SPRINKMOD – pressure and discharge simulation model for pressurized irrigation systems. 2. Case study

A computer model, SPRINKMOD, was tested with field data collected from a complex sprinkler irrigation system in operation. The original data collected were adjusted in order to calibrate the model for the irrigation system. Five modifications were made in the original data so that the model sensitivity could be evaluated. The model predicted the system operating point with less than 1% error, after some adjustments in the data. The relative mean standard error was 4.1% for the upstream pressure heads and 2.1% for the downstream pressure heads of all laterals analyzed together. Measurement of pressure and discharge at pump stations along with a reasonable estimate of leakage appears to be essential for simulation of old systems. Adjustments made to pipe wall thickness and pipe roughness were not as important as the adjustments made to the lateral valves closure in getting SPRINKMOD to simulate pressure heads that were close to the measured values. For long laterals, like center pivot laterals, a variable local loss coefficient for flow past a riser outlet worked better than a fixed value of 0.3. Received: 24 November 1997     

Effects of temperature, density and early weaning on the survival and growth of Atlantic ditch shrimp Palaemonetes varians larvae

This investigation examined the effects of temperature, density and early weaning on the survival and growth of Palaemonetes varians larvae. Survival of larvae raised at 17.5 °C was not significantly different (average + standard deviation) (94 ± 5%) from the survival of those raised at 19.5 °C (95 ± 5%) and at 21.5 °C (94 ± 4%). However, the duration of the larval stage was significantly longer for shrimp reared at 17.5 °C (17.3 ± 0.8 days) compared with shrimp reared at 19.5 °C (14.3 ± 0.7 days) and at 21.5 °C (11.3 ± 0.6 days). No significant differences ( P >0.05) were found in the survival rate, final weight and length of larvae reared at the densities of 5, 10, 20 and 50 larvae L⁻¹. The survival of P. varians larvae fed solely on Artemia was significantly higher ( P <0.05) than larvae weaned with an artificial practical diet from Zoea II stage (94 ± 4% and 82 ± 1%, respectively, for Artemia and artificial diet-fed larvae), but no significant differences ( P >0.05) were observed in the final larval weight or length between these two treatments. The survival and growth of the larvae fed with the practical diet tested is a promising step ahead in the development of the culture of this species as it eliminates both the need for Artemia throughout all larval stages, and the need for more expensive artificial diets.     

Multi-method assessment of nitrate and pesticide contamination in shallow alluvial groundwater as a function of hydrogeological setting and land use

In this study deterministic, multivariate and stochastic methods are applied to a combined temporal and spatial monitoring data set, in order to assess nitrate and pesticide levels and contamination risk in shallow groundwater. The case study involves an area in the Mondego River alluvial body in central Portugal, where agriculture is the main land use, with predominantly maize, rice and some vegetable crops supported by river water irrigation. Factorial correspondence analysis (FCA), reducing the original data matrix to a small number of independent orthogonal factors, is applied to detect associations between nitrate levels, land use (crop type), lithology and groundwater depth. Indicator-geostatistical techniques are used to create maps indicating the probability of nitrate concentrations in groundwater exceeding predetermined threshold values, including the drinking water standard (98/83/EC) and vulnerable zone designation criterion (91/676/EEC) of 50 mg/l NO₃⁻. For pesticides the leaching potential is determined by calculating the Groundwater Ubiquity Score (GUS), based on the sorption coefficient and soil half-life for each pesticide compound. Results for nitrate show an overall very low risk of exceeding 50 or 25 mg/l, whereas the risk of exceeding 9.5 mg/l (third data quartile) is particularly high in areas where FCA shows correlation of nitrate contamination with vegetable and maize crops, aerobic conditions, lower groundwater levels and to some extent, coarser grained sediments. On the contrary, nitrate levels under rice are lowest and correlated to a reduced environment, finer-grained sediments and a higher water table. Denitrification is found to be an important attenuation process, as well as dilution by surface water irrigation and precipitation. Crop type and irrigation source are seen to have a large influence on the nitrate contamination potential of groundwater. Total concentrations of the analysed pesticide compounds above the regulatory limit of 0.5 μg/l are observed in 32% of the analysed water samples, with a maximum value of 16.09 μg/l. The probability maps provide a particularly interesting example of how multiple-well monitoring results over a certain period can be condensed into single maps and used by water engineers, managers and policy-makers.     

Symbiotic efficiency and identification of rhizobia that nodulate cowpea in a Rhodic Eutrudox

Cowpea (Vigna unguiculata (L.) Walp.) is one of the most important crops in the north and northeast regions of Brazil, where it is grown under the subsistence regime, mainly because of its adaptation to the local edaphoclimatic conditions. This species is an important legume in Brazil because of its significant nutritional value in the diet of low-income populations. Moreover, it is able to benefit from the process of biological nitrogen fixation, which leads to a significant reduction in production costs. The objective of this research was to evaluate the agronomic efficiency of bacterial strains approved by the Ministry of Agriculture, Livestock and Supply for commercial inoculant production when in symbiosis with cowpea in a Rhodic Eutrudox in Lavras, MG, as well as to identify and verify the efficiency of the native populations that nodulate cowpea. Agronomic efficiency of nitrogen-fixing nodulating bacterial strains (UFLA 03-84, INPA 03-11B, and BR 3267) in symbiosis with cowpea was evaluated in the field. Subsequently, the efficiency and diversity of isolates from the nodules obtained in the field were evaluated under greenhouse conditions. The genetic diversity of the efficient isolates was determined by partial sequencing of the 16S rRNA gene. Grain yields obtained by the inoculation of seeds in the field with the strains were similar to those of the controls without inoculation with and without mineral N addition indicating the existence of efficient native populations. In the native community, we identified isolates with similar or higher efficiency than the strains approved for cowpea inoculation and the control that received mineral N. The isolates subjected to partial sequencing of the 16S rRNA gene were phylogenetically related to the Bradyrhizobium genus.     

Antioxidant activity of Centaurium erythraea infusion evidenced by its superoxide radical scavenging and xanthine oxidase inhibitory activity.

Centaurium erythraea Rafin. (Gentianaceae) has long been used in traditional medicine. This plant contains considerable amounts of polyphenolic compounds, namely, xanthones and phenolic acids as the main constituents. Because phenolic groups exhibit activity as radical scavengers and/or metal chelators, this study evaluated the superoxide radical scavenging properties of a lyophilized infusion obtained from C. erythraea flowering tops. Superoxide radical scavenging activity was assayed using enzymatic (xanthine/xanthine oxidase) and nonenzymatic (NADH/phenazine methosulfate) superoxide generating systems. This study provided evidence that C. erythraea exhibits interesting antioxidant properties, expressed either by the capacity to scavenge superoxide radical or to noncompetitively inhibit xanthine oxidase. The main phenolic compounds present in this extract were several esters of hydroxycinnamic acids, namely, p-coumaric, ferulic, and sinapic acids.     

沧州市滨海盐碱区耕层土壤盐分特征

为了解沧州市滨海盐碱区耕层土壤的盐渍化特征,采集三个时期沧州不同地区耕层土壤（0~20 cm）样品,结合样品实验分析,探究土壤盐分特征。结果表明：①沧州滨海盐碱区耕层土壤离子类型多样,检测的八大离子中氯离子、钠离子、硫酸根、碳酸根+碳酸氢根离子为主要盐分离子,土壤类型为硫酸盐-氯化物型。②相关分析表明,耕层土样中总含盐量与氯离子和钠离子均存在显著或极显著相关关系,沧州市滨海盐碱地耕层土壤的总含盐量一定程上取决于土壤中氯化钠的含量;氯化钠、氯化镁和氯化钙为氯化物的主要组成部分;主要硫酸盐类为硫酸钠、硫酸镁和硫酸钙。③方差分析表明,三个不同采样时期和不同地区均对沧州市滨海区盐碱地的盐渍化的影响存在显著或极显著差异。④主成分分析表明,钠离子、氯离子、镁离子、钙离子和硫酸根与第1主成分相关性较高;钾离子和碳酸根+碳酸氢根与第2主成分相关性较高;第3主成分主要反映硅酸盐类对土壤离子成分的影响。由于钠离子、氯离子、钙离子和硫酸根在土壤中含量相对较高,是表征沧州滨海盐碱区土壤盐渍化的主要特征因子。     

Cardiovascular effects of desflurane following acute hemorrhage in dogs

Objective: To determine the cardiovascular effects of desflurane in dogs following acute hemorrhage. Design: Experimental study. Animals: Eight mix breed dogs. Interventions: Hemorrhage was induced by withdrawal of blood until mean arterial pressure (MAP) dropped to 60 mmHg in conscious dogs. Blood pressure was maintained at 60 mmHg for 1 hour by further removal or replacement of blood. Desflurane was delivered by facemask until endotracheal intubation could be performed and a desflurane expiratory end‐tidal concentration of 10.5 V% was maintained. Measurements and main results: Systolic, diastolic, and mean arterial blood pressure (SAP, DAP and MAP), central venous pressure (CVP), cardiac output (CO), stroke volume (SV), cardiac index (CI), systemic vascular resistance (SVR), heart rate (HR), respiratory rate (RR), partial pressure of carbon dioxide in arterial blood (PaCO₂), and arterial pH were recorded before and 60 minutes after hemorrhage, and 5, 15, 30, 45 and 60 minutes after intubation. Sixty minutes after hemorrhage, SAP, DAP, MAP, CVP, CO, CI, SV, PaCO₂, and arterial pH decreased, and HR and RR increased when compared with baselines values. Immediately after intubation, MAP and arterial pH decreased, and PaCO₂ increased. Fifteen minutes after intubation SAP, DAP, MAP, arterial pH, and SVR decreased. At 30 and 45 minutes, MAP and DAP remained decreased and PaCO₂ increased, compared with values measured after hemorrhage. Arterial pH increased after 30 minutes of desflurane administration compared with values measured 5 minutes after intubation. Conclusions: Desflurane induced significant changes in blood pressure and arterial pH when administered to dogs following acute hemorrhage.     

Circulating Metabolic Hormones During the Peripubertal Period and Their Association with Testicular Development in Bulls

The objective of the present study was to characterize changes in serum metabolic hormones concentrations from 20 weeks before to 20 weeks post-puberty in bulls and to investigate the associations of metabolic hormones concentrations with testicular development. Leptin concentrations increased from 16 weeks before puberty to 8 weeks post-puberty and insulin concentrations increased from puberty to 8 weeks post-puberty. Growth hormone concentrations decreased after 4 weeks post-puberty, whereas IGF-I concentrations increased from 8 weeks before puberty to 8 weeks post-puberty. During this period, testicular growth was accelerated and testosterone secretion increased substantially, without any significant changes in gonadotropin secretion. Monthly circulating concentrations of leptin, IGF-I and insulin accounted for 63% of the variation in scrotal circumference and 59% of the variation in paired testes volume. In conclusion, the secretion of metabolic hormones was not associated with changes in gonadotropins concentrations. Furthermore, the associations of leptin, IGF-I and insulin concentrations with testes size indicated that these hormones might be involved in a gonadotropin-independent mechanism regulating the testicular development in peripubertal bulls.