1,721,338 research outputs found
Pedotransfer functions for estimating soil water retention curve of Sicilian soils
Full text linkPedotransfer functions (PTFs) make use of routinely surveyed soil data to estimate soil properties but their application to soils different from those used for their development can yield inaccurate estimates. This investigation aimed at evaluating the water retention prediction accuracy of eight existing PTFs using a database of 217 Sicilian soils exploring 11 USDA textural classes. PTFs performance was assessed by root mean square differences (RMSD) and average differences (AD) between estimated and measured data. Extended Nonlinear Regression (ENR) technique was adopted to recalibrate or develop four new PTFs and Wind’s evaporation method was applied to validate the effectiveness of the relationships proposed. PTFs evaluation resulted in RMSD and AD values in the range 0.0630–0.0972 and 0.0021–0.0618 cm3 cm–3, respectively. Best and worst performances were obtained respectively by PTF-MI and PTF-ZW. ENR allowed to recalibrate PTF-MI and PTF-ZW with improvements of RMSD (0.0594 and 0.0508 cm3 cm–3) and to develop two relationships that improved RMSD by 75–78% as compared to PTF-MI. The results confirmed the potential of ENR technique in calibrating existing PTFs or developing new ones. Validation conducted with an independent dataset suggested that recalibrated/developed PTFs represent a viable alternative for water retention estimation of Sicilian soils
CHOLINERGIC INPUTS TO THE MEDIAL SEPTAL NUCLEI OF THE RAT FOREBRAIN INCREASE PLASMA VASOPRESSIN LEVELS
No full textInverse modeling of evaporation and multistep outflow experiments for determining soil hydraulic properties: A comparison
No full text[Effects of septal lesions on the response of vasopressin to angiotensin II]. PLASMA VASOPRESSIN RELEASE TO ANGIOTENSIN-II IN SEPTAL-LESIONED RATS
No full textElectrolytic lesion of the medio-ventral septal (MVS) area produces a sustained increase in daily water intake and urine output. This polyuria and hyperdipsia are associated with decreased levels of circulating radioimmunoassayable ADH. In addition, the usual ADH release to angiotensin II observed in normal controls and sham-lesioned rats was markedly blunted in MVS-lesioned animals
Soil reuse effects on determination of saturated hydraulic conductivity of different loamy soils
No full textLaboratory measurement of saturated hydraulic conductivity, Ks, of sieved and packed soil is important for many scientific purposes. A given soil mass can be used once or several times. Little is known of the dependence of the Ks data on the reuse of the same soil mass. For three loamy soils, this investigation tested reuse effects of exactly the same soil mass on determination of Ks with the simplified falling head technique. For a given soil, the Ks values of 15 repacked soil samples were determined by using the same soil for a total of eight times. The means of Ks, initially equal to 45–159 mm/h, depending on the soil, decreased by nearly two or three times with the reuse of the same material, and they settled on values of 23–59 mm/h by the end of the experiment. Low, stable and little variable (coefficients of variation ≤15%) Ks values were obtained after the soil was used three to five times although there was some sign that stabilization of Ks could also require more reuses. The soil became finer with more reuses and the textural characteristics of the undispersed soil explained a large amount of the mean Ks results (coefficient of determination between means of Ks and the mean weight diameter = 0.65–0.76, depending on the soil). Taking into account that the best procedure for determination of Ks of sieved and packed soil samples yields the lowest variability of the individual Ks data, the conclusion was that a soil pre-treatment including several wetting and drying cycles should be realized to obtain a soil mass usable repeatedly. The history of the used soil mass should be reported in the investigations dealing with sieved and repacked soil samples
Combined alpha-adrenergic stimulation results in biphasic response of growth hormone release in man.
No full textOral clonidine administration or insulin-induced hypoglycemia may enhance GH secretion through alpha 2-adrenergic stimulation in man. To further characterize the role of adrenergic transmission in the regulation of GH release, the effects of combined administration of clonidine and insulin were investigated in 16 normal men randomly assigned to 2 groups. The first group received 0.1 U/kg regular insulin, iv, followed by placebo or clonidine (0.150 mg), orally, on 2 different days, 2 weeks apart. The second group received oral clonidine (0.150 mg), followed by iv placebo or insulin (0.1 U/kg) on 2 different days, 2 weeks apart. Insulin induced a clear-cut increase in plasma GH (F = 79.88; P less than 0.001) that was not affected by placebo, whereas it was significantly inhibited by oral clonidine (P less than 0.001 at 60, 90, and 120 min). Similarly, oral clonidine administration resulted in a clear-cut rise in plasma GH levels (F = 16.44; P less than 0.001) that was significantly reduced by insulin (P less than 0.001, P less than 0.02, and P less than 0.05 at 60, 90, and 120 min, respectively). These results suggest that while moderate activation of the alpha 2-adrenergic system stimulates GH release, further stimulation of the same system may result in inhibition, rather than further activation, of GH secretion
Water retention characteristics of substrates containing biochar and compost as peat and perlite replacements for ornamental plant production
No full textIn Italy peat and perlite are commonly used as growth substrates in ornamental plant nurseries. Requests for ecologically sustainable growth substrates have recently focused research on the study of new media. In this context, biochar and compost, by-products of other production chains, may play a relevant role. Four growth substrates were prepared by mixing (v/v) different porous matrices including a 2-mm sieved sandy loam soil namely: 50% peat and 50% perlite (PPr), 50% compost and 50% biochar (CB), 25% peat, 25% perlite, 25% compost and 25% biochar (PPrCB) and 25% peat, 25% compost and 50% mineral soil (PCM). Water retention curves of porous matrices and growth substrates were determined by standard techniques and the unimodal and bimodal van Genuchten models were fitted to experimental data. The three growth substrates obtained by mixing by-products (CB, PPrCB and PCM) were tested for Lantana camara L. production in a three-months trial performed on 3 L pot plants. The highest plant available water content (PAWC) was obtained for biochar (PAWC = 0.28 cm3 cm-3), while the highest saturated volumetric water content (θs) was obtained for peat (θs = 0.67 cm3 cm-3). Perlite and biochar water retention curves showed a steep decrease in volumetric water content when desaturated probably due to the high macroporosity of the media. The PPr showed higher water retention performances than CB growth substrate. Despite the differences in water retention characteristics, Lantana camara above ground and total plant dry weight were not affected by the growth substrates
A numerical test of soil layering effects on theoretical and practical Beerkan infiltration runs
Full text linkWith reference to a more compacted and less conductive upper soil layer overlying a less compacted and more conductive subsoil, a simple three-dimensional (3D) infiltration run is expected to yield more representative results of the upper layer than the subsoil. However, there is the need to quantitatively establish what is meant by more representativeness. At this aim, numerically simulated infiltration was investigated for a theoretically unconfined process under a null ponded head of water (d0H0 setup, with d = depth of ring insertion and H = ponded depth of water) and a practical Beerkan run (d1H1 setup, d = H = 1 cm). The considered layered soils differed by both the layering degree (from weak to strong; subsoil more conductive than the upper soil layer by 2.3–32.4 times, depending on the layering degree) and the thickness of the upper soil layer (0.5–3 cm). It was confirmed that water infiltration should be expected to be more representative of the upper soil layer when this layer is the less permeable since, for a 2-h experiment, the instantaneous infiltration rates for the layered soil were 1.0–2.1 times greater than those of the homogeneous low-permeable soil and 1.3–20.7 smaller than those of the homogeneous coarser soil that constituted the subsoil. Similarity with the homogeneous fine soil increased as expected as the upper layer became thicker. For a weak layering condition, the layered soil yielded an intermediate infiltration as compared with that of the two homogeneous soils forming the layered system. For a strong layering degree, the layered soil was more similar to the homogeneous fine soil than to the homogeneous coarse soil. Using the practical setup instead of the theoretical one should have a small to moderate effect on the instantaneous infiltration rates since all the calculated percentage differences between the d1H1 and d0H0 setups fell into the relatively narrow range of −18.8% to +17.4%. A sequential analysis procedure appeared usable to detect layering conditions but with some modifications as compared with the originally proposed procedure. The practical setup enhanced the possibility to recognize the time at which the characteristics of the subsoil start to influence the infiltration process. In conclusion, this investigation contributed to better interpret both the theoretical and the practically established 3D infiltration process in a soil composed of a less conductive upper soil layer overlying a more conductive subsoil and it also demonstrated that modifying the recently proposed sequential analysis procedure only using infiltration data could be advisable to determine the time when layering starts to influence the process
Testing the hydrodynamic behavior of a loam soil by beerkan infiltration runs with six heights of water pouring
Full text linkInterpreting and simulating rainfall partition into infiltration and surface runoff has to consider that surface soil hydraulic properties, including saturated soil hydraulic conductivity (Ks) and sorptivity (S), could change even at very short temporal scales. Soil deterioration due to water impact can be tested in the field by the multi-height beerkan (MHB) method, that is, by pouring water on the infiltration surface from different heights. Soil hydraulic properties can be estimated coupling the MHB method with the steady version of the Beerkan Estimation of Soil Transfer parameters procedure (BEST-steady). The MHB method with six heights of water pouring (H) in the range 0.03-2 m was applied on a relatively dry loam soil to investigate height of water pouring effects on i) the established infiltration process, and ii) Ks, S, the scale parameter of the water retention curve (hg) and the characteristic microscopic pore radius (m). Higher heights of water pouring generally induced a slowdown of the infiltration process, smaller S, Ks and m values and higher |hg| values. The S, Ks, |hg| and m vs. H relationships were statistically significant but the fitted relationships for S and Ks were stronger than those for |hg| and m, indicating a different sensitivity of the considered parameters to the height of water pouring. Small or negligible soil deterioration was observed for both small (H < 0.25 m) and large (H > 1.5 m) heights. Between these two extremes, the soil deteriorated as H increased, suggesting that the external solicitations were high enough to overcome the resistance of the porous medium but not so high to determine a complete soil alteration. The tested methodology appears promising to determine the effects of water impact on the soil hydrodynamic behavior and it could be applied to perform a soil hydraulic characterization usable for modelling hydrological processes
Combined alpha-adrenergic stimulation results in biphasic response of growth hormone release in man
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