用放射追蹤技術研究桶柑有效根根群之分佈狀況

Determination of Functional Root Distribution of Citrus tankan by Radiotracer Technique

欲達成有效之肥料施用，對某一作物之有效根群活動，必須事行先了解。本試驗即以生長於本省北部，海拔400至450公尺坡地砂壤土之8年生桶柑（Citrus tankan Hayata）為試材，採用磷32標識之正磷酸，循放射追蹤技術而從事此一研究。試驗始於一九六八年早春至同年初夏之多雨季節，處理方法係以特製工具將密封於玻璃管內之放射性磷32液分放置於環境柑桔主幹四週地下各預定處理點，並加壓碎，其處理深度分別為離土面10, 30, 45及60公分以及距主幹50, 100, 150及200公分等處。試驗共16處理3重複，分於早春及初夏之不同和生長季節由兩次試驗達成，故全部試驗柑桔樹共96株。處理後10, 20, 30及40日分別採摘植株上部樹冠及下部樹冠嫩葉及老熟葉供作化學及放射分析；其中全磷量以光譜比色測定，放射活性則使成磷酸銨鎂沉澱後測算其比活性。至試驗進行前後之天氣狀況，土壤特性，以及果園管理等與果樹養分吸收有關之諸等條件均詳加調查，分析。以上兩次試驗，根據各不同放射性磷32處理位置，及由葉片收回之比活性關係，結果顯示其最有效根群密集分佈於離土表10公分下而又遍佈於距樹幹100至200公分半徑之區域；此一情況，或因最上層土壤中較高有機物含量及交換性陽離子含量，以至土壤含水，通氣等較優條件，同時又因8年生桶柑之有效支根群已伸展至100至200公分範圍之事實使然。葉片中所含放射活性，隨吸收之時間延長而增加，如以葉片組織之比活性觀之，則以下部嫩葉為最高，此點似與生長勢旺盛：力圖攝取養分以求發育之嫩葉以及其著生位置有關。影響葉片內所含成份使觀察所得往往未能齊一之原因與採樣方法有關，蓋葉片成熟度，葉形，接受陽光程度，著生位置等均足以造成影響。其次，此一試驗固期從放射活性之收回率作為判斷之依據，故進行類似試驗時，宜對某一作物之生長週期先作了解。此外，表土較淺之果園，如本試驗所選用者，其60公分深處理點已常遭岩石，不但增加困難，且對磷酸吸收以至放射性收回均不無影響，是則同類研究，似可以不增加每株處理劑量，而畫可能增加處理點下獲得改進。

To reveal the rooting habit and its activity of the tree crop are important before implementing the effective fertilization. Radiotracer technique involving the use of phosphorus-32 labelled orthophosphate was applied around the citrus tree to approach this study. Citrus tankan trees growing in sandy loam on 400-450 m above sea level terrace in north Taiwan were used as the material. The experiments were conducted in early spring through early summer during the rainy season in 1968. The treatments included setting the ampoules containing 32P labellad ortho-phosphate in various depths from 10 cm to 60 cm and radii from 50 cm to 200 cm circling the trunk by a special designed placing crusher were administered. The samplings were respectively conducted 10, 20, 30 and 40 days thereafter. Colour spectrometry using Barton's reagent and solid sample radioassay in magnesium phosphate precipitate were carried out in determining the specific activities in terms of count rate per unit weight of plant leaves and count rate per unit weight of total phosphorus content. Soil characteristics, climatic conditions as well as orchard administration relating to the nutrient uptake were thoroughly investigated. In both experiments, the results showed that the most active functional root systems distributed around 10 cm depth soil and spreaded within 100-200 cm radius from the trunk. The higher organ matter content in uppermost topsoil favoring in base-holding, aeration and water-holding capacities might bring about this condition on the one hand, and it was due to the fact that the ramifying functional roots extended from parent roots of the 8-year-old Citrus tankan to this area on the other. The radioactivity in leaf samples were proportion increasing following the extension of absorption period. The specific activities of most the young leaves in the lower crown of a tree were apparently higher than those of other samples in this investigation. Hereof, the speeding nutrient uptake in those of vigorous developing young leaves and the close transportation position were speculated. The major factors influencing the composition of the leaves may be due to sampling in which its age, position and size are closely related. In facilitating the performance of analogous experiments in view of higher radioactivity yield, an understanding of the growth cycle of a given citrus variety is necessary. Furthermore, the shallow topsoil as the case in these experiments, rocks were occasionally encountered in 60 cm depth treatments which way influence the counting yield as well. By increasing the treating points without increasing the total dose must be helpful under this condition.