthrin in the latter and relatively prolonged activity in the former.     

Degradation behaviour of pyrazosulfuron-ethyl in water as affected by pH

Pyrazosulfuron-ethyl, a new herbicide belonging to the sulfonylurea group, is used for weed control in rice crops growing in areas varying from acidic to alkaline soils. This study was undertaken to determine the degradation behaviour of pyrazosulfuron-ethyl in distilled water and buffer solutions at pH 4, 7 and 9. Degradation was pH-dependent and herbicide was least persistent in acidic pH followed by alkaline and neutral pH. The half-life of pyrazosulfuron-ethyl varied from 2.6 days (pH 4) to 19.4 days (pH 7) and half-life in distilled water was comparable to half-life at pH 7 buffer. HPLC analysis of different pH samples showed the formation of three metabolites viz., 5-(aminosulfonyl)-1-methyl-1H-pyrazole-4-carboxylic acid; ethyl 5-(aminosulfonyl)-1-methyl-1H-pyrazole-4-carboxylate and 2-amino-4,6-dimethoxy pyrimidine. The formation of pyrazosulfuron acid [5-([([(4,6-dimethoxy-2 pyrimidinyl)-amino]-carbonyl) amino]-sulfonyl)-1-methyl-1H-pyrazole-4-carboxylic acid] was not observed at any pH. The study indicated that the herbicide was least stable under acidic conditions and the predominant degradation route of pyrazosulfuron-ethyl in water is hydrolysis of sulfonamide linkage.