Effect of pencycuron on microbial parameters of waterlogged soil

Abstract: Fluorescein diacetate (FDA) was applied as a vital stain to soil bacteria in pure cultures, sterilized soil, and natural soils. The staining ability of FDA was tested on 111 isolates of soil bacteria in pure cultures in a diluted laboratory medium and in sterilized soil. Nearly 80% of the isolates were stained. In a growth experiment in sterilized soil, FDA was compared to acridine orange (AO). At a given time, when most bacteria were considered metabolically active, the number of FDA-stained bacteria exceeded that stained by AO. The staining efficiency and the simple procedure indicate that the FDA-method is useful for estimating the number of metabolically active bacteria in soil. This was confirmed by examination of ten different soils, where the FDA-method was compared to AO-staining, fluorescein isothiocyanate (FITC)-staining, and plate counts.

Abstract: An experiment was carried out to determine the plant growth-promoting activities of fipronil- and pyriproxyfen-tolerant Mesorhizobium isolates in the presence and absence of insecticides. The bioremediation and plant growth-promoting potentials of Mesorhizobium isolate (MRC4) was assessed using chickpea as a test crop grown under fipronil- and pyriproxyfen-stressed soils. In this study, the most promising mesorhizobial isolate (MRC4) tolerated fipronil and pyriproxyfen up to a concentration of 1600 μg ml−1 and 1400 μg ml−1, respectively. Isolate MRC4 produced a substantial amount of indole acetic acid (44.3 μg ml−1), salicylic acid (35 μg ml−1), 2,3 di-hydroxybenzoic acid (19 μg ml−1), and exo-polysaccharides (21 μg ml−1) in the absence of insecticides. The plant growth-promoting substances displayed by the isolate MRC4 declined progressively with increasing concentrations of each insecticide. The insecticide tolerant isolate MRC4 was further tested for its effect on chickpea plants grown in fipronil- and pyriproxyfen-treated soils. The insecticide-tolerant isolate MRC4 increased the dry matter accumulation progressively. A maximum increase of 80 (at 600 μg kg−1 soil of fipronil) and 118% (at 3900 μg kg−1 soil of pyriproxyfen) was recorded 135 days after sowing when compared to noninoculated plants treated with the same rates of each insecticide. Moreover, Mesorhizobium isolate MRC4 when used in fipronil- and pyriproxyfen-treated soil also increased symbiotic properties (nodulation and leghaemoglobin content), root N, shoot N, root P, shoot P, seed yield, and seed protein compared to the un-inoculated but treated solely with insecticide. The present finding suggests that the mesorhizobial isolate endowed with multiple properties could be used to facilitate the productivity of chickpea under insecticidestressed soils.

Abstract: Laboratory and field/pot experiments were conducted to determine the effect of two insecticides, fipronil and pyriproxyfen, on growth, symbiotic properties (nodulation and leghaemoglobin content), amount of N and P nutrients in plant organs, seed yield and seed protein of pea plants. In addition, the role of the most promising fipronil and pyriproxyfen tolerant Rhizobium leguminosarum strain MRP1 having plant growth promoting traits such as, production of phytohormones and siderophores, was also assessed in the presence and absence of both insecticides. Generally, fipronil and pyriproxyfen at the tested rates (recommended and higher doses) decreased the growth of both R. leguminosarum inoculated or uninoculated pea plants. Of the various concentrations of the two insecticides, pyriproxyfen at all concentrations in general, showed comparatively more severe toxicity to pea plants by decreasing plant biomass, symbiotic attributes, nutrients (nitrogen and phosphorus) uptake, seed yield and grain protein over the uninoculated control. The sole application of 3900 μg pyriproxyfen kg−1 soil (three times the recommended dose) showed the highest toxicity and decreased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 20%, 27%, 25%, 29%, 15% and 2% respectively, compared to the control. Interestingly, when the inoculant strain MRP1 was used with any concentration of the two insecticides, it significantly (P ≤ 0.05) increased the measured variables (plant dry weight, nodule numbers, dry nodule biomass, leghaemoglobin, nitrogen and phosphorus uptake, seed yield and grain protein) when compared to the plants grown in sandy clay loam soils treated solely (without inoculant) with the same individual treatment of each insecticide. For instance, three times the recommended dose of pyriproxyfen with strain MRP1 showed a highest stimulatory effect and increased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 108%, 124%, 119%, 153%, 112% and 6% respectively, compared to the plants grown in soil treated solely with three times the recommended dose of pyriproxyfen.

Abstract: Modern application of insecticides belonging to different chemical families to boost agricultural productivity has led to their accumulation in soils to levels that affect, directly and indirectly, soil enzyme activities and physiol-ogical characteristics of nontarget soil microflora including plant growth-promoting rhizobacteria, and, consequently the performance of crop plants. Various biological strategies can be applied for removing toxic substances, including insecticides, from the environment and are collectively known as bioremediation. Among biological approaches, the use of microbes with degradative ability is considered the most efficient and cost-effective option to clean pesticide-contaminated sites. The present review focuses on the role of naturally occurring rhizosphere microbes involved in degradation or transformation of insecticides.

Abstract: The effects of fumigation on organic C extractable by 0.5 M K2SO4 were examined in a contrasting range of soils. EC (the difference between organic C extracted by 0.5 M K2SO4 from fumigated and non-fumigated soil) was about 70% of FC (the flush of CO2-C caused by fumigation during a 10 day incubation), meaned for ten soils. There was a close relationship between microbial biomass C, measured by fumigation-incubation (from the relationship Biomass C = FC/0.45) and EC given by the equation: Biomass C = (2.64 ± 0.060) EC that accounted for 99.2% of the variance in the data. This relationship held over a wide range of soil pH (3.9–8.0). ATP and microbial biomass N concentrations were measured in four of the soils. The (ATP)(EC) ratios were very similar in the four soils, suggesting that both ATP and the organic C rendered decomposable by CHCl3 came from the soil microbial biomass. The C:N ratio of the biomass in a strongly acid (pH 4.2) soil was greater (9.4) than in the three less-acid soils (mean C:N ratio 5.1). We propose that the organic C rendered extractable to 0.5 m K2SO4 after a 24 h CHCl3-fumigation (EC) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.

Abstract: Characterizes soil microflora from descriptive and functional viewpoints; considers the biological processes that take place in the soil and their importance to soil fertility, plant growth, and environmental quality. Deals with the biochemical basis for soil processes, including microbial ecology, the carbon and nitrogen cycles, mineral transformation, and ecological interrelationships.

Abstract: Publisher Summary This chapter discusses the chemistry of submerged soils. The chemical changes in the submerged materials influence: (a) the character of the sediment or soil that forms, (b) the suitability of wet soils for crops, (c) the distribution of plant species around lakes and streams and in estuaries, deltas, and marine flood plains, (d) the quality and quantity of aquatic life, and (e) the capacity of lakes and seas to serve as sinks for terrestrial wastes. The single electrochemical property that serves to distinguish a submerged soil from a well-drained soil is its redox potential. The redox potential of a soil or sediment provides a quick, useful, semiquantitative measure of its oxidation–reduction status. Two recent developments have stimulated interest in the chemistry of submerged soils: the breeding of lowland rice varieties, with a high yield potential, and the pollution of streams, lakes, and seas, by domestic, agricultural, and industrial wastes. The chemistry of submerged soils is valuable: (a) in understanding the soil problems, limiting the performance of high-yielding rice varieties, and (b) in assessing the role of lake, estuarine, and ocean sediments as reservoirs of nutrients for aquatic plants and as sinks for terrestrial wastes.

Abstract: (Chapter Headings): Introduction. Quality Control and Quality Assurance in Applied Soil Microbiology and Biochemistry. Soil Sampling, Handling, Storage, And Analysis. Enrichment, Isolation and Counting of Soil Microorganisms. Estimation of Microbial Activities. Anaerobic Microbial Activities in Soil. Enzyme Activities. Micorbial Biomass. Community Structure. Field Methods. Bioremediation of Soil. Subject Index.

Abstract: Metabolic quotients for CO2C (qCO2C) and microbial-C-loss (qD) were studied on soil microbial communities under long-term monoculture (M) or continuous crop rotations (CR). Under defined laboratory conditions the mean qCO2C (unit CO2C unit−1 Cmic h−1) of different microbial biomasses from 17 M systems amounted to 1.097 μg CO2qCO2CC as compared to 0.645 μg CO2C of microbial biomasses from 19 CR systems. The 1.7 times higher CO2C release per unit biomass and time of microbial biomasses from M systems was significantly different at the P =0.001 level. In addition, microbial C-loss in samples from M or CR plots was followed for 5 weeks. Again, mean qD per unit microbial biomass and time was 1.6 times higher (P = 0.01) for microbial biomasses from M systems (0.301 μg C, 14 soils) when compared with CR systems (0.188μg C, 14 soils). These differences were not related to soil texture, Corg or pH of these soils. The effects of environmental influences (soil management) on the microbial pool in terms of a changing energy demand are discussed.