森林立地55（2），119〜126 2013

Jpn J For Environ 55 (2), 119―126, 2013

 

北関東の中山間地域の農用林における落葉および

落葉堆肥生産と水田施用の有効性

 

逢沢峰昭¹・乾友恵¹・平井英明²・大澤和敏³・池田純子¹・大久保達弘¹

¹宇都宮大学農学部森林科学科・²宇都宮大学農学部生物資源科学科・

³宇都宮大学農学部農業環境工学科

 

北関東の中山間地域において，林地と農地の一体的利活用と有機物を用いた米生産に向けて，農用林から得られる落葉量，落葉堆肥の材料となる落葉量，そこから生産される堆肥量，水田投入量の測定を行い，水田1 haへの施用に必要な落葉および落葉堆肥を得ることができる農用林の林分面積を調べた。さらに，これらの有機物を用いて水稲栽培試験を行い，養分組成からみた水田施用の有効性を検討した。測定の結果，農用林から少なくとも5Mg/haの落葉を確保できること，低温季からでは約9ヶ月で落葉487kgから230kgの落葉堆肥を生産できることがわかった。また，水田1 haへの施用に必要な落葉および落葉堆肥を確保することができる林分面積は1 ha程度であることがわかった。落葉および落葉堆肥の養分組成を調べた結果，肥効率を考慮した落葉および落葉堆肥の窒素量は，一般的な施肥基準量に達していなかった。しかし，落葉および落葉堆肥のリン酸とカリウムは，施肥基準量の10％以下であったため，リン酸やカリウムの過剰蓄積に対する低成分肥料として期待された。ただ，落葉および落葉堆肥を用いて栽培した2011年の米収量は，化成肥料を用いた慣行農法の8割程度と低くはないものの，無施肥区と比べると肥料効果は限定的であった。

キーワード：農用林，落葉，落葉堆肥，養分，水稲栽培

 

Mineaki Aizawa, Tomoe Inui, Hideaki Hirai, Kazutoshi Osawa, Junko Ikeda and Tatsuhiro Ohkubo：Yields of fallen leaves and the compost from a farm forest and their efficacy for paddy rice cultivation in a hilly and lower mountainous area in northern Kanto. Japanese Journal of Forest Environment 55:119―126, 2013.

In order to understand the past integrated use of farm forests and agricultural fields in a hilly and lower mountainous region in northern Kanto, as well as the production of rice using organic materials, we measured the mass of raw fallen leaves gathered from a farm forest, the mass of yielded compost made from fallen leaves, and the mass of raw fallen leaves and compost supplied to paddy rice fields. Based on our results, we estimated the area of farm forest required to foster a 1-ha paddy rice field. We also performed experimental cultivation to assess the efficacy of the fallen leaves and compost in terms of nutrient composition. We found that at least 5 Mg/ha of raw fallen leaves was obtained from the forest, and 1 ha of farm forest was necessary to cultivate a 1-ha paddy rice field using these organic materials. Analysis of nutrient composition indicated that the total amount of nitrogen in these organic materials did not meet the general recommended quantity. The quantities of phosphate and potassium in these organic materials were less than 10% of the general recommended level. However, these organic materials were expected to be effective fertilizers containing small amounts of phosphate and potassium for the soil in which excessive amounts of phosphate and potassium had accumulated. In 2011, the yield of cultivated rice using raw fallen leaves and compost was not so low, namely, 80% of that produced with conventional cultivation using chemical fertilizers, but was roughly equivalent to that produced with no fertilizer application, indicating the limited efficacy of these organic materials.

Key words : farm forest, fallen leaves, compost, nutrient, paddy rice cultivation