棚田における土壌流出と土壌流亡予測式の係数算出  [in Japanese] Soil outflow from paddy field and calculation of coefficient for soil loss equation  [in Japanese]

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Abstract

多面的機能維持増進調査(農林水産省)の一環として中国四国農政局が2006年6月~2007年8月に島根県出雲地方の棚田2地点(耕作田/遊休田)で実施した土壌流出観測のデータを用い、各観測水田からの20分間隔の土壌流出量を求めた。このデータと観測水田最寄りの水文水質観測所の降水量データ(60分間雨量)を用い、冬季の欠測期間を含む1年間(2006年8月~2007年8月)の土壌流出量を全期間、一連降雨時、及び耕作田については代かきとその前後期間別に集計した。また、一連降雨前の観測水田からの流出水の有無を把握した。その結果、観測水田においては耕作田、遊休田とも欠測期間を含む年間総土壌流出量の7割前後が一連降雨時に流出していること、土壌流出は湛水状態において生じていること、及び耕作田においては代かきとその前後期間の土壌流出は小さいことを明らかした。また、USLE(汎用土壌流亡式)を基として日本の実情に適合するよう係数の一部を修正してとりまとめられた土壌流亡予測式を対象に、耕作田における予測式の係数を畑地に準じて算出した。特に、従来求められた事例の少ない水稲・水田の作物係数Cと保全係数Pに関する値を、両者の積である作物・保全係数CPとして通期(全観測期間)、作付期(4月20日~9月30日)、及び非作付期別に集計した土壌流出量と降雨係数Rから求めた。係数の算出にあたっては、観測水田において一連降雨毎に降雨侵食指数EI60と土壌流出量を求め、両者の間に高い相関関係があることを確認した。また、得られた作物・保全係数CPから観測水田(耕作田)は原地形のまま傾斜畑として利用する場合と比して現況の棚田としての利用は土壌保全的であることを示した。

The Chugoku and Shikoku Regional Agricultural Administration Office of the Agriculture, Forestry and Fisheries Ministry conducted a survey on two patches of paddy fields, one unused and one cultivated, in Izumo and Unnan, Shimane Prefecture, between June 2006 and August 2007 as a part of a feasibility study of maintaining and strengthening multiple functions of paddy fields. Using the data on the runoff collected during the survey, the amount of soil runoff of each area at 20-minute intervals was calculated. Then, these results and data on rainfall per hour as measured at the rain and water observatory at the nearest location were used to tally the total volume of soil runoff in the year between August 2006 and August 2007, including winter months when rainfall was not measured, in which data for periods of continuous rainfall and for cultivated paddy field patches, data for before soil puddling, during soil puddling, and after soil puddling were tallied separately. More so, the existence of runoff water on the observation paddy field before the fall of rain was made out. We found that periods of continuous rainfall accounted for about 70 percent of the annual amount of soil runoff for both cultivated and unused paddy fields, soil runoff occurred when paddies were flooded, and that soil runoff was minimal during soil puddling and shortly before and after soil puddling.In order to determine the suitableness of the Universal Soil Loss Equation (USLE) with a modified coefficient adapted to the actual condition in Japan for the observation paddy fields, the amount of rainfall erosion and soil runoff for each period of continuous rainfall was tallied, and the correlation coefficient of both were obtained. As a result, a correlation coefficient of 0.9 and higher was found between the amount of rainfall erosion and soil runoff, indicating that the USLE can most probably be applied to the two observation paddy fields. Further, for the observation paddy fields (cultivated paddy), all paddy-related coefficients in the USLE were calculated as was done with dry fields. The calculated coefficients indicated that cultivated rice paddies were able to retain a greater amount of soil when used as such than when converted to a dry, hillside farm maintaining the present geographical features.

Journal

  • Journal of the Japanese Agricultural Systems Society

    Journal of the Japanese Agricultural Systems Society 25(4), 205-213, 2009-10-10

    The Japanese Agricultural Systems Society

References:  5

Codes

  • NII Article ID (NAID)
    10026203932
  • NII NACSIS-CAT ID (NCID)
    AN10164125
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    09137548
  • NDL Article ID
    10576316
  • NDL Source Classification
    ZR7(科学技術--農林水産--農産)
  • NDL Call No.
    Z18-1989
  • Data Source
    CJP  NDL  J-STAGE 
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