森林生態系内のチッ素量測定について

Abstract

森林内の樹体, A_o層および土壌中に存在するチッ素量を求めるために今まで用いてきたsamplingの方法が十分であったかどうかを検討した。その結果, 今までの方法で求めた林分あたりのチッ素量はまずまずの値いであった。1) 樹体 : チッ素含有率が安定した8, 9月頃に, およそ10本前後の単木を直径階別に選び伐倒し, 各単木ごとに葉, 枝, 幹, 根の分に部分ける。葉と枝は新しい部分と旧い部分とに分ける。幹は高さ別にその高さの重量に比例して円板をとる。根は太さ別に区分するか, または, それぞれの太さの重量を考慮して採取する。2) A_o層 : A_o層の有機物は落葉を主とするものと大枝との2つに分ける。前者の量の測定には1×1m_2のプロットを7個をとれば十分であるが, 後者の量はより大きな面積を必要とする。3) 土壌 : 任意に4つの深さ70cmまでの土壌断面をほり, 各断面を表層から0 - 5, 5 - 10, 10 - 20, 20 - 30, 30 - 50, 50 - 70cmの6層に分けて採取し, 層別に4点を一つにまとめて分析する。

This paper is concered with sampling methods used heretofore and currently in use to measure the amounts of nitrogen in trees, the Ao horizon and soils in forests see whether or not they adequately and accurately measre those amounts. In the evaluation of the results of various methods studied, those applied to the tree, Ao horizon and soil as explained below were found to be mostly satisfactory. 1) The tree: In August or September when the nitrogen content is stable, about 10 sample trees with sizes averaging from large to small in DBH are selected cut down and separated into leaves, branches, stems and roots. Samples of each are collected separately for the individual trees. Both new and old leaves and branches are taken. Stem samples are collected as disks that are in proportion to the weight of stems at each height collected. Roots are sampled separately according to diameter, or according to the weight of each diameter. 2) The Ao horizon: The organic matter of the litter layer is divided into 2 groups, big branches and others. The amounts of those big branches are measured in 7 quadrants (1×1m2) which can be considered satisfactory, but the big branches need to be measured areas larger than 1×1m2 quadrants. 3) The soil: Soil samples are taken from each horizon (0-5, 5-10, 10-20, 20-30, 30-50, 50-70cm) of four soil profiles that are selected randomly. The soil for each horizon is measured and analyzed by the total of all the cores from within that profile.