森林立地学会誌 森林立地36(2), 1994, 15〜21
論 文
スギ・ヒノキ造林地での斜面位置別の
表層土壌の窒素無機化量
高 橋 輝 昌・生 原 喜久雄・相 場 芳 憲
高橋輝昌・生原喜久雄・相場芳憲：スギ・ヒノキ造林地での斜面位置別の表層土壌の窒素無機化量
野外培養法の一つであるシリンダー法を用い，スギとヒノキの壮齢林（83年生）及び幼齢林（2年生）の表層土壌（地表0〜10cm）の窒素無機化量を自然により近い状態で推定した。壮齢林の斜面上部，中部，幼齢林の斜面上部にはヒノキが，壮齢林の斜面下部，幼齢林の斜面中部，下部にはスギが植栽されている。植生や斜面位置による土壌中（地表0〜10cm）の無機態窒素量の違いは明確でなく，年間を通して1〜10kg・ha-1で，無機態窒素量に占めるNH4-Nの割合は，壮齢林，幼齢林ともに斜面下部になるほど小さかった。1か月間の平均地温がおよそ5℃以上になると，みかけの窒素無気化が始まり，地温の上昇に伴って増加した。窒素無機化量は壮齢林，幼齢林ともに斜面下部になるほど多かった。窒素無機化量に占めるNH4-Nの割合は壮齢林に比べて幼齢林で少なかった。また斜面位置による窒素無機化量に占めるNH4-N割合は壮齢林の斜面上部になるほど高かったが，幼齢林では明らかでなかった。1年間の窒素無機化量は壮齢林で45〜55kg・ha-1，幼齢林で50〜80kg・ha-1であった。
Terumasa TAKAHASHl , Kikuo HAIBARA and Yoshinori
AIBA: Nitrogen minaralization of surface
soil along slope in sugi and hinoki stands
The cylinder method was used in situ to estimate
net mineralization in surface soil (0-10cm depth) of an established
(83-year-old) stand and young (2-year-old) stand of sugi (Cryptomeria japonica) and
hinoki (Chamaecyparis obutusa). The
upper and middle part of the established stand and the upper part of the young
stand consisted of hinoki and the lower part of the established stand and
middle and lower part of the young stand consisted of sugi. Measurement sites
were in the upper, middle, and lower sections in both stands. The amounts of
inorganic nitrogen (NO3-N+NH4-N) found in the soil
(0-l0cm depth) were 1-10kg・ha-1 during one year, and no obvious differences between
the sugi and hinoki stands or among the plots. The ratio of NH4-N to
inorganic nitrogen were decreaed from the upper to lower slope position in both
the established and young stands. When the average soil temperature for one
month became higher than above 5℃, net nitrigen mineralization occured and was accelerated with an
increase of soil temperature. Net nitrogen mineralization increased from the
upper to lower slope position in both the established and young stands. The
ratio of NH4-N to net nitrogen mineralization was higher in the
established stand than in young stand. The ratio increased from the lower to
upper slope position in the established stand, but there was no differece among
the plots in the young stand. The net nitrogen mineralization in surface soil
(0-10cm depth) in the established stand was 45-55kg ha-1・yr.-1 and in the young stand
was 50-80kg ha-１・yr.-1.