ABSTRACT
Los procesos microbianos como la mineralización, la nitrificación y la desnitrificación regulan la dinámica del nitrógeno en el suelo. Estos 2 últimos son los principales responsables de la emisión de óxido nitroso (N2O). En este trabajo se determinaron los flujos de N2O en momentos clave del ciclo de cultivo del arroz en 2 sitios que diferían principalmente en el contenido de materia orgánica del suelo (MO), en las localidades de Salto (mayor MO) y de Treinta y Tres. Dichos momentos clave fueron a la siembra, en macollaje, en primordio floral y a la madurez. También se determinó el potencial de mineralización neta de N y las actividades y los números más probables (NMP) de oxidantes de NH4+ y de desnitrificantes. El potencial de mineralización de N, así como la actividad y el NMP de oxidantes de NH4+, no variaron con el tipo de suelo. Sin embargo, la actividad y el NMP de desnitrificantes fueron mayores en el suelo con mayor contenido de MO, independiente de la etapa del cultivo. A su vez, en las etapas finales del ciclo del cultivo, el NMP de desnitrificantes aumentó coincidiendo con el mayor potencial de mineralización y el mayor contenido de N mineral del suelo. Solo se observó un incremento en el flujo de N2O en el suelo de Salto a la madurez del arroz y cuando el suelo ya había sido drenado (44,2g N-N2O/ha d, frente a 20,8g N-N2O/ha d en Treinta y Tres). Esta investigación señala la importancia de estudiar las emisiones en distintos tipos de suelos y de continuar la medición luego del drenaje del cultivo de arroz para la elaboración de los inventarios de gases de efecto invernadero.
Microbial processes such as mineralization, nitrification and denitrification regulate nitrogen dynamics in the soil. The last two processes may produce nitrous oxide (N2O). In this work N2O fluxes were quantified at four moments of the rice cycle, sowing, tillering, panicle initiation and maturity, in two sites that differed mainly in their soil organic matter (OM) content, Salto (higher OM) and Treinta y Tres. Potential net N mineralization, ammonium oxidation and denitrification as well as the most probable numbers (MPN) of ammonia oxidizers and denitrifiers were determined. Potential N mineralization did not vary with the soil type and increased at rice maturity. Neither ammonia oxidation potential nor MPN were different among the soils. However, the soil with higher OM exhibited higher activity and MPN of denitrifiers, irrespective of the rice stage. In turn, at the latest phases of the crop, the MPN of denitrifiers increased coinciding with the highest mineralization potential and mineral N content of the soil. Significant differences in N2O flux were observed in Salto, where the highest emissions were detected at rice maturity, after the soil was drained (44.2 vs 20.8g N-N2O/ha d in Treinta y Tres). This work shows the importance of considering the soil type and end-of-season drainage of the rice field to elaborate GHGs (greenhouse gases) inventories.
Subject(s)
Denitrification , Nitrification , Nitrous Oxide , Oryza , Seasons , Soil , Uruguay , NitrogenABSTRACT
RESUMEN Se cuantificaron y compararon los melanomacrófagos (MM) y la actividad de la enzima Glutatión S-Transferasa (GST) en hígados de ejemplares adultos de Leptodactylus chaquensis (Anura, Leptodactylidae) colectados en un cultivo de arroz (CA) (siete días posteriores a la aplicación de clorpirifos, CPF) y en un sitio de referencia (SR) en el departamento San Javier, provincia de Santa Fe (Argentina). El análisis histológico reveló una mayor cantidad (p = 0.028) y área ocupada por MM (p = 0.017) y se registró una inhibición en la actividad de la GST (p = 0.030) en individuos del CA respecto a los del SR. Los efectos descriptos evidencian el riesgo ecotoxicológico para los anuros en los cultivos de arroz con aplicaciones de CPF.
ABSTRACT We quantified and compared the hepatic melanomacrophage (MM) and glutathione S-transferase (GST) enzyme activity (two oxidative stress biomarkers) in the liver of Leptodatylus chaquensis adults (Anura, Leptodactylidae) collected in a rice field (CA) in San Javier department, Santa Fe (Argentina), seven days after the application of chlorpyrifos and in a reference site (SR). The histological analysis revealed a significant amount (p = 0.028) and area occupied by MM (p = 0.017) in livers of CA compared to SR. Furthermore, a significant inhibition of GST activity was recorded in the CA frogs compared to the SR (p = 0.030). The histopathological and enzymatic effects provide evidences of ecotoxicological risk for anurans in rice field with CPF application.
ABSTRACT
Rice fields occupy large areas in Northeastern Argentina, and in Corrientes this widespead activity has become a feature in the landscape, as it is one of the main producing provinces. The aquatic Coleoptera is part of the fauna inhabiting these artificial environments but little is known about this group in irrigated rice fields. The aims of this study were to determine the diversity and species richness of coleopterans in a typical rice field, and to characterize the community of water beetles through different abundance models. For this, samples were collected from an active rice field located in "El Sombrero" town, in Corrientes Province, between November 2011 and April 2012. An entomological net of 30 cm diameter was used, and species richness, diversity and equitability were calculated monthly; besides, the community composition was characterized by means of rank-abundance models. A total of 74 species of aquatic coleopterans were identified. January and February resulted the months with the highest diversity. The aquatic Coleoptera species found in most of the sampled months were adjusted to the logarithmic rank-abundance model. The data suggests that, if it is properly managed, rice cropping in Northeastern Argentina can support a diverse aquatic coleopteran fauna.
Las plantaciones de arroz ocupan grandes áreas en el NE argentino. Corrientes es una de las principales provincias productoras de este cereal y al ser un cultivo extensivo ocupa grandes áreas, las cuales pasan a ser una parte característica del paisaje. Los coleópteros acuáticos forman parte de la fauna que habita en estos ambientes artificiales y poco se sabe de la fauna que habita en ellos. Los objetivos de este estudio fueron determinar la diversidad y la riqueza de especies de coleópteros en un campo típico de arroz, y caracterizar la comunidad de escarabajos de agua a través de los diferentes modelos de abundancia. Para ello, se realizaron muestreos con una red entomológica de 30 cm de diámetro en un campo de arroz ubicada en la localidad "El Sombrero", en la provincia de Corrientes. Las muestras fueron recolectadas entre noviembre 2011 y abril 2012. La riqueza de especies, diversidad y equitatividad para todos los meses muestreados fueron calculadas. La composición de la comunidad se caracterizó por medio de modelos de ranking-abundancia. Se identificaron 74 especies de coleópteros acuáticos. Enero y febrero fueron los meses con mayor diversidad. Las especies de coleópteros acuáticos que se registraron en la mayoría de los meses muestreados se ajustaron al modelo logarítmico. Los datos sugieren que, si se gestiona adecuadamente, los cultivos de arroz en el noreste de Argentina pueden albergar una fauna diversa de coleópteros acuáticos.
Subject(s)
Animals , Biodiversity , Coleoptera/classification , Agriculture , Argentina , Fresh Water , Oryza , Population Density , SeasonsABSTRACT
The distribution of Chlorophyceae (Green algae) in relation to seasonal variation of paddy fields at Lalgutwa area, Ranchi has been under taken for the first time in this area. A regular seasonal collection has been made during several field trips in year 2010 to 2011. Total 24 chlorophycean taxa with wide range of thallus structure were collected belonging to various orders i.e., Chlorococcales, Ulotrichales, Cladophorales, Oedogoniales, Zygnematales etc. Moderate temperature, high light nutrient and water availability appears to be better conditions for algal growth in the rice field habitat. This study reveals that comparatively lesser number of Chlorophycean members is growing in summers in comparison to rainy and winter seasons.
ABSTRACT
The diversity of airborne pollen grains was studied over Sonapur Rice Field, Kamrup district, Assam. The Burkard personal sampler was used to carry out the aeropalynological survey for the period of two consecutive years from March’08 to February’10. A total of 31 pollen types were reported during the study period. In the present study total number of spores recorded from March’08 to February’09 were 3658 pollen/m3 and from March’09 to February’10 were 4149.58 pollen/m3. The dominant pollen types recorded were, Poaceae, Amaranthaceae/ Chenopodiaceae, Asteraceae and Mimosa pudica. Some allergenically significant pollen types recorded were Amaranthaceae/ Chenopodiaceae, Argemone mexicana Linn., Mangifera indica Linn., Poaceae, Terminalia cuneata Roth. It was observed that entomophilous pollen ranked first in order of dominance.
ABSTRACT
An investigation was made to see the salt tolerance of 10 weed species of rice. Properly dried and treated seeds of weed species were placed on 9 cm diameter petridishes lined with Whatman No. 1 filter paper under 6 salinity regimes, viz. 0 (control), 4, 8, 16, 24 and 32 dS m-1. The petri dishes were then kept in germinator at 25±1.0oC and 12 hr light. The number of germinated seeds were recorded daily. The final germination percentage, germination index (GI), seedling vigour index, mean germination time and time for 50% germination were estimated. Root and shoot lengths of the weed seedlings were measured at 20 days after salt application and relative growth values were calculated. Results revealed that salinity decreased final germination percentage, seed of germination as measured by GI, and shoot and root length in all the species. Germination of most of the weed seeds was completely arrested (0) at 32 dS m-1 salinity except in E. colona (12%) and C. iria (13.9%). The species C. iria, E. colona, J. linifolia and E. crusgalli showed better germination (above 30%) upto 24 dS m-1 salinity level and were regarded as salt-tolerant weed species. J. linifolia, F. miliacea, L. chinensis and O. sativa L. (weedy rice) were graded as moderately tolerant and S. zeylanica, S. grosus and C. difformis were regarded as least tolerant weed species.
ABSTRACT
Na lavoura arrozeira, o uso de agroquímicos no controle de plantas daninhas e insetos é recomendado para garantir maior produtividade. Entretanto, sua utilização pode acarretar uma série de efeitos em organismos não alvos, como os peixes. Deste modo, esta revisão tem como objetivo analisar os dados existentes sobre os efeitos dos agroquímicos utilizados no cultivo de arroz em peixes, de modo a propor estratégias que minimizem seu impacto. Existe grande variação entre os agroquímicos testados quanto à toxicidade, sendo a determinação da concentração letal mediana em 96 horas apenas uma estimativa inicial para estudos adicionais, uma vez que para muitos deles concentrações inferiores podem provocar alterações bioquímicas nos tecidos dos peixes, as quais se mostram mais efetivas como biomarcadores. Para minimizar o impacto dos agroquímicos deve-se utilizar sempre a dose mínima recomendada, e manter estática a lâmina de água do cultivo por um período mínimo de duas semanas após a aplicação, de modo que o princípio ativo seja degradado, reduzindo a toxicidade. Além disso, o manejo integrado de pragas é recomendando, bem como a rizipiscicultura, a qual evita a utilização dos agroquímicos e em alguns casos pode promover um rendimento semelhante.
In the rice field, the use of agrochemicals to control rice weeds and pests is recommended to improve yield. However, their use may affect non-target organisms, as the fishes. Therefore, this review has like objective to analyze data regarding the effects of agrochemicals used in the rice field in fishes to propose strategies to minimize their impact. There is a large variation in the agrochemicals toxicity, and the determination of the medium lethal concentration in 96 hours is only an initial approach for additional studies, because many of them can provoke changes in biochemical parameters in fish tissues at lower concentrations. These biochemical parameters are more appropriate as biomarkers for agrochemicals. It is suggested to use the minimum recommended dose to minimize the impact of the agrochemicals, as well as to keep the water layer of the rice field for at least two weeks after the application to decompose the active principle and reduce toxicity. Besides, the integrated pest management is recommended, even as the rice-fish culture, which avoids the use of agrochemicals and in some situations, may give similar yields.