ナギナタガヤ草生ミカン園における春肥窒素の吸収特性(土壌管理・施肥・灌水)  [in Japanese] Absorption of Spring Applied Nitrogen in Satsuma Mandarin Orchard Covered with Rat's-tail Fescue, Vulpia myuros(Soil Management, Fertilization & Irrigation)  [in Japanese]

ナギナタガヤ草生ミカン園における,春肥窒素のウンシュウミカン樹とナギナタガヤによる吸収特性を把握するため,60Lポット植え'南柑20号'を供試し,^<15>Nトレーサー法を用いて検討した.草生区の樹体は裸地区に比べ,新葉の着生数が減少し,乾物重および全窒素量も少なかった.ナギナタガヤの乾物重は樹体の24%程度であった.樹体の春肥窒素吸収量は,草生区が裸地区の約47%と著しく少なく,特に新葉における差異が大きかった.草生区におけるナギナタガヤの吸収量は,樹体の約2倍であった.また,ナギナタガヤは吸収窒素の大部分が地上部に分配されていた.樹体の^<15>N寄与率は,いずれの器官においても裸地区の方が高く,特に新生器官における差異が大きかった.一方,ナギナタガヤにおける^<15>N寄与率は,樹体に比べ著しく高かった.春肥窒素の利用率は,樹体を比較すると草生区16.7%,裸地区35.3%であり,裸地区の方が顕著に高かった.しかし,ナギナタガヤによる吸収量を加えた草生区の利用率は51.6%となり,裸地区の約1.5倍であった.

A ^<15>N-tracer method was used to study the absorption of nitrogen applied in the spring to Satsuma mandarin trees and Rat's-tail fescue, Vulpia myuros, in a mandarin orange orchard covered with Rat's-tail fescue. The amount of nitrogen applied in the spring that was absorbed by mandarin orange trees in a plot covered with Rat's-tail fescue was markedly smaller, about 47%, than that in a clean cultivated plot; the difference was particularly large in new leaves. The amount of nitrogen absorbed by Rat's-tail fescue in a sod culture plot was about twice as large as that absorbed by the trees in the plot. Trees in the clean cultivated plot showed higher rates of ^<15>N occupied by supplied nitrogen in all organs than trees in the sod culture plot did; the difference was particularly large in newly developed organs. However, Rat's-tail fescue in the sod culture plot showed a markedly higher rate of ^<15>N occupied by supplied nitrogen than the trees showed. A comparison of the utilization rates of nitrogen applied in the spring to trees in two different plots demonstrated that the rate was 16.7% in the sod culture plot and 35.3% in the clean cultivated plot; the rate was markedly higher in the clean cultivated plot. However, the utilization rate including an absorbed amount by Rat's-tail fescue was 51.6% in the sod culture plot, which was about 1.5 times as high as that in the clean cultivated plot.