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71.
For a long while Japanese agricultural workers have centered their efforts to an increase in rice production, confirming the extreme importance of appropriate water controlling for a good crop. Meanwhile, Japanese farmers have traditionally practiced to keep their fields in a dry state for several days in the mid-summer. They have been convinced of healthy plants with temporarily draining off water. Its season is generally in the dog-days from the end of July to the beginning of August, and the degree of drainage seems to be decided by farmer's private views or experience. For instance, the Japan's No. 1 prize winner in technical skill of rice competition in 1950 withdrew water until light marks remained when stepped in the field, while the 1952's winner drained his field until slight cracking on ground for the period August 11 to 13 (4). They were really successful in obtaining 7.71 and 9.27 tons of brown rice per hectare, respectively. However, it appears to be needed to bring out the scientific meanings of the practice more clearly in order to make it reasonably and universaly, provided the practice is indispensable for a good rice crop. 相似文献
72.
The identification and characterization of clay minerals in the soil have been carried out on the clay fraction separated from a dispersed soil suspension. The process of dispersion includes the replacement of exchangeable divalent cations with H-ions by the dilute acid treatment, the removal of organic matter with hydrogen peroxide, and the dissolution of free iron oxides with reducing and/or chelating agents. 相似文献
73.
Texture is one of the major criterions in soil classification, probably because it has a decisive influence on soil properties. This is particularly true for volcanic ash soils. Most ashes are largely composed of sand and silt particles with little clay (11, 15). The ash weathers very rapidly (1), and clay site particles less than 2 microns in diameter occur even within a few months, as shown by Ishii at the authors' laboratory. Those clay size particles produced in the early stage of weathering are slightly weathered ones (2), and are still subject to rapid weathering, losing bases and silica under humid and well drained conditions. In consequence the clay fraction of volcanic ash soils is composed of particles which vary in degree of weathering from slightly altered glass and feldspar to true clay mineraloids and minerals. The clay fraction of younger soils as a whole is less and that of older ones is more weathered. Weathering brings a remarkable change in the properties of volcanic ash soils; for example, an inerease in soil acidity, lowering of base saturation and bulk density, or accumlation of organic matter. These changes must exert a great influence on soil fertility directly or indirectly. 相似文献
74.
Amorphous soil inorganic materials, specifically allophane. are believed to have a marked effect on soil properties and soil productivity, even in a relatively small amount, due to their large specific surface area, peculiar nature of surface and high chemical reactivity. They seem be present in soils, more or less, but determination of their content is generally semiquantitative or not fully reliable, because allophane includes aluminosilicates in a wide range of chemical composition and of properties, and any satisfactory, quantitative analytical method has not been established. 相似文献
75.
Genetic population evaluation of two closely related flatfish species, the rare barfin flounder and spotted halibut, along the Japanese coast 总被引:3,自引:1,他引:3
María Del Mar Ortega-Villaizán Romo Masato Aritaki Shigenori Suzuki Minoru Ikeda Takashi Asahida Nobuhiko Taniguchi 《Fisheries Science》2006,72(3):556-567
ABSTRACT: Barfin flounder and spotted halibut have been selected as target species for stock enhancement in Japan. Understanding the genetic condition of the wild stock is a principal requirement in any stock enhancement program. The genetic variability of barfin flounder and spotted halibut, and the population structure of spotted halibut were evaluated using microsatellite DNA markers (msDNA) and the control region of the mitocondrial DNA (mtDNA). Barfin flounder and spotted halibut showed high genetic variability at the msDNA level. Barfin flounder A was 16.7 and H e was 0.860; spotted halibut A n ranged from 7.7 to 10.2 and H e ranged from 0.710 to 0.774. At the mtDNA level, high haplotype ( h = 0.922) and low nucleotide (π = 0.002) diversities were observed for barfin flounder; however, low haplotype and nucleotide diversities ( h = 0.603–0.620 and π = 0.001–0.002), and very low haplotype and nucleotide diversities ( h = 0.193 and π = 0.0003) were observed for spotted halibut in the north and south locations, respectively. Slight genetic differentiation among spotted halibut sampling locations was observed from the msDNA. MtDNA analyses showed genetic differentiation between north and south locations, but not within them. The designation of north-specific and south-specific management units in the future stock enhancement activities of spotted halibut is recommended. 相似文献