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Intensive microbial growth on 4 nutrient media (containing glucose, starch, nutrient broth or peptone + yeast extract) in soil suspension experiments, changing pH (acidification or alkalization) caused partial liberation of Cd sorbed by soil particles to liquid phase. At the same time a considerable transformation of the solid phase Cd to soluble in 0.1 N NaOH form was observed. Increased Cd concentration in the alkaline extract was accompanied by decrease of the heavy metal extractability with DTPA. The mechanisms which might be responsible for the observed phenomena are discussed. The obtained results suggest that microbial action can simultaneously increase and decrease availability of Cd to plants.
In a 38-year microplot experiment, very poor sandy soil deprived of the humus layer was amended with waste bentonite (BNT) in four doses of 0, 30, 60, and 120 t ha⁻¹ in order to improve the properties of the soil. During the first 30 years, the soils were fertilized with organic and mineral fertilizers and planted with various crops, while during the next eight years they were exposed to bare fallowing without fertilization. At the beginning of the experiment, the soils were inoculated with Azotobacter chroococcum. During the next 12 consecutive years we observed a gradual decrease of colony forming units (CFU) of these bacteria. The decrease of the CFU numbers of A. chroococcum was the fastest in the control soil (after 10 years A. chroococcum was not found in this soil). BNT significantly slowed down this decrease (1.7-3.3-times), and the effect was dose-dependent. The CFU numbers were strongly positively correlated with soil pH. After 7/8-year fallowing, when pH of the soils drastically decreased (especially in the 5-30 cm layer), A. chroococcum was found only in a 30-55 cm layer in the soil with 120 t ha⁻¹ BNT, where soil pH(H₂O) was above 6. In a four-year field experiment with another sandy soil, BNT addition increased the CFU number of native Azotobacter spp. (30, 80, and 900-times for 30, 60, and 120 t ha⁻¹ of BNT, respectively).
Microplots (0.8 m²) were filled with a subsoil of a very poor, acidic sandy soil. This soil was enriched with bentonite (BNT) at rates of 0, 3, 6, and 12 kg/m² . For 30 years the microplots were planted with different crops and regularly enriched with mineral and organic fertilizers. For the next eight years the microplots were left barren. After that time, the soils with added BNT had higher pH and content of available Mg than the control soil (CS) in the whole studied 5-80 cm soil profile. The soil with the highest dose of added BNT contained more total Ca, Mg, Zn, and Mn, as well as available P and K in 5-30 cm layer than the other soils. Furthermore, in comparison to CS, the soil with 12 kg/m² of BNT had higher cation exchange capacity (CEC).
Procesy zagęszczania i prasowania materiałów roślinnych w stanie sypkim są wykorzystywane w produkcji granulatów i brykietów przeznaczonych do skarmiania zwierząt oraz na opał. Procesy te wymagają dużych nakładów energetycznych sięgających 40-70 kWh⋅t-1 W pracy przedstawiono podstawy teorii plastyczności materiałów sypkich ze wzmocnieniem gęstościowym. Opierając się o warunek plastyczności sformułowany przez Kuhna i Downey'a oraz jego modyfikacje, opisano związki fizyczne umożliwiające analizę stanu odkształcenia i naprężenia w modelowaniu procesów zagęszczania materiałów roślinnych o cechach plastycznych. W analizie wykorzysta-no podstawowe funkcje porowatości oraz prawa tarcia Amontonsa-Coulomba i Prandla dla ośrodka porowatego. Badania doświadczalne i teoretyczne prasowania mieszanki paszowej z udziałem słomy przeprowadzono w komorze zamkniętej. Identyfikacji podstawowych stałych materiałowych dokonano na drodze numerycznej wykorzystując metody regresji nieliniowej oraz zależności opisującej naciski na stemplu komory. Wyniki przedstawionych badań wskazały na możliwość szerszego wykorzystania teorii plastyczności materiałów sypkich do modelowania innych, bardziej skomplikowanych procesów brykietowania i granulowania sypkich materiałów roślinnych w prasach stemplowych i rotacyjnych.
Because dilution plating is more labor intensive than direct plating, we would like to propose the use of a direct plating technique for estimation of Penicillium verrucosum abundance in cereal grain in incubation studies, with use of very selective and indicative for the fungus agar DYSG medium. The proposed method is based on the measurement of the diameter of P. verrucosum colonies grown around cereal kernels placed on DYSG medium. In three different experiments wheat grain contained a great range of P. verrucosum CFU number (from <25 to 77 x 10⁶ per 1 g). When P. verrucosum CFU number was at least as high as 10² per 1 g of the grain, 100% of the wheat kernels, placed on the surface of DYSG medium, were surrounded by colonies of P. verrucosum. The diameter (x, mm) of P. verrucosum colonies surrounding wheat kernels on DYSG medium was correlated with the fungal CFU number (y) on the wheat grain. The relationship is described by the exponential regression equation (y = 0.1258 e 0.9309x, R²=0.96). The relationship became linear (y = 0.404 x-0.901, R² = 0.96) after transformation of P. verrucosum CFU numbers to logarithms to base 10.
Results of laboratory soil suspension experiments with two soils differing in organic C content (1.1 and 4.2%) and texture (14.6 – 61.0 – 24.4% and 67.5 – 20.0 -12.5% for sand – silt – clay, respectively) showed that intensive microbial growth after the addition of a sucrose nutrient medium (SNMed) caused partial transformation of the solid phase Cd to forms soluble in 0.1 M NaOH. The transformation of Cd was accompanied by a simultaneous decrease of the solid phase Cd extractability by a solvent consisting of 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M triethanolamine (DTPA). These changes of the solid phase Cd extractability were probably caused by Cd binding to microbial biomass and microbial metabolism products. After the addition of SNMed, a concomitant phenomenon of an increase of Cd DTPA-extractability was observed, especially in the case of the course-textured soil with the higher organic C content. In a soil (not soil suspension) experiment, stimulation of microbial growth by SNMed addition caused different changes of Cd DTPA-extractability in the examined soils. In the fine-textured soil with the lower organic C content the process decreasing the solid phase Cd solubility in DTPA prevailed, but in the other soil, the opposite phenomenon predominated. The occurrence in nature of the phenomena observed under laboratory conditions is discussed.
In 0.8 m² microplots, a very poor sandy soil that contained only traces of organic matter was enriched with bentonite (BNT) at rates of 0, 3, 6, and 12 kg/m² . For 30 years the microplots were planted with different crops and regularly enriched with mineral and organic fertilizers. For the next eight years the microplots were left barren. The soils with BNT added contained significantly higher amounts of organic carbon (OC) and total nitrogen than the control soil (CS). Furthermore, in comparison to CS, organic matter in the soil with 12 kg/m² of BNT contained significantly more humins. Such durable stabilization of OC by BNT can be important for processes of carbon sequestration in soil.
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