{"created":"2022-01-27T02:43:55.351191+00:00","id":2002954,"links":{},"metadata":{"_buckets":{"deposit":"60db2a82-64f9-4028-9327-6f6d80086919"},"_deposit":{"id":"2002954","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"2002954"},"status":"published"},"_oai":{"id":"oai:u-ryukyu.repo.nii.ac.jp:02002954","sets":["1642837622505:1642837905044:1642837915094","1642838403551:1642838407312"]},"author_link":[],"item_1617186331708":{"attribute_name":"Title","attribute_value_mlt":[{"subitem_1551255647225":"沖縄島北部地方における土壌侵食の実証的研究(農業工学科)","subitem_1551255648112":"ja"},{"subitem_1551255647225":"Practical studies on soil erosion in the northern parts of Okinawa (Department of Agricultural Engineering)","subitem_1551255648112":"en"}]},"item_1617186419668":{"attribute_name":"Creator","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"翁長, 謙良","creatorNameLang":"ja"}]},{"creatorNames":[{"creatorName":"Onaga, Kenryo","creatorNameLang":"en"}]}]},"item_1617186476635":{"attribute_name":"Access Rights","attribute_value_mlt":[{"subitem_1522299639480":"open access","subitem_1600958577026":"http://purl.org/coar/access_right/c_abf2"}]},"item_1617186626617":{"attribute_name":"Description","attribute_value_mlt":[{"subitem_description":"農地における土壌侵食現象に関しては国の内外を問わず古くから大きな社会問題とされてきた。侵食の機構やその対策に関してはこれまでも世界各地で多くの研究があるが, 各地域によって侵食要因の特性が異なり, その間に普遍性は見出せない。これは侵食量に影響をおよぼす各因子が複雑に錯綜するので, 定量的把握は困難であることによる。したがって侵食度の高い沖縄地方においても現地に即した研究が必要である。本研究は沖縄島北部地方の降雨侵食の要因についての実態調査に基づく実証的研究である。まず沖縄島北部地方における侵食の概況について記述する。沖縄島の地形, 地質を概観すると, 中南部は緩傾斜地であるが, 北部は山岳地帯でミクロ的には傾斜地が多く, 谷密度が高い。従って降雨による表流水は速やかに河海に達する。また土壌は, 受食性の高い赤・黄色土が卓越しており, 降雨量も中南部より多く, 年雨量の平均が約2,300mmである。このような自然条件の下で区画の大きい農地を造成する際は改良山成工が採用されるので土壌の大量移動が伴う。従って土壌構造が破壊され, 脆弱化され, 降雨による分散, 表流水の運搬に対する抵抗性が弱くなる。しかも, 受食性作物とされるパイナップルが植栽されているので侵食は益々受け易くなる。以上のように沖縄島北部地方は降雨による土壌侵食性のポテンシャルが高い。このことを現場における実態調査結果から要約するとつぎのとおりである。農地の造成中は, 砂防施設等の滞砂や濁水浄化の機能が十分に発揮されてなく, 大量の土砂が河川や沿岸に流失し流域環境の悪化を招いている。河川の中流域で浮遊土砂量を観測した結果, 1雨(97mm)で100トン余に上る土砂量(乾燥重量)が流亡した事例があり, 造成初期の畑地において, 600mmの雨により, 2haの圃場から433m^3の土砂流亡が観測され, 造成後やや落着いた農地からでも5ケ月間で1,000mmの雨量によりその表土層が1.1cmも侵食される事例もある。さらにパイナップル畑での流出水の濁度観測では濁度のピークが10,000ppmにも達することも認められ, 土壌侵食はかなり顕著に出現している。侵食の実態調査結果からこのような現象を出現させる要因を検討すると, 人為的作用によるほかは, 主として土性, 降雨, 傾斜要因であることが考えられたので, これらの要因についての解析結果をつぎに述べる。","subitem_description_type":"Other"},{"subitem_description":"(1)土性 沖縄地方は湿潤亜熱帯のアジアモンスーン地域に位置している。それ故その地域の気候を反映して本土と異なる特殊な土壌(赤黄色土 : 国頭マージ)が分布している。中でも沖縄島北部や石垣島, 西表島などではこの種の土壌が卓越している。国頭マージは沖縄県の国頭(北部)地方に分布する赤い土という意味の沖縄方言による呼称であるが, 土壌の大分類では赤色土・黄色土とされている。細分類としては13の土壌統に区分され, それぞれの特徴づけがなされているが, 造成・整備農地ではその性質が異なる種々の土壌が混在している場合が多い。したがって物理性の記述に関しては国頭マージとして扱った。この土壌の侵食に関与する2,3の物理性について広範な調査に基づき, 粘土含有量, 団粒化度, 分散率, 浸入能を検討すると次の結果が得られた。1)粘土含有量は9.0∿58.5%の広い範囲にまたがっており, 土性が砂土から植土まで多岐にわたっている。2)沖縄の主要な土壌について団粒化度を調べた。その結果島尻マージ(暗赤色土)10試料中, ジャーガル(灰色台地土)8試料中については団粒化度80%以上のものがそれぞれ9試料, 6試料であったのに対し国頭マージは35試料中わずかに7試料であり, 耐水性団粒が極めて少ないことがわかった。3)分散率について, わが国の基準にしたがって分類すると, 分散率が40以上の受食性域にある土壌は国頭マージ, ジャーガル, 島尻マージでそれぞれ, 34試料中16,13試料中4,22試料中2であった。4)浸入能について本州土壌のそれと比較すると浸入の初期においては大差はないが時間の経過につれて小さくなり, ベーシックインテークレートはかなり低くなる。なお4時間後の浸入能を比較すると国頭マージ(4試料)では7mm/h∿95mm/hの範囲にあるが本州土壌(5試料)では81mm/h∿360mm/hの範囲にある。また現地裸地圃場での散水インテークの試験結果では畑面勾配が3°, 降雨強度65mm/hのとき耕起, 不耕起別の浸入能は散水開始後それぞれ, 17∿18分, 12∿13分で, 降雨強度以下になり表面流出が見られた。さらにパイン畑では9mmの雨でも大量の流亡土が観測されるなど, 圃場条件によってもかなりの差があることが認められた。以上によりこの地方のとくにパイナップル畑では土壌の受食性が高いことが明らかになった。(2)降雨エネルギー 降雨の侵食能力はそのエネルギーである。このエネルギーは雨滴の分布型と降雨強度に左右され, 当然, 地域特性をもつものである。沖縄の降雨に関して約12万個の採取雨滴の","subitem_description_type":"Other"},{"subitem_description":"The phenomenon of soil erosion of farmlands has been a societal problem all over the world since ancient times. Although there have been numerous studies of the mechanism and prevention of soil erosion, it is difficult to find a universal method of erosion control because of the differences in the factors that affect soil loss. Therefore, in order to understand the complicated nature of the factors that influence soil erosion and to formulate some effective erosion control measures that conform to the local conditions, such as those of the northern parts of Okinawa, it is essential for extensive studies to be undertaken. This dissertation presents the results of practical studies based on actual conditions occurring in the investigation of rainfall erosion in the northern parts of Okinawa Island during March 1975∿Feb. 1985. Okinawa Island consists of gently sloped terrain in the central and southern parts, but in the northern parts the slope is steep with many valleys, for which reason runoff to the rivers and ocean is rapid in the north. Additionally, the annual rainfall is about 2,300mm, which is more than that of the central and southern parts of the island. And finally, the predominant soil in the north, which is red and yellow in color, is readily erodible. Reclamation of land under these conditions usually involves the moving of great quantities of soil by heavy equipment. As a consequence, the natural resistance of the soil against dispersion by rainfall is weakened because of the destruction of its structure and because of the augmented transportation power of the runoff. Moreover, the reclaimed fields are often planted with pineapple, which is generally regarded as a soil-eroding plant. Such fields as these are therefore more erodible than other vegetated fields. In brief, the northern part of Okinawa Island has a high potential for soil erosion caused by rainfall. Based on the investigation of actual circumstances, the situation may be summarized as follows : During reclamation construction, erosion control facilities, such as sedimentation tanks, soil catch dams, and gabions, do not function sufficiently well to purify the muddy runoff.","subitem_description_type":"Other"},{"subitem_description":"Therefore great quantities of soil are carried off by runoff to the rivers and ocean, and this has a deleterious effect on the situation of the watershed environment. Observation reveals that one storm (97mm) caused more than one hundred tons of wash load to be carried by runoff from reclaimed fields located two kilometers above the mouth of a river. In another case, 433m^3 of soil loss was confirmed from a field lot of 2 ha. which had been recently reclaimed. This was caused by a 600mm rainstorm. It was also observed that one field, 5 months after reclamation, lost 11mm of surface layer because of a rainfall of 1,000mm. Furthermore, the degree of the muddiness of the runoff from pineapple fields (10,000ppm) showed that there was significant soil erosion taking place in the Kunigami Maaji farmland area. It was observed that in pineapple fields great quantities of soil loss were caused by as little as 9mm rainfall because of lack of good management. This fact indicates that the management factor is very important in erosion control. The results of such investigation indicates that the factors primarily responsible for soil erosion, other than human factors, are soil properties, rainfall characteristics, and surface inclination. Therefore, these factors should be thoroughly analyzed. 1. Soil properties Okinawa is located in the monsoon region of Asia and has a humid subtropical climate. Therefore the properties of the soils in this district reflect the climatic factors. One particular kind of soil, called Kunigami Maaji because of the locality and the local dialect, is distributed mainly in the northern parts of Okinawa island, Ishigaki island, and Iriomote island. Kunigami Maaji soil is red-yellow in color and is regarded as a problem soil from the point of view of erosion. This s","subitem_description_type":"Other"},{"subitem_description":"紀要論文","subitem_description_type":"Other"}]},"item_1617186643794":{"attribute_name":"Publisher","attribute_value_mlt":[{"subitem_1522300295150":"ja","subitem_1522300316516":"琉球大学農学部"}]},"item_1617186702042":{"attribute_name":"Language","attribute_value_mlt":[{"subitem_1551255818386":"jpn"}]},"item_1617186783814":{"attribute_name":"Identifier","attribute_value_mlt":[{"subitem_identifier_type":"HDL","subitem_identifier_uri":"http://hdl.handle.net/20.500.12000/3925"}]},"item_1617186920753":{"attribute_name":"Source Identifier","attribute_value_mlt":[{"subitem_1522646500366":"ISSN","subitem_1522646572813":"0370-4246"},{"subitem_1522646500366":"NCID","subitem_1522646572813":"AN00250548"}]},"item_1617186941041":{"attribute_name":"Source Title","attribute_value_mlt":[{"subitem_1522650068558":"ja","subitem_1522650091861":"琉球大学農学部学術報告"},{"subitem_1522650068558":"en","subitem_1522650091861":"The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus"}]},"item_1617187056579":{"attribute_name":"Bibliographic Information","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"1986-12-05","bibliographicIssueDateType":"Issued"},"bibliographicIssueNumber":"33","bibliographicPageEnd":"209","bibliographicPageStart":"111"}]},"item_1617258105262":{"attribute_name":"Resource Type","attribute_value_mlt":[{"resourcetype":"departmental bulletin paper","resourceuri":"http://purl.org/coar/resource_type/c_6501"}]},"item_1617265215918":{"attribute_name":"Version Type","attribute_value_mlt":[{"subitem_1522305645492":"VoR","subitem_1600292170262":"http://purl.org/coar/version/c_970fb48d4fbd8a85"}]},"item_1617605131499":{"attribute_name":"File","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_access","filename":"KJ00000162267.pdf","mimetype":"application/pdf","url":{"objectType":"fulltext","url":"https://u-ryukyu.repo.nii.ac.jp/record/2002954/files/KJ00000162267.pdf"},"version_id":"7847b1aa-8469-4373-9252-ce0224071a84"}]},"item_title":"沖縄島北部地方における土壌侵食の実証的研究(農業工学科)","item_type_id":"15","owner":"1","path":["1642837915094","1642838407312"],"pubdate":{"attribute_name":"PubDate","attribute_value":"2008-02-14"},"publish_date":"2008-02-14","publish_status":"0","recid":"2002954","relation_version_is_last":true,"title":["沖縄島北部地方における土壌侵食の実証的研究(農業工学科)"],"weko_creator_id":"1","weko_shared_id":-1},"updated":"2022-10-31T01:12:24.917476+00:00"}