土壌の物理性

新鮮な土壌物理学をめざして

宮崎毅

2001 年 88 巻 p. 1-2
発行日: 2001年
公開日: 2021/10/25

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_1

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泥炭土の透水性および保水性について一美唄湿原地帯の土壌物理性(Ⅱ)—

井本博美, 宮崎毅, 斎藤広隆, 中野政詩

2001 年 88 巻 p. 3-9
発行日: 2001年
公開日: 2021/10/25

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_3

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We measured saturated hydraulic conductivities, unsaturated hydraulic conductivities and water retentivities of Bibai peat soils, consisted of highmoor peat (natural moss), transitional peat and lowmoor peat. The transitional moor soils exhibited remarkable anisotropy of permeability. The vertical saturated hydraulic conductivity was utmost about 400 times more than its horizontal saturated hydraulic conductivity probably due to the horizontal sedimentation of plant fiber. This anisotropy was most remarkable in the subsoil of a paddy field under the dressed soil and was less in the undisturbed soils under windbreak. Soil dressings and continuous cultivations may have affected the appearance of the intensive anisotropy. The unsaturated hydraulic conductivities of transitional peat and highmoor peat were quite small and were less than those of sand. This feature caused the necessity of relatively long time for the equilibration of water retention.

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植生帯を用いた畑地土壌の流出負荷制御

上野貴司, 三原真智人, SANG-ARUN Janya, 土器屋由紀子

2001 年 88 巻 p. 11-18
発行日: 2001年
公開日: 2021/10/25

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_11

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The effect of grass strips on the reduction of sediment and eutrophic salt loads is been widely recognized. However, there is very little knowledge of the effect of grass strips on the reduction of sediment and eutrophic salt losses. Attention was hence focused on the investigation of what grass strips should be managed. Soil suspension was supplied to the experimental plots under simulated rainfall. During the experiment, surface discharge and sediment concentration were measured. In order to observe the effect of grass strips on the reduction of sediment loss, the difference between the amounts of sediment supplied and sediment loss was investigated in each plot. While the sediment concentration and load from the bare upland field exceeded the concentration and load of the soil suspension supplied, the sediment concentration and load from all the grass strips were lower than the concentration and load of the supplied soil suspension. The difference between the sediment supplied and the sediment loss from the cutting weeds plot for pest control was approximately equivalent to that of the plot with the natural weeds. Therefore, it was concluded that cutting weeds for pest control can be applied to the grass strip for reduction of the sediment loss. There was little difference between the reduction of the sediment loss from the plot with 800 stems/m2 and that from the plot with 1,480 stems/m2 of Tall Fescue [F. arundinacea). However the plot with 2,330 stems/m2 of Tall Fescue was effective for the reduction of sediment loss comparing with 800 stems/m2 and 1,480 stems/m2. It suggests that stem density for grass strips should be maintain 2,330 stems/m2 to control soil loss from upland field.

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土壌中の水分•溶質移動解析への汎用PDEソルバーの適用

登尾浩助

2001 年 88 巻 p. 19-25
発行日: 2001年
公開日: 2021/10/25

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_19

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For the proper management of water and fertilizer resources, distributions of water and solute in soil should be precisely predicted. The movement of water and solute in soil may be expressed with partial differential equations (PDEs). The PDEs should be numerically solved for real world applications because of complex initial and boundary conditions and high non-linearity in some cases. The recent development of a general PDE solver using the finite element method enabled us to more easily solve these PDEs governing water and solute transport in soil. FlexPDE Lite can be freely obtained through the Internet, and its applicability to solve water and solute transport in soil was investigated. FlexPDE Lite successfully simulated water infiltration into Haverkamp’s sandy soil with <2% of mass balance errors. However, it failed to calculate water infiltration into dry loamy sand when initial pressure head was < — 60 cm. Results of simulating solute transport with FlexPDE Lite also agreed well with analytical solutions especially when the convective transport was not dominant. Therefore, FlexPDE Lite, although its performances were purposely limited, could be an ideal tool for a training purpose or a small-scale simulation.

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東北タイ塩類土壌地域における森林再生のための涵養地域と排出地域の決定への地盤電磁誘導法の応用について

Dissataporn Chaiyanam, 成岡市, Yamclee Pramot, Arunin Somsri

2001 年 88 巻 p. 27-35
発行日: 2001年
公開日: 2021/10/25

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_27

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東北タイ•マハサラカム層を主体とした塩類化土壌地域における地下水動態について,地盤電磁誘導法すなわち EITCM (multi frequency Electromagnetic Induction Terrain Conductivity Meter) により得られた測定値,およびピエゾメーター法により得られた観測値が比較検討された。この電磁気学的手法は,地域土壌の塩含有量の空間分布を概略的に識別するために有益な技術ばかりでなく,水文学的データを併用することによって地域的な地下汽水の涵養地域と排出地域の概要を知ることができる有効な手法である。本論では,この手法が当該塩害地の再生を考慮した大規模な森林計画の検討に有効であることを論議し,EITCMによる地下水の涵養/排出分布図を作成した。

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北海道上川地方の堅密固結性土壌に対するオプナー式有材心土改良耕の効果

横井義雄, 北川巌, 後藤英次, 田丸浩幸

2001 年 88 巻 p. 37-44
発行日: 2001年
公開日: 2021/10/26

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_37

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The effects of subsoil improvements were examined on hardsetting soils in Kamikawa, Hokkaido. The soils were fine-textured gray terrace soils. They are clayey, hard, and compacted and have a shallow soil layer. For subsoil improvement, a new technique has been developed that makes use of soil amendments. The technique is a modified method of subsoiling. It requires the construction of trenches that are 10cm wide and 25-55 cm deep at 60-120 cm intervals. Soil amendments are put into the trench. The effects of the subsoil improvements and the construction standards for the trenches are as follows : 1. Three years after the subsoil was amended, soil hardness and bulk density decreased along the trench, and air filled porosity was maintained at around 0.10 m3 m'3. Penetration resistance was greater than 2.45 MPa at a depth of 25 cm before treatment; however, it decreased to 0.98 to 1.47 MPa after the treatment. 2. The amended parts of the field worked as a supplementary underground drain in the upland field and by the improvements agricultural machinery can be operated more effectively even after rainfall. 3. The subsoil improvements caused the root zone of crops to expand. Nutrient absorption improved remarkably, and yields increased. The improvements were especially effective to deep-rooted crops which are susceptible to wet injury. 4. The trench intervals were set at 60 cm when soil hardness was greater than 1.16 MPa ; however, the intervals were expanded to 120 cm when the soil hardness was 0.53 to 1.16 MPa.

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心土破砕が傾斜畑の表面流出量と圧力水頭•地温に与える影響

諸泉利嗣, 佐藤裕一, 佐藤幸一, 三浦健志

2001 年 88 巻 p. 45-52
発行日: 2001年
公開日: 2021/10/26

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_45

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This paper discusses the effects of subsoil breaking on the change of pressure head, soil temperature and runoff discharge in space and time in a sloping field. A controlled comparison experiment was conducted in a subsoil breaking field and a no-subsoil breaking field. The results showed that the runoff ratio of the subsoil-breaking field was about 1/10 of that in the no-subsoil breaking field. This indicates that subsoil breaking promotes the infiltration of rainfall into the soil and can reduce the surface runoff discharge. The spatial distribution of the equi-pressure heads during rainfall was complicated, and the coefficients of variation were large. However, that of the equi-pressure heads before and after rainfall showed the similar patterns of variation in both fields. As for soil temperatures, we didn’t observe a large difference between the subsoil breaking field and the no-subsoil breaking field, and the spatial variation was smaller than that of the pressure head.

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粘質水田土壌の乾燥による内部微細亀裂の発生に対する根系の影響

吉田修一郎, 足立一日出

2001 年 88 巻 p. 53-60
発行日: 2001年
公開日: 2021/10/26

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_53

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土塊内部に潜在する小ひびは,易耕性に重要な役割を果たしている。代かきが行われた粘土質水田土壌では,乾燥収縮にともない,これらの小ひびの形成が認められる。しかし,その挙動は,根系の有無により大きく異なっている。根系が土壌の収縮に及ぼす影響は,土壌の物理的な固定と水分吸収の二つの働きに起因する。通常,これらは同時に作用するため,機構的な区別が十分なされていない。本研究では,水稲栽培期間中の水田を乾燥させた後に土壌を採取し,それらの体積含水比および気相比と,含まれる根の密度との関係を解析した。その結果,根系は,水分の吸収と土壌の固定の両者を同時に作用させて乾燥時に土壌中に小ひびを誘起しているが,水分を吸収しなくとも,土壌中の細かいひびの発生を増大させる作用があることが明らかになった。

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編集後記

安中武幸

2001 年 88 巻 p. 63-
発行日: 2001年
公開日: 2021/10/26

DOIhttps://doi.org/10.34467/jssoilphysics.88.0_63

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