Plant-available water capacity of soils at a regional scale: Analysis of fixed and dynamic field capacities

Estimation of the plant-available water capacity (PAWC) of soils at a regional scale helps in adopting better land use planning, developing suitable irrigation schedules for crops, and optimizing the use of scarce water resources. In the current study, 72 soil profiles were sampled from the Barossa region of South Australia to estimate pedo-transfer functions deduced from easily estimated soil properties. These functions were then used to estimate the fixed (10 and 33 kPa) and dynamic pressure head (h_fc) water contents at field capacity (FC) for minimum drainage flux (0.01 and 0.001 cm d^-1), which serves as the upper boundary for plant-available water in soils. The estimated residual water content was corrected for subsoil constraints, especially the exchangeable sodium percentage (ESP). The results showed that the mean values of h_fc in sand-dominated light and medium textured soils (i.e., sand, loamy sand, sandy loam, and loam) varied in a narrow range (15.8–18.2 kPa), whereas those in the clay-dominated heavy textured soils (i.e., clay loam) showed a wide range (11.3–49.3 kPa). There were large differences in PAWC for dynamic FC (PAWC_fc) and fixed FC at 10 kPa (PAWC₁₀), 33 kPa (PAWC₃₃), and a mix of 10 and 33 kPa (PAWC_10,33) pressure heads depending on soil texture. Normally, the difference between PAWC at 10 kPa and h_fc (∆PAWC₁₀) was positive, whereas that between 33 kPa and h_fc (∆PAWC₃₃) was negative across all sites. Nevertheless, the estimation of PAWC assuming a fixed FC at 10 and 33 kPa pressures (i.e., PAWC_10,33) for sandy, clay, and silty soils reduced the difference between fixed and dynamic pressure PAWCs to < 10% across the region. The estimation of PAWC was improved by incorporating the impact of subsoil constraints, such as high ESP, which was more pronounced for clay and silty soils. These findings demonstrate the inherent inconsistencies between static pressure and flux-based dynamic FC estimations in soils. Soil heterogeneity, intra-texture variability, subsoil constraints, and swell-shrink clays can have great impacts on the water retention capacity in response to dynamic and fixed pressure FC values.     

上海嘉定区杨白潜蛾的生物学特性及防治

2002～2004年对杨白潜蛾(LeucopterasusinellaHerrich-Schаffer)的生物学特性进行了研究,结果发现杨白潜蛾在上海1年发生5代,幼虫共5龄,1年有2个发生高峰期:6月中旬和9月中下旬;老熟幼虫作白色“H”形茧化蛹;以蛹在树干周围场所越冬;成虫产卵单列成行。药剂试验表明杀虫安、甲氨基阿维菌素、快绿扬、斑潜净对喷雾杨白潜蛾具有很高的防效,对杨树也有很好的保叶效果。     

Esters produced by Chalaropsis thielavioides

Chalaropsis thielavioides, a filamnentous fungus. produces a characteristic ester-like aroma on potato dextrose broth. By gas-liquid chromatographic techniques, the major aroma-producing substances have been identified as isobutyl and ethyl acetate. Lesser amounts of isoamyl acetate, ethanol, and methanol were also present.     

Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7

Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.94 to 2.00 angstroms) observed in phases based on LaMnO3 perovskites that exhibit CMR. Both results in Tl2Mn2O7 indicate oxidation states very close to Tl23+Mn24+O7. Thus, Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials. An alternate mechanism for CMR in Tl2Mn2O7 based on magnetic ordering driven by superexchange and strong spin-fluctuation scattering above the Curie temperature is proposed here.     

The effects of poloxalene on ingestion by cattle grazing Lucerne†

The mechanisms that terminate meals of cattle grazing lucerne (Medicago sativa L.) are not well defined. Sub-acute bloat may lead to cessation of grazing and, consequently, surface active substances used in the treatment and prevention of bloat, such as poloxalene, may extend grazing meals and increase herbage intake. Twelve mature Angus cows (Bos taurus) were offered 0, 12·5 and 25·0 g poloxalene in 0·5 kg of crushed maize (Zea mays L.) kernels each day, immediately before two consecutive 1-h measured parts of a grazing meal on 21- to 24-day-old lucerne swards with a herbage dry matter (DM) mass (> 5 cm) of 2·03 t ha^?1 and herbage DM mass allowance of 3·55 kg hd^?1h^?1. Total herbage DM intake was 2·52 kg hd^?1 during the first hour and 1·54 kg hd^?1 during the second hour of the 2-h grazing meal. Differences in herbage intake were attributable to a cessation of grazing. Mean rates of biting were 26·3 and 14·8 bites min^?1 and mean DM intakes per bite were 1·82 and 4·38 g during the first and second part of meals, respectively. Poloxalene treatments caused a small linear decline in grazing time during the first part of meals and a larger increase in grazing time during the second part of meals. Lower rates of DM intake caused by poloxalene were offset by increases in grazing time. It was concluded that poloxalene moderated ingestive behaviour within grazing meals of immature lucerne and this response may have been at least partly due to the relief of sub-acute bloat.     

Chromatin Configurations in the Ferret Germinal Vesicle that Reflect Developmental Competence for In Vitro Maturation

In several mammalian species, the configuration of germinal vesicle (GV) chromatin correlates with the developmental competence of oocytes. Yet, no study has been published on the configuration of GV chromatin in ferret, nor is it known whether a specific configuration predicts meiotic competence in this species, in spite of the potential importance of ferret cloning to the study of human disease and to species conservation efforts. Here, we report on an analysis of the chromatin configuration in ferret GV oocytes and on how they correlate with meiotic development. Three distinct configurations were identified based on the degree of chromatin condensation: (1) fibrillar chromatin (FC), featuring strands of intertwined chromatin occupying most of the visible GV region; (2) intermediate condensed chromatin (ICC), characterized by dense, irregular chromatin masses throughout the GV; and (3) condensed chromatin (CC), which is highly compact and centered around the nucleolus. We also found that chromatin configuration was related to the extent of association with cumulus cells in cumulus–oocyte complexes; CC-configured oocytes were most often surrounded by a compact cumulus layer and also a compact corona but FC-configured oocytes were associated with neither. In addition, increasing chromatin condensation corresponded to an increase in oocyte diameter. Finally, following in vitro culture, significantly more CC-configured oocytes underwent maturation to meiotic metaphase II than did FC- or ICC-configured oocytes. We conclude that, in ferret, chromatin condensation is related to the sequential achievement of meiotic competencies during oocyte growth and differentiation, and thus can be used as a predictor of competence.